A New Loophole in Recent Bell Test Experiments

TL;DR

Recent photon-based Bell test experiments may have a loophole due to fixed measurement configurations, requiring new analysis methods to conclusively close the detection loophole.

Contribution

This paper identifies a new potential loophole in recent Bell test experiments caused by fixed measurement settings across trials.

Findings

Fixed measurement configurations can undermine Bell test conclusions

Current analysis methods may be invalidated by this loophole

A new statistical analysis approach is needed

Abstract

Recent experiments have reached detection efficiencies sufficient to close the detection loophole with photons. Both experiments ran multiple successive trials in fixed measurement configurations, rather than randomly re-setting the measurement configurations before each measurement trial. This opens a new potential loophole for a local hidden variable theory. The loophole invalidates one proposed method of statistical analysis of the experimental results, as demonstrated in this note. Therefore a different analysis will be necessary to definitively assert that these experiments are subject only to the locality loophole.