Cosmic Bell Test using Random Measurement Settings from High-Redshift Quasars

TL;DR

This experiment used high-redshift quasars to determine measurement settings in a Bell test, significantly closing the 'freedom-of-choice' loophole by linking settings to ancient cosmic photons, and observed a strong violation of Bell's inequality.

Contribution

It introduces a novel Bell test using cosmic photons from billions of years ago to choose measurement settings, enhancing the closure of the freedom-of-choice loophole.

Findings

Observed Bell inequality violation with 9.3 sigma significance.

Excluded local-realist influences from 96% of the past light cone.

Extended the temporal boundary of free-choice assumptions to about 7.8 billion years ago.

Abstract

In this Letter, we present a cosmic Bell experiment with polarization-entangled photons, in which measurement settings were determined based on real-time measurements of the wavelength of photons from high-redshift quasars, whose light was emitted billions of years ago, the experiment simultaneously ensures locality. Assuming fair sampling for all detected photons and that the wavelength of the quasar photons had not been selectively altered or previewed between emission and detection, we observe statistically significant violation of Bell's inequality by $9.3$ standard deviations, corresponding to an estimated $p$ value of $\lesssim 7.4 \times 10^{-21}$. This experiment pushes back to at least $\sim 7.8$ Gyr ago the most recent time by which any local-realist influences could have exploited the "freedom-of-choice" loophole to engineer the observed Bell violation, excluding any such mechanism from $96\%$ of the space-time volume of the past light cone of our experiment, extending from the big bang to today.