Identical particles as a genuine non-local resource

TL;DR

This paper investigates whether states of identical particles can serve as non-local resources in Bell-type experiments using classical optical setups, revealing that most such states exhibit non-locality except for certain boson states.

Contribution

It fully characterizes the non-locality potential of multi-particle states of identical particles in classical optical experiments, linking indistinguishability to Bell non-locality.

Findings

All fermion states exhibit non-locality in classical setups.

Most boson states exhibit non-locality, except for single-mode reducible states.

Single-mode boson states are locally simulable and do not show non-locality.

Abstract

All particles of the same type are indistinguishable, according to a fundamental quantum principle. This entails a description of many-particle states using symmetrised or anti-symmetrised wave functions, which turn out to be formally entangled. However, the measurement of individual particles is hampered by a mode description in the second-quantised theory that masks this entanglement. Is it nonetheless possible to use such states as a resource in Bell-type experiments? More specifically, which states of identical particles can demonstrate non-local correlations in passive linear optical setups that are considered purely classical component of the experiment? Here, the problem is fully solved for multi-particle states with a definite number of identical particles. We show that all fermion states and most boson states provide a sufficient quantum resource to exhibit non-locality in classical optical setups. The only exception is a special class of boson states that are reducible to a single mode, which turns out to be locally simulable for any passive linear optical experiment. This finding highlights the connection between the basic concept of particle indistinguishability and Bell non-locality, which can be observed by classical means for almost every state of identical particles.