Bell violation with entangled photons, free of the fair-sampling assumption

TL;DR

This paper reports a loophole-free Bell inequality violation using entangled photons and high-efficiency detectors, advancing fundamental tests of quantum mechanics and enabling secure quantum communication.

Contribution

It demonstrates a Bell test free of the fair-sampling assumption and implements one-sided device-independent quantum key distribution.

Findings

Loophole-free Bell violation achieved with photons and superconducting detectors.

Successful demonstration of one-sided device-independent quantum key distribution.

Advances in fundamental quantum tests and quantum cryptography applications.

Abstract

The violation of a Bell inequality is an experimental observation that forces one to abandon a local realistic worldview, namely, one in which physical properties are (probabilistically) defined prior to and independent of measurement and no physical influence can propagate faster than the speed of light. All such experimental violations require additional assumptions depending on their specific construction making them vulnerable to so-called "loopholes." Here, we use photons and high-efficiency superconducting detectors to violate a Bell inequality closing the fair-sampling loophole, i.e. without assuming that the sample of measured photons accurately represents the entire ensemble. Additionally, we demonstrate that our setup can realize one-sided device-independent quantum key distribution on both sides. This represents a significant advance relevant to both fundamental tests and promising quantum applications.