Closing the detection loophole in multipartite Bell tests using GHZ states

TL;DR

This paper demonstrates that multipartite Bell tests using GHZ states can significantly lower detection efficiency requirements, enabling loophole-free tests even with high noise levels and many parties.

Contribution

It introduces Bell tests based on n-qubit GHZ states that tolerate much lower detection efficiencies than bipartite tests, advancing experimental feasibility.

Findings

Detection efficiencies as low as 38% are sufficient for certain multipartite Bell tests.

Efficiencies below 50% can be tolerated despite high noise levels.

Arbitrarily small efficiencies are possible with many parties and measurements, even with large noise.

Abstract

We investigate the problem of closing the detection loophole in multipartite Bell tests, and show that the required detection efficiencies can be significantly lowered compared to the bipartite case. In particular, we present Bell tests based on n-qubit Greenberger-Horne-Zeilinger states, which can tolerate efficiencies as low as 38% for a reasonable number of parties and measurements. Even in the presence of a significant amount of noise, efficiencies below 50% can be tolerated, which is encouraging given recent experimental progress. Finally we give strong evidence that, for a sufficiently large number of parties and measurements, arbitrarily small efficiencies can be tolerated, even in the presence of an arbitrary large amount of noise.