Preparing the bound instance of entanglement. (arXiv:1006.4651v1 [quant-ph])

Entanglement is the feature of quantum mechanics that renders it crucially
different from any classical statistical theory. Among the possibly most
remarkable aspects of quantum entanglement is that it comes in “free” and
“bound” instances. Bound entangled states require entangled states in
preparation but, once realized, no free entanglement and therefore no pure
maximally entangled pairs can be locally regained. Their existence hence
certifies an intrinsic irreversibility of entanglement in nature and suggests a
connection with a thermodynamical picture of entanglement. In this work, we
present a first experimental unconditional preparation and detection of a bound
entangled state of light. We use convex optimization to identify regimes
rendering the bound character of continuous-variable entanglement well
certifiable and realize an experiment that continuously produced a bound
entangled state with an extraordinary significance of more than ten standard
deviations away from both separability and distillability. This platform allows
for the efficient preparation of multi-mode entangled states of light with
various applications in quantum information, quantum state engineering and
metrology.

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