Application
Quantum, variational and adiabatic genetic algorithms and their applications
Quantum Information Science and Technology (QUINST)
Group Description:
Quantum mechanics is at the heart of our technology and economy (laser and transistor are quantum devices), but its full potential is far from being realized. Recent technological advances in optics, nanoscience, and engineering enable experimenters to create artificial structures or subject microscopic and mesoscopic systems to new manipulable conditions where quantum phenomena play a fundamental role.
Quantum technologies exploit these effects for practical purposes. Quantum science aims to discover, study, and control quantum effects at a fundamental level. These are two sides of a virtuous circle: new technologies lead to the discovery and study of new phenomena that will lead to new technologies.
Our goal is to control and understand quantum phenomena at the multidisciplinary intersection of Quantum Information, Quantum Optics, Cold Atoms, Quantum Control, Spintronics, Quantum Metrology, Atomic Interferometry, Superconducting Qubits and Circuit QED, and Foundations of Quantum Mechanics.
The QUINST team comprises principal investigators Iñigo L. Egusquiza and Mikel Sanz, along with Xi Chen, Gonzalo Muga, Enrique Rico, and Liano Wu.
Activity description:
This activity focuses on the tasks necessary to characterize and improve quantum algorithms and processes and search for their applications in industrial processes, finance, logistics, AI, quantum chemistry, among others. It consists of the following tasks:
- Development of mathematical tools for the analysis of the properties of quantum algorithms. In particular, the use of operator theory will be studied to bound errors in approximate quantum algorithms, and quantum channel theory will be employed to analyze the convergence of heuristic algorithms, such as quantum genetic algorithms.
- Analyse alternative quantum computing paradigms in NISQ processors against control errors, coherence errors, cross-talk, etc. In this context, the development of new “self-protected” quantum algorithms like Shor or Grover will be studied, as well as simulations and quantum AI software more resilient to errors.
- Optimization and acceleration of adiabatic-type algorithms using quantum control techniques or “adiabatic shortcuts,” introducing iterative and adaptive methods that only use knowledge of the initial and final Hamiltonians, and artificial intelligence and machine learning techniques to optimize speed and robustness against errors.
- Development of industrial applications and use cases for quantum algorithms, particularly in finance, logistics, artificial intelligence, and quantum chemistry, among others.
- Application of quantum algorithms (free from sign problems and other difficulties of classical computing) to the simulation of models of interest in nuclear and high-energy physics. Specifically, problems of many strongly correlated bodies with dynamic abelian and non-abelian gauge degrees of freedom and their application to the study of gauge theories.
Results
Biswas, S.; Rico, E.; Grass, T.
Ring-exchange physics in a chain of three-level ions Journal Article
In: Quantum , 2025.
Abstract | Links | BibTeX | Tags: 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.
Espinosa, E. M.; Wu, L. A.
Study on quantum thermalization from thermal initial states in a superconducting quantum computer Unpublished
Preprint, 2024.
Abstract | Links | BibTeX | Tags: UPV/EHU
@unpublished{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},
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.},
howpublished = {Preprint},
keywords = {UPV/EHU},
pubstate = {published},
tppubtype = {unpublished}
}
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 Unpublished
2024.
Abstract | Links | BibTeX | Tags: UPV/EHU
@unpublished{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},
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 = {unpublished}
}
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 Unpublished
Preprint, 2024.
Abstract | Links | BibTeX | Tags: UPV/EHU
@unpublished{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},
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.},
howpublished = {Preprint},
keywords = {UPV/EHU},
pubstate = {published},
tppubtype = {unpublished}
}
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.
Mariella, N.; Murphy, T.; Di Marcantonio, F.; Najafi, K.; Vallecorsa, S.; Zhuk, S.; Rico, E.
Order Parameter Discovery for Quantum Many-Body Systems Unpublished
Preprint, 2024.
Abstract | Links | BibTeX | Tags: UPV/EHU
@unpublished{nokey,
title = {Order Parameter Discovery for Quantum Many-Body Systems},
author = {Mariella, N. and Murphy, T. and Di Marcantonio, F. and Najafi, K. and Vallecorsa, S. and Zhuk, S. and Rico, E.},
url = {https://arxiv.org/abs/2408.01400},
doi = {doi.org/10.48550/arXiv.2408.01400},
year = {2024},
date = {2024-11-18},
abstract = {Quantum phase transitions reveal deep insights into the behavior of many-body quantum systems, but identifying these transitions without well-defined order parameters remains a significant challenge. In this work, we introduce a novel approach to constructing phase diagrams using the vector field of the reduced fidelity susceptibility (RFS). This method maps quantum phases and formulates an optimization problem to discover observables corresponding to order parameters. We demonstrate the effectiveness of our approach by applying it to well-established models, including the Axial Next Nearest Neighbour Interaction (ANNNI) model, a cluster state model, and a chain of Rydberg atoms. By analyzing observable decompositions into eigen-projectors and finite-size scaling, our method successfully identifies order parameters and characterizes quantum phase transitions with high precision. Our results provide a powerful tool for exploring quantum phases in systems where conventional order parameters are not readily available.},
howpublished = {Preprint},
keywords = {UPV/EHU},
pubstate = {published},
tppubtype = {unpublished}
}
Quantum phase transitions reveal deep insights into the behavior of many-body quantum systems, but identifying these transitions without well-defined order parameters remains a significant challenge. In this work, we introduce a novel approach to constructing phase diagrams using the vector field of the reduced fidelity susceptibility (RFS). This method maps quantum phases and formulates an optimization problem to discover observables corresponding to order parameters. We demonstrate the effectiveness of our approach by applying it to well-established models, including the Axial Next Nearest Neighbour Interaction (ANNNI) model, a cluster state model, and a chain of Rydberg atoms. By analyzing observable decompositions into eigen-projectors and finite-size scaling, our method successfully identifies order parameters and characterizes quantum phase transitions with high precision. Our results provide a powerful tool for exploring quantum phases in systems where conventional order parameters are not readily available.
Pranav, C.; Koushik, P.; Garcia-de-Andoin, M.; Ban, Y.; Sanz, M.; Chen, X.
Photonic counterdiabatic quantum optimization algorithm Journal Article
In: Communications Physics, no. 315, 2024, ISBN: 2399-3650.
Abstract | Links | BibTeX | Tags: UPV/EHU
@article{nokey,
title = {Photonic counterdiabatic quantum optimization algorithm},
author = {Pranav, C. and Koushik, P. and Garcia-de-Andoin, M. and Ban, Y. and Sanz, M. and Chen, X.},
url = {https://www.nature.com/articles/s42005-024-01807-2.pdf},
doi = {doi.org/10.1038/s42005-024-01807-2},
isbn = {2399-3650},
year = {2024},
date = {2024-09-30},
journal = {Communications Physics},
number = {315},
abstract = {One of the key applications of near-term quantum computers has been the development of quantum optimization algorithms. However, these algorithms have largely been focused on qubit-based technologies. Here, we propose a hybrid quantum-classical approximate optimization algorithm for photonic quantum computing, specifically tailored for addressing continuous-variable optimization problems. Inspired by counterdiabatic protocols, our algorithm reduces the required quantum operations for optimization compared to adiabatic protocols. This reduction enables us to tackle non-convex continuous optimization within the near-term era of quantum computing. Through illustrative benchmarking, we show that our approach can outperform existing state-of-the-art hybrid adiabatic quantum algorithms in terms of convergence and implementability. Our algorithm offers a practical and accessible experimental realization, bypassing the need for high-order operations and overcoming experimental constraints. We conduct a proof-of-principle demonstration on Xanadu’s eight-mode nanophotonic quantum chip, successfully showcasing the feasibility and potential impact of the algorithm.},
keywords = {UPV/EHU},
pubstate = {published},
tppubtype = {article}
}
One of the key applications of near-term quantum computers has been the development of quantum optimization algorithms. However, these algorithms have largely been focused on qubit-based technologies. Here, we propose a hybrid quantum-classical approximate optimization algorithm for photonic quantum computing, specifically tailored for addressing continuous-variable optimization problems. Inspired by counterdiabatic protocols, our algorithm reduces the required quantum operations for optimization compared to adiabatic protocols. This reduction enables us to tackle non-convex continuous optimization within the near-term era of quantum computing. Through illustrative benchmarking, we show that our approach can outperform existing state-of-the-art hybrid adiabatic quantum algorithms in terms of convergence and implementability. Our algorithm offers a practical and accessible experimental realization, bypassing the need for high-order operations and overcoming experimental constraints. We conduct a proof-of-principle demonstration on Xanadu’s eight-mode nanophotonic quantum chip, successfully showcasing the feasibility and potential impact of the algorithm.
Reichert, M.; Zhuang, Q.; Sanz, M.
Heisenberg-Limited Quantum Lidar for Joint Range and Velocity Estimation Journal Article
In: Physical Review Letters (PRL), vol. 133, iss. 13, 2024, ISBN: 0031-9005.
Abstract | Links | BibTeX | Tags: UPV/EHU
@article{nokey,
title = {Heisenberg-Limited Quantum Lidar for Joint Range and Velocity Estimation},
author = {Reichert, M. and Zhuang, Q. and Sanz, M.
},
doi = {10.1103/PhysRevLett.133.130801},
isbn = {0031-9005},
year = {2024},
date = {2024-09-26},
journal = {Physical Review Letters (PRL)},
volume = {133},
issue = {13},
abstract = {We propose a quantum lidar protocol to jointly estimate the range and velocity of a target by illuminating it with a single beam of pulsed displaced squeezed light. In the lossless scenario, we show that the mean-squared errors of both range and velocity estimations are inversely proportional to the squared number of signal photons, simultaneously attaining the Heisenberg limit. This is achieved by engineering the multiphoton squeezed state of the temporal modes and adopting standard homodyne detection. To assess the robustness of the quantum protocol, we incorporate photon losses and detuning of the homodyne receiver. Our findings reveal a quantum advantage over the best-known classical strategy across a wide range of round-trip transmissivities. Particularly, the quantum advantage is substantial for sufficiently small losses, even when compared to the optimal—potentially unattainable—classical performance limit. The quantum advantage also extends to the practical case where quantum engineering is done on top of a strong classical coherent state with watts of power. This, together with the robustness against losses and the feasibility of the measurement with state-of-the-art technology, make the protocol highly promising for near-term implementation.},
keywords = {UPV/EHU},
pubstate = {published},
tppubtype = {article}
}
We propose a quantum lidar protocol to jointly estimate the range and velocity of a target by illuminating it with a single beam of pulsed displaced squeezed light. In the lossless scenario, we show that the mean-squared errors of both range and velocity estimations are inversely proportional to the squared number of signal photons, simultaneously attaining the Heisenberg limit. This is achieved by engineering the multiphoton squeezed state of the temporal modes and adopting standard homodyne detection. To assess the robustness of the quantum protocol, we incorporate photon losses and detuning of the homodyne receiver. Our findings reveal a quantum advantage over the best-known classical strategy across a wide range of round-trip transmissivities. Particularly, the quantum advantage is substantial for sufficiently small losses, even when compared to the optimal—potentially unattainable—classical performance limit. The quantum advantage also extends to the practical case where quantum engineering is done on top of a strong classical coherent state with watts of power. This, together with the robustness against losses and the feasibility of the measurement with state-of-the-art technology, make the protocol highly promising for near-term implementation.
Cobos, J.; Locher, D. F.; Bermudez, A.; Müller, M.; Rico, E.
Noise-Aware Variational Eigensolvers: A Dissipative Route for Lattice Gauge Theories Journal Article
In: PRX Quantum, vol. 5, iss. 3, pp. 030340, 2024, ISSN: 2691-3399.
Abstract | Links | BibTeX | Tags: UPV/EHU
@article{nokey,
title = {Noise-Aware Variational Eigensolvers: A Dissipative Route for Lattice Gauge Theories},
author = {Cobos, J. and Locher, D.F. and Bermudez, A. and Müller, M. and Rico, E. },
url = {https://journals.aps.org/prxquantum/abstract/10.1103/PRXQuantum.5.030340},
doi = {doi.org/10.1103/PRXQuantum.5.030340},
issn = {2691-3399},
year = {2024},
date = {2024-08-26},
urldate = {2024-08-26},
journal = {PRX Quantum},
volume = {5},
issue = {3},
pages = {030340},
abstract = {We propose a novel variational ansatz for the ground-state preparation of the lattice gauge theory (LGT) in quantum simulators. It combines dissipative and unitary operations in a completely deterministic scheme with a circuit depth that does not scale with the size of the considered lattice. We find that, with very few variational parameters, the ansatz can achieve precision in energy in both the confined and deconfined phase of the LGT. We benchmark our proposal against the unitary Hamiltonian variational ansatz showing a reduction in the required number of variational layers to achieve a target precision. After performing a finite-size scaling analysis, we show that our dissipative variational ansatz can predict accurate critical exponents without requiring a number of layers that scales with the system size, which is the standard situation for unitary ansätze. Furthermore, we investigate the performance of this variational eigensolver subject to circuit-level noise, determining variational error thresholds that fix the error rate below which it would be beneficial to increase the number of layers. In light of these quantities and for typical gate errors in current quantum processors, we provide a detailed assessment of the prospects of our scheme to explore the LGT on near-term devices.},
keywords = {UPV/EHU},
pubstate = {published},
tppubtype = {article}
}
We propose a novel variational ansatz for the ground-state preparation of the lattice gauge theory (LGT) in quantum simulators. It combines dissipative and unitary operations in a completely deterministic scheme with a circuit depth that does not scale with the size of the considered lattice. We find that, with very few variational parameters, the ansatz can achieve precision in energy in both the confined and deconfined phase of the LGT. We benchmark our proposal against the unitary Hamiltonian variational ansatz showing a reduction in the required number of variational layers to achieve a target precision. After performing a finite-size scaling analysis, we show that our dissipative variational ansatz can predict accurate critical exponents without requiring a number of layers that scales with the system size, which is the standard situation for unitary ansätze. Furthermore, we investigate the performance of this variational eigensolver subject to circuit-level noise, determining variational error thresholds that fix the error rate below which it would be beneficial to increase the number of layers. In light of these quantities and for typical gate errors in current quantum processors, we provide a detailed assessment of the prospects of our scheme to explore the LGT on near-term devices.
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 Unpublished
Preprint, 2024.
Abstract | Links | BibTeX | Tags: UPV/EHU
@unpublished{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 = {2024},
date = {2024-08-08},
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},
howpublished = {Preprint},
keywords = {UPV/EHU},
pubstate = {published},
tppubtype = {unpublished}
}
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
Gonzalez-Raya, T.; Pirandola, S.; Sanz, M.
Satellite-based entanglement distribution and quantum teleportation with continuous variables Journal Article
In: Communications Physics, vol. 7, no. 126, 2024, ISBN: 2399-3650.
Abstract | Links | BibTeX | Tags: UPV/EHU
@article{nokey,
title = {Satellite-based entanglement distribution and quantum teleportation with continuous variables},
author = {Gonzalez-Raya, T. and Pirandola, S. and Sanz, M. },
url = {https://www.nature.com/articles/s42005-024-01612-x.pdf},
doi = {doi.org/10.1038/s42005-024-01612-x},
isbn = {2399-3650},
year = {2024},
date = {2024-04-11},
journal = {Communications Physics},
volume = {7},
number = {126},
abstract = {Advances in satellite quantum communications aim at reshaping the global telecommunication network by increasing the security of the transferred information. Here, we study the effects of atmospheric turbulence in continuous-variable entanglement distribution and quantum teleportation in the optical regime between a ground station and a satellite. More specifically, we study the degradation of entanglement due to various error sources in the distribution, namely, diffraction, atmospheric attenuation, turbulence, and detector inefficiency, in both downlink and uplink scenarios. As the fidelity of a quantum teleportation protocol using these distributed entangled resources is not sufficient, we include an intermediate station for either state generation, or beam refocusing, in order to reduce the effects of atmospheric turbulence and diffraction, respectively. The results show the feasibility of free-space entanglement distribution and quantum teleportation in downlink paths up to the LEO region, but also in uplink paths with the help of the intermediate station. Finally, we complete the study with microwave-optical comparison in bad weather situations, and with the study of horizontal paths in ground-to-ground and inter-satellite quantum communication.},
keywords = {UPV/EHU},
pubstate = {published},
tppubtype = {article}
}
Advances in satellite quantum communications aim at reshaping the global telecommunication network by increasing the security of the transferred information. Here, we study the effects of atmospheric turbulence in continuous-variable entanglement distribution and quantum teleportation in the optical regime between a ground station and a satellite. More specifically, we study the degradation of entanglement due to various error sources in the distribution, namely, diffraction, atmospheric attenuation, turbulence, and detector inefficiency, in both downlink and uplink scenarios. As the fidelity of a quantum teleportation protocol using these distributed entangled resources is not sufficient, we include an intermediate station for either state generation, or beam refocusing, in order to reduce the effects of atmospheric turbulence and diffraction, respectively. The results show the feasibility of free-space entanglement distribution and quantum teleportation in downlink paths up to the LEO region, but also in uplink paths with the help of the intermediate station. Finally, we complete the study with microwave-optical comparison in bad weather situations, and with the study of horizontal paths in ground-to-ground and inter-satellite quantum communication.
Gonzalez-Conde, J.; Watts, T. W.; Rodriguez-Grasa, P.; Sanz, M.
Efficient quantum amplitude encoding of polynomial functions Journal Article
In: Quantum, vol. 8, pp. 1297, 2024, ISBN: 2521-327X.
Abstract | Links | BibTeX | Tags: UPV/EHU
@article{nokey,
title = {Efficient quantum amplitude encoding of polynomial functions},
author = {Gonzalez-Conde, J. and Watts, T.W. and Rodriguez-Grasa, P. and Sanz, M.},
url = {https://quantum-journal.org/papers/q-2024-03-21-1297/},
doi = {doi.org/10.22331/q-2024-03-21-1297},
isbn = {2521-327X},
year = {2024},
date = {2024-03-21},
urldate = {2024-03-21},
journal = {Quantum},
volume = {8},
pages = {1297},
abstract = {Loading functions into quantum computers represents an essential step in several quantum algorithms, such as quantum partial differential equation solvers. Therefore, the inefficiency of this process leads to a major bottleneck for the application of these algorithms. Here, we present and compare two efficient methods for the amplitude encoding of real polynomial functions on n qubits. This case holds special relevance, as any continuous function on a closed interval can be uniformly approximated with arbitrary precision by a polynomial function. The first approach relies on the matrix product state representation. We study and benchmark the approximations of the target state when the bond dimension is assumed to be small. The second algorithm combines two subroutines. Initially we encode the linear function into the quantum registers with a shallow sequence of multi-controlled gates that loads the linear function's Hadamard-Walsh series, exploring how truncating the Hadamard-Walsh series of the linear function affects the final fidelity. Applying the inverse discrete Hadamard-Walsh transform transforms the series coefficients into an amplitude encoding of the linear function. Then, we use this construction as a building block to achieve a block encoding of the amplitudes corresponding to the linear function on k0 qubits and apply the quantum singular value transformation that implements a polynomial transformation to the block encoding of the amplitudes. This unitary together with the Amplitude Amplification algorithm will enable us to prepare the quantum state that encodes the polynomial function on k0 qubits. Finally we pad n−k0 qubits to generate an approximated encoding of the polynomial on n qubits, analyzing the error depending on k0. In this regard, our methodology proposes a method to improve the state-of-the-art complexity by introducing controllable errors.},
keywords = {UPV/EHU},
pubstate = {published},
tppubtype = {article}
}
Loading functions into quantum computers represents an essential step in several quantum algorithms, such as quantum partial differential equation solvers. Therefore, the inefficiency of this process leads to a major bottleneck for the application of these algorithms. Here, we present and compare two efficient methods for the amplitude encoding of real polynomial functions on n qubits. This case holds special relevance, as any continuous function on a closed interval can be uniformly approximated with arbitrary precision by a polynomial function. The first approach relies on the matrix product state representation. We study and benchmark the approximations of the target state when the bond dimension is assumed to be small. The second algorithm combines two subroutines. Initially we encode the linear function into the quantum registers with a shallow sequence of multi-controlled gates that loads the linear function's Hadamard-Walsh series, exploring how truncating the Hadamard-Walsh series of the linear function affects the final fidelity. Applying the inverse discrete Hadamard-Walsh transform transforms the series coefficients into an amplitude encoding of the linear function. Then, we use this construction as a building block to achieve a block encoding of the amplitudes corresponding to the linear function on k0 qubits and apply the quantum singular value transformation that implements a polynomial transformation to the block encoding of the amplitudes. This unitary together with the Amplitude Amplification algorithm will enable us to prepare the quantum state that encodes the polynomial function on k0 qubits. Finally we pad n−k0 qubits to generate an approximated encoding of the polynomial on n qubits, analyzing the error depending on k0. In this regard, our methodology proposes a method to improve the state-of-the-art complexity by introducing controllable errors.
Garcia-de-Andoin, M.; Saiz, A.; Perez-Fernandez, P.; Lamata, L.; Oregi, I.; Sanz, M.
Digital-analog quantum computation with arbitrary two-body Hamiltonians Journal Article
In: Physical Review Research, vol. 6, iss. 1, 2024, ISBN: 2643-1564.
Abstract | Links | BibTeX | Tags: UPV/EHU
@article{nokey,
title = {Digital-analog quantum computation with arbitrary two-body Hamiltonians},
author = {Garcia-de-Andoin, M. and Saiz, A. and Perez-Fernandez, P. and Lamata, L. and Oregi, I. and Sanz, M. },
url = {https://journals.aps.org/prresearch/pdf/10.1103/PhysRevResearch.6.013280},
doi = {doi.org/10.1103/PhysRevResearch.6.013280},
isbn = {2643-1564},
year = {2024},
date = {2024-03-14},
urldate = {2024-03-14},
journal = {Physical Review Research},
volume = {6},
issue = {1},
abstract = {Digital-analog quantum computing is a computational paradigm which employs an analog Hamiltonian resource together with single-qubit gates to reach universality. Here, we design a new scheme which employs an arbitrary two-body source Hamiltonian, extending the experimental applicability of this computational paradigm to most quantum platforms. We show that the simulation of an arbitrary two-body target Hamiltonian of 𝑛 qubits requires 𝒪(𝑛2) analog blocks with guaranteed positive times, providing a polynomial advantage compared to the previous scheme. Additionally, we propose a classical strategy which combines a Bayesian optimization with a gradient descent method, improving the performance by ∼55% for small systems measured in the Frobenius norm.},
keywords = {UPV/EHU},
pubstate = {published},
tppubtype = {article}
}
Digital-analog quantum computing is a computational paradigm which employs an analog Hamiltonian resource together with single-qubit gates to reach universality. Here, we design a new scheme which employs an arbitrary two-body source Hamiltonian, extending the experimental applicability of this computational paradigm to most quantum platforms. We show that the simulation of an arbitrary two-body target Hamiltonian of 𝑛 qubits requires 𝒪(𝑛2) analog blocks with guaranteed positive times, providing a polynomial advantage compared to the previous scheme. Additionally, we propose a classical strategy which combines a Bayesian optimization with a gradient descent method, improving the performance by ∼55% for small systems measured in the Frobenius norm.
Cea, M.; Grossi, M.; Monaco, S.; Rico, E.; Tagliacozzo, L.; Vallecorsa, S.
Exploring the Phase Diagram of the quantum one-dimensional ANNNI model Unpublished
Preprint, 2024.
Abstract | Links | BibTeX | Tags: UPV/EHU
@unpublished{nokey,
title = {Exploring the Phase Diagram of the quantum one-dimensional ANNNI model},
author = {Cea, M. and Grossi, M. and Monaco, S. and Rico, E. and Tagliacozzo, L. and Vallecorsa, S. },
url = {https://arxiv.org/abs/2402.11022},
doi = {doi.org/10.48550/arXiv.2402.11022},
year = {2024},
date = {2024-02-16},
abstract = {In this manuscript, we explore the intersection of QML and TN in the context of the one-dimensional ANNNI model with a transverse field. The study aims to concretely connect QML and TN by combining them in various stages of algorithm construction, focusing on phase diagram reconstruction for the ANNNI model, with supervised and unsupervised techniques. The model's significance lies in its representation of quantum fluctuations and frustrated exchange interactions, making it a paradigm for studying magnetic ordering, frustration, and the presence of a floating phase. It concludes with discussions of the results, including insights from increased system sizes and considerations for future work, such as addressing limitations in QCNN and exploring more realistic implementations of QC.},
howpublished = {Preprint},
keywords = {UPV/EHU},
pubstate = {published},
tppubtype = {unpublished}
}
In this manuscript, we explore the intersection of QML and TN in the context of the one-dimensional ANNNI model with a transverse field. The study aims to concretely connect QML and TN by combining them in various stages of algorithm construction, focusing on phase diagram reconstruction for the ANNNI model, with supervised and unsupervised techniques. The model's significance lies in its representation of quantum fluctuations and frustrated exchange interactions, making it a paradigm for studying magnetic ordering, frustration, and the presence of a floating phase. It concludes with discussions of the results, including insights from increased system sizes and considerations for future work, such as addressing limitations in QCNN and exploring more realistic implementations of QC.
Xu, R.; Tang, J.; Chandarana, P.; Paul, K.; Xu, X.; Yung, M.; Chen, X.
Benchmarking hybrid digitized-counterdiabatic quantum optimization Journal Article
In: Physical Review Research, vol. 6, iss. 1, 2024, ISBN: 2643-1564.
Abstract | Links | BibTeX | Tags: UPV/EHU
@article{nokey,
title = {Benchmarking hybrid digitized-counterdiabatic quantum optimization},
author = {Xu, R. and Tang, J. and Chandarana, P. and Paul, K. and Xu, X. and Yung, M. and Chen, X. },
url = {https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.6.013147},
doi = {doi.org/10.1103/PhysRevResearch.6.013147},
isbn = {2643-1564},
year = {2024},
date = {2024-02-07},
journal = {Physical Review Research},
volume = {6},
issue = {1},
abstract = {Hybrid digitized-counterdiabatic quantum computing (DCQC) is a promising approach for leveraging the capabilities of nearterm quantum computers, utilizing parameterized quantum circuits designed with counterdiabatic protocols. However, the classical aspect of this approach has received limited attention. In this study, we systematically analyze the convergence behavior and solution quality of various classical optimizers when used in conjunction with the digitized-counterdiabatic approach. We demonstrate the effectiveness of this hybrid algorithm by comparing its performance to the traditional QAOA on systems containing up to 28 qubits. Furthermore, we employ principal component analysis to investigate the cost landscape and explore the crucial influence of parametrization on the performance of the counterdiabatic ansatz. Our findings indicate that fewer iterations are required when local cost landscape minima are present, and the SPSA-based BFGS optimizer emerges as a standout choice for the hybrid DCQC paradigm.},
keywords = {UPV/EHU},
pubstate = {published},
tppubtype = {article}
}
Hybrid digitized-counterdiabatic quantum computing (DCQC) is a promising approach for leveraging the capabilities of nearterm quantum computers, utilizing parameterized quantum circuits designed with counterdiabatic protocols. However, the classical aspect of this approach has received limited attention. In this study, we systematically analyze the convergence behavior and solution quality of various classical optimizers when used in conjunction with the digitized-counterdiabatic approach. We demonstrate the effectiveness of this hybrid algorithm by comparing its performance to the traditional QAOA on systems containing up to 28 qubits. Furthermore, we employ principal component analysis to investigate the cost landscape and explore the crucial influence of parametrization on the performance of the counterdiabatic ansatz. Our findings indicate that fewer iterations are required when local cost landscape minima are present, and the SPSA-based BFGS optimizer emerges as a standout choice for the hybrid DCQC paradigm.
Xu, R.; Tang, J.; Chandarana, P.; Paul, K.; Xu, X.; Yung, M.; Chen, X.
Benchmarking hybrid digitized-counterdiabatic quantum optimization Journal Article
In: Physical Review Research, vol. 6, iss. 1, 2024, ISBN: 2643-1564.
Abstract | Links | BibTeX | Tags: UPV/EHU
@article{nokey,
title = {Benchmarking hybrid digitized-counterdiabatic quantum optimization},
author = {Xu, R. and Tang, J. and Chandarana, P. and Paul, K. and Xu, X. and Yung, M. and Chen, X. },
url = {https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.6.013147},
doi = {doi.org/10.1103/PhysRevResearch.6.013147},
isbn = {2643-1564},
year = {2024},
date = {2024-02-07},
journal = {Physical Review Research},
volume = {6},
issue = {1},
abstract = {Hybrid digitized-counterdiabatic quantum computing (DCQC) is a promising approach for leveraging the capabilities of nearterm quantum computers, utilizing parameterized quantum circuits designed with counterdiabatic protocols. However, the classical aspect of this approach has received limited attention. In this study, we systematically analyze the convergence behavior and solution quality of various classical optimizers when used in conjunction with the digitized-counterdiabatic approach. We demonstrate the effectiveness of this hybrid algorithm by comparing its performance to the traditional QAOA on systems containing up to 28 qubits. Furthermore, we employ principal component analysis to investigate the cost landscape and explore the crucial influence of parametrization on the performance of the counterdiabatic ansatz. Our findings indicate that fewer iterations are required when local cost landscape minima are present, and the SPSA-based BFGS optimizer emerges as a standout choice for the hybrid DCQC paradigm.
},
keywords = {UPV/EHU},
pubstate = {published},
tppubtype = {article}
}
Hybrid digitized-counterdiabatic quantum computing (DCQC) is a promising approach for leveraging the capabilities of nearterm quantum computers, utilizing parameterized quantum circuits designed with counterdiabatic protocols. However, the classical aspect of this approach has received limited attention. In this study, we systematically analyze the convergence behavior and solution quality of various classical optimizers when used in conjunction with the digitized-counterdiabatic approach. We demonstrate the effectiveness of this hybrid algorithm by comparing its performance to the traditional QAOA on systems containing up to 28 qubits. Furthermore, we employ principal component analysis to investigate the cost landscape and explore the crucial influence of parametrization on the performance of the counterdiabatic ansatz. Our findings indicate that fewer iterations are required when local cost landscape minima are present, and the SPSA-based BFGS optimizer emerges as a standout choice for the hybrid DCQC paradigm.
Ding, Y.; Chen, X.; Magdalena-Benedito, R.; Martín-Guerrero, J. D.
Closed-loop control of a noisy qubit with reinforcement learning Bachelor Thesis
2023, ISBN: 2632-2153.
Abstract | Links | BibTeX | Tags: UPV/EHU
@bachelorthesis{nokey,
title = {Closed-loop control of a noisy qubit with reinforcement learning},
author = {Ding, Y. and Chen, X. and Magdalena-Benedito, R. and Martín-Guerrero, J.D.},
url = {https://iopscience.iop.org/article/10.1088/2632-2153/acd048},
doi = {10.1088/2632-2153/acd048},
isbn = {2632-2153},
year = {2023},
date = {2023-05-05},
journal = {Machine Learning: Science and Technology},
volume = {4},
number = {2},
abstract = {The exotic nature of quantum mechanics differentiates machine learning applications in the quantum realm from classical ones. Stream learning is a powerful approach that can be applied to extract knowledge continuously from quantum systems in a wide range of tasks. In this paper, we propose a deep reinforcement learning method that uses streaming data from a continuously measured qubit in the presence of detuning, dephasing, and relaxation. The model receives streaming quantum information for learning and decision-making, providing instant feedback on the quantum system. We also explore the agent's adaptability to other quantum noise patterns through transfer learning. Our protocol offers insights into closed-loop quantum control, potentially advancing the development of quantum technologies.},
keywords = {UPV/EHU},
pubstate = {published},
tppubtype = {bachelorthesis}
}
The exotic nature of quantum mechanics differentiates machine learning applications in the quantum realm from classical ones. Stream learning is a powerful approach that can be applied to extract knowledge continuously from quantum systems in a wide range of tasks. In this paper, we propose a deep reinforcement learning method that uses streaming data from a continuously measured qubit in the presence of detuning, dephasing, and relaxation. The model receives streaming quantum information for learning and decision-making, providing instant feedback on the quantum system. We also explore the agent's adaptability to other quantum noise patterns through transfer learning. Our protocol offers insights into closed-loop quantum control, potentially advancing the development of quantum technologies.
Ding, Y.; Gonzalez-Conde, J.; Lamata, L.; Martín-Guerrero, J. D.; Lizaso, E.; Mugel, S.; Chen, X.; Orús, R.; Solano, E.; Sanz, M.
Toward Prediction of Financial Crashes with a D-Wave Quantum Annealer Journal Article
In: Entropy, vol. 25, no. 2, pp. 323, 2023, ISBN: 1099-4300.
Abstract | Links | BibTeX | Tags: UPV/EHU
@article{nokey,
title = {Toward Prediction of Financial Crashes with a D-Wave Quantum Annealer},
author = {Ding, Y. and Gonzalez-Conde, J. and Lamata, L. and Martín-Guerrero, J.D. and Lizaso, E. and Mugel, S. and Chen, X. and Orús, R. and Solano, E. and Sanz, M. },
url = {https://www.mdpi.com/1099-4300/25/2/323},
doi = {doi.org/10.3390/e25020323},
isbn = {1099-4300},
year = {2023},
date = {2023-02-10},
journal = {Entropy},
volume = {25},
number = {2},
pages = {323},
abstract = {The prediction of financial crashes in a complex financial network is known to be an NP-hard problem, which means that no known algorithm can efficiently find optimal solutions. We experimentally explore a novel approach to this problem by using a D-Wave quantum annealer, benchmarking its performance for attaining a financial equilibrium. To be specific, the equilibrium condition of a nonlinear financial model is embedded into a higher-order unconstrained binary optimization (HUBO) problem, which is then transformed into a spin-1/2 Hamiltonian with at most, two-qubit interactions. The problem is thus equivalent to finding the ground state of an interacting spin Hamiltonian, which can be approximated with a quantum annealer. The size of the simulation is mainly constrained by the necessity of a large number of physical qubits representing a logical qubit with the correct connectivity. Our experiment paves the way for the codification of this quantitative macroeconomics problem in quantum annealers.},
keywords = {UPV/EHU},
pubstate = {published},
tppubtype = {article}
}
The prediction of financial crashes in a complex financial network is known to be an NP-hard problem, which means that no known algorithm can efficiently find optimal solutions. We experimentally explore a novel approach to this problem by using a D-Wave quantum annealer, benchmarking its performance for attaining a financial equilibrium. To be specific, the equilibrium condition of a nonlinear financial model is embedded into a higher-order unconstrained binary optimization (HUBO) problem, which is then transformed into a spin-1/2 Hamiltonian with at most, two-qubit interactions. The problem is thus equivalent to finding the ground state of an interacting spin Hamiltonian, which can be approximated with a quantum annealer. The size of the simulation is mainly constrained by the necessity of a large number of physical qubits representing a logical qubit with the correct connectivity. Our experiment paves the way for the codification of this quantitative macroeconomics problem in quantum annealers.
