A possible solution to the which-way problem of quantum interference

TL;DR

This paper challenges the traditional view that interference patterns exclude path information by showing that polarization effects reveal particles are delocalized and can carry path information without destroying interference.

Contribution

It demonstrates experimentally that polarization rotations can encode path information while still maintaining observable interference patterns.

Findings

Particles in maxima show no polarization fluctuations.

Particles near minima experience large polarization rotations.

Delocalization allows for path information without losing interference.

Abstract

It is commonly assumed that the observation of an interference pattern is incompatible with any information about the path taken by a quantum particle. Here we show that, contrary to this assumption, the experimentally observable effects of small polarization rotations applied in the slits of a double slit experiment indicate that individual particles passing the slits before their detection in the interference pattern are physically delocalized with regard to their interactions with the local polarization rotations. The rate at which the polarization is flipped to the orthogonal state is a direct measure of the fluctuations of the polarization rotation angles experienced by each particle. Particles detected in the interference maxima experience no fluctuations at all, indicating a presence of exactly one half of the particle in each slit, while particles detected close to the minima experience polarization rotations much larger than the local rotations, indicating a negative presence in one of the slits and a presence of more than one in the other.