Adiabatic approximation in the ultrastrong-coupling regime of a system consisting of an oscillator and two qubits

TL;DR

This paper investigates a system of two flux qubits coupled to a transmission-line resonator beyond the rotating wave approximation, using adiabatic approximation methods to analyze energy spectra and compare with numerical solutions.

Contribution

It introduces an analysis of a qubit-resonator system in the ultrastrong coupling regime using adiabatic approximation, extending beyond the RWA.

Findings

Energy spectrum calculated and compared with numerical solutions.

Adiabatic approximation provides accurate insights in ultrastrong coupling.

System properties differ significantly from RWA predictions.

Abstract

We present a system composed of two flux qubits and a transmission-line resonator. Instead of using the rotating wave approximation (RWA), we analyse the system by the adiabatical approximation methods under two opposite extreme conditions. Basic properties of the system are calculated and compared under these two different conditions. Energy-level spectrum of the system in the adiabatical displaced oscillator basis is shown, and the theoretical result is compared with the numerical solution.