Quadripartite continuous-variable entanglement via quadruply concurrent down-conversion

Abstract

We investigate an experimentally feasible intracavity coupled down-conversion scheme to generate quadripartite entanglement using concurrent nonlinearities. We verify that quadripartite entanglement is present in this system by calculating the output fluctuation spectra and then considering violations of optimized inequalities of the van Loock--Furusawa type. The entanglement characteristics both above and below the oscillation threshold are considered. We also present analytic solutions for the quadrature operators and the van Loock--Furusawa correlations in the undepleted pump approximation.