论文标题
测试量子退火器作为量子热采样器
Testing a quantum annealer as a quantum thermal sampler
论文作者
论文摘要
最近的实验激励了复杂多体系统的特定热性能在市售的量子退火器上成功再现，我们研究了量子退火硬件可以在与目标量子量大型汉密尔顿相关的特定基础上可靠地从热状态下可靠地样品。我们通过研究D-Wave 2000Q量子退火处理器上规范的一维横向局部ISING模型的对角线热性能来解决这个问题。我们发现，量子处理器无法产生量子蒙特卡洛预测的正确期望值。与主方程模拟相比，我们发现这种差异最好通过如何在设备上制定有限横向场的测量值来解释。具体而言，有限横向场的测量结果要求将系统从目标哈密顿量淬灭到具有可忽略的横向场的哈密顿量，并且该淬火太慢。这种硬件施加的局限性使其成为热抽样的不太可能候选，并且仍然是一个开放的问题，对于任意量子多体系统，可以一般估计哪种热期望值。
Motivated by recent experiments in which specific thermal properties of complex many-body systems were successfully reproduced on a commercially available quantum annealer, we examine the extent to which quantum annealing hardware can reliably sample from the thermal state in a specific basis associated with a target quantum Hamiltonian. We address this question by studying the diagonal thermal properties of the canonical one-dimensional transverse-field Ising model on a D-Wave 2000Q quantum annealing processor. We find that the quantum processor fails to produce the correct expectation values predicted by Quantum Monte Carlo. Comparing to master equation simulations, we find that this discrepancy is best explained by how the measurements at finite transverse fields are enacted on the device. Specifically, measurements at finite transverse field require the system to be quenched from the target Hamiltonian to a Hamiltonian with negligible transverse field, and this quench is too slow. The limitations imposed by such hardware make it an unlikely candidate for thermal sampling, and it remains an open question what thermal expectation values can be robustly estimated in general for arbitrary quantum many-body systems.
