Enhanced spin squeezing and quantum entanglement near the critical point of the Jaynes–Cummings–Dicke model

We investigate spin squeezing (SS) and the quantum Fisher information (QFI) for the Jaynes–Cummings–Dicke (JCD) model in a two-component atomic Bose–Einstein condensate (BEC) inside an optical cavity. Analytical expressions for spin squeezing and the reciprocal of the quantum Fisher information per particle (RMQFI) are derived using the frozen spin approximation. It is shown that in the superradiant phase near the critical point, maximum squeezing and maximum quantum entanglement occur and thus the critical point emerges as a useful resource for precision measurements. In the presence of decoherence and particle loss, we show that gradually with time, even though the ability of squeezing and entanglement generation are weakened, yet significant amounts are still present which can be relevant to quantum information processing and precision spectroscopy.