The loophole-free Bell tests of 2015 as seen by a purveyor of randomness

by Morgan Mitchel (ICFO - The Institute of Photonic Sciences)

Tuesday 2 Feb 2016, 16:00 → 18:00 Europe/Rome

Aula Conversi (Dipartimento di Fisica - Ed. G. Marconi)

In 1964, John Bell analyzed the following scenario: pairs of particles are sent to widely-separated measurement stations, where one property of each particle is measured. If the particles show sufficiently well-correlated behaviour, Bell proved, something in local realism must be wrong: either the particle properties had no prior existence, or particles can communicate with each other faster than light (or both). Starting in 1972, several experiments has approximated Bell's scenario with increasing sophistication. Until this year, however, all experiments contained weaknesses, or “loopholes,” allowing alternate explanations. In 2015 three experiments, succeeded in simultaneously closing all of the closable loopholes, and in doing so solidly rejected local realism. I will attempt to summarize the issues facing a modern Bell test, with particular attention to questions that have only arisen in recent years: what does it mean to be unpredictable in a Bell test, and how can you guarantee unpredictability?