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arXiv 1601.03030quant-phcond-mat.stat-mechcs.DSmath.PR
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模拟量子退火可以比经典模拟退火快指数

Simulated Quantum Annealing Can Be Exponentially Faster than Classical Simulated Annealing

Elizabeth Crosson, Aram W. Harrow

摘要:

模拟量子退火(SQA)是一种马尔可夫链蒙特卡罗算法,它对量子退火(QA)哈密顿量的平衡热状态进行采样。除了模拟量子系统之外,SQA也被提出作为另一种受物理启发的经典组合优化算法,与经典模拟退火一起。然而,在许多情况下,确定QA和SQA的性能仍然是一个开放的挑战。QA优于经典模拟退火的一个证据来自Farhi,Goldstone和Gutmann的一个例子。设计了一个具有薄的高能量势垒的位对称代价函数,以显示经典模拟退火和量子退火之间的指数分离,对于经典模拟退火,热波动需要指数时间来爬上势垒,量子退火通过势垒并在多时间内达到全局最小值,可以说是利用量子隧穿。在这项工作中,我们应用比较方法严格地表明,马尔可夫链的基础SQA有效地采样的目标分布,并找到全局最小值的尖峰成本函数在多项式时间。我们的工作提供了证据,越来越多的共识,SQA继承至少有一些隧道在QA的优势,所以QA是不太可能实现指数加速超过经典计算仅仅通过使用量子隧道。因为我们只分析一个特定的模型,所以这个证据不是决定性的。然而,这里应用的技术-包括从绝热路径的热启动和使用量子基态概率分布来理解SQA的平稳分布-可能对未来的研究有价值的性能SQA的成本函数QA是有效的。

英文摘要:

Simulated Quantum Annealing (SQA) is a Markov Chain Monte-Carlo algorithm that samples the equilibrium thermal state of a Quantum Annealing (QA) Hamiltonian. In addition to simulating quantum systems, SQA has also been proposed as another physics-inspired classical algorithm for combinatorial optimization, alongside classical simulated annealing. However, in many cases it remains an open challenge to determine the performance of both QA and SQA. One piece of evidence for the strength of QA over classical simulated annealing comes from an example by Farhi, Goldstone and Gutmann . There a bit-symmetric cost function with a thin, high energy barrier was designed to show an exponential seperation between classical simulated annealing, for which thermal fluctuations take exponential time to climb the barrier, and quantum annealing which passes through the barrier and reaches the global minimum in poly time, arguably by taking advantage of quantum tunneling. In this work we apply a comparison method to rigorously show that the Markov chain underlying SQA efficiently samples the target distribution and finds the global minimum of this spike cost function in polynomial time. Our work provides evidence for the growing consensus that SQA inherits at least some of the advantages of tunneling in QA, and so QA is unlikely to achieve exponential speedups over classical computing solely by the use of quantum tunneling. Since we analyze only a particular model this evidence is not decisive. However, techniques applied here---including warm starts from the adiabatic path and the use of the quantum ground state probability distribution to understand the stationary distribution of SQA---may be valuable for future studies of the performance of SQA on cost functions for which QA is efficient.

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