Non-Hermicity-induced multistability in two-level atom-cavity optomechanics

Non-Hermitian physics of optical as well as atomic systems is crucial for modern quantum mechanics and is the subject of increasing investigations. Here, we investigate the multi-stability of a non-Hermitian atomic optomechanical system consisting of a high-Q Fabry-Perot cavity with Bose-Einstein condensate (BEC). The external pump laser drives a strong cavity mode, which then interacts with trapped BEC. We engineer non-Hermicity in the atomic system by considering the dissipation of excited state to the ground state. The non-Hermitian effects induced by the excited state dissipation result in the modified atom-optomechanical interactions and form non-Hermitian optical potential. We develop coupled non-Hermitian quantum Langevin equations for optical and atomic (BEC) degrees of freedom. By governing the steady-state of the system, we show that the non-Hermicity in the system yields in multi-stable state of cavity photon number, unlike the Hermitian optomechanical systems. Further, we illustrate that the dissipation rate of the atomic excited state will also alter the multi-stable behavior of cavity photon number. We illustrate these effects by computing the effective steady-state potential of the system as a function of cavity photon number. The dissipation rate appears to be reducing steady-state photon number over a particular interval of effective potential. Our findings are not only important for the understanding of the non-Hermitian atom-cavity systems but our findings regarding the optical multi-stability are also crucial for the subject of optical switching.