Towards a loophole-free test of Bell's inequality with entangled pairs of neutral atoms

TL;DR

This paper discusses a feasible experimental approach to conclusively test Bell's inequality by closing both the locality and detection loopholes using entangled neutral atoms and photons.

Contribution

It proposes a method to perform a loophole-free Bell test with entangled neutral atoms, combining high detection efficiency and space-like separation.

Findings

Feasibility of closing both loopholes in future experiments

Use of atom-photon entanglement for long-distance atomic entanglement

Estimations based on current experimental capabilities

Abstract

Experimental tests of Bell's inequality allow to distinguish quantum mechanics from local hidden variable theories. Such tests are performed by measuring correlations of two entangled particles (e.g. polarization of photons or spins of atoms). In order to constitute conclusive evidence, two conditions have to be satisfied. First, strict separation of the measurement events in the sense of special relativity is required ("locality loophole"). Second, almost all entangled pairs have to be detected (for particles in a maximally entangled state the required detector efficiency is 82.8%), which is hard to achieve experimentally ("detection loophole"). By using the recently demonstrated entanglement between single trapped atoms and single photons it becomes possible to entangle two atoms at a large distance via entanglement swapping. Combining the high detection efficiency achieved with atoms with the space-like separation of the atomic state detection events, both loopholes can be closed within the same experiment. In this paper we present estimations based on current experimental achievements which show that such an experiment is feasible in future.