Quasiprobabilistic imaginary-time evolution on quantum computers

• URL: http://arxiv.org/abs/2505.06343v2
• Date: Mon, 21 Jul 2025 15:19:25 GMT
• Title: Quasiprobabilistic imaginary-time evolution on quantum computers
• Authors: Annie Ray, Esha Swaroop, Ningping Cao, Michael Vasmer, Anirban Chowdhury,
• Abstract summary: We propose a new algorithm for computing imaginary-time evolved expectation values on quantum computers.<n>Our algorithm requires no ancillary qubits and can be made noise-resilient without additional error mitigation.
• Score: 0.3177496877224142
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: Imaginary-time evolution plays an important role in algorithms for computing ground-state and thermal equilibrium properties of quantum systems, but can be challenging to simulate on classical computers. Many quantum algorithms for imaginary-time evolution have resource requirements that are prohibitive for current quantum devices and face performance issues due to noise. Here, we propose a new algorithm for computing imaginary-time evolved expectation values on quantum computers, inspired by probabilistic error cancellation, an error-mitigation technique. Our algorithm works by decomposing a Trotterization of imaginary-time evolution into a probabilistic linear combination of operations, each of which is then implemented on a quantum computer. The measurement data is then classically post-processed to obtain the expectation value of the imaginary-time evolved state. Our algorithm requires no ancillary qubits and can be made noise-resilient without additional error mitigation. It is well-suited for estimating thermal expectation values by making use of the notion of a thermal pure quantum state. We demonstrate our algorithm by performing numerical simulations of thermal pure quantum state preparation for the 1D Heisenberg Hamiltonian on 8 qubits, and by using an IBM quantum computer to estimate the energy of the same Hamiltonian on 2 qubits. We observe promising results compared to the exact values, illustrating the potential of our algorithm for probing the physics of quantum many-body systems on current hardware.

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