Dynamics of intrinsic optical bistability in two weakly interacting quantum systems

The dynamics of the intrinsic optical bistability (IOB) in an elementary quantum system is investigated in the situation where this system is composed of two weakly interacting subsystems. Numerical calculations have been performed for two “real” systems where IOB has been experimentally observed. The first situation corresponds to the electron-nuclear spin system of β-Ga₂O₃, where the transition between electron spin states exhibit a strong bistability. The other situation corresponds to optical transitions in Yb³⁺ pairs in CsCdBr₃:Yb compound, where IOB has been experimentally observed. It is shown that, in addition to the classical hysteresis of the response of the system upon variation of the power of the external field, the observation of the so-called critical slowing down is a clear signature of IOB.