Understanding Modified Two-Slit Experiments using Path Markers

TL;DR

This paper analyzes modified two-slit experiments with path markers, clarifying wave-particle duality and interference using testable quantum correlations, resolving apparent paradoxes in the interpretation of which-path information.

Contribution

It introduces a theoretical framework using polarization-based path markers to test and clarify the nature of interference and which-path information in modified two-slit experiments.

Findings

Photons reaching a detector originate from both slits.

Interference photons cannot be assigned to a single slit.

Polarization analysis reveals the true nature of the photons' paths.

Abstract

Some modified two-slit interference experiments were carried out showing an apparent paradox in wave-particle duality. In a typical such experiment, the screen, where the interference pattern is supposed to be formed, is replaced by a converging lens. The converging lens forms the images of the two slits at two spatially separated detectors. It was claimed that each of these two detectors give information about which slit a photon came from, even though they come from the region of interference. These experiments generated a lot of debate. The various refutations pointed out that the controversial claims involved some questionable assumptions. However the refutations were largely philosophical in nature, and one may like to substantiate those with arguments which are testable, at least in principle. Here such an experiment is theoretically analyzed by introducing path markers which are two orthogonal polarization states of the photon. Analyzing the polarization at the two detectors shows that the photons which give rise to interference, and reach a particular detector, always come from both the slits. This provides clarity in understanding such experiments by making use of testable quantum correlations.