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Chinese Physics Letters

A ``Which Way'' Experiment of Two-Photon Interference

Qin Wang, Huang Yun-Feng, Fang‐Wen Sun, Zhang Yong-Sheng, Guo Guang-Can

Published Jan 27, 2005• 7 citations
Publisher

Abstract

It is well known that the indistinguishability of particles causes interference. We give a ``which way'' experiment of two-photon interference marked with polarization. The result shows that the greater the distinguishability of the path by which two-photon passes, the lower the fringe visibility will be, and this phenomenon will disappear when the path becomes completely distinguishable.

DOI
10.1088/0256-307x/22/2/019

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It is well known that the indistinguishability of particles causes interference. We give a ``which way'' experiment of two-photon interference marked with polarization. The result shows that the greater the distinguishability of the path by which two-photon passes, the lower the fringe visibility will be, and this phenomenon will disappear when the path becomes completely distinguishable.
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When a photon is detected after passing through an interferometer one might wonder which path it took, and a meaningful answer can only be given if one has the means of monitoring the photon's whereabouts. We report the realization of a single-photon experiment for a two-path interferometer with path marking. In this experiment, the path of a photon (``signal'') through a Mach-Zehnder interferometer becomes known by unambiguous discrimination between the two paths. We encode the signal path in the polarization state of a partner photon (``idler'') whose polarization is examined by a three-outcome measurement: one outcome each for the two signal paths plus an inconclusive outcome. Our results agree fully with the theoretical predictions from a common-sense analysis of what can be said about the past of a quantum particle: The signals for which we get the inconclusive result have full interference strength, as their paths through the interferometer cannot be known; and every photon that emerges from the dark output port of the balanced interferometer has a known path.
We establish that a connection exists between wave-particle duality of photons and partial polarization of a light beam. We perform a two-path lowest-order (single photon) interference experiment and demonstrate both theoretically and experimentally that the degree of polarization of the light beam emerging from an output of the interferometer depends on path distinguishability. In our experiment, we are able to change the quantum state of the emerging photon from a pure state to a fully mixed state without any direct interaction with the photon. Although most lowest-order interference experiments can be explained by classical theory, our experiment has no genuine classical analog. Our results show that a case exists where the cause of partial polarization is beyond the scope of classical theory.
Abstract A well-known result for the interference of two single-mode fields is that the degree of coherence and the degree of indistinguishability are the same when we consider the detection of a single photon. In this article, we present the relation between the degree of coherence, path indistinguishability and the fringe visibility considering interference of multiple numbers of single-mode fields while being interested in the detection of a single photon only. We will also mention how Born’s rule of interference for multiple sources is reflected in these results.