Where is the photon in an interferometer?

TL;DR

This paper analyzes a nested Mach-Zehnder interferometer experiment, arguing that standard quantum mechanics explains the results without invoking disconnected trajectories or non-classical photon paths.

Contribution

It provides a critique of the interpretation that photons skip certain mirrors, showing that orthodox quantum mechanics suffices to explain the experimental observations.

Findings

Standard quantum mechanics explains the experimental results.

No evidence for photons skipping mirrors within orthodox framework.

Critique of the non-classical trajectory interpretation.

Abstract

In a paper titled "Asking photons where they have been?" \cite{LV} Danan, Farfurnik, Bar-Ad and Vaidman describe an experiment with pre and post selected photons going through nested Mach-Zehnder interferometers. They find that some of the mirrors leave no footprints on the signal and interpret this as evidence that the photon skipped these mirrors. They argue that the experiment supports Aharonov-Vaidman's formulation of quantum mechanics \cite{AharonovVaidman} where post-selected particles are assigned disconnected trajectories. I review the experiment and analyze it within the orthodox framework of quantum mechanics. The standard view of interfering trajectories accounts for the experimental findings.