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Baghali Khanian, Z.; Winter, A.
A Rate-Distortion Perspective on Quantum State Redistribution Artículo de revista
En: IEEE Transactions on Information Theory, 2025.
Resumen | Enlaces | BibTeX | Etiquetas: UAB
@article{nokey,
title = {A Rate-Distortion Perspective on Quantum State Redistribution},
author = {Baghali Khanian, Z. and Winter, A. },
url = {https://ieeexplore.ieee.org/document/10795756},
doi = {10.1109/TIT.2024.3516505},
year = {2025},
date = {2025-12-12},
journal = {IEEE Transactions on Information Theory},
abstract = {We consider a rate-distortion version of the quantum state redistribution task, where the error of the decoded state is judged via an additive distortion measure; it thus constitutes a quantum generalisation of the classical Wyner-Ziv problem. The quantum source is described by a tripartite pure state shared between Alice (A, encoder), Bob (B, decoder) and a reference (R). Both Alice and Bob are required to output a system (Ã and B̃, respectively), and the distortion measure is encoded in an observable on ÃB̃R. It includes as special cases most quantum rate-distortion problems considered in the past, and in particular quantum data compression with the fidelity measured per copy; furthermore, it generalises the well-known state merging and quantum state redistribution tasks for a pure state source, with per-copy fidelity, and a variant recently considered by us, where the source is an ensemble of pure states [ZBK & AW, Proc. ISIT 2020, pp. 1858-1863 and ZBK, PhD thesis, UAB 2020, arXiv:2012.14143]. We derive a single-letter formula for the rate-distortion function of compression schemes assisted by free entanglement. A peculiarity of the formula is that in general it requires optimisation over an unbounded auxiliary register, so the rate-distortion function is not readily computable from our result, and there is a continuity issue at zero distortion. However, we show how to overcome these difficulties in certain situations.},
keywords = {UAB},
pubstate = {published},
tppubtype = {article}
}
We consider a rate-distortion version of the quantum state redistribution task, where the error of the decoded state is judged via an additive distortion measure; it thus constitutes a quantum generalisation of the classical Wyner-Ziv problem. The quantum source is described by a tripartite pure state shared between Alice (A, encoder), Bob (B, decoder) and a reference (R). Both Alice and Bob are required to output a system (Ã and B̃, respectively), and the distortion measure is encoded in an observable on ÃB̃R. It includes as special cases most quantum rate-distortion problems considered in the past, and in particular quantum data compression with the fidelity measured per copy; furthermore, it generalises the well-known state merging and quantum state redistribution tasks for a pure state source, with per-copy fidelity, and a variant recently considered by us, where the source is an ensemble of pure states [ZBK & AW, Proc. ISIT 2020, pp. 1858-1863 and ZBK, PhD thesis, UAB 2020, arXiv:2012.14143]. We derive a single-letter formula for the rate-distortion function of compression schemes assisted by free entanglement. A peculiarity of the formula is that in general it requires optimisation over an unbounded auxiliary register, so the rate-distortion function is not readily computable from our result, and there is a continuity issue at zero distortion. However, we show how to overcome these difficulties in certain situations.
Capel, A.; Alhambra, A. M.; Gondolf, P.; Ruiz-de-Alarcón, A.; Scalet, S. O.
Conditional Independence of 1D Gibbs States with Applications to Efficient Learning Working paper
2025.
Resumen | Enlaces | BibTeX | Etiquetas: UCM-4.3
@workingpaper{nokey,
title = {Conditional Independence of 1D Gibbs States with Applications to Efficient Learning},
author = {Capel, A. and Alhambra, A.M. and Gondolf, P. and Ruiz-de-Alarcón, A. and Scalet, S.O.},
url = {https://doi.org/10.48550/arXiv.2402.18500},
doi = {doi.org/10.48550/arXiv.2402.18500},
year = {2025},
date = {2025-12-02},
urldate = {2025-12-02},
abstract = {We show that spin chains in thermal equilibrium have a correlation structure in which individual regions are strongly correlated at most with their near vicinity. We quantify this with alternative notions of the conditional mutual information, defined through the so-called Belavkin-Staszewski relative entropy. We prove that these measures decay superexponentially at every positive temperature, under the assumption that the spin chain Hamiltonian is translation-invariant. Using a recovery map associated with these measures, we sequentially construct tensor network approximations in terms of marginals of small (sublogarithmic) size. As a main application, we show that classical representations of the states can be learned efficiently from local measurements with a polynomial sample complexity. We also prove an approximate factorization condition for the purity of the entire Gibbs state, which implies that it can be efficiently estimated to a small multiplicative error from a small number of local measurements. The results extend from strictly local to exponentially-decaying interactions above a threshold temperature, albeit only with exponential decay rates. As a technical step of independent interest, we show an upper bound to the decay of the Belavkin-Staszewski relative entropy upon the application of a conditional expectation.},
keywords = {UCM-4.3},
pubstate = {published},
tppubtype = {workingpaper}
}
We show that spin chains in thermal equilibrium have a correlation structure in which individual regions are strongly correlated at most with their near vicinity. We quantify this with alternative notions of the conditional mutual information, defined through the so-called Belavkin-Staszewski relative entropy. We prove that these measures decay superexponentially at every positive temperature, under the assumption that the spin chain Hamiltonian is translation-invariant. Using a recovery map associated with these measures, we sequentially construct tensor network approximations in terms of marginals of small (sublogarithmic) size. As a main application, we show that classical representations of the states can be learned efficiently from local measurements with a polynomial sample complexity. We also prove an approximate factorization condition for the purity of the entire Gibbs state, which implies that it can be efficiently estimated to a small multiplicative error from a small number of local measurements. The results extend from strictly local to exponentially-decaying interactions above a threshold temperature, albeit only with exponential decay rates. As a technical step of independent interest, we show an upper bound to the decay of the Belavkin-Staszewski relative entropy upon the application of a conditional expectation.
Casas, B.; Bonet-Monroig, X.; Pérez-Salinas, A.
The role of data-induced randomness in quantum machine learning classification tasks Working paper
2025.
Resumen | Enlaces | BibTeX | Etiquetas: BSC
@workingpaper{nokey,
title = {The role of data-induced randomness in quantum machine learning classification tasks},
author = {Casas, B. and Bonet-Monroig, X. and Pérez-Salinas, A. },
url = {https://arxiv.org/pdf/2411.19281},
doi = {doi.org/10.48550/arXiv.2411.19281},
year = {2025},
date = {2025-11-28},
urldate = {2025-11-28},
abstract = {Quantum machine learning (QML) has surged as a prominent area of research with the objective to go beyond the capabilities of classical machine learning models. A critical aspect of any learning task is the process of data embedding, which directly impacts model performance. Poorly designed data-embedding strategies can significantly impact the success of a learning task. Despite its importance, rigorous analyses of data-embedding effects are limited, leaving many cases without effective assessment methods. In this work, we introduce a metric for binary classification tasks, the class margin, by merging the concepts of average randomness and classification margin. This metric analytically connects data-induced randomness with classification accuracy for a given data-embedding map. We benchmark a range of data-embedding strategies through class margin, demonstrating that data-induced randomness imposes a limit on classification performance. We expect this work to provide a new approach to evaluate QML models by their data-embedding processes, addressing gaps left by existing analytical tools.},
keywords = {BSC},
pubstate = {published},
tppubtype = {workingpaper}
}
Quantum machine learning (QML) has surged as a prominent area of research with the objective to go beyond the capabilities of classical machine learning models. A critical aspect of any learning task is the process of data embedding, which directly impacts model performance. Poorly designed data-embedding strategies can significantly impact the success of a learning task. Despite its importance, rigorous analyses of data-embedding effects are limited, leaving many cases without effective assessment methods. In this work, we introduce a metric for binary classification tasks, the class margin, by merging the concepts of average randomness and classification margin. This metric analytically connects data-induced randomness with classification accuracy for a given data-embedding map. We benchmark a range of data-embedding strategies through class margin, demonstrating that data-induced randomness imposes a limit on classification performance. We expect this work to provide a new approach to evaluate QML models by their data-embedding processes, addressing gaps left by existing analytical tools.
O de Almeida, J.; Kleinmann, M.; Sentís, G.
Comparison of confidence regions for quantum state tomography Artículo de revista
En: New Journal of Physics , vol. 25, iss. 11, no 113018, 2025.
Resumen | Enlaces | BibTeX | Etiquetas: ICFO-4.17
@article{nokey,
title = {Comparison of confidence regions for quantum state tomography},
author = {O de Almeida, J. and Kleinmann, M. and Sentís, G. },
url = {https://iopscience.iop.org/article/10.1088/1367-2630/ad06d9},
doi = {10.1088/1367-2630/ad06d9},
year = {2025},
date = {2025-11-13},
urldate = {2025-11-13},
journal = {New Journal of Physics },
volume = {25},
number = {113018},
issue = {11},
abstract = {The quantum state associated to an unknown experimental preparation procedure can be determined by performing quantum state tomography. If the statistical uncertainty in the data dominates over other experimental errors, then a tomographic reconstruction procedure must express this uncertainty. A rigorous way to accomplish this is via statistical confidence regions (CRs) in state space. Naturally, the size of this region decreases when increasing the number of samples, but it also depends critically on the construction method of the region. We compare recent methods for constructing CRs as well as a reference method based on a Gaussian approximation. For the comparison, we propose an operational measure with the finding, that there is a significant difference between methods, but which method is preferable can depend on the details of the state preparation scenario.},
keywords = {ICFO-4.17},
pubstate = {published},
tppubtype = {article}
}
The quantum state associated to an unknown experimental preparation procedure can be determined by performing quantum state tomography. If the statistical uncertainty in the data dominates over other experimental errors, then a tomographic reconstruction procedure must express this uncertainty. A rigorous way to accomplish this is via statistical confidence regions (CRs) in state space. Naturally, the size of this region decreases when increasing the number of samples, but it also depends critically on the construction method of the region. We compare recent methods for constructing CRs as well as a reference method based on a Gaussian approximation. For the comparison, we propose an operational measure with the finding, that there is a significant difference between methods, but which method is preferable can depend on the details of the state preparation scenario.
Dastbasteh, R.; Padashnick, F.; Crespo, P.; Grassl, M.; Sharafi, J.
Equivalence of constacyclic codes with shift constants of different orders Artículo de revista
En: Designs, Codes and Cryptography, 2025.
Resumen | Enlaces | BibTeX | Etiquetas: TECNUN
@article{nokey,
title = {Equivalence of constacyclic codes with shift constants of different orders},
author = {Dastbasteh, R. and Padashnick, F. and Crespo, P. and Grassl, M. and Sharafi, J.
},
url = {https://link.springer.com/article/10.1007/s10623-024-01512-9},
doi = {doi.org/10.48550/arXiv.2403.04600},
year = {2025},
date = {2025-10-18},
journal = {Designs, Codes and Cryptography},
abstract = {Let a and b be two non-zero elements of a finite field F_q, where q > 2. It has been shown that if a and b have the same multiplicative order in F_q, then the families of a-constacyclic and b-constacyclic codes over F_q are monomially equivalent. In this paper, we investigate the monomial equivalence of a-constacyclic and b-constacyclic codes when a and b have distinct multiplicative orders. We present novel conditions for establishing monomial equivalence in such constacyclic codes, surpassing previous methods of determining monomially equivalent constacyclic and cyclic codes. As an application, we use these results to search for new linear codes more systematically. In particular, we present more than 70 new record-breaking linear codes over various finite fields, as well as new binary quantum codes.},
keywords = {TECNUN},
pubstate = {published},
tppubtype = {article}
}
Let a and b be two non-zero elements of a finite field F_q, where q > 2. It has been shown that if a and b have the same multiplicative order in F_q, then the families of a-constacyclic and b-constacyclic codes over F_q are monomially equivalent. In this paper, we investigate the monomial equivalence of a-constacyclic and b-constacyclic codes when a and b have distinct multiplicative orders. We present novel conditions for establishing monomial equivalence in such constacyclic codes, surpassing previous methods of determining monomially equivalent constacyclic and cyclic codes. As an application, we use these results to search for new linear codes more systematically. In particular, we present more than 70 new record-breaking linear codes over various finite fields, as well as new binary quantum codes.
Skotiniotis, M.; Llorens, S.; Hotz, R.; J. Muñoz-Tapia Calsamiglia, R.
Identification of malfunctioning quantum devices Artículo de revista
En: Physical Review Research, vol. 6, 2025.
Resumen | Enlaces | BibTeX | Etiquetas: UAB
@article{nokey,
title = {Identification of malfunctioning quantum devices},
author = {Skotiniotis, M. and Llorens, S. and Hotz, R. and Calsamiglia, J. Muñoz-Tapia, R. },
url = {https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.6.033329},
doi = {doi.org/10.1103/PhysRevResearch.6.033329},
year = {2025},
date = {2025-09-23},
journal = {Physical Review Research},
volume = {6},
abstract = {We consider the problem of correctly identifying a malfunctioning quantum device that forms part of a network of 𝑁 such devices, which can be considered as the quantum analog of classical anomaly detection. In the case where the devices in question are sources assumed to prepare identical quantum pure states, with the faulty source producing a different anomalous pure state, we show that the optimal probability of successful identification requires a global quantum measurement. We also put forth several local measurement strategies—both adaptive and nonadaptive—that achieve the same optimal probability of success in the limit where the number of devices to be checked is large. In the case where the faulty device performs a known unitary operation, we show that the use of entangled probes provides an improvement that even allows perfect identification for values of the unitary parameter that surpass a certain threshold. Finally, if the faulty device implements a known qubit channel, we find that the optimal probability for detecting the position of rank-one and rank-two Pauli channels can be achieved by product state inputs and separable measurements for any size of network, whereas for rank-three and general amplitude damping channels, optimal identification requires entanglement with 𝑁 qubit ancillas.},
keywords = {UAB},
pubstate = {published},
tppubtype = {article}
}
We consider the problem of correctly identifying a malfunctioning quantum device that forms part of a network of 𝑁 such devices, which can be considered as the quantum analog of classical anomaly detection. In the case where the devices in question are sources assumed to prepare identical quantum pure states, with the faulty source producing a different anomalous pure state, we show that the optimal probability of successful identification requires a global quantum measurement. We also put forth several local measurement strategies—both adaptive and nonadaptive—that achieve the same optimal probability of success in the limit where the number of devices to be checked is large. In the case where the faulty device performs a known unitary operation, we show that the use of entangled probes provides an improvement that even allows perfect identification for values of the unitary parameter that surpass a certain threshold. Finally, if the faulty device implements a known qubit channel, we find that the optimal probability for detecting the position of rank-one and rank-two Pauli channels can be achieved by product state inputs and separable measurements for any size of network, whereas for rank-three and general amplitude damping channels, optimal identification requires entanglement with 𝑁 qubit ancillas.
Bou-Comas, A.; Marimón, C. R.; Schneider, J. T.; Ramos Marimón, C.; Schneider, J. T.; Carignano, S.; Tagliacozzo, L.
Measuring temporal entanglement in experiments as a hallmark for integrability Working paper
2025.
Resumen | Enlaces | BibTeX | Etiquetas: CSIC-4.7
@workingpaper{nokey,
title = {Measuring temporal entanglement in experiments as a hallmark for integrability},
author = {Bou-Comas, A. and Marimón, C.R. and Schneider, J.T. and Ramos Marimón, C. and Schneider, J.T. and Carignano, S. and Tagliacozzo, L. },
url = {https://arxiv.org/abs/2409.05517},
doi = {doi.org/10.48550/arXiv.2409.05517},
year = {2025},
date = {2025-09-09},
abstract = {We introduce a novel experimental approach to probe many-body quantum systems by developing a protocol to measure generalized temporal entropies. We demonstrate that the recently proposed generalized temporal entropies [Phys. Rev. Research 6, 033021] are equivalent to observing the out-of-equilibrium dynamics of a replicated system induced by a double quench protocol using local operators as probes. This equivalence, confirmed through state-of-the-art tensor network simulations for one-dimensional systems, validates the feasibility of measuring generalized temporal entropies experimentally. Our results reveal that the dynamics governed by the transverse field Ising model integrable Hamiltonian differ qualitatively from those driven by the same model with an additional parallel field, breaking integrability. They thus suggest that generalized temporal entropies can serve as a tool for identifying different dynamical classes. This work represents the first practical application of generalized temporal entropy characterization in one-dimensional many-body quantum systems and offers a new pathway for experimentally detecting integrability. We conclude by outlining the experimental requirements for implementing this protocol with state of the art quantum simulators.},
keywords = {CSIC-4.7},
pubstate = {published},
tppubtype = {workingpaper}
}
We introduce a novel experimental approach to probe many-body quantum systems by developing a protocol to measure generalized temporal entropies. We demonstrate that the recently proposed generalized temporal entropies [Phys. Rev. Research 6, 033021] are equivalent to observing the out-of-equilibrium dynamics of a replicated system induced by a double quench protocol using local operators as probes. This equivalence, confirmed through state-of-the-art tensor network simulations for one-dimensional systems, validates the feasibility of measuring generalized temporal entropies experimentally. Our results reveal that the dynamics governed by the transverse field Ising model integrable Hamiltonian differ qualitatively from those driven by the same model with an additional parallel field, breaking integrability. They thus suggest that generalized temporal entropies can serve as a tool for identifying different dynamical classes. This work represents the first practical application of generalized temporal entropy characterization in one-dimensional many-body quantum systems and offers a new pathway for experimentally detecting integrability. We conclude by outlining the experimental requirements for implementing this protocol with state of the art quantum simulators.
Edmunds, C. L.; Rico, E.; Arrazola, I.; Brennen, G. K.; Meth, M.; Blatt, R.; Ringbauer, M.
Constructing the spin-1 Haldane phase on a qudit quantum processor Working paper
2025.
Resumen | Enlaces | BibTeX | Etiquetas: CSIC-4.7
@workingpaper{nokey,
title = {Constructing the spin-1 Haldane phase on a qudit quantum processor},
author = {Edmunds, C. L. . and Rico, E. and Arrazola, I. and Brennen, G. K. and Meth, M. and Blatt, R. and Ringbauer, M.},
url = {https://arxiv.org/abs/2408.04702},
doi = {doi.org/10.48550/arXiv.2408.04702},
year = {2025},
date = {2025-08-08},
abstract = {Symmetry-protected topological phases have fundamentally changed our understanding of quantum matter. An archetypal example of such a quantum phase of matter is the Haldane phase, containing the spin-1 Heisenberg chain. The intrinsic quantum nature of such phases, however, often makes it challenging to study them using classical means. Here, we use trapped-ion qutrits to natively engineer spin-1 chains within the Haldane phase. Using a scalable, deterministic procedure to prepare the Affleck-Kennedy-Lieb-Tasaki (AKLT) state within the Haldane phase, we study the topological features of this system on a qudit quantum processor. Notably, we verify the long-range string order of the state, despite its short-range correlations, and observe spin fractionalization of the physical spin-1 particles into effective qubits at the chain edges, a defining feature of this system. The native realization of Haldane physics on a qudit quantum processor and the scalable preparation procedures open the door to the efficient exploration of a wide range of systems beyond spin-1/2},
keywords = {CSIC-4.7},
pubstate = {published},
tppubtype = {workingpaper}
}
Symmetry-protected topological phases have fundamentally changed our understanding of quantum matter. An archetypal example of such a quantum phase of matter is the Haldane phase, containing the spin-1 Heisenberg chain. The intrinsic quantum nature of such phases, however, often makes it challenging to study them using classical means. Here, we use trapped-ion qutrits to natively engineer spin-1 chains within the Haldane phase. Using a scalable, deterministic procedure to prepare the Affleck-Kennedy-Lieb-Tasaki (AKLT) state within the Haldane phase, we study the topological features of this system on a qudit quantum processor. Notably, we verify the long-range string order of the state, despite its short-range correlations, and observe spin fractionalization of the physical spin-1 particles into effective qubits at the chain edges, a defining feature of this system. The native realization of Haldane physics on a qudit quantum processor and the scalable preparation procedures open the door to the efficient exploration of a wide range of systems beyond spin-1/2
García-Azorín, P.; Cárdenas-López, F. A.; Huber, H. B. P.; Romero, G.; Werninghaus, M.; Motzoi, F.; Filipp, S.; Sanz, M. (Ed.)
Robust multi-mode superconducting qubit designed with evolutionary algorithms Working paper
2025.
Resumen | Enlaces | BibTeX | Etiquetas: UPV/EHU
@workingpaper{nokey,
title = {Robust multi-mode superconducting qubit designed with evolutionary algorithms},
editor = {García-Azorín, P. and Cárdenas-López, F.A. and Huber, H.B.P. and Romero, G. and Werninghaus, M. and Motzoi, F. and Filipp, S. and Sanz, M.},
url = {https://arxiv.org/abs/2407.18895},
doi = {doi.org/10.48550/arXiv.2407.18895},
year = {2025},
date = {2025-07-26},
abstract = {Multi-mode superconducting circuits offer a promising platform for engineering robust systems for quantum computation. Previous studies have shown that single-mode devices cannot simultaneously exhibit resilience against multiple decoherence sources due to conflicting protection requirements. In contrast, multi-mode systems offer increased flexibility and have proven capable of overcoming these fundamental limitations. Nevertheless, exploring multi-mode architectures is computationally demanding due to the exponential scaling of the Hilbert space dimension. Here, we present a multi-mode device designed using evolutionary optimization techniques, which have been shown to be effective for this computational task. The proposed device was optimized to feature an anharmonicity of a third of the qubit frequency and reduced energy dispersion caused by charge and magnetic flux fluctuations. It exhibits improvements over the fundamental errors limiting Transmon and Fluxonium coherence and manipulation, aiming for a balance between low depolarization error and fast manipulation; furthermore demonstrating robustness against fabrication errors, a major limitation in many proposed multi-mode devices. Overall, by striking a balance between coupling matrix elements and noise protection, we propose a device that paves the way towards finding proper characteristics for the construction of superconducting quantum processors.},
keywords = {UPV/EHU},
pubstate = {published},
tppubtype = {workingpaper}
}
Multi-mode superconducting circuits offer a promising platform for engineering robust systems for quantum computation. Previous studies have shown that single-mode devices cannot simultaneously exhibit resilience against multiple decoherence sources due to conflicting protection requirements. In contrast, multi-mode systems offer increased flexibility and have proven capable of overcoming these fundamental limitations. Nevertheless, exploring multi-mode architectures is computationally demanding due to the exponential scaling of the Hilbert space dimension. Here, we present a multi-mode device designed using evolutionary optimization techniques, which have been shown to be effective for this computational task. The proposed device was optimized to feature an anharmonicity of a third of the qubit frequency and reduced energy dispersion caused by charge and magnetic flux fluctuations. It exhibits improvements over the fundamental errors limiting Transmon and Fluxonium coherence and manipulation, aiming for a balance between low depolarization error and fast manipulation; furthermore demonstrating robustness against fabrication errors, a major limitation in many proposed multi-mode devices. Overall, by striking a balance between coupling matrix elements and noise protection, we propose a device that paves the way towards finding proper characteristics for the construction of superconducting quantum processors.
Colomer, P.; Deppe, C.; Boche, H.; Winter, A.
Quantum Hypothesis Testing Lemma for Deterministic Identification over Quantum Channels Working paper
2025.
Resumen | Enlaces | BibTeX | Etiquetas: UAB
@workingpaper{nokey,
title = {Quantum Hypothesis Testing Lemma for Deterministic Identification over Quantum Channels},
author = {Colomer, P. and Deppe, C. and Boche, H. and Winter, A. },
url = {https://arxiv.org/abs/2504.20991},
doi = {doi.org/10.48550/arXiv.2504.20991},
year = {2025},
date = {2025-07-24},
abstract = {In our previous work, we presented the emph{Hypothesis Testing Lemma}, a key tool that establishes sufficient conditions for the existence of good deterministic identification (DI) codes for memoryless channels with finite output, but arbitrary input alphabets. In this work, we provide a full quantum analogue of this lemma, which shows that the existence of a DI code in the quantum setting follows from a suitable packing in a modified space of output quantum states. Specifically, we demonstrate that such a code can be constructed using product states derived from this packing. This result enables us to tighten the capacity lower bound for DI over quantum channels beyond the simultaneous decoding approach. In particular, we can now express these bounds solely in terms of the Minkowski dimension of a certain state space, giving us new insights to better understand the nature of the protocol, and the separation between simultaneous and non-simultaneous codes. We extend the discussion with a particular channel example for which we can construct an optimum code.},
keywords = {UAB},
pubstate = {published},
tppubtype = {workingpaper}
}
In our previous work, we presented the emph{Hypothesis Testing Lemma}, a key tool that establishes sufficient conditions for the existence of good deterministic identification (DI) codes for memoryless channels with finite output, but arbitrary input alphabets. In this work, we provide a full quantum analogue of this lemma, which shows that the existence of a DI code in the quantum setting follows from a suitable packing in a modified space of output quantum states. Specifically, we demonstrate that such a code can be constructed using product states derived from this packing. This result enables us to tighten the capacity lower bound for DI over quantum channels beyond the simultaneous decoding approach. In particular, we can now express these bounds solely in terms of the Minkowski dimension of a certain state space, giving us new insights to better understand the nature of the protocol, and the separation between simultaneous and non-simultaneous codes. We extend the discussion with a particular channel example for which we can construct an optimum code.
Gopalkrishna Naik, S.; Zartab, M.; Gisin, N.; Banik, M.
No-Go Theorem for Generic Simulation of Qubit Channels with Finite Classical Resources Working paper
2025.
Resumen | Enlaces | BibTeX | Etiquetas: UAB
@workingpaper{nokey,
title = {No-Go Theorem for Generic Simulation of Qubit Channels with Finite Classical Resources},
author = {Gopalkrishna Naik, S. and Zartab, M. and Gisin, N. and Banik, M. },
url = {https://arxiv.org/abs/2501.15807},
doi = {doi.org/10.48550/arXiv.2501.15807},
year = {2025},
date = {2025-07-16},
urldate = {2025-07-16},
abstract = {The mathematical framework of quantum theory, though fundamentally distinct from classical physics, raises the question of whether quantum processes can be efficiently simulated using classical resources. For instance, a sender (Alice) possessing the classical description of a qubit state can simulate the action of a qubit channel through finite classical communication with a receiver (Bob), enabling Bob to reproduce measurement statistics for any observable on the state. In this work, we contend that a more general simulation requires reproducing statistics of joint measurements, potentially involving entangled effects, on Alice's system and an additional system held by Bob, even when Bob's system state is unknown or entangled with a larger system. Within this broad framework, we prove that no finite amount of classical messaging, regardless of how many rounds are used or how large each message can be, can reproduce a perfect qubit channel, highlighting an inescapable barrier in quantum channel simulation with classical resources. We also establish that entangled effects crucially underlies this no-go result. However, for noisy qubit channels, such as those with depolarizing noise, we demonstrate that general simulation is achievable with finite communication. Notably, the required communication increases as the noise decreases, revealing an intricate relationship between the noise in the channel and the resources necessary for its classical simulation.},
keywords = {UAB},
pubstate = {published},
tppubtype = {workingpaper}
}
The mathematical framework of quantum theory, though fundamentally distinct from classical physics, raises the question of whether quantum processes can be efficiently simulated using classical resources. For instance, a sender (Alice) possessing the classical description of a qubit state can simulate the action of a qubit channel through finite classical communication with a receiver (Bob), enabling Bob to reproduce measurement statistics for any observable on the state. In this work, we contend that a more general simulation requires reproducing statistics of joint measurements, potentially involving entangled effects, on Alice's system and an additional system held by Bob, even when Bob's system state is unknown or entangled with a larger system. Within this broad framework, we prove that no finite amount of classical messaging, regardless of how many rounds are used or how large each message can be, can reproduce a perfect qubit channel, highlighting an inescapable barrier in quantum channel simulation with classical resources. We also establish that entangled effects crucially underlies this no-go result. However, for noisy qubit channels, such as those with depolarizing noise, we demonstrate that general simulation is achievable with finite communication. Notably, the required communication increases as the noise decreases, revealing an intricate relationship between the noise in the channel and the resources necessary for its classical simulation.
Bǎzǎvan, O.; Saner, S.; Tirrito, E.; Araneda, G.; Srinivas, R.; Bermudez, A.
Synthetic Z2 gauge theories based on parametric excitations of trapped ions Artículo de revista
En: Communications Physics, vol. 7, pp. 229, 2025.
Resumen | Enlaces | BibTeX | Etiquetas: CSIC-4.7
@article{nokey,
title = {Synthetic Z2 gauge theories based on parametric excitations of trapped ions},
author = {Bǎzǎvan, O. and Saner, S. and Tirrito, E. and Araneda, G. and Srinivas, R. and Bermudez, A.},
url = {https://www.nature.com/articles/s42005-024-01691-w#citeas},
doi = {doi.org/10.1038/s42005-024-01691-w},
year = {2025},
date = {2025-07-12},
journal = {Communications Physics},
volume = {7},
pages = {229},
abstract = {Resource efficient schemes for the quantum simulation of lattice gauge theories can benefit from hybrid encodings of gauge and matter fields that use the native degrees of freedom, such as internal qubits and motional phonons in trapped-ion devices. We propose to use a parametric scheme to induce a tunneling of the phonons conditioned to the internal qubit state which, when implemented with a single trapped ion, corresponds to a minimal Z2 gauge theory. To evaluate the feasibility of this scheme, we perform numerical simulations of the state-dependent tunneling using realistic parameters, and identify the leading sources of error in future experiments. We discuss how to generalize this minimal case to more complex settings by increasing the number of ions, moving from a single link to a Z2 plaquette, and to an entire Z2 chain. We present analytical expressions for the gauge-invariant dynamics and the corresponding confinement, which are benchmarked using matrix product state simulations.},
keywords = {CSIC-4.7},
pubstate = {published},
tppubtype = {article}
}
Resource efficient schemes for the quantum simulation of lattice gauge theories can benefit from hybrid encodings of gauge and matter fields that use the native degrees of freedom, such as internal qubits and motional phonons in trapped-ion devices. We propose to use a parametric scheme to induce a tunneling of the phonons conditioned to the internal qubit state which, when implemented with a single trapped ion, corresponds to a minimal Z2 gauge theory. To evaluate the feasibility of this scheme, we perform numerical simulations of the state-dependent tunneling using realistic parameters, and identify the leading sources of error in future experiments. We discuss how to generalize this minimal case to more complex settings by increasing the number of ions, moving from a single link to a Z2 plaquette, and to an entire Z2 chain. We present analytical expressions for the gauge-invariant dynamics and the corresponding confinement, which are benchmarked using matrix product state simulations.
Fadel, M.; Yadin, B.; Mao, Y.; Byrnes, T.; Gessner, M.
Multiparameter quantum metrology and mode entanglement with spatially split nonclassical spin ensembles Artículo de revista
En: New Journal of Physics , vol. 25, iss. 7, 2025.
Resumen | Enlaces | BibTeX | Etiquetas: ICFO-4.16
@article{nokey,
title = {Multiparameter quantum metrology and mode entanglement with spatially split nonclassical spin ensembles},
author = {Fadel, M. and Yadin, B. and Mao, Y. and Byrnes, T. and Gessner, M.},
url = {https://iopscience.iop.org/article/10.1088/1367-2630/ace1a0},
doi = {10.1088/1367-2630/ace1a0},
year = {2025},
date = {2025-07-12},
urldate = {2025-07-12},
journal = {New Journal of Physics },
volume = {25},
issue = {7},
abstract = {We identify the multiparameter sensitivity of entangled spin states, such as spin-squeezed and Dicke states that are spatially distributed into several addressable spatial modes. Analytical expressions for the spin-squeezing matrix of families of states that are accessible by current atomic experiments reveal the quantum gain in multiparameter metrology, as well as the optimal strategies to maximize the sensitivity gain for the estimation of any linear combination of parameters. We further study the mode entanglement of these states by deriving a witness for genuine k-partite mode entanglement from the spin-squeezing matrix. Our results highlight the advantage of mode entanglement for distributed sensing, and outline optimal protocols for multiparameter estimation with nonclassical spatially-distributed spin ensembles. We illustrate our findings with the design of a protocol for gradient sensing with a Bose–Einstein condensate in an entangled spin state in two modes.},
keywords = {ICFO-4.16},
pubstate = {published},
tppubtype = {article}
}
We identify the multiparameter sensitivity of entangled spin states, such as spin-squeezed and Dicke states that are spatially distributed into several addressable spatial modes. Analytical expressions for the spin-squeezing matrix of families of states that are accessible by current atomic experiments reveal the quantum gain in multiparameter metrology, as well as the optimal strategies to maximize the sensitivity gain for the estimation of any linear combination of parameters. We further study the mode entanglement of these states by deriving a witness for genuine k-partite mode entanglement from the spin-squeezing matrix. Our results highlight the advantage of mode entanglement for distributed sensing, and outline optimal protocols for multiparameter estimation with nonclassical spatially-distributed spin ensembles. We illustrate our findings with the design of a protocol for gradient sensing with a Bose–Einstein condensate in an entangled spin state in two modes.
Olivera-Atencio, M. L.; Lamata, L.; Casado-Pascual, J.
Impact of amplitude and phase damping noise on quantum reinforcement learning: challenges and opportunities Artículo de revista
En: The European Physical Journal Special Topics (EPJ ST), 2025.
Resumen | Enlaces | BibTeX | Etiquetas: US
@article{nokey,
title = {Impact of amplitude and phase damping noise on quantum reinforcement learning: challenges and opportunities},
author = {Olivera-Atencio, M.L. and Lamata, L. and Casado-Pascual, J.},
editor = {Olivera-Atencio, M.L. and Lamata, L. and Casado-Pascual, J. },
url = {https://link.springer.com/article/10.1140/epjs/s11734-025-01760-3},
doi = {doi.org/10.1140/epjs/s11734-025-01760-3},
year = {2025},
date = {2025-07-04},
urldate = {2025-07-04},
journal = {The European Physical Journal Special Topics (EPJ ST)},
abstract = {Quantum machine learning (QML) is an emerging field with significant potential, yet it remains highly susceptible to noise, which poses a major challenge to its practical implementation. While various noise mitigation strategies have been proposed to enhance algorithmic performance, the impact of noise is not fully understood. In this work, we investigate the effects of amplitude and phase damping noise on a quantum reinforcement learning algorithm. Through analytical and numerical analysis, we assess how these noise sources influence the learning process and overall performance. Our findings contribute to a deeper understanding of the role of noise in quantum learning algorithms and suggest that, rather than being purely detrimental, unavoidable noise may present opportunities to enhance QML processes.},
keywords = {US},
pubstate = {published},
tppubtype = {article}
}
Quantum machine learning (QML) is an emerging field with significant potential, yet it remains highly susceptible to noise, which poses a major challenge to its practical implementation. While various noise mitigation strategies have been proposed to enhance algorithmic performance, the impact of noise is not fully understood. In this work, we investigate the effects of amplitude and phase damping noise on a quantum reinforcement learning algorithm. Through analytical and numerical analysis, we assess how these noise sources influence the learning process and overall performance. Our findings contribute to a deeper understanding of the role of noise in quantum learning algorithms and suggest that, rather than being purely detrimental, unavoidable noise may present opportunities to enhance QML processes.
Bou-Comas, A.; Płodzień, M.; Tagliacozzo, L.; García-Ripoll, J. J.
Quantics Tensor Train for solving Gross-Pitaevskii equation Working paper
2025.
Resumen | Enlaces | BibTeX | Etiquetas: CSIC-4.7
@workingpaper{nokey,
title = {Quantics Tensor Train for solving Gross-Pitaevskii equation},
author = {Bou-Comas, A. and Płodzień, M. and Tagliacozzo, L. and García-Ripoll, J.J.},
url = {https://arxiv.org/abs/2507.03134},
doi = {doi.org/10.48550/arXiv.2507.03134},
year = {2025},
date = {2025-07-03},
abstract = {We present a quantum-inspired solver for the one-dimensional Gross-Pitaevskii equation in the Quantics Tensor-Train (QTT) representation. By evolving the system entirely within a low-rank tensor manifold, the method sidesteps the memory and runtime barriers that limit conventional finite-difference and spectral schemes. Two complementary algorithms are developed: an imaginary-time projector that drives the condensate toward its variational ground state and a rank-adapted fourth-order Runge-Kutta integrator for real-time dynamics. The framework captures a broad range of physical scenarios - including barrier-confined condensates, quasi-random potentials, long-range dipolar interactions, and multicomponent spinor dynamics - without leaving the compressed representation. Relative to standard discretizations, the QTT approach achieves an exponential reduction in computational resources while retaining quantitative accuracy, thereby extending the practicable regime of Gross-Pitaevskii simulations on classical hardware. These results position tensor networks as a practical bridge between high-performance classical computing and prospective quantum hardware for the numerical treatment of nonlinear Schrodinger-type partial differential equations.},
keywords = {CSIC-4.7},
pubstate = {published},
tppubtype = {workingpaper}
}
We present a quantum-inspired solver for the one-dimensional Gross-Pitaevskii equation in the Quantics Tensor-Train (QTT) representation. By evolving the system entirely within a low-rank tensor manifold, the method sidesteps the memory and runtime barriers that limit conventional finite-difference and spectral schemes. Two complementary algorithms are developed: an imaginary-time projector that drives the condensate toward its variational ground state and a rank-adapted fourth-order Runge-Kutta integrator for real-time dynamics. The framework captures a broad range of physical scenarios - including barrier-confined condensates, quasi-random potentials, long-range dipolar interactions, and multicomponent spinor dynamics - without leaving the compressed representation. Relative to standard discretizations, the QTT approach achieves an exponential reduction in computational resources while retaining quantitative accuracy, thereby extending the practicable regime of Gross-Pitaevskii simulations on classical hardware. These results position tensor networks as a practical bridge between high-performance classical computing and prospective quantum hardware for the numerical treatment of nonlinear Schrodinger-type partial differential equations.
Berardini, E.; Dastbasteh, R.; Etxezarreta Martinez, J.; Jain, S.; Sanz Larrarte, O.
Asymptotically good CSS-T codes and a new construction of triorthogonal codes Artículo de revista
En: IEEE Journal on Selected Areas in Information Theory, 2025.
Resumen | Enlaces | BibTeX | Etiquetas: TECNUN
@article{nokey,
title = {Asymptotically good CSS-T codes and a new construction of triorthogonal codes},
author = {Berardini, E. and Dastbasteh, R. and Etxezarreta Martinez, J. and Jain, S. and Sanz Larrarte, O. },
url = {https://arxiv.org/abs/2412.08586},
doi = {10.1109/JSAIT.2025.3582156},
year = {2025},
date = {2025-06-20},
journal = {IEEE Journal on Selected Areas in Information Theory},
abstract = {We propose a new systematic construction of CSS-T codes from any given CSS code using a map ϕ. When ϕ is the identity map I, we retrieve the construction of hu2021mitigating and use it to prove the existence of asymptotically good binary CSS-T codes, resolving a previously open problem in the literature, and of asymptotically good quantum LDPC CSS-T codes. We analyze the structure of the logical operators corresponding to certain non-Clifford gates supported by the quantum codes obtained from this construction (ϕ=I), concluding that they always result in the logical identity. An immediate application of these codes in dealing with coherent noise is discussed. We then develop a new doubling transformation for obtaining triorthogonal codes, which generalizes the doubling construction presented in jain2024. Our approach permits using self-orthogonal codes, instead of only doubly-even codes, as building blocks for triorthogonal codes. This broadens the range of codes available for magic state distillation.},
keywords = {TECNUN},
pubstate = {published},
tppubtype = {article}
}
We propose a new systematic construction of CSS-T codes from any given CSS code using a map ϕ. When ϕ is the identity map I, we retrieve the construction of hu2021mitigating and use it to prove the existence of asymptotically good binary CSS-T codes, resolving a previously open problem in the literature, and of asymptotically good quantum LDPC CSS-T codes. We analyze the structure of the logical operators corresponding to certain non-Clifford gates supported by the quantum codes obtained from this construction (ϕ=I), concluding that they always result in the logical identity. An immediate application of these codes in dealing with coherent noise is discussed. We then develop a new doubling transformation for obtaining triorthogonal codes, which generalizes the doubling construction presented in jain2024. Our approach permits using self-orthogonal codes, instead of only doubly-even codes, as building blocks for triorthogonal codes. This broadens the range of codes available for magic state distillation.
Rodriguez-Grasa, P.; Ban, Y.; Sanz, M.
Neural quantum kernels: Training quantum kernels with quantum neural networks Artículo de revista
En: Physical Review Research, vol. 7, iss. 2, no 23269 , 2025.
Resumen | Enlaces | BibTeX | Etiquetas: UPV/EHU
@article{nokey,
title = {Neural quantum kernels: Training quantum kernels with quantum neural networks},
author = {Rodriguez-Grasa, P. and Ban, Y. and Sanz, M.},
url = {https://journals.aps.org/prresearch/abstract/10.1103/xphb-x2g4},
doi = {doi.org/10.1103/xphb-x2g4},
year = {2025},
date = {2025-06-16},
urldate = {2025-06-16},
journal = {Physical Review Research},
volume = {7},
number = {23269 },
issue = {2},
abstract = {Quantum and classical machine learning have been naturally connected through kernel methods, which have also served as proof-of-concept for quantum advantage. Quantum embeddings encode classical data into quantum feature states, enabling the construction of embedding quantum kernels (EQKs) by measuring vector similarities and projected quantum kernels (PQKs) through projections of these states. However, in both approaches, the model is influenced by the choice of the embedding. In this work, we propose using the training of a quantum neural network (QNN) to construct neural quantum kernels, specifically neural EQKs and neural PQKs—problem-inspired kernel functions. Unlike previous approaches, our method requires the kernel matrix to be constructed only once, significantly reducing computational overhead. To achieve this, we introduce a scalable training method for an 𝑛-qubit data reuploading QNN. Furthermore, we demonstrate neural quantum kernels can alleviate exponential concentration and enhance generalization capabilities compared to problem-agnostic kernels, positioning them as a scalable and robust solution for quantum machine learning applications.},
keywords = {UPV/EHU},
pubstate = {published},
tppubtype = {article}
}
Quantum and classical machine learning have been naturally connected through kernel methods, which have also served as proof-of-concept for quantum advantage. Quantum embeddings encode classical data into quantum feature states, enabling the construction of embedding quantum kernels (EQKs) by measuring vector similarities and projected quantum kernels (PQKs) through projections of these states. However, in both approaches, the model is influenced by the choice of the embedding. In this work, we propose using the training of a quantum neural network (QNN) to construct neural quantum kernels, specifically neural EQKs and neural PQKs—problem-inspired kernel functions. Unlike previous approaches, our method requires the kernel matrix to be constructed only once, significantly reducing computational overhead. To achieve this, we introduce a scalable training method for an 𝑛-qubit data reuploading QNN. Furthermore, we demonstrate neural quantum kernels can alleviate exponential concentration and enhance generalization capabilities compared to problem-agnostic kernels, positioning them as a scalable and robust solution for quantum machine learning applications.
Ruiz, R.; Sopena, A.; López, E.; Sierra, G.; Pozsgay, B.
Bethe Ansatz, quantum circuits, and the F-basis Artículo de revista
En: SciPost Physics, vol. 18, pp. 187, 2025.
Resumen | Enlaces | BibTeX | Etiquetas: CSIC-4.7
@article{nokey,
title = {Bethe Ansatz, quantum circuits, and the F-basis},
author = {Ruiz, R. and Sopena, A. and López, E. and Sierra, G. and Pozsgay, B. },
url = {https://scipost.org/SciPostPhys.18.6.187},
doi = {doi: 10.21468/SciPostPhys.18.6.187},
year = {2025},
date = {2025-06-12},
journal = {SciPost Physics},
volume = {18},
pages = {187},
abstract = {The Bethe Ansatz is a method for constructing exact eigenstates of quantum-integrable spin chains. Recently, deterministic quantum algorithms, referred to as "algebraic Bethe circuits", have been developed to prepare Bethe states for the spin-1/2 XXZ model. These circuits represent a unitary formulation of the standard algebraic Bethe Ansatz, expressed using matrix-product states that act on both the spin chain and an auxiliary space. In this work, we systematize these previous results, and show that algebraic Bethe circuits can be derived by a change of basis in the auxiliary space. The new basis, identical to the "F-basis" known from the theory of quantum-integrable models, generates the linear superposition of plane waves that is characteristic of the coordinate Bethe Ansatz. We explain this connection, highlighting that certain properties of the F-basis (namely, the exchange symmetry of the spins) are crucial for the construction of algebraic Bethe circuits. We demonstrate our approach by presenting new quantum circuits for the inhomogeneous spin-1/2 XXZ model.},
keywords = {CSIC-4.7},
pubstate = {published},
tppubtype = {article}
}
The Bethe Ansatz is a method for constructing exact eigenstates of quantum-integrable spin chains. Recently, deterministic quantum algorithms, referred to as "algebraic Bethe circuits", have been developed to prepare Bethe states for the spin-1/2 XXZ model. These circuits represent a unitary formulation of the standard algebraic Bethe Ansatz, expressed using matrix-product states that act on both the spin chain and an auxiliary space. In this work, we systematize these previous results, and show that algebraic Bethe circuits can be derived by a change of basis in the auxiliary space. The new basis, identical to the "F-basis" known from the theory of quantum-integrable models, generates the linear superposition of plane waves that is characteristic of the coordinate Bethe Ansatz. We explain this connection, highlighting that certain properties of the F-basis (namely, the exchange symmetry of the spins) are crucial for the construction of algebraic Bethe circuits. We demonstrate our approach by presenting new quantum circuits for the inhomogeneous spin-1/2 XXZ model.
Gonzalez-Conde, J.; Lewis, D.; Bharadwaj, S. S.; Sanz, M.
Quantum Carleman linearization efficiency in nonlinear fluid dynamics Artículo de revista
En: Physical Review Research, vol. 7, iss. 2, no 23254, 2025.
Resumen | Enlaces | BibTeX | Etiquetas: UPV/EHU
@article{nokey,
title = {Quantum Carleman linearization efficiency in nonlinear fluid dynamics},
author = {Gonzalez-Conde, J. and Lewis, D. and Bharadwaj, S.S. and Sanz, M. },
url = {https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.7.023254},
doi = {doi.org/10.1103/PhysRevResearch.7.023254},
year = {2025},
date = {2025-06-12},
urldate = {2025-06-12},
journal = {Physical Review Research},
volume = {7},
number = {23254},
issue = {2},
abstract = {Computational fluid dynamics (CFD) is a specialized branch of fluid mechanics that utilizes numerical methods and algorithms to solve and analyze fluid-flow problems. One promising avenue to enhance CFD is the use of quantum computing, which has the potential to resolve nonlinear differential equations more efficiently than classical computers. Here, we try to answer the question of which regimes of nonlinear partial differential equations for fluid dynamics can have an efficient quantum algorithm. We propose a connection between the numerical parameter 𝑅, which guarantees efficiency in the truncation of the Carleman linearization, and the physical parameters that describe the fluid flow. This link can be made thanks to the Kolmogorov scale, which determines the minimum size of the grid needed to properly resolve the energy cascade induced by the nonlinear term. Additionally, we introduce the formalism for vector field simulation in different spatial dimensions, providing the discretization of the operators and the boundary conditions.},
keywords = {UPV/EHU},
pubstate = {published},
tppubtype = {article}
}
Computational fluid dynamics (CFD) is a specialized branch of fluid mechanics that utilizes numerical methods and algorithms to solve and analyze fluid-flow problems. One promising avenue to enhance CFD is the use of quantum computing, which has the potential to resolve nonlinear differential equations more efficiently than classical computers. Here, we try to answer the question of which regimes of nonlinear partial differential equations for fluid dynamics can have an efficient quantum algorithm. We propose a connection between the numerical parameter 𝑅, which guarantees efficiency in the truncation of the Carleman linearization, and the physical parameters that describe the fluid flow. This link can be made thanks to the Kolmogorov scale, which determines the minimum size of the grid needed to properly resolve the energy cascade induced by the nonlinear term. Additionally, we introduce the formalism for vector field simulation in different spatial dimensions, providing the discretization of the operators and the boundary conditions.
García-Beni, J.; Paparelle, I.; Parigi, V.; Giorgi, G. L.; Soriano, M. C.; Zambrini, R.
Quantum machine learning via continuous-variable cluster states and teleportation Artículo de revista
En: EPJ Quantum Technology, vol. 12, iss. 1, no 63, 2025.
Resumen | Enlaces | BibTeX | Etiquetas: UIB
@article{nokey,
title = {Quantum machine learning via continuous-variable cluster states and teleportation},
author = {García-Beni, J. and Paparelle, I. and Parigi, V. and Giorgi, G.L. and Soriano, M.C. and Zambrini, R.},
url = {https://epjquantumtechnology.springeropen.com/articles/10.1140/epjqt/s40507-025-00352-3},
doi = {doi.org/10.1140/epjqt/s40507-025-00352-3},
year = {2025},
date = {2025-06-02},
journal = {EPJ Quantum Technology},
volume = {12},
number = {63},
issue = {1},
abstract = {We propose a new approach for a photonic platform suitable for distributed quantum machine learning and exhibiting memory. This measurement-based quantum reservoir computing takes advantage of continuous variable cluster states as the main quantum resource. Cluster states are key to several photonic quantum technologies, enabling universal quantum computing as well as quantum communication protocols. The proposed measurement-based quantum reservoir computing is based on a neural network of cluster states and local operations, where input data are encoded through measurement, thanks to quantum teleportation. In this design, measurements enable input injections, information processing and continuous monitoring for time series processing. The architecture’s power and versatility are tested by performing a set of benchmark tasks showing that the protocol displays internal memory and is suitable for both static and temporal information processing without hardware modifications. This design opens the way to distributed machine learning.},
keywords = {UIB},
pubstate = {published},
tppubtype = {article}
}
We propose a new approach for a photonic platform suitable for distributed quantum machine learning and exhibiting memory. This measurement-based quantum reservoir computing takes advantage of continuous variable cluster states as the main quantum resource. Cluster states are key to several photonic quantum technologies, enabling universal quantum computing as well as quantum communication protocols. The proposed measurement-based quantum reservoir computing is based on a neural network of cluster states and local operations, where input data are encoded through measurement, thanks to quantum teleportation. In this design, measurements enable input injections, information processing and continuous monitoring for time series processing. The architecture’s power and versatility are tested by performing a set of benchmark tasks showing that the protocol displays internal memory and is suitable for both static and temporal information processing without hardware modifications. This design opens the way to distributed machine learning.
Etxezarreta Martinez, J.; Schnabl, P.; Oliva del Moral, P.; Dastbasteh, R.; Crespo, P. M.; Otxoa, R. M.
Leveraging biased noise for more efficient quantum error correction at the circuit-level with two-level qubits Working paper
2025.
Resumen | Enlaces | BibTeX | Etiquetas: TECNUN
@workingpaper{nokey,
title = {Leveraging biased noise for more efficient quantum error correction at the circuit-level with two-level qubits},
author = {Etxezarreta Martinez, J. and Schnabl, P. and Oliva del Moral, P. and Dastbasteh, R. and Crespo, P.M. and Otxoa, R.M.},
url = {https://arxiv.org/abs/2505.17718},
doi = {doi.org/10.48550/arXiv.2505.17718},
year = {2025},
date = {2025-05-23},
abstract = {Tailoring quantum error correction codes (QECC) to biased noise has demonstrated significant benefits. However, most of the prior research on this topic has focused on code capacity noise models. Furthermore, a no-go theorem prevents the construction of CNOT gates for two-level qubits in a bias preserving manner which may, in principle, imply that noise bias cannot be leveraged in such systems. In this work, we show that a residual bias up to η ∼5 can be maintained in CNOT gates under certain conditions. Moreover, we employ controlled-phase (CZ) gates in syndrome extraction circuits and show how to natively implement these in a bias-preserving manner for a broad class of qubit platforms. This motivates the introduction of what we call a hybrid biased-depolarizing (HBD) circuit-level noise model which captures these features. We numerically study the performance of the XZZX surface code and observe that bias-preserving CZ gates are critical for leveraging biased noise. Accounting for the residual bias present in the CNOT gates, we observe an increase in the code threshold up to a 1.27% physical error rate, representing a 90% improvement. Additionally,
we find that the required qubit footprint can be reduced by up to a 75% at relevant physical error rates.},
keywords = {TECNUN},
pubstate = {published},
tppubtype = {workingpaper}
}
Tailoring quantum error correction codes (QECC) to biased noise has demonstrated significant benefits. However, most of the prior research on this topic has focused on code capacity noise models. Furthermore, a no-go theorem prevents the construction of CNOT gates for two-level qubits in a bias preserving manner which may, in principle, imply that noise bias cannot be leveraged in such systems. In this work, we show that a residual bias up to η ∼5 can be maintained in CNOT gates under certain conditions. Moreover, we employ controlled-phase (CZ) gates in syndrome extraction circuits and show how to natively implement these in a bias-preserving manner for a broad class of qubit platforms. This motivates the introduction of what we call a hybrid biased-depolarizing (HBD) circuit-level noise model which captures these features. We numerically study the performance of the XZZX surface code and observe that bias-preserving CZ gates are critical for leveraging biased noise. Accounting for the residual bias present in the CNOT gates, we observe an increase in the code threshold up to a 1.27% physical error rate, representing a 90% improvement. Additionally,
we find that the required qubit footprint can be reduced by up to a 75% at relevant physical error rates.
we find that the required qubit footprint can be reduced by up to a 75% at relevant physical error rates.
H.C., Zhang; Sierra, G.
Kramers-Wannier self-duality and non-invertible translation symmetry in quantum chains: a wave-function perspective Artículo de revista
En: Journal of High Energy Physics (JHEP), 2025.
Resumen | Enlaces | BibTeX | Etiquetas: CSIC-4.7
@article{nokey,
title = {Kramers-Wannier self-duality and non-invertible translation symmetry in quantum chains: a wave-function perspective},
author = {Zhang H.C. and Sierra, G. },
url = {https://link.springer.com/article/10.1007/JHEP05(2025)157},
doi = {doi.org/10.1007/JHEP05(2025)157},
year = {2025},
date = {2025-05-20},
urldate = {2025-05-20},
journal = {Journal of High Energy Physics (JHEP)},
abstract = {The Kramers-Wannier self-duality of critical quantum chains is examined from the perspective of model wave functions. We demonstrate, using the transverse-field Ising chain and the 3-state Potts chain as examples, that the symmetry operator for the Kramers-Wannier self-duality follows in a simple and direct way from a ‘generalised’ translation symmetry of the model wave function in the anyonic fusion basis. This translation operation, in turn, comprises a sequence of F-moves in the underlying fusion category. The symmetry operator thus obtained naturally admits the form of a matrix product operator and obeys non-invertible fusion rules. The findings reveal an intriguing connection between the (non-invertible) translation symmetry on the lattice and topological aspects of the conformal field theory describing the scaling limit.},
keywords = {CSIC-4.7},
pubstate = {published},
tppubtype = {article}
}
The Kramers-Wannier self-duality of critical quantum chains is examined from the perspective of model wave functions. We demonstrate, using the transverse-field Ising chain and the 3-state Potts chain as examples, that the symmetry operator for the Kramers-Wannier self-duality follows in a simple and direct way from a ‘generalised’ translation symmetry of the model wave function in the anyonic fusion basis. This translation operation, in turn, comprises a sequence of F-moves in the underlying fusion category. The symmetry operator thus obtained naturally admits the form of a matrix product operator and obeys non-invertible fusion rules. The findings reveal an intriguing connection between the (non-invertible) translation symmetry on the lattice and topological aspects of the conformal field theory describing the scaling limit.
Garcia-de-Andoin, M.; Álvarez-Ahedo, A.; Franco-Rubio, A.; Sanz, M.
Impact and mitigation of Hamiltonian characterization errors in digital-analog quantum computation Working paper
2025.
Resumen | Enlaces | BibTeX | Etiquetas: UPV/EHU
@workingpaper{nokey,
title = {Impact and mitigation of Hamiltonian characterization errors in digital-analog quantum computation},
author = {Garcia-de-Andoin, M. and Álvarez-Ahedo, A. and Franco-Rubio, A. and Sanz, M. },
url = {https://arxiv.org/abs/2505.03642},
doi = {doi.org/10.48550/arXiv.2505.03642},
year = {2025},
date = {2025-05-06},
urldate = {2025-05-06},
abstract = {Digital-analog is a universal quantum computing paradigm which employs the natural entangling
Hamiltonian of the system and single-qubit gates as resources. Here, we study the stability of
these protocols against Hamiltonian characterization errors. For this, we bound the maximum
separation between the target and the implemented Hamiltonians. Additionally, we obtain an upper
bound for the deviation in the expected value of an observable. We further propose a protocol for
mitigating calibration errors which resembles dynamical-decoupling techniques. These results open
the possibility of scaling digital-analog to intermediate and large scale systems while having an
estimation on the errors committed.},
keywords = {UPV/EHU},
pubstate = {published},
tppubtype = {workingpaper}
}
Digital-analog is a universal quantum computing paradigm which employs the natural entangling
Hamiltonian of the system and single-qubit gates as resources. Here, we study the stability of
these protocols against Hamiltonian characterization errors. For this, we bound the maximum
separation between the target and the implemented Hamiltonians. Additionally, we obtain an upper
bound for the deviation in the expected value of an observable. We further propose a protocol for
mitigating calibration errors which resembles dynamical-decoupling techniques. These results open
the possibility of scaling digital-analog to intermediate and large scale systems while having an
estimation on the errors committed.
Hamiltonian of the system and single-qubit gates as resources. Here, we study the stability of
these protocols against Hamiltonian characterization errors. For this, we bound the maximum
separation between the target and the implemented Hamiltonians. Additionally, we obtain an upper
bound for the deviation in the expected value of an observable. We further propose a protocol for
mitigating calibration errors which resembles dynamical-decoupling techniques. These results open
the possibility of scaling digital-analog to intermediate and large scale systems while having an
estimation on the errors committed.
Tejedor, M.; Casas, B.; Conejero, J.; Cervera-Lierta, A.; R Badia, M.
Distributed Quantum Circuit Cutting for Hybrid Quantum-Classical High-Performance Computing Working paper
2025.
Resumen | Enlaces | BibTeX | Etiquetas: BSC
@workingpaper{nokey,
title = {Distributed Quantum Circuit Cutting for Hybrid Quantum-Classical High-Performance Computing},
author = {Tejedor, M. and Casas, B. and Conejero, J. and Cervera-Lierta, A. and Badia, R,M. },
url = {https://arxiv.org/pdf/2505.01184},
doi = {doi.org/10.48550/arXiv.2505.01184},
year = {2025},
date = {2025-05-05},
urldate = {2025-05-05},
abstract = {Most quantum computers today are constrained by hardware limitations, particularly the number of available qubits, causing significant challenges for executing large-scale quantum algorithms. Circuit cutting has emerged as a key technique to overcome these limitations by decomposing large quantum circuits into smaller subcircuits that can be executed independently and later reconstructed. In this work, we introduce Qdislib, a distributed and flexible library for quantum circuit cutting, designed to seamlessly integrate with hybrid quantum-classical high-performance computing (HPC) systems. Qdislib employs a graph-based representation of quantum circuits to enable efficient partitioning, manipulation and execution, supporting both wire cutting and gate cutting techniques. The library is compatible with multiple quantum computing libraries, including Qiskit and Qibo, and leverages distributed computing frameworks to execute subcircuits across CPUs, GPUs, and quantum processing units (QPUs) in a fully parallelized manner. We present a proof of concept demonstrating how Qdislib enables the distributed execution of quantum circuits across heterogeneous computing resources, showcasing its potential for scalable quantum-classical workflows.},
keywords = {BSC},
pubstate = {published},
tppubtype = {workingpaper}
}
Most quantum computers today are constrained by hardware limitations, particularly the number of available qubits, causing significant challenges for executing large-scale quantum algorithms. Circuit cutting has emerged as a key technique to overcome these limitations by decomposing large quantum circuits into smaller subcircuits that can be executed independently and later reconstructed. In this work, we introduce Qdislib, a distributed and flexible library for quantum circuit cutting, designed to seamlessly integrate with hybrid quantum-classical high-performance computing (HPC) systems. Qdislib employs a graph-based representation of quantum circuits to enable efficient partitioning, manipulation and execution, supporting both wire cutting and gate cutting techniques. The library is compatible with multiple quantum computing libraries, including Qiskit and Qibo, and leverages distributed computing frameworks to execute subcircuits across CPUs, GPUs, and quantum processing units (QPUs) in a fully parallelized manner. We present a proof of concept demonstrating how Qdislib enables the distributed execution of quantum circuits across heterogeneous computing resources, showcasing its potential for scalable quantum-classical workflows.
S. Ding Romero, Y.; Chen, Xi.; Ban, Y.
Scrambling in the charging of quantum batteries Artículo de revista
En: High Energy Physics, vol. 2025, no 21, 2025.
Resumen | Enlaces | BibTeX | Etiquetas: UPV/EHU
@article{nokey,
title = {Scrambling in the charging of quantum batteries},
author = {Romero, S. Ding, Y. and Chen, Xi. and Ban, Y.},
url = {https://link.springer.com/content/pdf/10.1007/JHEP05(2025)021.pdf},
doi = {doi.org/10.1007/JHEP05(2025)021},
year = {2025},
date = {2025-05-05},
journal = {High Energy Physics},
volume = {2025},
number = {21},
abstract = {Exponentially fast scrambling of an initial state characterizes quantum chaotic systems. Given the importance of quickly populating higher energy levels from low-energy states in quantum battery charging protocols, this work investigates the role of quantum scrambling in quantum batteries and its effect on optimal power and charging times by means of the Sachdev-Ye-Kitaev model, a maximally-chaotic black hole physics model that has been recently proposed as a quantum battery. We adopt a bare representation with normalized bandwidths to suppress system energy dependence. To our knowledge, this is the first in-depth exploration of quantum scrambling in the context of quantum batteries. By analyzing the dynamics of out-of-time-order correlators, our findings indicate that quantum scrambling does not necessarily lead to faster charging, despite its potential for accelerating the process.},
keywords = {UPV/EHU},
pubstate = {published},
tppubtype = {article}
}
Exponentially fast scrambling of an initial state characterizes quantum chaotic systems. Given the importance of quickly populating higher energy levels from low-energy states in quantum battery charging protocols, this work investigates the role of quantum scrambling in quantum batteries and its effect on optimal power and charging times by means of the Sachdev-Ye-Kitaev model, a maximally-chaotic black hole physics model that has been recently proposed as a quantum battery. We adopt a bare representation with normalized bandwidths to suppress system energy dependence. To our knowledge, this is the first in-depth exploration of quantum scrambling in the context of quantum batteries. By analyzing the dynamics of out-of-time-order correlators, our findings indicate that quantum scrambling does not necessarily lead to faster charging, despite its potential for accelerating the process.
Rout, S.; Sakharwade, N.; Sankar Bhattacharya, S.; Ramanathan, R.; Horodecki, P.
Unbounded quantum advantage in communication with minimal input scaling Artículo de revista
En: Physical Review Research, 2025.
Resumen | Enlaces | BibTeX | Etiquetas: UAB
@article{nokey,
title = {Unbounded quantum advantage in communication with minimal input scaling},
author = {Rout, S. and Sakharwade, N. and Sankar Bhattacharya, S. and Ramanathan, R. and Horodecki, P. },
url = {https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.7.023104},
doi = {doi.org/10.1103/PhysRevResearch.7.023104},
year = {2025},
date = {2025-04-30},
journal = {Physical Review Research},
abstract = {In communication complexity-like problems, previous studies have shown either an exponential quantum advantage or an unbounded quantum advantage with an exponentially large input set Θ(2𝑛) bit with respect to classical communication Θ(𝑛) bit. In the former, the quantum and classical separation grows exponentially in input while the latter's quantum communication resource is a constant. Remarkably, it was still open whether an unbounded quantum advantage exists while the inputs do not scale exponentially. Here we answer this question affirmatively using an input size of optimal order. Considering two variants as tasks: (1) distributed computation of relation and (2) relation reconstruction, we study the one-way zero-error communication complexity of a relation induced by a distributed clique labeling problem for orthogonality graphs. While we prove no quantum advantage in the first task, we show an unbounded quantum advantage in relation reconstruction without public coins. Specifically, for a class of graphs with order 𝑚, the quantum complexity is Θ(1) while the classical complexity is Θ(log2𝑚). Remarkably, the input size is Θ(log2𝑚) bit and the order of its scaling with respect to classical communication is minimal. This is exponentially better compared to previous works. Additionally, we prove a lower bound (linear in the number of maximum cliques) on the amount of classical public coin necessary to overcome the separation in the scenario of restricted communication and connect this to the existence of orthogonal arrays. Finally, we highlight some applications of this task to semi-device-independent dimension witnessing as well as to the detection of mutually unbiased bases.},
keywords = {UAB},
pubstate = {published},
tppubtype = {article}
}
In communication complexity-like problems, previous studies have shown either an exponential quantum advantage or an unbounded quantum advantage with an exponentially large input set Θ(2𝑛) bit with respect to classical communication Θ(𝑛) bit. In the former, the quantum and classical separation grows exponentially in input while the latter's quantum communication resource is a constant. Remarkably, it was still open whether an unbounded quantum advantage exists while the inputs do not scale exponentially. Here we answer this question affirmatively using an input size of optimal order. Considering two variants as tasks: (1) distributed computation of relation and (2) relation reconstruction, we study the one-way zero-error communication complexity of a relation induced by a distributed clique labeling problem for orthogonality graphs. While we prove no quantum advantage in the first task, we show an unbounded quantum advantage in relation reconstruction without public coins. Specifically, for a class of graphs with order 𝑚, the quantum complexity is Θ(1) while the classical complexity is Θ(log2𝑚). Remarkably, the input size is Θ(log2𝑚) bit and the order of its scaling with respect to classical communication is minimal. This is exponentially better compared to previous works. Additionally, we prove a lower bound (linear in the number of maximum cliques) on the amount of classical public coin necessary to overcome the separation in the scenario of restricted communication and connect this to the existence of orthogonal arrays. Finally, we highlight some applications of this task to semi-device-independent dimension witnessing as well as to the detection of mutually unbiased bases.
Xu, Z. P.; Schwonnek, R.; Winter, A.
Bounding the Joint Numerical Range of Pauli Strings by Graph Parameters Artículo de revista
En: PRX Quantum, vol. 5, iss. 2, no 20318, 2025.
Resumen | Enlaces | BibTeX | Etiquetas: UAB
@article{nokey,
title = {Bounding the Joint Numerical Range of Pauli Strings by Graph Parameters},
author = {Xu, Z.P. and Schwonnek, R. and Winter, A.
},
url = {https://journals.aps.org/prxquantum/abstract/10.1103/PRXQuantum.5.020318},
doi = {doi.org/10.1103/PRXQuantum.5.020318},
year = {2025},
date = {2025-04-22},
journal = {PRX Quantum},
volume = {5},
number = {20318},
issue = {2},
abstract = {The relations among a given set of observables on a quantum system are effectively captured by their so-called joint numerical range, which is the set of tuples of jointly attainable expectation values. Here we explore geometric properties of this construct for Pauli strings, whose pairwise commutation and anticommutation relations determine a graph 𝐺. We investigate the connection between the parameters of this graph and the structure of minimal ellipsoids encompassing the joint numerical range, and we develop this approach in different directions. As a consequence, we find counterexamples to a conjecture by de Gois et al. [Phys. Rev. A 107, 062211 (2023)], and answer an open question raised by Hastings and O’Donnell [STOC 2022: Proceedings of the 54th Annual ACM SIGACT Symposium on Theory of Computing, pp. 776–789], which implies a new graph parameter that we call “𝛽(𝐺).” Furthermore, we provide new insights into the perennial problem of estimating the ground-state energy of a many-body Hamiltonian. Our methods give lower bounds on the ground-state energy, which are typically hard to come by, and might therefore be useful in a variety of related fields.},
keywords = {UAB},
pubstate = {published},
tppubtype = {article}
}
The relations among a given set of observables on a quantum system are effectively captured by their so-called joint numerical range, which is the set of tuples of jointly attainable expectation values. Here we explore geometric properties of this construct for Pauli strings, whose pairwise commutation and anticommutation relations determine a graph 𝐺. We investigate the connection between the parameters of this graph and the structure of minimal ellipsoids encompassing the joint numerical range, and we develop this approach in different directions. As a consequence, we find counterexamples to a conjecture by de Gois et al. [Phys. Rev. A 107, 062211 (2023)], and answer an open question raised by Hastings and O’Donnell [STOC 2022: Proceedings of the 54th Annual ACM SIGACT Symposium on Theory of Computing, pp. 776–789], which implies a new graph parameter that we call “𝛽(𝐺).” Furthermore, we provide new insights into the perennial problem of estimating the ground-state energy of a many-body Hamiltonian. Our methods give lower bounds on the ground-state energy, which are typically hard to come by, and might therefore be useful in a variety of related fields.
Navarro, J.; Ravell Rodríguez, R.; Sanz, M.
Existence of unbiased estimators in discrete quantum systems Artículo de revista
En: Physical Review Research, vol. 7, 2025.
Resumen | Enlaces | BibTeX | Etiquetas: UPV/EHU
@article{nokey,
title = {Existence of unbiased estimators in discrete quantum systems},
author = {Navarro, J. and Ravell Rodríguez, R. and Sanz, M. },
url = {https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.7.023060},
doi = {doi.org/10.1103/PhysRevResearch.7.023060},
year = {2025},
date = {2025-04-16},
journal = {Physical Review Research},
volume = {7},
abstract = {The Cramér-Rao bound serves as a crucial lower limit for the mean square error of an estimator in frequentist parameter estimation. Paradoxically, it requires highly accurate prior knowledge of the estimated parameter for constructing the optimal unbiased estimator. In contrast, Bhattacharyya bounds offer a more robust estimation framework with respect to prior accuracy by introducing additional constraints on the estimator. In this work, we examine divergences that arise in the computation of these bounds and establish the conditions under which they remain valid. Notably, we show that when the number of constraints exceeds the number of measurement outcomes, an estimator with finite variance typically does not exist. Furthermore, we systematically investigate the properties of these bounds using paradigmatic examples, comparing them to the Cramér-Rao and Bayesian approaches.},
keywords = {UPV/EHU},
pubstate = {published},
tppubtype = {article}
}
The Cramér-Rao bound serves as a crucial lower limit for the mean square error of an estimator in frequentist parameter estimation. Paradoxically, it requires highly accurate prior knowledge of the estimated parameter for constructing the optimal unbiased estimator. In contrast, Bhattacharyya bounds offer a more robust estimation framework with respect to prior accuracy by introducing additional constraints on the estimator. In this work, we examine divergences that arise in the computation of these bounds and establish the conditions under which they remain valid. Notably, we show that when the number of constraints exceeds the number of measurement outcomes, an estimator with finite variance typically does not exist. Furthermore, we systematically investigate the properties of these bounds using paradigmatic examples, comparing them to the Cramér-Rao and Bayesian approaches.
Casas, B.; Mieldzioć, G. R.; Ahmad, S.; Płodzień, M.; Bruzda, W.; Cervera-Lierta, A.; Życzkowski, K.
Quantum Circuits for High-Dimensional Absolutely Maximally Entangled States Working paper
2025.
Resumen | Enlaces | BibTeX | Etiquetas: BSC
@workingpaper{nokey,
title = {Quantum Circuits for High-Dimensional Absolutely Maximally Entangled States},
author = {Casas, B. and Mieldzioć, G.R. and Ahmad, S. and Płodzień, M. and Bruzda, W. and Cervera-Lierta, A. and Życzkowski, K. },
url = {https://arxiv.org/pdf/2504.05394},
doi = {doi.org/10.48550/arXiv.2504.05394},
year = {2025},
date = {2025-04-07},
urldate = {2025-04-07},
abstract = {Absolutely maximally entangled (AME) states of multipartite quantum systems exhibit maximal entanglement across all possible bipartitions. These states lead to teleportation protocols that surpass standard teleportation schemes, determine quantum error correction codes and can be used to test performance of current term quantum processors. Several AME states can be constructed from graph states using minimal quantum resources. However, there exist other constructions that depart from the stabilizer formalism. In this work, we present explicit quantum circuits to generate exemplary non-stabilizer AME states of four subsystems with four, six, and eight levels each and analyze their capabilities to perform quantum information tasks.},
keywords = {BSC},
pubstate = {published},
tppubtype = {workingpaper}
}
Absolutely maximally entangled (AME) states of multipartite quantum systems exhibit maximal entanglement across all possible bipartitions. These states lead to teleportation protocols that surpass standard teleportation schemes, determine quantum error correction codes and can be used to test performance of current term quantum processors. Several AME states can be constructed from graph states using minimal quantum resources. However, there exist other constructions that depart from the stabilizer formalism. In this work, we present explicit quantum circuits to generate exemplary non-stabilizer AME states of four subsystems with four, six, and eight levels each and analyze their capabilities to perform quantum information tasks.
Fanizza, M.; Rouzé, C.; Stilck França, D.
Efficient Hamiltonian, structure and trace distance learning of Gaussian states Working paper
2025.
Resumen | Enlaces | BibTeX | Etiquetas: UAB
@workingpaper{nokey,
title = {Efficient Hamiltonian, structure and trace distance learning of Gaussian states},
author = {Fanizza, M. and Rouzé, C. and Stilck França, D.},
url = {https://arxiv.org/abs/2411.03163},
doi = {doi.org/10.48550/arXiv.2411.03163},
year = {2025},
date = {2025-04-07},
abstract = {In this work, we initiate the study of Hamiltonian learning for positive temperature bosonic Gaussian states, the quantum generalization of the widely studied problem of learning Gaussian graphical models. We obtain efficient protocols, both in sample and computational complexity, for the task of inferring the parameters of their underlying quadratic Hamiltonian under the assumption of bounded temperature, squeezing, displacement and maximal degree of the interaction graph. Our protocol only requires heterodyne measurements, which are often experimentally feasible, and has a sample complexity that scales logarithmically with the number of modes. Furthermore, we show that it is possible to learn the underlying interaction graph in a similar setting and sample complexity. Taken together, our results put the status of the quantum Hamiltonian learning problem for continuous variable systems in a more advanced state when compared to spins, where state-of-the-art results are either unavailable or quantitatively inferior to ours. In addition, we use our techniques to obtain the first results on learning Gaussian states in trace distance with a quadratic scaling in precision and polynomial in the number of modes, albeit imposing certain restrictions on the Gaussian states. Our main technical innovations are several continuity bounds for the covariance and Hamiltonian matrix of a Gaussian state, which are of independent interest, combined with what we call the local inversion technique. In essence, the local inversion technique allows us to reliably infer the Hamiltonian of a Gaussian state by only estimating in parallel submatrices of the covariance matrix whose size scales with the desired precision, but not the number of modes. This way we bypass the need to obtain precise global estimates of the covariance matrix, controlling the sample complexity.},
keywords = {UAB},
pubstate = {published},
tppubtype = {workingpaper}
}
In this work, we initiate the study of Hamiltonian learning for positive temperature bosonic Gaussian states, the quantum generalization of the widely studied problem of learning Gaussian graphical models. We obtain efficient protocols, both in sample and computational complexity, for the task of inferring the parameters of their underlying quadratic Hamiltonian under the assumption of bounded temperature, squeezing, displacement and maximal degree of the interaction graph. Our protocol only requires heterodyne measurements, which are often experimentally feasible, and has a sample complexity that scales logarithmically with the number of modes. Furthermore, we show that it is possible to learn the underlying interaction graph in a similar setting and sample complexity. Taken together, our results put the status of the quantum Hamiltonian learning problem for continuous variable systems in a more advanced state when compared to spins, where state-of-the-art results are either unavailable or quantitatively inferior to ours. In addition, we use our techniques to obtain the first results on learning Gaussian states in trace distance with a quadratic scaling in precision and polynomial in the number of modes, albeit imposing certain restrictions on the Gaussian states. Our main technical innovations are several continuity bounds for the covariance and Hamiltonian matrix of a Gaussian state, which are of independent interest, combined with what we call the local inversion technique. In essence, the local inversion technique allows us to reliably infer the Hamiltonian of a Gaussian state by only estimating in parallel submatrices of the covariance matrix whose size scales with the desired precision, but not the number of modes. This way we bypass the need to obtain precise global estimates of the covariance matrix, controlling the sample complexity.
Sannia, A.; Giorgi, G. L.; Longhi, S.; Zambrini, R.
Skin effect in quantum neural networks Artículo de revista
En: Optica Quantum , vol. 3, iss. 2, pp. 189–194 , 2025.
Resumen | Enlaces | BibTeX | Etiquetas: UIB
@article{nokey,
title = {Skin effect in quantum neural networks},
author = {Sannia, A. and Giorgi, G. L. and Longhi, S. and Zambrini, R. },
url = {https://opg.optica.org/opticaq/fulltext.cfm?uri=opticaq-3-2-189&id=569978},
doi = {doi.org/10.1364/OPTICAQ.541744},
year = {2025},
date = {2025-04-04},
journal = {Optica Quantum },
volume = {3},
issue = {2},
pages = {189–194 },
abstract = {In the field of dissipative systems, the non-Hermitian skin effect has generated significant interest due to its unexpected implications. A system is said to exhibit a skin effect if its properties are largely affected by the boundary conditions. Despite the burgeoning interest, the potential impact of this phenomenon on emerging quantum technologies remains unexplored. In this work, we address this gap by demonstrating that quantum neural networks can exhibit this behavior and that skin effects, beyond their fundamental interest, can also be exploited in computational tasks. Specifically, we show that the performance of a given complex network used as a quantum reservoir computer is dictated solely by the boundary conditions of a dissipative line within its architecture. The closure of one (edge) link is found to drastically change the performance in time-series processing, proving the possibility of exploiting skin effects for machine learning.},
keywords = {UIB},
pubstate = {published},
tppubtype = {article}
}
In the field of dissipative systems, the non-Hermitian skin effect has generated significant interest due to its unexpected implications. A system is said to exhibit a skin effect if its properties are largely affected by the boundary conditions. Despite the burgeoning interest, the potential impact of this phenomenon on emerging quantum technologies remains unexplored. In this work, we address this gap by demonstrating that quantum neural networks can exhibit this behavior and that skin effects, beyond their fundamental interest, can also be exploited in computational tasks. Specifically, we show that the performance of a given complex network used as a quantum reservoir computer is dictated solely by the boundary conditions of a dissipative line within its architecture. The closure of one (edge) link is found to drastically change the performance in time-series processing, proving the possibility of exploiting skin effects for machine learning.
Gonzalez-Raya, T.; Mena, A.; Lazo, M.; L., Leggio; Novoa, D.; Sanz, M.
Entanglement transfer during quantum frequency conversion in gas-filled hollow-core fibers Artículo de revista
En: APL Photonics, vol. 10, 2025.
Resumen | Enlaces | BibTeX | Etiquetas: UPV/EHU
@article{nokey,
title = {Entanglement transfer during quantum frequency conversion in gas-filled hollow-core fibers},
author = {Gonzalez-Raya, T. and Mena, A. and Lazo, M. and Leggio L. and Novoa, D. and Sanz, M. },
url = {https://pubs.aip.org/aip/app/article/10/4/041302/3341958/Entanglement-transfer-during-quantum-frequency},
doi = {doi.org/10.1063/5.0246782},
year = {2025},
date = {2025-04-02},
journal = {APL Photonics},
volume = {10},
abstract = {Quantum transduction is essential for the future hybrid quantum networks, connecting devices across different spectral ranges. In this regard, molecular modulation in hollow-core fibers has proven to be exceptional for efficient and tunable frequency conversion of arbitrary light fields down to the single-photon limit. However, insights into this conversion method for quantum light have remained elusive beyond standard semi-classical models. In this Letter, we employ a quantum Hamiltonian framework to characterize the behavior of entanglement during molecular modulation while describing the quantum dynamics of both molecules and photons in agreement with recent experiments. In particular, apart from obtaining analytical expressions for the final opto-molecular states, our model predicts a close correlation between the evolution of the average photon numbers and the transfer of entanglement between the interacting parties. These results will contribute to the development of new fiber-based strategies to tackle the challenges associated with the upcoming generation of lightwave quantum technologies.},
keywords = {UPV/EHU},
pubstate = {published},
tppubtype = {article}
}
Quantum transduction is essential for the future hybrid quantum networks, connecting devices across different spectral ranges. In this regard, molecular modulation in hollow-core fibers has proven to be exceptional for efficient and tunable frequency conversion of arbitrary light fields down to the single-photon limit. However, insights into this conversion method for quantum light have remained elusive beyond standard semi-classical models. In this Letter, we employ a quantum Hamiltonian framework to characterize the behavior of entanglement during molecular modulation while describing the quantum dynamics of both molecules and photons in agreement with recent experiments. In particular, apart from obtaining analytical expressions for the final opto-molecular states, our model predicts a close correlation between the evolution of the average photon numbers and the transfer of entanglement between the interacting parties. These results will contribute to the development of new fiber-based strategies to tackle the challenges associated with the upcoming generation of lightwave quantum technologies.
Biswas, S.; Rico, E.; Grass, T.
Ring-exchange physics in a chain of three-level ions Artículo de revista
En: Quantum , 2025.
Resumen | Enlaces | BibTeX | Etiquetas: UPV/EHU
@article{nokey,
title = {Ring-exchange physics in a chain of three-level ions},
author = {Biswas, S. and Rico, E. and Grass, T. },
url = {https://quantum-journal.org/papers/q-2025-04-01-1683/},
doi = {doi.org/10.22331/q-2025-04-01-1683},
year = {2025},
date = {2025-04-01},
journal = {Quantum },
abstract = {In the presence of ring exchange interactions, bosons in a ladder-like lattice may form the bosonic analogon of a correlated metal, known as the d-wave Bose liquid (DBL). In this paper, we show that a chain of trapped ions with three internal levels can mimic a ladder-like system constrained to a maximum occupation of one boson per rung. The setup enables tunable ring exchange interactions, transitioning between a polarized regime with all bosons confined to one leg and the DBL regime. The latter state is characterized by a splitting of the peak in the momentum distribution and an oscillating pair correlation function.},
keywords = {UPV/EHU},
pubstate = {published},
tppubtype = {article}
}
In the presence of ring exchange interactions, bosons in a ladder-like lattice may form the bosonic analogon of a correlated metal, known as the d-wave Bose liquid (DBL). In this paper, we show that a chain of trapped ions with three internal levels can mimic a ladder-like system constrained to a maximum occupation of one boson per rung. The setup enables tunable ring exchange interactions, transitioning between a polarized regime with all bosons confined to one leg and the DBL regime. The latter state is characterized by a splitting of the peak in the momentum distribution and an oscillating pair correlation function.
Schindler, J.; Strasberg, P.; Galke, N.; Winter, A.; Jabbour, M.
Unification of observational entropy with maximum entropy principles Working paper
2025.
Resumen | Enlaces | BibTeX | Etiquetas: UAB
@workingpaper{nokey,
title = {Unification of observational entropy with maximum entropy principles},
author = {Schindler, J. and Strasberg, P. and Galke, N. and Winter, A. and Jabbour, M.
},
url = {https://arxiv.org/abs/2503.15612},
doi = {doi.org/10.48550/arXiv.2503.15612},
year = {2025},
date = {2025-03-19},
abstract = {We introduce a definition of coarse-grained entropy that unifies measurement-based (observational entropy) and max-entropy-based (Jaynes) approaches to coarse-graining, by identifying physical constraints with information theoretic priors. The definition is shown to include as special cases most other entropies of interest in physics. We then consider second laws, showing that the definition admits new entropy increase theorems and connections to thermodynamics. We survey mathematical properties of the definition, and show it resolves some pathologies of the traditional observational entropy in infinite dimensions. Finally, we study the dynamics of this entropy in a quantum random matrix model and a classical hard sphere gas. Together the results suggest that this generalized observational entropy can form the basis of a highly general approach to statistical mechanics.},
keywords = {UAB},
pubstate = {published},
tppubtype = {workingpaper}
}
We introduce a definition of coarse-grained entropy that unifies measurement-based (observational entropy) and max-entropy-based (Jaynes) approaches to coarse-graining, by identifying physical constraints with information theoretic priors. The definition is shown to include as special cases most other entropies of interest in physics. We then consider second laws, showing that the definition admits new entropy increase theorems and connections to thermodynamics. We survey mathematical properties of the definition, and show it resolves some pathologies of the traditional observational entropy in infinite dimensions. Finally, we study the dynamics of this entropy in a quantum random matrix model and a classical hard sphere gas. Together the results suggest that this generalized observational entropy can form the basis of a highly general approach to statistical mechanics.
Rodriguez-Grasa, P.; Ibarrondo, R.; Gonzalez-Conde, J.; Ban, Y.; Rebentrost, P.; Sanz, M.
Quantum approximated cloning-assisted density matrix exponentiation Artículo de revista
En: Physical Review Research, vol. 7, 2025.
Resumen | Enlaces | BibTeX | Etiquetas: UPV/EHU
@article{nokey,
title = {Quantum approximated cloning-assisted density matrix exponentiation},
author = {Rodriguez-Grasa, P. and Ibarrondo, R. and Gonzalez-Conde, J. and Ban, Y. and Rebentrost, P. and Sanz, M. },
url = {https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.7.013264},
doi = {doi.org/10.1103/PhysRevResearch.7.013264},
year = {2025},
date = {2025-03-12},
journal = {Physical Review Research},
volume = {7},
abstract = {Classical information loading is an essential task for many processing quantum algorithms, constituting a cornerstone in the field of quantum machine learning. In particular, the embedding techniques based on Hamiltonian simulation techniques enable the loading of matrices into quantum computers. A representative example of these methods is the Lloyd-Mohseni-Rebentrost (LMR) protocol, which efficiently implements matrix exponentiation when multiple copies of a quantum state are available. However, this is a quite ideal setup, and in a realistic scenario, the copies are limited and the noncloning theorem prevents one from producing more exact copies in order to increase the accuracy of the protocol. Here, we propose a method to circumvent this limitation by introducing imperfect quantum copies, which significantly improve the performance of the LMR when the eigenvectors are known.},
keywords = {UPV/EHU},
pubstate = {published},
tppubtype = {article}
}
Classical information loading is an essential task for many processing quantum algorithms, constituting a cornerstone in the field of quantum machine learning. In particular, the embedding techniques based on Hamiltonian simulation techniques enable the loading of matrices into quantum computers. A representative example of these methods is the Lloyd-Mohseni-Rebentrost (LMR) protocol, which efficiently implements matrix exponentiation when multiple copies of a quantum state are available. However, this is a quite ideal setup, and in a realistic scenario, the copies are limited and the noncloning theorem prevents one from producing more exact copies in order to increase the accuracy of the protocol. Here, we propose a method to circumvent this limitation by introducing imperfect quantum copies, which significantly improve the performance of the LMR when the eigenvectors are known.
Fanizza, M.; Galke, N.; Lumbreras, J.; Rouzé, C.; Winter, A.
Learning finitely-correlated states: stability of the spectral reconstruction Working paper
2025.
Resumen | Enlaces | BibTeX | Etiquetas: UAB
@workingpaper{nokey,
title = {Learning finitely-correlated states: stability of the spectral reconstruction},
author = {Fanizza, M. and Galke, N. and Lumbreras, J. and Rouzé, C. and Winter, A. },
url = {https://arxiv.org/abs/2312.07516},
doi = {doi.org/10.48550/arXiv.2312.07516},
year = {2025},
date = {2025-03-06},
abstract = {Matrix product operators allow efficient descriptions (or realizations) of states on a 1D lattice. We consider the task of learning a realization of minimal dimension from copies of an unknown state, such that the resulting operator is close to the density matrix in trace norm. For finitely correlated translation-invariant states on an infinite chain, a realization of minimal dimension can be exactly reconstructed via linear algebra operations from the marginals of a size depending on the representation dimension. We establish a bound on the trace norm error for an algorithm that estimates a candidate realization from estimates of these marginals and outputs a matrix product operator, estimating the state of a chain of arbitrary length . This bound allows us to establish an upper bound on the sample complexity of the learning task, with an explicit dependence on the site dimension, realization dimension and spectral properties of a certain map constructed from the state. A refined error bound can be proven for -finitely correlated states, which have an operational interpretation in terms of sequential quantum channels applied to the memory system. We can also obtain an analogous error bound for a class of matrix product density operators on a finite chain reconstructible by local marginals. In this case, a linear number of marginals must be estimated, obtaining a sample complexity of . The learning algorithm also works for states that are sufficiently close to a finitely correlated state, with the potential of providing competitive algorithms for other interesting families of states.},
keywords = {UAB},
pubstate = {published},
tppubtype = {workingpaper}
}
Matrix product operators allow efficient descriptions (or realizations) of states on a 1D lattice. We consider the task of learning a realization of minimal dimension from copies of an unknown state, such that the resulting operator is close to the density matrix in trace norm. For finitely correlated translation-invariant states on an infinite chain, a realization of minimal dimension can be exactly reconstructed via linear algebra operations from the marginals of a size depending on the representation dimension. We establish a bound on the trace norm error for an algorithm that estimates a candidate realization from estimates of these marginals and outputs a matrix product operator, estimating the state of a chain of arbitrary length . This bound allows us to establish an upper bound on the sample complexity of the learning task, with an explicit dependence on the site dimension, realization dimension and spectral properties of a certain map constructed from the state. A refined error bound can be proven for -finitely correlated states, which have an operational interpretation in terms of sequential quantum channels applied to the memory system. We can also obtain an analogous error bound for a class of matrix product density operators on a finite chain reconstructible by local marginals. In this case, a linear number of marginals must be estimated, obtaining a sample complexity of . The learning algorithm also works for states that are sufficiently close to a finitely correlated state, with the potential of providing competitive algorithms for other interesting families of states.
Llorens, S.; González, W.; Sentís, G.; Calsamiglia, J.; Muñoz-Tapia, R.; Bagan, Em.
Quantum Edge Detection Artículo de revista
En: Quantum, vol. 8, pp. 1289, 2025.
Resumen | Enlaces | BibTeX | Etiquetas: UAB
@article{nokey,
title = {Quantum Edge Detection},
author = {Llorens, S. and González, W. and Sentís, G. and Calsamiglia, J. and Muñoz-Tapia, R. and Bagan, Em.},
url = {https://quantum-journal.org/papers/q-2025-04-03-1687/},
doi = {doi.org/10.22331/q-2025-04-03-1687},
year = {2025},
date = {2025-03-04},
journal = {Quantum},
volume = {8},
pages = {1289},
abstract = {We consider a quantum system that is being continuously monitored, giving rise to a measurement signal. From such a stream of data, information needs to be inferred about the underlying system's dynamics. Here we focus on hypothesis testing problems and put forward the usage of sequential strategies where the signal is analyzed in real time, allowing the experiment to be concluded as soon as the underlying hypothesis can be identified with a certified prescribed success probability. We analyze the performance of sequential tests by studying the stopping-time behavior, showing a considerable advantage over currently-used strategies based on a fixed predetermined measurement time.},
keywords = {UAB},
pubstate = {published},
tppubtype = {article}
}
We consider a quantum system that is being continuously monitored, giving rise to a measurement signal. From such a stream of data, information needs to be inferred about the underlying system's dynamics. Here we focus on hypothesis testing problems and put forward the usage of sequential strategies where the signal is analyzed in real time, allowing the experiment to be concluded as soon as the underlying hypothesis can be identified with a certified prescribed success probability. We analyze the performance of sequential tests by studying the stopping-time behavior, showing a considerable advantage over currently-used strategies based on a fixed predetermined measurement time.
Dastbasteh, R.; Sanz Larrarte, O.; J. deMarti iOlius Etxezarreta Martinez, A.; Oliva del Moral, J.; Crespo Bofill, P.
Quantum CSS Duadic and Triadic Codes: New Insights and Properties Artículo de revista
En: Lecture Notes in Computer Science, vol. 15 176, 2025.
Resumen | Enlaces | BibTeX | Etiquetas: TECNUN
@article{nokey,
title = {Quantum CSS Duadic and Triadic Codes: New Insights and Properties},
author = {Dastbasteh, R. and Sanz Larrarte, O. and Etxezarreta Martinez, J. deMarti iOlius, A. and Oliva del Moral, J. and Crespo Bofill, P. },
url = {https://link.springer.com/chapter/10.1007/978-3-031-81824-0_5},
doi = { https://doi.org/10.48550/arXiv.2407.07753},
year = {2025},
date = {2025-02-28},
urldate = {2025-02-28},
journal = {Lecture Notes in Computer Science},
volume = {15 176},
abstract = {In this study, we investigate the construction of quantum CSS duadic codes with dimensions greater than one. We introduce a method for extending smaller splittings of quantum duadic codes to create larger, potentially degenerate quantum duadic codes. Furthermore, we present a technique for computing or bounding the minimum distances of quantum codes constructed through this approach. Additionally, we introduce quantum CSS triadic codes, a family of quantum codes with a rate of at least 1/3.},
keywords = {TECNUN},
pubstate = {published},
tppubtype = {article}
}
In this study, we investigate the construction of quantum CSS duadic codes with dimensions greater than one. We introduce a method for extending smaller splittings of quantum duadic codes to create larger, potentially degenerate quantum duadic codes. Furthermore, we present a technique for computing or bounding the minimum distances of quantum codes constructed through this approach. Additionally, we introduce quantum CSS triadic codes, a family of quantum codes with a rate of at least 1/3.
Styliaris, G.; Trivedi, R.; Pérez-García, D.; Cirac, J. I.
Matrix-product unitaries: Beyond quantum cellular automata Working paper
2025.
Resumen | Enlaces | BibTeX | Etiquetas: UCM-4.2
@workingpaper{nokey,
title = {Matrix-product unitaries: Beyond quantum cellular automata},
author = {Styliaris, G. and Trivedi, R. and Pérez-García, D. and Cirac, J. I.
},
url = {https://arxiv.org/abs/2406.10195},
doi = {doi.org/10.22331/q-2025-02-25-1645},
year = {2025},
date = {2025-02-20},
abstract = {Matrix-product unitaries (MPU) are 1D tensor networks describing time evolution and unitary symmetries of quantum systems, while their action on states by construction preserves the entanglement area law. MPU which are formed by a single repeated tensor are known to coincide with 1D quantum cellular automata (QCA), i.e., unitaries with an exact light cone. However, this correspondence breaks down for MPU with open boundary conditions, even if the resulting operator is translation-invariant. Such unitaries can turn short- to long-range correlations and thus alter the underlying phase of matter. Here we make the first steps towards a theory of MPU with uniform bulk but arbitrary boundary. In particular, we study the structure of a subclass with a direct-sum form which maximally violates the QCA property. We also consider the general case of MPU formed by site-dependent (nonuniform) tensors and show a correspondence between MPU and locally maximally entanglable states.},
keywords = {UCM-4.2},
pubstate = {published},
tppubtype = {workingpaper}
}
Matrix-product unitaries (MPU) are 1D tensor networks describing time evolution and unitary symmetries of quantum systems, while their action on states by construction preserves the entanglement area law. MPU which are formed by a single repeated tensor are known to coincide with 1D quantum cellular automata (QCA), i.e., unitaries with an exact light cone. However, this correspondence breaks down for MPU with open boundary conditions, even if the resulting operator is translation-invariant. Such unitaries can turn short- to long-range correlations and thus alter the underlying phase of matter. Here we make the first steps towards a theory of MPU with uniform bulk but arbitrary boundary. In particular, we study the structure of a subclass with a direct-sum form which maximally violates the QCA property. We also consider the general case of MPU formed by site-dependent (nonuniform) tensors and show a correspondence between MPU and locally maximally entanglable states.
Rodriguez-Grasa, P.; Farzan-Rodríguez, R.; Novelli, G.; Ban, Y.; Sanz, M.
Satellite image classification with neural quantum kernels Artículo de revista
En: Machine Learning: Science and Technology, vol. 6, no 1, 2025.
Resumen | Enlaces | BibTeX | Etiquetas: UPV/EHU
@article{nokey,
title = {Satellite image classification with neural quantum kernels},
author = {Rodriguez-Grasa, P. and Farzan-Rodríguez, R. and Novelli, G. and Ban, Y. and Sanz, M. },
url = {https://iopscience.iop.org/article/10.1088/2632-2153/ada86c/pdf},
doi = {10.1088/2632-2153/ada86c},
year = {2025},
date = {2025-02-18},
journal = {Machine Learning: Science and Technology},
volume = {6},
number = {1},
abstract = {Achieving practical applications of quantum machine learning (QML) for real-world scenarios
remains challenging despite significant theoretical progress. This paper proposes a novel approach
for classifying satellite images, a task of particular relevance to the earth observation industry, using
QML techniques. Specifically, we focus on classifying images that contain solar panels, addressing a
complex real-world classification problem. Our approach begins with classical pre-processing to
reduce the dimensionality of the satellite image dataset. We then apply neural quantum
kernels-quantum kernels derived from trained quantum neural networks-for classification. We
evaluate several strategies within this framework, demonstrating results that are competitive with
the best classical methods. Key findings include the robustness of or results and their scalability,
with successful performance achieved up to 8 qubits.
},
keywords = {UPV/EHU},
pubstate = {published},
tppubtype = {article}
}
Achieving practical applications of quantum machine learning (QML) for real-world scenarios
remains challenging despite significant theoretical progress. This paper proposes a novel approach
for classifying satellite images, a task of particular relevance to the earth observation industry, using
QML techniques. Specifically, we focus on classifying images that contain solar panels, addressing a
complex real-world classification problem. Our approach begins with classical pre-processing to
reduce the dimensionality of the satellite image dataset. We then apply neural quantum
kernels-quantum kernels derived from trained quantum neural networks-for classification. We
evaluate several strategies within this framework, demonstrating results that are competitive with
the best classical methods. Key findings include the robustness of or results and their scalability,
with successful performance achieved up to 8 qubits.
remains challenging despite significant theoretical progress. This paper proposes a novel approach
for classifying satellite images, a task of particular relevance to the earth observation industry, using
QML techniques. Specifically, we focus on classifying images that contain solar panels, addressing a
complex real-world classification problem. Our approach begins with classical pre-processing to
reduce the dimensionality of the satellite image dataset. We then apply neural quantum
kernels-quantum kernels derived from trained quantum neural networks-for classification. We
evaluate several strategies within this framework, demonstrating results that are competitive with
the best classical methods. Key findings include the robustness of or results and their scalability,
with successful performance achieved up to 8 qubits.
Lamata, L.
Digital-Analog Quantum Machine Learning Artículo de revista
En: Advanced Intelligent Discovery, vol. 1, iss. 1, 2025.
Resumen | Enlaces | BibTeX | Etiquetas: US
@article{nokey,
title = {Digital-Analog Quantum Machine Learning},
author = {Lamata, L.},
url = {https://advanced.onlinelibrary.wiley.com/doi/10.1002/aidi.202400023},
doi = {doi.org/10.1002/aidi.202400023},
year = {2025},
date = {2025-02-13},
journal = {Advanced Intelligent Discovery},
volume = {1},
issue = {1},
abstract = {Machine learning algorithms are extensively used in an increasing number of systems, applications, technologies, and products, both in industry and in society as a whole. They enable computing devices to learn from previous experience and therefore improve their performance in a certain context or environment. In this way, many useful possibilities have been made accessible. However, dealing with an increasing amount of data poses difficulties for classical devices. Quantum systems may offer a way forward, possibly enabling to scale up machine learning calculations in certain contexts. On the contrary, quantum systems themselves are also hard to scale up, due to decoherence and the fragility of quantum superpositions. In the short and mid term, it has been evidenced that a quantum paradigm that combines evolution under large analog blocks with discrete quantum gates, may be fruitful to achieve new knowledge of classical and quantum systems with no need of having a fault-tolerant quantum computer. In this perspective, we review some recent works that employ this digital-analog quantum paradigm to carry out efficient machine learning calculations with current quantum devices.},
keywords = {US},
pubstate = {published},
tppubtype = {article}
}
Machine learning algorithms are extensively used in an increasing number of systems, applications, technologies, and products, both in industry and in society as a whole. They enable computing devices to learn from previous experience and therefore improve their performance in a certain context or environment. In this way, many useful possibilities have been made accessible. However, dealing with an increasing amount of data poses difficulties for classical devices. Quantum systems may offer a way forward, possibly enabling to scale up machine learning calculations in certain contexts. On the contrary, quantum systems themselves are also hard to scale up, due to decoherence and the fragility of quantum superpositions. In the short and mid term, it has been evidenced that a quantum paradigm that combines evolution under large analog blocks with discrete quantum gates, may be fruitful to achieve new knowledge of classical and quantum systems with no need of having a fault-tolerant quantum computer. In this perspective, we review some recent works that employ this digital-analog quantum paradigm to carry out efficient machine learning calculations with current quantum devices.
Romero-Pallejà, J.; Ahiable, J.; Marconi, C.; Sanpera, A.
Multipartite entanglement in the diagonal symmetric subspace Artículo de revista
En: Journal of Mathematical Physics, vol. 66, pp. 22203, 2025.
Resumen | Enlaces | BibTeX | Etiquetas: UAB
@article{nokey,
title = {Multipartite entanglement in the diagonal symmetric subspace},
author = {Romero-Pallejà, J. and Ahiable, J. and Marconi, C. and Sanpera, A. },
url = {https://pubs.aip.org/aip/jmp/article-abstract/66/2/022203/3335365/Multipartite-entanglement-in-the-diagonal?redirectedFrom=fulltext},
doi = {doi.org/10.1063/5.0240964},
year = {2025},
date = {2025-02-11},
journal = {Journal of Mathematical Physics},
volume = {66},
pages = {22203},
abstract = {We investigate the entanglement properties in the symmetric subspace of N-partite d-dimensional systems (qudits). As it happens already for bipartite diagonal symmetric states, also in the multipartite case the local dimension d plays a crucial role. Here, we demonstrate that there is no bound entanglement for d = 3, 4 and N = 3. Using different techniques, we present strong analytical evidence that no bound entanglement exist for any N if d ≤ 4. Interestingly, bound entanglement of diagonal symmetric states exist for any number of parties, N ≥ 2, and local dimensions d ≥ 5.},
keywords = {UAB},
pubstate = {published},
tppubtype = {article}
}
We investigate the entanglement properties in the symmetric subspace of N-partite d-dimensional systems (qudits). As it happens already for bipartite diagonal symmetric states, also in the multipartite case the local dimension d plays a crucial role. Here, we demonstrate that there is no bound entanglement for d = 3, 4 and N = 3. Using different techniques, we present strong analytical evidence that no bound entanglement exist for any N if d ≤ 4. Interestingly, bound entanglement of diagonal symmetric states exist for any number of parties, N ≥ 2, and local dimensions d ≥ 5.
Escrig, G.; Campos, R.; Qi, H.; Martin-Delgado, M. A.
Quantum Bayesian Inference with Renormalization for Gravitational Waves Artículo de revista
En: The Astrophysical Journal Letters, vol. 979, iss. 2, pp. L36, 2025.
Resumen | Enlaces | BibTeX | Etiquetas: UCM-4.3
@article{nokey,
title = {Quantum Bayesian Inference with Renormalization for Gravitational Waves},
author = {Escrig, G. and Campos, R. and Qi, H. and Martin-Delgado, M.A. },
url = {https://iopscience.iop.org/article/10.3847/2041-8213/ada6ae},
doi = {10.3847/2041-8213/ada6ae},
year = {2025},
date = {2025-01-28},
journal = {The Astrophysical Journal Letters},
volume = {979},
issue = {2},
pages = {L36},
abstract = {Advancements in gravitational-wave (GW) interferometers, particularly the next generation, are poised to enable the detections of orders of magnitude more GWs from compact binary coalescences. While the surge in detections will profoundly advance GW astronomy and multimessenger astrophysics, it also poses significant computational challenges in parameter estimation. In this work, we introduce a hybrid quantum algorithm qBIRD, which performs quantum Bayesian inference with renormalization and downsampling to infer GW parameters. We validate the algorithm using both simulated and observed GWs from binary black hole mergers on quantum simulators, demonstrating that its accuracy is comparable to classical Markov Chain Monte Carlo methods. Currently, our analyses focus on a subset of parameters, including chirp mass and mass ratio, due to the limitations from classical hardware in simulating quantum algorithms. However, qBIRD can accommodate a broader parameter space when the constraints are eliminated with a small-scale quantum computer of sufficient logical qubits.},
keywords = {UCM-4.3},
pubstate = {published},
tppubtype = {article}
}
Advancements in gravitational-wave (GW) interferometers, particularly the next generation, are poised to enable the detections of orders of magnitude more GWs from compact binary coalescences. While the surge in detections will profoundly advance GW astronomy and multimessenger astrophysics, it also poses significant computational challenges in parameter estimation. In this work, we introduce a hybrid quantum algorithm qBIRD, which performs quantum Bayesian inference with renormalization and downsampling to infer GW parameters. We validate the algorithm using both simulated and observed GWs from binary black hole mergers on quantum simulators, demonstrating that its accuracy is comparable to classical Markov Chain Monte Carlo methods. Currently, our analyses focus on a subset of parameters, including chirp mass and mass ratio, due to the limitations from classical hardware in simulating quantum algorithms. However, qBIRD can accommodate a broader parameter space when the constraints are eliminated with a small-scale quantum computer of sufficient logical qubits.
Hernández Caceres, J. M.; Fernández Rúa, I.; Fernández-Combarro Álvarez, E.
Efficient quantum algorithms to find substructures on finite algebras Artículo de revista
En: Quantum Information and Computation , vol. 23, no 15, 2024, ISBN: 1533-7146.
Resumen | Enlaces | BibTeX | Etiquetas: UNIOVI
@article{nokey,
title = {Efficient quantum algorithms to find substructures on finite algebras},
author = {Hernández Caceres, J. M. and Fernández Rúa, I. and Fernández-Combarro Álvarez, E. },
url = {https://www.rintonpress.com/xxqic23/qic-23-1516/1275-1290.pdf},
doi = {doi.org/10.26421/QIC23.15-16-2},
isbn = {1533-7146},
year = {2024},
date = {2024-12-16},
journal = {Quantum Information and Computation },
volume = {23},
number = {15},
abstract = {When classifying a collection of finite algebras (for instance, in the computational classification of finite semifields), an important task is the determination of substructures such as the right, middle, and left nuclei, the nucleus, and the center. Finding these structures may become computationally expensive when there is no additional information about the algebra properties. In this paper, we introduce quantum algorithms than solve this task efficiently, by formulating it as an instance of the Hidden Subgroup Problem (HSP) {over Abelian groups}. We give detailed constructions of the quantum circuits involved in the process and prove that the overall (quantum) complexity of our algorithm is polynomial in the dimension of the algebra, while a similar approach with classical computers would require an exponential number of queries to the HSP function},
keywords = {UNIOVI},
pubstate = {published},
tppubtype = {article}
}
When classifying a collection of finite algebras (for instance, in the computational classification of finite semifields), an important task is the determination of substructures such as the right, middle, and left nuclei, the nucleus, and the center. Finding these structures may become computationally expensive when there is no additional information about the algebra properties. In this paper, we introduce quantum algorithms than solve this task efficiently, by formulating it as an instance of the Hidden Subgroup Problem (HSP) {over Abelian groups}. We give detailed constructions of the quantum circuits involved in the process and prove that the overall (quantum) complexity of our algorithm is polynomial in the dimension of the algebra, while a similar approach with classical computers would require an exponential number of queries to the HSP function
Lazar, J.; Giner Olavarrieta, S.; Gatti, G.; Argüelles, C.; Sanz, M.
New Pathways in Neutrino Physics via Quantum-Encoded Data Analysis Working paper
2024.
Resumen | Enlaces | BibTeX | Etiquetas: UPV/EHU
@workingpaper{nokey,
title = {New Pathways in Neutrino Physics via Quantum-Encoded Data Analysis},
author = {Lazar, J. and Giner Olavarrieta, S. and Gatti, G. and Argüelles, C. and Sanz, M. },
url = {https://arxiv.org/abs/2402.19306},
doi = {doi.org/10.48550/arXiv.2402.19306},
year = {2024},
date = {2024-12-11},
urldate = {2024-12-11},
abstract = {Ever-increasing amount of data is produced by particle detectors in their quest to unveil the laws of Nature. The large data rate requires the use of specialized triggers that promptly reduce the data rate to a manageable level; however, in doing so, unexpected new phenomena may escape detection. Additionally, the large data rate is increasingly difficult to analyze effectively, which has led to a recent revolution on machine learning techniques. Here, we present a methodology based on recent quantum compression techniques that has the capacity to store exponentially more amount of information than classically available methods. To demonstrate this, we encode the full neutrino telescope event information using parity observables in an IBM quantum processor using 8 qubits. Then we show that we can recover the information stored on the quantum computer with a fidelity of 84%. Finally, we illustrate the use of our protocol by performing a classification task that separates electron-neutrino events to muon-neutrinos events in a neutrino telescope. This new capability would eventually allow us to solve the street light effect in particle physics, where we only record signatures of particles with which we are familiar.},
keywords = {UPV/EHU},
pubstate = {published},
tppubtype = {workingpaper}
}
Ever-increasing amount of data is produced by particle detectors in their quest to unveil the laws of Nature. The large data rate requires the use of specialized triggers that promptly reduce the data rate to a manageable level; however, in doing so, unexpected new phenomena may escape detection. Additionally, the large data rate is increasingly difficult to analyze effectively, which has led to a recent revolution on machine learning techniques. Here, we present a methodology based on recent quantum compression techniques that has the capacity to store exponentially more amount of information than classically available methods. To demonstrate this, we encode the full neutrino telescope event information using parity observables in an IBM quantum processor using 8 qubits. Then we show that we can recover the information stored on the quantum computer with a fidelity of 84%. Finally, we illustrate the use of our protocol by performing a classification task that separates electron-neutrino events to muon-neutrinos events in a neutrino telescope. This new capability would eventually allow us to solve the street light effect in particle physics, where we only record signatures of particles with which we are familiar.
Simen, A.; Flores-Garrigos, C.; Hegade, N. N.; Montalban, I.; Vives-Gilabert, Y.; Michon, E.; Zhang, Q.; Solano, E.; J.D. 2 Martín-Guerrero, 3
Digital-analog quantum convolutional neural networks for image classification Artículo de revista
En: Physical Review Research, vol. 6, iss. 4, pp. 2060, 2024.
Resumen | Enlaces | BibTeX | Etiquetas: UV
@article{nokey,
title = {Digital-analog quantum convolutional neural networks for image classification},
author = {Simen, A. and Flores-Garrigos, C. and Hegade, N.N. and Montalban, I. and Vives-Gilabert, Y. and Michon, E. and Zhang, Q. and Solano, E. and Martín-Guerrero, J.D.
2,3,§},
url = {https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.6.L042060},
doi = {doi.org/10.1103/PhysRevResearch.6.L042060},
year = {2024},
date = {2024-12-11},
journal = {Physical Review Research},
volume = {6},
issue = {4},
pages = {2060},
abstract = {We propose digital-analog quantum kernels for enhancing the detection of complex features in the classification of images. We consider multipartite-entangled analog blocks, stemming from native Ising interactions in neutral-atom quantum processors, and individual operations as digital steps to implement the protocol. To further improve the detection of complex features, we apply multiple quantum kernels by varying the qubit connectivity according to the hardware constraints. An architecture that combines nontrainable quantum kernels and standard convolutional neural networks is used to classify realistic medical images, from breast cancer and pneumonia diseases, with a significantly reduced number of parameters. Despite this fact, the model exhibits better performance than its classical counterparts and achieves comparable metrics according to public benchmarks. These findings highlight the potential of digital-analog quantum convolutions in extracting complex and meaningful features from images, positioning them as a candidate model for addressing challenging classification problems.},
keywords = {UV},
pubstate = {published},
tppubtype = {article}
}
We propose digital-analog quantum kernels for enhancing the detection of complex features in the classification of images. We consider multipartite-entangled analog blocks, stemming from native Ising interactions in neutral-atom quantum processors, and individual operations as digital steps to implement the protocol. To further improve the detection of complex features, we apply multiple quantum kernels by varying the qubit connectivity according to the hardware constraints. An architecture that combines nontrainable quantum kernels and standard convolutional neural networks is used to classify realistic medical images, from breast cancer and pneumonia diseases, with a significantly reduced number of parameters. Despite this fact, the model exhibits better performance than its classical counterparts and achieves comparable metrics according to public benchmarks. These findings highlight the potential of digital-analog quantum convolutions in extracting complex and meaningful features from images, positioning them as a candidate model for addressing challenging classification problems.
Espinosa, E. M.; Wu, L. A.
Study on quantum thermalization from thermal initial states in a superconducting quantum computer Working paper
2024.
Resumen | Enlaces | BibTeX | Etiquetas: UPV/EHU
@workingpaper{nokey,
title = {Study on quantum thermalization from thermal initial states in a superconducting quantum computer},
author = {Espinosa, E.M. and Wu, L.A.},
url = {https://arxiv.org/abs/2403.14630},
doi = {doi.org/10.48550/arXiv.2403.14630},
year = {2024},
date = {2024-12-04},
urldate = {2024-12-04},
abstract = {Quantum thermalization in contemporary quantum devices, in particular quantum computers, has recently attracted significant theoretical interest. Unusual thermalization processes, such as the Quantum Mpemba Effect (QME), have been explored theoretically. However, there is a shortage of experimental results due to the difficulty in preparing thermal states. In this paper, we propose a protocol to indirectly address this challenge. Moreover, we experimentally validate our protocol using IBM quantum devices, providing results for unusual relaxation in equidistant quenches as predicted for the IBM qubit. We also assess the formalism introduced for the QME, obtaining results consistent with the theoretical predictions. This demonstration underscores that our protocol can provide an alternative way of studying thermal states physics when their direct preparation may be too difficult.},
keywords = {UPV/EHU},
pubstate = {published},
tppubtype = {workingpaper}
}
Quantum thermalization in contemporary quantum devices, in particular quantum computers, has recently attracted significant theoretical interest. Unusual thermalization processes, such as the Quantum Mpemba Effect (QME), have been explored theoretically. However, there is a shortage of experimental results due to the difficulty in preparing thermal states. In this paper, we propose a protocol to indirectly address this challenge. Moreover, we experimentally validate our protocol using IBM quantum devices, providing results for unusual relaxation in equidistant quenches as predicted for the IBM qubit. We also assess the formalism introduced for the QME, obtaining results consistent with the theoretical predictions. This demonstration underscores that our protocol can provide an alternative way of studying thermal states physics when their direct preparation may be too difficult.
Sun, Y.; Wu, L. A.
Quantum search algorithm on weighted databases Working paper
2024.
Resumen | Enlaces | BibTeX | Etiquetas: UPV/EHU
@workingpaper{nokey,
title = {Quantum search algorithm on weighted databases},
author = {Sun, Y. and Wu, L.A. },
url = {https://arxiv.org/abs/2312.01590},
doi = {doi.org/10.48550/arXiv.2312.01590},
year = {2024},
date = {2024-12-03},
urldate = {2024-12-03},
abstract = {The Grover algorithm is a crucial solution for addressing unstructured search problems and has emerged as an essential quantum subroutine in various complex algorithms. By using a different approach with previous studies, this research extensively investigates Grover's search methodology within non-uniformly distributed databases, a scenario frequently encountered in practical applications. Our analysis reveals that the behavior of the Grover evolution differs significantly when applied to non-uniform databases compared to uniform or 'unstructured databases'. Based on the property of differential equation, it is observed that the search process facilitated by this evolution does not consistently result in a speed-up, and we have identified specific criteria for such situations. Furthermore, we have extended this investigation to databases characterized by coherent states, confirming the speed-up achieved through Grover evolution via rigorous numerical verification. In conclusion, our study provides an enhancement to the original Grover algorithm, offering insights to optimize implementation strategies and broaden its range of applications.},
keywords = {UPV/EHU},
pubstate = {published},
tppubtype = {workingpaper}
}
The Grover algorithm is a crucial solution for addressing unstructured search problems and has emerged as an essential quantum subroutine in various complex algorithms. By using a different approach with previous studies, this research extensively investigates Grover's search methodology within non-uniformly distributed databases, a scenario frequently encountered in practical applications. Our analysis reveals that the behavior of the Grover evolution differs significantly when applied to non-uniform databases compared to uniform or 'unstructured databases'. Based on the property of differential equation, it is observed that the search process facilitated by this evolution does not consistently result in a speed-up, and we have identified specific criteria for such situations. Furthermore, we have extended this investigation to databases characterized by coherent states, confirming the speed-up achieved through Grover evolution via rigorous numerical verification. In conclusion, our study provides an enhancement to the original Grover algorithm, offering insights to optimize implementation strategies and broaden its range of applications.
Wang, Z. M.; Wu, S. L.; Byrd, M. S.; Wu, L. A.
Going beyond quantum Markovianity and back to reality: An exact master equation study Working paper
2024.
Resumen | Enlaces | BibTeX | Etiquetas: UPV/EHU
@workingpaper{nokey,
title = {Going beyond quantum Markovianity and back to reality: An exact master equation study},
author = {Wang, Z.M. and Wu, S.L. and Byrd, M.S. and Wu, L.A. },
url = {https://arxiv.org/abs/2411.17197},
doi = {doi.org/10.48550/arXiv.2411.17197},
year = {2024},
date = {2024-12-03},
urldate = {2024-12-03},
abstract = {The precise characterization of dynamics in open quantum systems often presents significant challenges, leading to the introduction of various approximations to simplify a model. One commonly used strategy involves Markovian approximations, assuming a memoryless environment. In this study, such approximations are not used and an analytical dynamical depiction of an open quantum system is provided. The system under consideration is an oscillator that is surrounded by a bath of oscillators. The resulting dynamics are characterized by a second-order complex coefficient linear differential equation, which may be either homogeneous or inhomogeneous. Moreover, distinct dynamical regions emerge, depending on certain parameter values. Notably, the steady-state average excitation number (AEN) of the system shows rapid escalation with increasing non-Markovianity, reflecting the intricacies of real-world dynamics. In cases where there is detuning between the system frequency and the environmental central frequency within a non-Markovian regime, the AEN maintains its initial value for an extended period. Furthermore, the application of pulse control can effectively protect the quantum system from decoherence effects without using approximations. The pulse control can not only prolong the relaxation time of the oscillator, but can also be used to speed up the relaxation process, depending on the specifications of the pulse. By employing a kick pulse, the Mpemba effect can be observed in the non-Markovian regime in a surprisingly super-cooling-like effect.},
keywords = {UPV/EHU},
pubstate = {published},
tppubtype = {workingpaper}
}
The precise characterization of dynamics in open quantum systems often presents significant challenges, leading to the introduction of various approximations to simplify a model. One commonly used strategy involves Markovian approximations, assuming a memoryless environment. In this study, such approximations are not used and an analytical dynamical depiction of an open quantum system is provided. The system under consideration is an oscillator that is surrounded by a bath of oscillators. The resulting dynamics are characterized by a second-order complex coefficient linear differential equation, which may be either homogeneous or inhomogeneous. Moreover, distinct dynamical regions emerge, depending on certain parameter values. Notably, the steady-state average excitation number (AEN) of the system shows rapid escalation with increasing non-Markovianity, reflecting the intricacies of real-world dynamics. In cases where there is detuning between the system frequency and the environmental central frequency within a non-Markovian regime, the AEN maintains its initial value for an extended period. Furthermore, the application of pulse control can effectively protect the quantum system from decoherence effects without using approximations. The pulse control can not only prolong the relaxation time of the oscillator, but can also be used to speed up the relaxation process, depending on the specifications of the pulse. By employing a kick pulse, the Mpemba effect can be observed in the non-Markovian regime in a surprisingly super-cooling-like effect.
Ruiz, R.; Sopena, A.; Pozsgay, B.; López, E.
Efficient Eigenstate Preparation in an Integrable Model with Hilbert Space Fragmentation Working paper
2024.
Resumen | Enlaces | BibTeX | Etiquetas: CSIC-4.7
@workingpaper{nokey,
title = {Efficient Eigenstate Preparation in an Integrable Model with Hilbert Space Fragmentation},
author = {Ruiz, R. and Sopena, A. and Pozsgay, B. and López, E. },
url = {https://arxiv.org/abs/2411.15132},
doi = {doi.org/10.48550/arXiv.2411.15132},
year = {2024},
date = {2024-12-03},
abstract = {We consider the preparation of all the eigenstates of spin chains using quantum circuits. It is known that generic eigenstates of free-fermionic spin chains can be prepared with circuits whose depth grows only polynomially with the length of the chain and the number of particles. We show that the polynomial growth is also achievable for selected interacting models where the interaction between the particles is sufficiently simple. Our working example is the folded XXZ model, an integrable spin chain that exhibits Hilbert space fragmentation. We present the explicit quantum circuits that prepare arbitrary eigenstates of this model on an open chain efficiently. We perform error-mitigated noisy simulations with circuits of up to 13 qubits and different connectivities between qubits, achieving a relative error below 5%. As a byproduct, we extend a recent reformulation of the Bethe ansatz as a quantum circuit from closed to open boundary conditions.},
keywords = {CSIC-4.7},
pubstate = {published},
tppubtype = {workingpaper}
}
We consider the preparation of all the eigenstates of spin chains using quantum circuits. It is known that generic eigenstates of free-fermionic spin chains can be prepared with circuits whose depth grows only polynomially with the length of the chain and the number of particles. We show that the polynomial growth is also achievable for selected interacting models where the interaction between the particles is sufficiently simple. Our working example is the folded XXZ model, an integrable spin chain that exhibits Hilbert space fragmentation. We present the explicit quantum circuits that prepare arbitrary eigenstates of this model on an open chain efficiently. We perform error-mitigated noisy simulations with circuits of up to 13 qubits and different connectivities between qubits, achieving a relative error below 5%. As a byproduct, we extend a recent reformulation of the Bethe ansatz as a quantum circuit from closed to open boundary conditions.
