Significant-loophole-free test of Bell's theorem with entangled photons

TL;DR

This paper reports a loophole-free Bell test using entangled photons, closing major experimental gaps and strongly supporting quantum mechanics over local realism with high statistical significance.

Contribution

It presents the first simultaneous closure of major loopholes in Bell tests using optimized entangled photon sources and advanced detectors.

Findings

Violation of Bell inequality with high statistical significance

Probability of results under local realism is less than 3.74 x 10^-31

Observed an 11.5 standard deviation effect

Abstract

Local realism is the worldview in which physical properties of objects exist independently of measurement and where physical influences cannot travel faster than the speed of light. Bell's theorem states that this worldview is incompatible with the predictions of quantum mechanics, as is expressed in Bell's inequalities. Previous experiments convincingly supported the quantum predictions. Yet, every experiment requires assumptions that provide loopholes for a local realist explanation. Here we report a Bell test that closes the most significant of these loopholes simultaneously. Using a well-optimized source of entangled photons, rapid setting generation, and highly efficient superconducting detectors, we observe a violation of a Bell inequality with high statistical significance. The purely statistical probability of our results to occur under local realism does not exceed $3.74 \times 10^{-31}$, corresponding to an 11.5 standard deviation effect.