Visibility bound caused by a distinguishable noise particle

TL;DR

This paper studies how the distinguishability of a noise photon affects the interference visibility of a signal photon, revealing a quantitative relationship and experimentally confirming the degradation effect.

Contribution

It introduces a quantitative analysis of how noise photon distinguishability impacts interference visibility, supported by experimental validation.

Findings

Visibility drops to 1/√2 when noise is distinguishable but technically indistinguishable

Maximum visibility reaches 1 for completely indistinguishable photons

Experimental results confirm the theoretical relationship between distinguishability and interference

Abstract

We investigate how distinguishability of a "noise" particle degrades interference of the "signal" particle. The signal, represented by an equatorial state of a photonic qubit, is mixed with noise, represented by another photonic qubit, via linear coupling on the beam splitter. We report on the degradation of the "signal" photon interference depending on the degree of indistinguishability between "signal" and "noise" photon. When the photons are principally completely distinguishable but technically indistinguishable the visibility drops to the value 1/sqrt(2). As the photons become more indistinguishable the maximal visibility increases and reaches the unit value for completely indistinguishable photons. We have examined this effect experimentally using setup with fiber optics two-photon Mach-Zehnder interferometer.