基于变分量子虚时演化和UCC Ansatz的基态求解器

Ground State Solver Based on Variational Quantum Imaginary Time Evolution and UCC Ansatz

对于量子多体体系,其基态的求解十分重要。变分量子本征求解器VQE是一种基于量子计算的变分基态求解算法,由于其需要结合量子电路和经典的变分算法,使得量子电路的复杂性和变分算法的有效性显得极其重要。针对量子分子体系,提出了一种变分基态求解器。运用单电子约化密度矩阵分析得到在自然分子轨道表象下的电子轨道占据数,根据占据数大小简化了体系哈密顿量和相应的UCC ansatz线路。并运用变分量子虚时演化算法替代VQE中常用的梯度算法,因此不易受到参数空间的梯度分布的影响,使得变分过程收敛更快,更具鲁棒性。

In the quantum many-body system,the calculation of the ground state is the key target problem.Variational quantum eigensolver(VQE)is a variational ground state solution algorithm based on quantum computation.However,since it requires combining quantum circuit and classical variational algorithm,the complexity of the quantum circuit and the choice of variational algorithm becomes extremely important.This paper focuses on quantum molecular systems and proposes a variational ground state solver.It uses the single-electron reduced density matrix analysis to obtain the number of electron occupations under the appearance of natural molecular orbitals.According to the number of occupations,the Hamiltonian of the system and the corresponding unitary couple cluster(UCC)ansatz circuit are greatly simplified.Secondly,the variational quantum imaginary time evolution algorithm is used to replace the commonly used gradient algorithm in VQE,which is not easily influenced by the gradient distribution of the parameter space,causing the variational process to converge more quickly and robustly.