50-km fiber interferometer for testing gravitational signatures in quantum interference

TL;DR

This paper reports a 50-km fiber interferometer capable of detecting gravitationally induced phase shifts at the quantum level, paving the way for laboratory tests of quantum gravity effects.

Contribution

The authors built a large-scale fiber interferometer with unprecedented phase sensitivity, enabling the detection of gravity-induced quantum phase shifts in a laboratory setting.

Findings

Achieved phase sensitivity of 4.42×10⁻⁶ rad RMS

Resolved a gravity-induced phase shift of approximately 6.18×10⁻⁵ rad

Demonstrated capability to detect gravitational redshifts in a controlled environment

Abstract

Quantum mechanics and general relativity are the foundational pillars of modern physics, yet experimental tests that combine the two frameworks remain rare. Measuring optical phase shifts of massless photons in a gravitational potential provides a unique quantum platform to probe gravity beyond Newtonian descriptions, but laboratory-based interferometers have not yet reached the sensitivity needed to access this regime. Here, we report the realization of a 50-km table-top Mach-Zehnder fiber interferometer operating at the single-photon level, achieving a phase sensitivity of $4.42\times10^{-6}$ rad root-mean-square (RMS) within the frequency range of 0.01 Hz to 5 Hz. We demonstrate that this sensitivity is sufficient to resolve a phase-shift signal of $(6.18 \pm 0.44)\times10^{-5}$ rad RMS at 0.1 Hz, associated with a modulated gravity-induced signal. Our results establish a milestone for quantum sensing with large-scale optical interferometry, demonstrating the capability to detect gravitational redshifts in a local laboratory, thereby paving the way for testing quantum phenomena within general relativistic frameworks.