18 December 2015 Special PRL December issue on Bell Tests

Cover of PRL with photos of ICFO researchers as part of the mosaic.

3 articles in this issue highlight ICFO technology which make possible loophole-free Bell tests Recently, Albert Einstein\'s famous objection \"God does not play dice\" has been tested with unprecedented rigor by groups at TU Delft, IQOQI Vienna, and NIST (USA). The accomplishments achieved in these studies, co-authored by ICFO researchers and published in three articles, have been of such importance that Physics Review Letters has decided to dedicate the December issue of the journal to Bell tests.

Bell’s 1964 Theorem, suggested to be one of the most profound discoveries in all of physics, effectively showed that the results predicted by quantum mechanics had to account for non-locality. For decades researchers have been inventing and designing new experimental setups to confirm that such nonlocal correlations really exist in Nature. Until now, all Bell tests left open at least one “loophole,” or flaw in the experimental proof. For example, the “locality loophole” is open if there is time for a signal to travel from one site to the other during the measurement, the “detection efficiency loophole” is open if too many photon pairs go undetected, and the exotic “freedom of choice loophole” is open if the detector settings could be chosen by the entangled particles themselves.

The three experiments co-authored by ICFO researchers were able to simultaneously close these \"loopholes\" that prevented earlier tests from being conclusive, and represent a milestone in both quantum technology and in our understanding of what could lie behind the oddities of quantum physics.

To close two of the three open loopholes, all three experiments used ICFO random number generators, developed by the groups of ICREA Professors at ICFO Dr. Morgan Mitchell and Dr. Valerio Pruneri, in collaboration with the ICFO electronic workshop. In total, seven ICFOnians appear in four Bell test publications: Carlos Abellan, Dr. Waldimar Amaya, Daniel Mitrani, Dr. Morgan Mitchell, Dr. Valerio Pruneri, Dr. Fabian Steinlechner (Vienna) and Dr. Tim Taminiau (Delft). In addition to answering a fundamental question debated by Einstein and Niels Bohr, the Bell tests open the way to new methods of quantum communication, some of them also invented at ICFO.