Unambiguous path discrimination in a two-path interferometer
arXiv:1708.01408 · doi:10.1103/PhysRevA.98.022110
Abstract
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 \emph{cannot be known}; and every photon that emerges from the dark output port of the balanced interferometer has a \emph{known path}.
5 pages, 5 figures; this paper reports the realization of the experiment proposed in section VII B of arXiv:1704.03722 v2: Includes new figure of the setup, and additional details such as preparation of the photon source, and implementation of phase stabilization and control
References in corpus (3)
Cited by in corpus (6)
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