Bounding the speed of `spooky action at a distance'

TL;DR

This paper reports a Bell inequality violation experiment that closes locality loopholes, establishing a lower bound on the speed of quantum entanglement correlations as significantly exceeding the speed of light.

Contribution

It provides the first loophole-free measurement setting a new lower bound on the speed of nonlocal quantum correlations.

Findings

Observed continuous Bell inequality violation over 12 hours.

Established the lower bound speed of 'spooky action' as over four orders of magnitude of light speed.

Closed all locality loopholes in the experiment.

Abstract

In the well-known EPR paper, Einstein et al. called the nonlocal correlation in quantum entanglement as `spooky action at a distance'. If the spooky action does exist, what is its speed? All previous experiments along this direction have locality loopholes and thus can be explained without having to invoke any `spooky action' at all. Here, we strictly closed the locality loopholes by observing a 12-hour continuous violation of Bell inequality and concluded that the lower bound speed of `spooky action' was four orders of magnitude of the speed of light if the Earth's speed in any inertial reference frame was less than 10^(-3) times of the speed of light.