Generation of three-mode light entanglement via double-channel resonant four-wave mixing

We present a scheme to generate tripartite continuous-variable entanglement at the steady state by using an ensemble of Na five-level double-Λ − V atoms embedded in a three-mode cavity. The scheme is based on the two-channel resonant four-wave mixing, which leads to the parametric interaction between the sum mode of two fields from the upper double-Λ system and the mode from the lower V system. It is for such reason that three cavity modes are correlated and entangled. The present scheme has the following two striking features. One is that the steady-state tripartite entanglement is achieved under the full-resonance condition. Another feature is the fact that all the fields are coupled to the different atomic transitions, respectively. In particular, the tripartite entanglement occurs among the fields with the large frequency differences, which may be necessary for the progress of quantum information.