Closing the detection loophole in Bell experiments using qudits

TL;DR

This paper demonstrates that using higher-dimensional quantum systems in Bell tests can substantially reduce the required detection efficiency to close the detection loophole, enhancing the feasibility of loophole-free Bell experiments.

Contribution

It introduces new Bell test schemes utilizing qudits that lower the detection efficiency thresholds compared to traditional qubit-based tests.

Findings

Asymmetric Bell tests tolerate efficiencies close to 1/N with N-dimensional systems.

Symmetric Bell test reduces efficiency threshold to 61.8% with four-dimensional systems.

Experimental prospects are promising with recent advances in atom-photon entanglement.

Abstract

We show that the detection efficiencies required for closing the detection loophole in Bell tests can be significantly lowered using quantum systems of dimension larger than two. We introduce a series of asymmetric Bell tests for which an efficiency arbitrarily close to 1/N can be tolerated using N-dimensional systems, and a symmetric Bell test for which the efficiency can be lowered down to 61.8% using four-dimensional systems. Experimental perspectives for our schemes look promising considering recent progress in atom-photon entanglement and in photon hyperentanglement.