Multipartite continuous-variable entanglement from concurrent nonlinearities

Abstract

We show theoretically that concurrent interactions in a second-order nonlinear medium placed inside an optical resonator can generate multipartite entanglement between the resonator modes. We show that there is a mathematical connection between this system and van Loock and Braunstein's proposal for entangling $N$ continuous quantum optical variables by interfering with the outputs of $N$ degenerate optical parametric amplifiers (OPA) at a $N$-port beam splitter. Our configuration, however, requires only one nondegenerate OPA and no interferometer. In a preliminary experimental study, we observe the concurrence of the appropriate interactions in periodically poled ${\mathrm{RbTiOAsO}}_{4}$.