3 years ago

Quantum Rabi-Stark model: Solutions and exotic energy spectra.

You-fei Xie, Liwei Duan, Qing-hu Chen

The quantum Rabi-Stark model, where the linear dipole coupling and the nonlinear Stark-like coupling are present on an equal footing, are studied within the Bogoliubov operators approach. Transcendental functions responsible for the exact solutions are derived in a compact way, much simpler than previous ones obtained in the Bargmann representation. The zeros of transcendental functions reproduce completely the regular spectra. In terms of the explicit pole structure of these functions, two kinds of exceptional eigenvalues are obtained and distinguished in a transparent manner. Very interestingly, a first-order quantum phase transition indicated by level crossing of the ground state and the first excited state is induced by the positive nonlinear Stark-like coupling, which is however absent in any previous isotropic quantum Rabi Models. When the absolute value of the nonlinear coupling strength is equal to twice the cavity frequency, this model can be reduced to an effective quantum harmonic oscillator, and solutions are then obtained analytically. Below a critical coupling, infinite discrete spectra accumulates into a point from below. While approaching the critical coupling, the spectra collapse is observed.

Publisher URL: http://arxiv.org/abs/1811.04431

DOI: arXiv:1811.04431v2

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