Comment on "One-state vector formalism for the evolution of a quantum state through nested Mach-Zehnder interferometers"

TL;DR

This paper critiques the analysis of photon paths in nested Mach-Zehnder interferometers, highlighting inconsistencies in previous quantum and classical approaches and emphasizing the need for proper interpretation of experimental results.

Contribution

It provides a critical assessment of existing analyses, clarifying the limitations of prior methods in describing photon behavior in interferometers.

Findings

Previous analyses are inconsistent and inappropriate.

Proper interpretation of photon paths requires careful analysis.

The critique clarifies misconceptions in past experiments.

Abstract

Bartkiewicz et al. [Phys. Rev. A 91, 012103 (2015)] provided an alternative analysis of experiment performed by Danan et al. [Phys. Rev. Lett. 111, 240402 (2013)] which presented surprising evidence regarding the past of photons passing through an interferometer. They argued that the quantity used by Danan et al. is not a suitable which-path witness, and proposed an alternative. It is argued that the quantum and classical analyses of Bartkiewicz et al. are inconsistent and both are inappropriate for describing the past of photons in a properly working interferometer.