Qubit-oscillator systems in the ultrastrong-coupling regime and their potential for preparing nonclassical states

TL;DR

This paper explores a qubit-oscillator system in the ultrastrong-coupling regime, analyzing its potential to generate and observe nonclassical states like squeezed, Schrödinger-cat, and entangled states, with implications for quantum state engineering.

Contribution

It compares analytical methods for describing the system, analyzes the ground state's nonclassical properties, and discusses experimental observation challenges in the ultrastrong-coupling regime.

Findings

Ground state exhibits nonclassical properties

Analytical methods vary in accuracy across regimes

Decoherence impacts state observability

Abstract

We consider a system composed of a two-level system (i.e. a qubit) and a harmonic oscillator in the ultrastrong-coupling regime, where the coupling strength is comparable to the qubit and oscillator energy scales. Special emphasis is placed on the possibility of preparing nonclassical states in this system. These nonclassical states include squeezed states, Schrodinger-cat states and entangled states. We start by comparing the predictions of a number of analytical methods that can be used to describe the system under different assumptions, thus analyzing the properties of the system in various parameter regimes. We then examine the ground state of the system and analyze its nonclassical properties. We finally discuss some questions related to the possible experimental observation of the nonclassical states and the effect of decoherence.