Quantum simulation of ultrastrongly coupled bosonic modes using superconducting circuits

TL;DR

This paper demonstrates how superconducting circuits can simulate ultrastrongly coupled bosonic modes, allowing observation of quantum correlations like squeezing that are otherwise unobservable in condensed matter systems.

Contribution

It introduces an analog quantum simulation method using superconducting circuits to explore ground-state properties of strongly coupled bosonic modes.

Findings

Detection of output excitations related to ground-state properties

Observation of simultaneous single- and two-mode squeezing

Emission spectra confirming quantum correlations

Abstract

The ground state of a pair of ultrastrongly coupled bosonic modes is predicted to be a two-mode squeezed vacuum. However, the corresponding quantum correlations are currently unobservable in condensed matter where such a coupling can be reached, since it cannot be extracted from these systems. Here, we show that superconducting circuits can be used to perform an analog simulation of a system of two bosonic modes in regimes ranging from strong to ultrastrong coupling. More importantly, our quantum simulation setup enables us to detect output excitations that are related to the ground-state properties of the bosonic modes. We compute the emission spectra of this physical system and show that the produced state presents single- and two-mode squeezing simultaneously.