Variational generalized rotating-wave approximation in the two-qubit quantum Rabi model

Abstract

We present an analytical method for the two-qubit quantum Rabi model. While still operating in the frame of the generalized rotating-wave approximation (GRWA), our method further embraces the idea of introducing variational parameters. The optimal value of the variational parameter is determined by minimizing the energy function of the ground state. Comparing with numerical exact results, we show that our method evidently improves the accuracy of the conventional GRWA in calculating fundamental physical quantities, such as energy spectra, mean photon number, and dynamics. Interestingly, the accuracy of our method allows us to reproduce the asymptotic behavior of mean photon number in large frequency ratio for the ground state and investigate the quasi-periodical structure of the time evolution, which are incapable of being predicted by the GRWA. The applicable parameter ranges cover the ultrastrong coupling regime, which will be helpful to recent experiments.

References in corpus (8)

• Beyond the Jaynes-Cummings model: circuit QED in the ultrastrong coupling regime
• Observation of the Bloch-Siegert Shift in a Qubit-Oscillator System in the Ultrastrong Coupling Regime
• Deep Strong Coupling Regime of the Jaynes-Cummings model
• Taming multiparticle entanglement
• Generalized rotating-wave approximation for arbitrarily large coupling
• Ultrastrong coupling regime of cavity QED with phase-biased flux qubits
• Generalized rotating-wave approximation to the two-qubit and cavity coupling system
• Optical Stern Gerlach Effect beyond the rotating wave approximation