Computing the many-body Green's function with adaptive variational quantum dynamics

TL;DR

This paper introduces an adaptive variational quantum algorithm to compute many-body Green's functions, enabling efficient real-time dynamics simulation on quantum hardware with error mitigation.

Contribution

It develops an adaptive variational method for calculating Green's functions, incorporating on-the-fly ansatz generation and a novel resolution enhancement for noisy quantum data.

Findings

Successfully evaluated Green's function on IBM Q hardware

Demonstrated improved spectral resolution with Padé approximants

Implemented error mitigation techniques for noisy quantum data

Abstract

We present a method to compute the many-body real-time Green's function using an adaptive variational quantum dynamics simulation approach. The real-time Green's function involves the time evolution of a quantum state with one additional electron with respect to the ground state wavefunction that is first expressed as a linear combination of state vectors. The real-time evolution and Green's function is obtained by combining the dynamics of the individual statevectors in the linear combination. The use of the adaptive protocol enables us to generate compact ans\"atze on-the-fly while running the simulation. In order to improve the convergence of spectral features Pad\'e approximants are applied to obtain the Fourier transform of Green's function. We demonstrate the evaluation of Green's function on an IBM Q quantum computer. As a part of our error mitigation strategy, we develop a resolution-enhancing method that we successfully apply on the noisy data from the real quantum hardware.