Tripartite entanglement generation via four-wave mixings: narrowband triphoton W state

We propose a method to generate a narrowband triphoton W state entangled in time (or energy) via two four-wave mixing processes in cold atomic gas media. The calculation of such a triphoton W state is performed with second-order perturbation theory. To characterize the optical properties of the state, we analyze the two-photon and three-photon temporal correlations in the photon coincidence counting measurement. Considering the role of determining the time coherence of triphotons between the nonlinear susceptibilities and phase matchings, we concentrate on two regimes, damped Rabi oscillation and group delay, to look at the temporal correlations. To further enhance the nonlinear interactions, it may be promising to consider cold atoms confined within hollow fibers or loaded into a high-Q cavity.