Quantum versus classical domains for teleportation with continuous variables - art. no. 022321

By considering the utilization of a classical channel without quantum entan glement, fidelity F-classical=1/2 has been established as setting the bound ary between classical and quantum domains in the teleportation of coherent states of the electromagnetic field [S. L. Braunstein, C. A. Fuchs, and H. J. Kimble, J. Mod. Opt. 47, 267 (2000)]. We further examine the quantum-cla ssical boundary by investigating questions of entanglement and Bell-inequal ity violations for the Einstein-Podolsky-Rosen states relevant to continuou s variable teleportation. The threshold fidelity for employing entanglement as a quantum resource in teleportation of coherent states is again found t o be F-classical=1/2. Likewise, violations of local realism onset at this s ame threshold, with the added requirement of overall efficiency eta >2/3 in the unconditional case. By contrast, recently proposed criteria adapted fr om the literature on quantum-nondemolition detection are shown to be largel y unrelated to the questions of entanglement and Bell-inequality violations .