Conclusive quantum steering with superconducting transition-edge sensors
Devin H. Smith, Geoff Gillett, Marcelo Pereira de Almeida, Cyril Branciard, Alessandro Fedrizzi, Till J. Weinhold, Adriana E. Lita, Brice Calkins, Thomas Gerrits, Howard M. Wiseman, Sae Woo Nam, Andrew G. White · Nature Communications · 2012
Quantum steering allows two parties to verify shared entanglement even if one measurement device is untrusted. A conclusive demonstration of steering through the violation of a steering inequality is of considerable fundamental interest and opens up applications in quantum communication. To date, all experimental tests with single-photon states have relied on post selection, allowing untrusted devices to cheat by hiding unfavourable events in losses. Here we close this 'detection loophole' by combining a highly efficient source of entangled photon pairs with superconducting transition-edge sensors. We achieve an unprecedented ∼62% conditional detection efficiency of entangled photons and violate a steering inequality with the minimal number of measurement settings by 48 s.d.s. Our results provide a clear path to practical applications of steering and to a photonic loophole-free Bell test. Untrustworthy sources or detectors mean that quantum entanglement cannot always be ensured, but quantum steering inequalities can verify its presence. Using a highly efficient system, Smithet al. are able to close the detection loophole and clearly demonstrate steering between two parties.