Generation of steady four-atom decoherence-free states via quantum-jump-based feedback

A scheme is presented for generating steady four-atom decoherence-free states via four atoms with the Raman level configuration interacting with a single-mode vacuum cavity field by using quantum-jump-based feedback. The scheme meets the condition of a strongly dissipative cavity easily and has a simplified feedback control. Although the spontaneous emission still plays a negative role in the proposed system, we can improve the feedback control to reduce its effect.