Loophole-free Bell test for one atom and less than one photon

TL;DR

This paper proposes a method to demonstrate loophole-free Bell inequality violations using entanglement between a single atom's internal states and low-photon-number optical states, highlighting experimental challenges for realization.

Contribution

It introduces a novel entanglement setup involving a single atom and low-photon states and discusses how to perform a loophole-free Bell test with this system.

Findings

Potential for loophole-free Bell test with atom-photon entanglement

Homodyne detection enables violation of Bell inequality in this setup

Identifies key experimental challenges for implementation

Abstract

We consider the entanglement between two internal states of a single atom and two photon number states describing either the vaccum or a single photon and thus containing, on average, less than one photon. We show that this intriguing entanglement can be characterized through substantial violations of a Bell inequality by performing homodyne detections on the optical mode. We present the experimental challenges that need to be overcome to pave the way towards a loophole-free Bell test in this setup.