Bell violation with entangled photons, free of the coincidence-time loophole

TL;DR

This paper presents methods to close the coincidence-time loophole in Bell tests with entangled photons, confirming violation of local realism without relying on the fair-coincidence assumption.

Contribution

It introduces and proves two general data analysis techniques that eliminate the coincidence-time loophole in Bell experiments.

Findings

Methods successfully applied to prior experiment

Bell violation confirmed without the coincidence-time loophole

No fair-coincidence assumption needed

Abstract

In a local realist world view, physical properties are defined prior to and independent of measurement, and no physical influence can propagate faster than the speed of light. Proper experimental violation of a Bell inequality would show that the world cannot be described within local realism. Such experiments usually require additional assumptions that make them vulnerable to a number of "loopholes." A recent experiment [Giustina et al, Nature, 2013] violated a Bell inequality without being vulnerable to the detection (or fair-sampling) loophole, therefore not needing the fair-sampling assumption. Here we analyze the more subtle coincidence-time loophole, and propose and prove the validity of two different methods of data analysis that avoid it. Both methods are general and can be used both for pulsed and continuous-wave experiments. We apply them to demonstrate that the experiment mentioned above violates local realism without being vulnerable to the coincidence-time loophole, therefore not needing the corresponding fair-coincidence assumption.