We present the first experimental realization of the quantum illumination protocol proposed by Lloyd [ Science 321 1463 (2008)] and S. Tan et al. [ Phys. Rev. Lett. 101 253601 (2008)], achieved in a simple feasible experimental scheme based on photon-number correlations. A main achievement of our result is the demonstration of a strong robustness of the quantum protocol to noise and losses that challenges some widespread wisdom about quantum technologies
Inconclusive photon subtraction (IPS) is a conditional measurement scheme to
force nonlinear evolution of a given state. In IPS the input state is mixed
with the vacuum in a beam splitter and then the reflected beam is revealed by
ON/OFF photodetection. When the detector clicks we have the (inconclusive)
photon subtracted state. We show that IPS on both channels of an entangled
twin-beam of radiation improves the fidelity of coherent state teleportation if
the energy of the incoming twin-beam is below a certain threshold, which
depends on the beam splitter transmissivity and the quantum efficiency of
photodetectors. We show that the energy threshold diverges when the
transmissivity and the efficiency approach unit and compare our results with
that of previous works on {\em conclusive} photon subtraction.Comment: slightly revised version, to appear in PR
Abstract. In this tutorial, we introduce the basic concepts and mathematical tools needed for phase-space description of a very common class of states, whose phase properties are described by Gaussian Wigner functions: the Gaussian states. In particular, we address their manipulation, evolution and characterization in view of their application to quantum information.
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