Particle Path Through a Nested Mach-Zehnder Interferometer

TL;DR

This paper investigates photon paths in a nested Mach-Zehnder interferometer using consistent histories and weak measurements, challenging claims of counterfactual communication protocols with negligible photon presence.

Contribution

It provides a novel analysis of photon trajectories in nested interferometers, questioning prior claims about counterfactual communication using weak measurement techniques.

Findings

Photon paths differ from Vaidman's analysis

Results align with Li et al.'s conclusions

Counterfactual communication claims are cast into doubt

Abstract

Possible paths of a photon passing through a nested Mach-Zehnder interferometer on its way to a detector are analyzed using the consistent histories formulation of quantum mechanics, and confirmed using a set of weak measurements (but not weak values). The results disagree with an analysis by Vaidman [ Phys.\ Rev.\ A 87 (2013) 052104 ], and agree with a conclusion reached by Li et al.\ [ Phys.\ Rev.\ A 88 (2013) 046102 ]. However, the analysis casts serious doubt on the claim of Salih et al.\ (whose authorship includes Li et al.) [ Phys.\ Rev.\ Lett.\ 110 (2013) 170502 ] to have constructed a protocol for counterfactual communication: a channel which can transmit information even though it contains a negligible number of photons.