Improved algorithms of quantum imaginary time evolution for ground and
excited states of molecular systems
- URL: http://arxiv.org/abs/2205.01983v3
- Date: Thu, 9 Jun 2022 10:48:25 GMT
- Title: Improved algorithms of quantum imaginary time evolution for ground and
excited states of molecular systems
- Authors: Takashi Tsuchimochi, Yoohee Ryo, Seiichiro L. Ten-no
- Abstract summary: Quantum imaginary time evolution (QITE) is a recently proposed quantum-classical hybrid algorithm that is guaranteed to reach the lowest state of system.
We analyze the derivation of the underlying QITE equation order-by-order, and suggest a modification that is theoretically well founded.
We also discuss how to accurately estimate the norm of an imaginary-time-evolved state, and applied it to excited state calculations.
- Score: 0.0
- License: http://creativecommons.org/licenses/by/4.0/
- Abstract: Quantum imaginary time evolution (QITE) is a recently proposed
quantum-classical hybrid algorithm that is guaranteed to reach the lowest state
of system. In this study, we present several improvements on QITE, mainly
focusing on molecular applications. We analyze the derivation of the underlying
QITE equation order-by-order, and suggest a modification that is theoretically
well founded. Our results clearly indicate the soundness of the here-derived
equation, enabling a better approximation of the imaginary time propagation by
a unitary. We also discuss how to accurately estimate the norm of an
imaginary-time-evolved state, and applied it to excited state calculations
using the quantum Lanczos algorithm. Finally, we propose the folded-spectrum
QITE scheme as a straightforward extension of QITE for general excited state
simulations. The effectiveness of all these developments is illustrated by
noiseless simulations, offering the further insights into quantum algorithms
for imaginary time evolution.
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