Exponentially fast generating and utilizing quantum entanglement in cavity QED system

An ensemble of atomic spin interacting with an optical cavity mode is widely studied and attracts many interests from quantum metrology to quantum many-body physics. The optical cavity can generate a coherent long-ranged spin-spin interaction among atomic ensembles via the one-axis twisting Hamiltonian. The dynamics of the spin system are significantly affected and exhibit rich quantum many-body phenomena by exposing the ensemble to an additional transverse field. In addition, by using a recently achieved time-reversal toolbox, one also has a probe of more non-trivial collective spin states, especially those with high quantum Fisher information. We will report here our experimental and theoretical progress in this direction and an outlook for exploring other exotic quantum properties.