Generalized rotating-wave approximation to the two-qubit and cavity coupling system

TL;DR

The paper introduces a generalized rotating-wave approximation (GRWA) for two-qubit and cavity systems, providing analytical solutions that are accurate across various coupling strengths, including the ultrastrong regime.

Contribution

It develops a first-order correction to the RWA, yielding an effective Hamiltonian that accurately predicts eigenvalues and eigenstates in the two-qubit cavity system.

Findings

Energy levels match numerical diagonalization results across coupling regimes.

Atomic population inversion agrees quantitatively with numerical results.

The method extends the applicability of RWA to ultrastrong coupling regimes.

Abstract

The generalized rotating-wave approximation (GRWA) is presented for the two-qubit and cavity coipling system . The analytical expressions in the zeroth order approximation recover the previous adiabatic ones. The counterrotating-wave terms can be eliminated by performing the first order corrections. An effective solvable Hamiltonian with the same form as the ordinary RWA one are then obtained, giving a significantly accurate eigenvalues and eigenstates. Energy levels in the present GRWA are in accordant with the numerical exact diagonalization ones in the a wide range of coupling strength. The atomic population inversion in the GRWA is in quantitative agreement with the numerical results for different detunings in the ultrastrong coupling regime.