# Past of a quantum particle: Common sense prevails

## TL;DR

This paper demonstrates that common sense correctly describes the path of a quantum particle in a three-path interferometer, challenging previous claims of discontinuous trajectories, and proposes an experimental test for this interpretation.

## Contribution

It clarifies the particle's path in a three-path interferometer using operational measurements, countering prior claims of non-classical trajectories.

## Key findings

- Common sense aligns with the particle’s path in the interferometer.
- Proposes an experimental setup for unambiguous path discrimination.
- Challenges the notion of discontinuous quantum trajectories.

## Abstract

We analyze Vaidman's three-path interferometer with weak path marking [Phys. Rev. A 87, 052104 (2013)] and find that common sense yields correct statements about the particle's path through the interferometer. This disagrees with the original claim that the particles have discontinuous trajectories at odds with common sense. In our analysis, "the particle's path" has operational meaning as acquired by a path-discriminating measurement. For a quantum-mechanical experimental demonstration of the case, one should perform a single-photon version of the experiment by Danan et al. [Phys. Rev. Lett. 111, 240402 (2013)] with unambiguous path discrimination. We present a detailed proposal for such an experiment.