Counterfactual quantum indistinguishability

Quantum indistinguishability and counterfactuality are two counterintuitive features of quantum mechanics. The latter refers to the possibility of detecting a particle without an interaction, whilst the former to the indistinguishability of identical particles. In this work, we describe a phenomenon, that we call "counterfactual indistinguishability", which combines these two features, and whereby the detection of a particle at a given station indicates a blockade on an indistinguishable particle elsewhere. From a foundational perspective, it is of interest to note that despite being a multi-particle phenomenon, this is ideally realized using single-photon (rather than multi-photon) interference.