论文标题
通过模型空间量子假想时间演变的多状态量子模拟
Multi-state quantum simulations via model-space quantum imaginary time evolution
论文作者
论文摘要
我们将模型空间的框架引入量子假想时间演化（QITE），以便使用量子计算机对地面和激发态进行稳定估算。模型空间QITE（MSQITE）通过保留其正交性将模型空间传播到确切的空间，因此能够同时描述多个状态。量子Lanczos（Qlanczos）算法扩展到MSQITE，以加速收敛。在模拟激发态时，发现本方案的表现均优于标准Qlanczos和最近提出的折叠频谱QITE。此外，我们证明，可以通过移动假想的时间传播器有效地去除自旋污染，因此，具有特定自旋量子数的激发态被有效地捕获而不属于具有较低能量的不同自旋状态。我们还研究了MSQITE中使用的不同水平的单一近似程度如何影响结果。 H4模型系统的噪声模拟证明了算法对QITE的有效性。
We introduce the framework of model space into quantum imaginary time evolution (QITE) to enable stable estimation of ground and excited states using a quantum computer. Model-space QITE (MSQITE) propagates a model space to the exact one by retaining its orthogonality, and hence is able to describe multiple states simultaneously. The quantum Lanczos (QLanczos) algorithm is extended to MSQITE to accelerate the convergence. The present scheme is found to outperform both the standard QLanczos and the recently proposed folded-spectrum QITE in simulating excited states. Moreover, we demonstrate that spin contamination can be effectively removed by shifting the imaginary time propagator, and thus excited states with a particular spin quantum number are efficiently captured without falling into the different spin states that have lower energies. We also investigate how different levels of the unitary approximation employed in MSQITE can affect the results. The effectiveness of the algorithm over QITE is demonstrated by noise simulations for the H4 model system.
