  Tripartite entangled states, such as GHZ and W states, are typically
generated by manipulating two pairs of polarization-entangled photons in bulk
optics. Here we propose a scheme to generate W states that are entangled in the
energy degree of freedom in an integrated optical circuit. Our approach employs
photon pairs generated by spontaneous four-wave mixing (SFWM) in a micro- ring
resonator. We also present a feasible procedure for demonstrating the
generation of such a state, and we compare polarization-entangled and
energy-entangled schemes for the preparation of W states.

Quantum Physics