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Nonunitary Coupled Cluster Enabled by Midcircuit Measurements on Quantum Computers.
Journal of Chemical Theory and Computation ( IF 5.7 ) Pub Date : 2024-12-08 , DOI: 10.1021/acs.jctc.4c00837
Alexandre Fleury,James Brown,Erika Lloyd,Maritza Hernandez,Isaac H Kim

Many quantum algorithms rely on a quality initial state for optimal performance. Preparing an initial state for specific applications can considerably reduce the cost of probabilistic algorithms such as the well studied quantum phase estimation (QPE). Fortunately, in the application space of quantum chemistry, generating approximate wave functions for molecular systems is well studied, and quantum computing algorithms stand to benefit from importing these classical methods directly into a quantum circuit. In this work, we propose a state preparation method based on coupled cluster (CC) theory, which is a pillar of quantum chemistry on classical computers, by incorporating midcircuit measurements into the circuit construction. Currently, the most well studied state preparation method for quantum chemistry on quantum computers is the variational quantum eigensolver (VQE) with a unitary-CC with single- and double-electron excitation terms (UCCSD) ansatz whose operations are limited to unitary gates. We verify the accuracy of our state preparation protocol using midcircuit measurements by performing energy evaluation and state overlap computation for a set of small chemical systems. We further demonstrate that our approach leads to a reduction of the classical computation overhead, and the number of CNOT and T gates by 28 and 57% on average when compared against the standard VQE-UCCSD protocol.

中文翻译:


由量子计算机上的 Midcircuit Measurements 启用的非幺正耦合簇。



许多量子算法依赖于质量初始状态来实现最佳性能。为特定应用程序准备初始状态可以大大降低概率算法的成本,例如经过充分研究的量子相位估计 (QPE)。幸运的是,在量子化学的应用领域,为分子系统生成近似波函数已经得到了很好的研究,量子计算算法可以从将这些经典方法直接导入量子电路中受益。在这项工作中,我们通过将中电路测量纳入电路构造,提出了一种基于耦合簇 (CC) 理论的状态准备方法,该理论是经典计算机上量子化学的支柱。目前,量子计算机上量子化学研究最充分的状态准备方法是变分量子特征求解器 (VQE),它具有具有单电子和双电子激发项 (UCCSD) 的酉 CC,其操作仅限于幺正门。我们通过对一组小型化学系统进行能量评估和状态重叠计算,使用中间电路测量来验证状态准备协议的准确性。我们进一步证明,与标准 VQE-UCCSD 协议相比,我们的方法减少了经典计算开销,并且 CNOT 和 T 门的数量平均减少了 28% 和 57%。
更新日期:2024-12-08
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