Generation of entanglement between bright light fields via spontaneous decay-induced quantum interference

In contrast to the general argument that the spontaneous decay is intrinsically incoherent in nature and harmful to entanglement, here, we show that nearly perfect entanglement between two bright pump fields can be realized via spontaneous decay-induced destructive quantum interference in a closed double \ensuremath{\Lambda}-type four-level system with the energy separation of the excited doublet comparable to their decay rates. The high degree of bipartite entanglement results from the cancellation of spontaneous emission and subsequent elimination of the associated noise due to the destructive quantum interference between the two spontaneous emission pathways from the upper doublet to each of the two lower levels when the two strong pump fields are tuned to the particular frequencies where quantum interference takes place. This scheme is particularly suitable for the generation of entanglement between two bright light fields, and may find potential applications in realistic quantum information processing.