Variational study of a two-level system coupled to a harmonic oscillator in a ultrastrong coupling regime

TL;DR

This paper improves the understanding of a two-level system coupled to a harmonic oscillator in the ultrastrong coupling regime by proposing a new variational wave function that better captures nonclassical effects like squeezing.

Contribution

It introduces a novel trial wave function that enhances the accuracy of variational solutions for quantum correlations and energy in ultrastrong coupling scenarios.

Findings

New wave function improves accuracy of quantum correlation predictions

Enhanced modeling of squeezing effects in ultrastrong coupling

Better energy estimates in variational ground state analysis

Abstract

The nonclassical behaviors of a two-level system coupled to a harmonic oscillator is investigated in the ultrastrong coupling regime. We revisit the variational solution of the ground state and find that the existing solution do not account accurately for nonclassical effects such squeezing. We suggest a new trial wave function and demonstrate that it has an excellent accuracy on the quantum correlation effects as well as on energy.