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arXiv 2106.08682quant-ph
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变分量子线性问题的经典优化方法比较

A Comparison of Various Classical Optimizers for a Variational Quantum Linear Solver

Aidan Pellow-Jarman, Ilya Sinayskiy, Anban Pillay, Francesco Petruccione

摘要:

变分混合量子经典算法(VHQCA)是一类旨在运行在有噪声的中间尺度量子(NISQ)设备上的量子算法。这些算法采用了一个参数化的量子线路(analog)和量子经典反馈回路。经典设备用于优化参数,以便最小化可以在量子设备上更有效地计算的成本函数。构造成本函数,使得找到使其值最小化的参数,解决了一些感兴趣的问题。我们专注于变分量子线性求解器(VQLS),并检查几个梯度的经典优化器的性能的影响。我们专注于研究的经典优化的平均收敛速度,以及他们的平均终止成本值的分布,以及这些是如何受到噪声的影响。我们的工作表明,NISQ器件上的实际噪声水平对优化过程提出了挑战。所有经典的优化器似乎都受到现实噪声的负面影响。如果噪声水平得到显著改善,那么将来可能有很好的理由更喜欢基于梯度的方法,它比仅存在散粒噪声的无梯度方法表现得更好。无梯度优化器,同时扰动随机近似(SPSA)和鲍威尔的方法,和基于梯度的优化器,AMSGrad和BFGS在噪声模拟中表现最好,并且似乎比其他方法受噪声的影响更小。SPSA似乎是性能最好的方法。COBYLA、Nelder-Mead和共轭梯度方法似乎受噪声影响最大,即使是轻微的噪声水平也会显著影响其性能。

英文摘要:

Variational Hybrid Quantum Classical Algorithms (VHQCAs) are a class of quantum algorithms intended to run on noisy intermediate-scale quantum (NISQ) devices. These algorithms employ a parameterized quantum circuit (ansatz) and a quantum-classical feedback loop. A classical device is used to optimize the parameters in order to minimize a cost function that can be computed far more efficiently on a quantum device. The cost function is constructed such that finding the ansatz parameters that minimize its value, solves some problem of interest. We focus specifically on the Variational Quantum Linear Solver (VQLS), and examine the effect of several gradient-free and gradient-based classical optimizers on performance. We focus on both the average rate of convergence of the classical optimizers studied, as well as the distribution of their average termination cost values, and how these are affected by noise. Our work demonstrates that realistic noise levels on NISQ devices present a challenge to the optimization process. All classical optimizers appear to be very negatively affected by the presence of realistic noise. If noise levels are significantly improved, there may be a good reason for preferring gradient-based methods in the future, which performed better than the gradient-free methods with the only shot-noise present. The gradient-free optimizers, Simultaneous Perturbation Stochastic Approximation (SPSA) and Powell's method, and the gradient-based optimizers, AMSGrad and BFGS performed the best in the noisy simulation, and appear to be less affected by noise than the rest of the methods. SPSA appears to be the best performing method. COBYLA, Nelder-Mead and Conjugate-Gradient methods appear to be the most heavily affected by noise, with even slight noise levels significantly impacting their performance.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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