Magnusson Erika, Fitzpatrick Aaron, Knecht Stefan, Rahm Martin, Dobrautz Werner
Department of Chemistry and Chemical Engineering, Chalmers University of Technology, 41296 Gothenburg, Sweden.
Algorithmiq Ltd, Kanavakatu 3C, FI-00160 Helsinki, Finland.
Faraday Discuss. 2024 Nov 6;254(0):402-428. doi: 10.1039/d4fd00039k.
The near-term utility of quantum computers is hindered by hardware constraints in the form of noise. One path to achieving noise resilience in hybrid quantum algorithms is to decrease the required circuit depth - the number of applied gates - to solve a given problem. This work demonstrates how to reduce circuit depth by combining the transcorrelated (TC) approach with adaptive quantum ansätze and their implementations in the context of variational quantum imaginary time evolution (AVQITE). The combined TC-AVQITE method is used to calculate ground state energies across the potential energy surfaces of H, LiH, and HO. In particular, H is a notoriously difficult case where unitary coupled cluster theory, including singles and doubles excitations, fails to provide accurate results. Adding TC yields energies close to the complete basis set (CBS) limit while reducing the number of necessary operators - and thus circuit depth - in the adaptive ansätze. The reduced circuit depth furthermore makes our algorithm more noise-resilient and accelerates convergence. Our study demonstrates that combining the TC method with adaptive ansätze yields compact, noise-resilient, and easy-to-optimize quantum circuits that yield accurate quantum chemistry results close to the CBS limit.
量子计算机的近期实用性受到噪声形式的硬件限制的阻碍。在混合量子算法中实现抗噪声能力的一条途径是减少解决给定问题所需的电路深度，即应用门的数量。这项工作展示了如何通过将转相关（TC）方法与自适应量子近似及其在变分量子虚时演化（AVQITE）背景下的实现相结合来减少电路深度。结合的TC-AVQITE方法用于计算H、LiH和HO势能面上的基态能量。特别地，H是一个出了名的难题，其中包括单激发和双激发的酉耦合簇理论无法提供准确结果。添加TC可得到接近完全基组（CBS）极限的能量，同时减少自适应近似中所需算符的数量，从而减少电路深度。减少的电路深度进而使我们的算法更具抗噪声能力并加速收敛。我们的研究表明，将TC方法与自适应近似相结合可产生紧凑、抗噪声且易于优化的量子电路，这些电路能产生接近CBS极限的准确量子化学结果。
