Observing momentum disturbance in double-slit "which-way" measurements

TL;DR

This study experimentally investigates how 'which-way' measurements in a double-slit experiment cause momentum disturbance, revealing that the disturbance accumulates nonclassically during photon propagation and relates to interference visibility loss.

Contribution

The paper provides the first experimental reconstruction of momentum change distribution in 'which-way' measurements, linking it quantitatively to interference visibility loss using Bohmian trajectories.

Findings

Momentum disturbance accumulates nonclassically during photon propagation.

A quantitative relation between visibility loss and momentum disturbance is established.

Bohmian momentum offers an intuitive understanding of wave-particle duality.

Abstract

Making a "which-way" measurement (WWM) to identify which slit a particle goes through in a double-slit apparatus will reduce the visibility of interference fringes. There has been a long-standing controversy over whether this can be attributed to an uncontrollable momentum transfer. To date, no experiment has characterised the momentum change in a way that relates quantitatively to the loss of visibility. Here, by reconstructing the Bohmian trajectories of single photons, we experimentally obtain the distribution of momentum change, which is observed to be not a momentum kick that occurs at the point of the WWM, but nonclassically accumulates during the propagation of the photons. We further confirm a quantitative relation between the loss of visibility consequent on a WWM and the total (late-time) momentum disturbance. Our results emphasize the role of the Bohmian momentum in giving an intuitive picture of wave-particle duality and complementarity.