Aplicación

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}

@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}

}