Decoherence-induced formation of sub-Poissonian entangled and steerable states of collective fields

Abstract Quantum decoherence has a tendency to cause the quantum-to-classical transition through the interaction of a system of interest with a large number of environmental degrees of freedom, which is the main obstacle to the realization of quantum information processing. We propose a scheme to create unconditionally sub-Poissonian entangled and steerable states of the collective cavity field modes by application of the dissipation process. Based on the suitable choice of combination modes, the scheme uses the inherent, efficient and controllable two-mode squeezed vacuum (TMSV) reservoir coupled to the combination modes of concern rather than the original cavity modes in the two-level quantum beat laser. The decoherence is shown to pull the combination modes into the sub-Poissonian entangled and steerable states in the stationary regime. However, the dissipation of the individual cavity fields yields the degradation of the entanglement between the two individual modes and inhibits the occurrence of the quantum steering from one cavity mode to the other. In particular for the case that the external driving field is close to the exact resonance with the atom, the combination modes are led asymptotically to the stationary Einstein–Podolsky–Rosen (EPR) state, while the two individual cavity modes are pulled asymptotically into the vacuum states at steady state. The absence of the decoherence disables the nonclassical states of the combination modes, while the ignorance of the dissipation process of the cavity fields guarantees the generation of the entangled states of the pair of individual modes. The decoherence-induced formation of a nonclassical source is ascribed to the four-wave mixing process in combination with the intrinsic amplitude and phase locking.