Einstein-Podolsky-Rosen Steering with No Detection Loophole over 1 km of Optical Fibre
Howard M. Wiseman, D. A. Evans, Cyril Branciard, Eric G. Cavalcanti, Adam Bennet, D. J. Saunders, Geoff J. Pryde · 2011
Whether for quantum cryptography or for testing fundamental properties of the universe, it will be essential to demonstrate nonclassical effects over longer and longer distances. The barrier to doing so is loss of photons during propagation, because considering only those cases where a photon is detected opens a “detection loophole” in the security of any quantum information task in which parties or devices are untrusted. EPR-steering is a nonclassical effect which allows one party to verify that he shares entanglement with another party, even though he doesn't trust her. Using new, arbitrarily loss-tolerant tests, we perform the first detection-loophole-free demonstration of EPR-steering with entangled photon pairs. The parties are separated by a coiled 1 km optical fibre, giving total losses of 8.9 dB (87%).