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CURRICULUM REINFORCEMENT LEARNING FOR quantum ARCHITECTURE SEARCH UNDER HARDWARE ERRORS 12

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CURRICULUM REINFORCEMENT LEARNING FOR QUANTUM ARCHITECTURE S...

12th International Conference on Learning Representations, ICLR 2024

作者： Patel, Yash J. Kundu, Akash Ostaszewski, Mateusz Bonet-Monroig, Xavier Dunjko, Vedran Danaci, Onur 〈aQaL〉 Applied Quantum Algorithms Leiden University Netherlands Institute of Theoretical and Applied Informatics Polish Academy of Sciences Poland Joint Doctoral School Silesian University of Technology Poland Warsaw University of Technology Institute of Computer Science Poland Lorentz Institute Leiden University Netherlands LIACS Leiden University Netherlands

The key challenge in the noisy intermediate-scale quantum era is finding useful circuits compatible with current device limitations. Variational quantum algorithms (VQAs) offer a potential solution by fixing the circuit architecture and optimizing individual gate parameters in an external loop. However, parameter optimization can become intractable, and the overall performance of the algorithm depends heavily on the initially chosen circuit architecture. Several quantum architecture search (QAS) algorithms have been developed to design useful circuit architectures automatically. In the case of parameter optimization alone, noise effects have been observed to dramatically influence the performance of the optimizer and final outcomes, which is a key line of study. However, the effects of noise on the architecture search, which could be just as critical, are poorly understood. This work addresses this gap by introducing a curriculum-based reinforcement learning QAS (CRLQAS) algorithm designed to tackle challenges in realistic VQA deployment. The algorithm incorporates (i) a 3D architecture encoding and restrictions on environment dynamics to explore the search space of possible circuits efficiently, (ii) an episode halting scheme to steer the agent to find shorter circuits, and (iii) a novel variant of simultaneous perturbation stochastic approximation as an optimizer for faster convergence. To facilitate studies, we developed an optimized simulator for our algorithm, significantly improving computational efficiency in simulating noisy quantum circuits by employing the Pauli-transfer matrix formalism in the Pauli-Liouville basis. Numerical experiments focusing on quantum chemistry tasks demonstrate that CRLQAS outperforms existing QAS algorithms across several metrics in both noiseless and noisy environments. © 2024 12th International Conference on Learning Representations, ICLR 2024. All rights reserved.

关键词： Reinforcement learning

Weighted Approximate quantum Natural Gradient for Variational quantum Eigensolver

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arXiv 2025年

作者： Shi, Chenyu Dunjko, Vedran Wang, Hao 〈aQaL〉 Applied Quantum Algorithms Universiteit Leiden Netherlands LIACS Universiteit Leiden Niels Bohrweg 1 Leiden2333 CA Netherlands

Variational quantum eigensolver (VQE) is one of the most prominent algorithms using near-term quantum devices, designed to find the ground state of a Hamiltonian. In VQE, a classical optimizer iteratively updates the parameters in the quantum circuit. Among various optimization methods, quantum natural gradient descent (QNG) stands out as a promising optimization approach for VQE. However, standard QNG only leverages the quantum Fisher information of the entire system and treats each subsystem equally in the optimization process, without accounting for the different weights and contributions of each subsystem corresponding to each observable. To address this limitation, we propose a Weighted Approximate quantum Natural Gradient (WA-QNG) method tailored for k-local Hamiltonians. In this paper, we theoretically analyze the potential advantages of WA-QNG compared to QNG from three distinct perspectives and reveal its connection with the Gauss-Newton method. We also show it outperforms standard quantum natural gradient descent in the numerical experiments for seeking the ground state of the Hamiltonian. Copyright © 2025, The Authors. All rights reserved.

关键词： quantum electronics

Trainability maximization using estimation of distribution algorithms assisted by surrogate modelling for quantum architecture search

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arXiv 2024年

作者： Soloviev, Vicente P. Dunjko, Vedran Bielza, Concha Larrañaga, Pedro Wang, Hao Universidad Politécnica de Madrid Spain Applied Quantum Algorithms Leiden 〈aQaL〉 Leiden University Netherlands Leiden University Netherlands

quantum architecture search (QAS) involves optimizing both the quantum parametric circuit configuration but also its parameters for a variational quantum algorithm. Thus, the problem is known to be multi-level as the performance of a given architecture is unknown until its parameters are tuned using classical routines. Moreover, the task becomes even more complicated since well-known trainability issues, e.g., barren plateaus (BPs), can occur. In this paper, we aim to achieve two improvements in QAS: (1) to reduce the number of measurements by an online surrogate model of the evaluation process that aggressively discards architectures of poor performance;(2) to avoid training the circuits when BPs are present. To detect the presence of the BPs, we employed a recently developed metric, information content, which only requires measuring the energy values of a small set of parameters to estimate the magnitude of cost function's gradient. The main idea of this proposal is to leverage a recently developed metric which can be used to detect the onset of vanishing gradients to ensure the overall search avoids such unfavorable regions. We experimentally validate our proposal for the variational quantum eigensolver and showcase that our algorithm is able to find solutions that have been previously proposed in the literature for the Hamiltonians;but also to outperform the state of the art when initializing the method from the set of architectures proposed in the literature. The results suggest that the proposed methodology could be used in environments where it is desired to improve the trainability of known architectures while maintaining good performance. Copyright © 2024, The Authors. All rights reserved.

关键词： Cost functions

Monitored quantum transport: full counting statistics of a quantum Hall interferometer

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arXiv 2025年

作者： Beenakker, C.W.J. Chen, Jin-Fu Instituut-Lorentz Universiteit Leiden P.O. Box 9506 Leiden2300 RA Netherlands 〈aQaL〉 Applied Quantum Algorithms Leiden Netherlands

We generalize the Levitov-Lesovik formula for the probability distribution function of the electron charge transferred through a phase coherent conductor, to include projective measurements that monitor the chiral propagation in quantum Hall edge modes. When applied to an electronic Mach-Zehnder interferometer, the monitoring reduces the visibility of the Aharonov-Bohm conductance oscillations while preserving the binomial form of the counting statistics, thereby removing a fundamental shortcoming of the dephasing-probe model of decoherence. Copyright © 2025, The Authors. All rights reserved.

关键词： Distribution functions

Thermodynamically Consistent Lindbladians for quantum Stochastic Thermodynamics

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arXiv 2025年

作者： Chen, Jin-Fu Instituut-Lorentz Universiteit Leiden P.O. Box 9506 Leiden2300 RA Netherlands 〈aQaL〉 Applied Quantum Algorithms Leiden Netherlands

We develop a Lindblad framework for quantum stochastic thermodynamics to study the nonequilibrium thermodynamics of open quantum systems. Our approach adopts the local quantum detailed balance condition, ensuring thermodynamic consistency and leading to a joint fluctuation theorem of quantum work and heat. Instead of solving the full evolution of the density matrix, we employ an effective parametrization to derive the full counting statistics of work and heat and determine the optimal protocols. As an application, we refine the quantum Brownian motion master equation to ensure the quantum detailed balance condition, derive the optimal protocols at different temperatures, and study the work statistics. Our framework provides fundamental insights and practical strategies for optimizing thermodynamic processes in open quantum systems. Copyright © 2025, The Authors. All rights reserved.

关键词： Stochastic systems

Gradients and frequency profiles of quantum re-uploading models

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arXiv 2023年

作者： Barthe, Alice Pérez-Salinas, Adrián 〈aQaL〉 Applied Quantum Algorithms Universiteit Leiden Netherlands Quantum Technology Initiative CERN Geneva Switzerland Instituut-Lorentz Universiteit Leiden Netherlands

quantum re-uploading models have been extensively investigated as a form of machine learning within the context of variational quantum algorithms. Their trainability and expressivity are not yet fully understood and are critical to their performance. In this work, we address trainability through the lens of the magnitude of the gradients of the cost function. We prove bounds for the differences between gradients of the better-studied data-less parameterized quantum circuits and reuploading models. We coin the concept of absorption witness to quantify such difference. For the expressivity, we prove that quantum reuploading models output functions with vanishing high-frequency components and upper-bounded derivatives with respect to data. As a consequence, such functions present limited sensitivity to fine details and offer protection against overfitting. We performed numerical experiments extending the theoretical results to more relaxed and realistic conditions. Overall, future designs of quantum re-uploading models will benefit from the strengthened knowledge delivered by the uncovering of absorption witnesses and vanishing high frequencies. © 2023, CC BY.

关键词： Cost functions

QDarts: A quantum Dot Array Transition Simulator for finding charge transitions in the presence of finite tunnel couplings, non-constant charging energies and sensor dots

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arXiv 2024年

作者： Krzywda, Jan A. Liu, Weikun van Nieuwenburg, Evert Krause, Oswin 〈aQaL〉 Applied Quantum Algorithms Universiteit Leiden Netherlands Dept. of Computer Science University of Copenhagen Copenhagen Denmark Instituut-Lorentz and LIACS Universiteit Leiden Netherlands

We present QDarts, an efficient simulator for realistic charge stability diagrams of quantum dot array (QDA) devices in equilibrium states. It allows for pinpointing the location of concrete charge states and their transitions in a high-dimensional voltage space (via arbitrary two-dimensional cuts through it), and includes effects of finite tunnel coupling, non-constant charging energy and a simulation of noisy sensor dots. These features enable close matching of various experimental results in the literature, and the package hence provides a flexible tool for testing QDA experiments, as well as opening the avenue for developing new methods of device tuning. © 2024, CC BY.

关键词： Nanocrystals

Equating quantum imaginary time evolution, Riemannian gradient flows, and stochastic implementations

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arXiv 2025年

作者： McMahon, Nathan A. Pervez, Mahum Arenz, Christian 〈aQaL〉 Applied Quantum Algorithms Leiden University Netherlands LIACS Leiden University Netherlands School of Electrical Computer and Energy Engineering Arizona State University TempeAZ85281 United States

We identify quantum imaginary time evolution as a Riemannian gradient flow on the unitary group. We develop an upper bound for the error between the two evolutions that can be controlled through the step size of the Riemannian gradient descent which minimizes the energy of the system. We discuss implementations through adaptive quantum algorithms and present a stochastic Riemannian gradient descent algorithm in which each step is efficiently implementable on a quantum computer. We prove that for a sufficiently small step size, the stochastic evolution concentrates around the imaginary time evolution, thereby providing performance guarantees for cooling the system through stochastic Riemannian gradient descent. © 2025, CC BY.

关键词： Qubits

Decoherence of electron spin qubit during transfer between two semiconductor quantum dots at low magnetic fields

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Physical Review B 2025年第11期111卷 115305-115305页

作者： Krzywda, Jan A. Cywiński, Łukasz AQaL Applied Quantum Algorithms Lorentz Institute Leiden Institute of Advanced Computer Science Leiden University P.O. Box 9506 Leiden 2300 RA Netherlands Institute of Physics Polish Academy of Sciences al. Lotników 32/46 Warsaw PL 02-668 Poland

Electron shuttling is one of the current avenues being pursued to scale semiconductor quantum dot-based spin qubits. Adiabatic spin qubit transfer along a chain of tunnel-coupled quantum dots is one of the possible schemes. In this scheme, we theoretically analyze the dephasing of a spin qubit that is adiabatically transferred between two tunnel-coupled quantum dots. We focus on the regime where the Zeeman splitting is lower than the tunnel coupling, such that interdot tunneling with spin flip is absent. We analyze the sources of errors in spin-coherent electron transfer for Si- and GaAs-based quantum dots. In addition to the obvious effect of fluctuations in spin splitting within each dot, leading to finite T2* for the stationary spin qubit, we consider the effects activated by detuning sweeps: failure of charge transfer due to charge noise and phonons, spin relaxation due to the enhancement of spin-orbit mixing at the tunnel-induced anticrossing of states localized in the two dots, and spin dephasing caused by low- and high-frequency noise coupling to the electron's charge. We show that the latter effect is activated by differences in Zeeman splittings between the two dots. Importantly, all the error mechanisms are more dangerous at low tunnel couplings. Our results indicate that away from micromagnets, maximizing the fidelity of coherent transfer aligns with minimizing charge transfer error that was previously considered in Krzywda and Cywiński [Phys. Rev. B 104, 075439 (2021)]. For silicon, we suggest having tunnel coupling fulfilling 2tc≳60µeV when one aims to coherently transfer a spin qubit across a ∼10µm long array of ∼100 quantum dots with error less than 10−3.

关键词： Nanocrystals