Chemical Research in Chinese Universities ›› 2025, Vol. 41 ›› Issue (5): 1029-1036.doi: 10.1007/s40242-025-5149-y

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Calculation of the Green’s Function on Near-term Quantum Computers via Cartan Decomposition

WAN Lingyun1, LIU Jie2, YANG Jinlong1,2   

  1. 1. State Key Laboratory of Precision and Intelligent Chemistry, University of Science and Technology of China, Hefei 230026, P. R. China;
    2. Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, P. R. China
  • Received:2025-07-15 Accepted:2025-09-10 Online:2025-10-01 Published:2025-09-26
  • Contact: LIU Jie, E-mail: liujie86@ustc.edu.cn E-mail:liujie86@ustc.edu.cn
  • Supported by:
    This work was supported by the Innovation Program for Quantum Science and Technology, China (No. 2021ZD0303306), the National Natural Science Foundation of China (Nos. 22393913, 22422304), and the Anhui Initiative in Quantum Information Technologies, China (No. AHY090400).

Abstract: Accurate computation of the Green’s function is crucial for connecting experimental observations to the underlying quantum states. A major challenge in evaluating the Green’s function in the time domain is the efficient simulation of quantum state evolution under a given Hamiltonian, a task that becomes exponentially complex for strongly correlated systems on classical computers. Quantum computing provides a promising pathway to overcome this challenge by enabling efficient simulation of the time evolution operator. However, for near-term quantum devices with limited coherence times and fidelity, the deep quantum circuits required to implement time-evolution operators present a significant challenge for practical applications. In this work, we introduce an efficient algorithm for computing Green's functions via Cartan decomposition, which requires only fixed-depth quantum circuits for arbitrarily long time simulations. Additionally, analytical gradients are formulated to accelerate the Cartan decomposition by leveraging a unitary transformation in the factorized form. The new algorithm is applied to simulating long-time Green’s functions for the Fermi-Hubbard and transverse-field Ising models, extracting the spectral functions through Fourier transformation.

Key words: Quantum computing, Green’s function, Cartan decomposition, Time evolution operator