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

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 ansätze on-the-fly while running the simulation. In order to improve the convergence of spectral features Padé 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.