Phase noise measurements in long fiber interferometers for quantum repeaters applications

TL;DR

This study investigates phase noise in long optical fibers, demonstrating that high-visibility interference is achievable over 75 km, and provides insights into phase stability timescales crucial for quantum repeater applications.

Contribution

It provides experimental measurements of phase noise in long fibers in both laboratory and urban environments, informing the feasibility of quantum repeater implementations.

Findings

High visibility interference achievable up to 75 km fiber length

Phase fluctuations follow Gaussian distribution

Mean phase change of 0.1 rad occurs in about 100 microseconds

Abstract

Many protocols for long distance quantum communication require interferometric phase stability over long distances of optical fibers. In this paper we investigate the phase noise in long optical fibers both in laboratory environment and in installed commercial fibers in an urban environment over short time scales (up to hundreds of us). We show that the phase fluctuations during the travel time of optical pulses in long fiber loops are small enough to obtain high visibility first order interference fringes in a Sagnac interferometer configuration for fiber lengths up to 75 km. We also measure phase fluctuations in a Mach-Zehnder interferometer in installed fibers with arm length 36.5 km. We verify that the phase noise respects gaussian distribution and measure the mean phase change as a function of time difference. The typical time needed for a mean phase change of 0.1 rad is of order of 100 us, which provides information about the time scale available for active phase stabilization. Our results are relevant for future implementations of quantum repeaters in installed optical fiber networks.