Imaginary-time evolution using forward and backward real-time evolution with a single ancilla: First-quantized eigensolver algorithm for quantum chemistry
Imaginary-time evolution using forward and backward real-time evolution with a single ancilla: First-quantized eigensolver algorithm for quantum chemistry
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DOI：
10.1103/physrevresearch.4.033121
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发表时间：
2022-08-11
影响因子：
4.2
通讯作者：
Matsushita, Yu-Ichiro
中科院分区：
文献类型：
--
作者：
Kosugi, Taichi;Nishiya, Yusuke;Matsushita, Yu-Ichiro
量子计算机上的假想时间演变（ITE）是获得量子系统基态的有前途的形式主义。概率ITE（PITE）利用测量值来实现非单身操作，并且可以避免将动态限制到与其他类型ITE不同的变量参数所施加的低维子空间。在本文中，我们提出了一种仅使用一个辅助量子的位方法。与现有的斑点方法不同，这里提出的一种在实用的近似下构造了从前进和向后实时进化（RTE）大门作为原始哈密顿式的黑匣子的电路。因此，所有有效的RTE的有效统一算法都可以转移到ITE中，而无需进行任何修改。我们的方法可用于在有限的温度和分区函数下获得Gibbs状态。我们通过几个说明性系统验证该方法，在这些系统中发现试验状态迅速汇聚到基态。此外，我们通过关注计算成本的缩放来讨论其对量子化学的适用性。这导致开发一个被称为第一量化的eigensolver的框架。非不同的通用方法将扩大用于多功能目标的实用量子计算的范围。
Imaginary-time evolution (ITE) on a quantum computer is a promising formalism for obtaining the ground state of a quantum system. The probabilistic ITE (PITE) exploits measurements to implement nonunitary operations, and it can avoid the restriction of dynamics to a low-dimensional subspace imposed by variational parameters unlike other types of ITE. In this paper, we propose a PITE approach that uses only one ancillary qubit. Unlike the existing PITE approaches, the one proposed here constructs, under a practical approximation, the circuit from forward and backward real-time evolution (RTE) gates as black boxes for the original Hamiltonian. Thus all efficient unitary algorithms for RTE can be transferred to the ITE without any modifications. Our approach can be used to obtain the Gibbs state at a finite temperature and partition function. We validate the approach via several illustrative systems where the trial states are found to converge rapidly to the ground states. In addition, we discuss its applicability to quantum chemistry by focusing on the scaling of computational cost; this leads to the development of a framework referred to as a first-quantized eigensolver. The nonvariational generic approach will expand the scope of practical quantum computation for versatile objectives.