Fidelity matters: the birth of entanglement in the interference of Gaussian states

Stefano Olivares, Matteo G. A. Paris

Published 2011-03-20, updated 2011-09-21Version 3

We address the interaction of two Gaussian states interferring at a beam splitter and analyze the correlations exhibited by the resulting bipartite system. We demonstrate that nonlocal correlations (entanglement) arise if and only if the fidelity between the two input Gaussian states falls under a threshold value depending only on their purities and on the transmissivity of the beam splitter. Our result clarifies the role of squeezing as a prerequisite for entanglement and provide a tool to optimize the generation of entanglement by passive devices.