Determination of Molecular Energies via Quantum Imaginary Time Evolution in a Superconducting Qubit System

• URL: http://arxiv.org/abs/2303.01098v1
• Date: Thu, 2 Mar 2023 09:31:59 GMT
• Title: Determination of Molecular Energies via Quantum Imaginary Time Evolution in a Superconducting Qubit System
• Authors: Zhiwen Zong, Sainan Huai, Tianqi Cai, Wenyan Jin, Ze Zhan, Zhenxing Zhang, Kunliang Bu, Liyang Sui, Ying Fei, Yicong Zheng, Shengyu Zhang, Jianlan Wu, Yi Yin
• Abstract summary: We experimentally realize the variational-based quantum imaginary time evolution (QITE) algorithm to simulate the ground state energy of hydrogen (H2) and lithium hydride (LiH) molecules in a superconducting qubit system. All the experimental results show a convergence within 4 iterations, with high-fidelity ground state energy obtained.
• Score: 12.609858316758794
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: As a valid tool for solving ground state problems, imaginary time evolution (ITE) is widely used in physical and chemical simulations. Different ITE-based algorithms in their quantum counterpart have recently been proposed and applied to some real systems. We experimentally realize the variational-based quantum imaginary time evolution (QITE) algorithm to simulate the ground state energy of hydrogen (H2) and lithium hydride (LiH) molecules in a superconducting qubit system. The H2 molecule is directly simulated using the 3-qubit circuit with unitary-coupled clusters (UCC) ansatz. We also combine QITE with the cluster mean-field (CMF) method to obtain an effective Hamiltonian. The LiH molecule is correspondingly simulated using the 3-qubit circuit with hardware-efficient ansatz. For comparison, the LiH molecule is also directly simulated using the 4-qubit circuit with UCC ansatz at the equilibrium point. All the experimental results show a convergence within 4 iterations, with high-fidelity ground state energy obtained. For a more complex system in the future, the CMF may allow further grouping of interactions to obtain an effective Hamiltonian, then the hybrid QITE algorithm can possibly simulate a relatively large-scale system with fewer qubits.

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