Searching for dark matter with an unequal delay interferometer

TL;DR

This paper introduces a novel experiment using an unequal delay interferometer to search for ultra-light oscillating dark matter, setting new constraints on dark matter coupling constants across a range of masses.

Contribution

The paper presents the first experimental implementation of a delay-based interferometric method for dark matter detection, enhancing sensitivity around mechanical resonances and improving existing constraints.

Findings

No evidence of dark matter was found in the tested mass range.

Constraints on dark matter coupling constants were improved by up to an order of magnitude.

Enhanced sensitivity was achieved at the mechanical resonances of the cavity.

Abstract

We propose a new type of experiment that compares the frequency of a clock (an ultra-stable optical cavity in this case) at time $t$ to its own frequency some time $t-T$ earlier, by "storing" the output signal (photons) in a fibre delay line. In ultra-light oscillating dark matter (DM) models, such an experiment is sensitive to coupling of DM to the standard model fields, through oscillations of the cavity and fibre lengths and of the fibre refractive index. Additionally, the sensitivity is significantly enhanced around the mechanical resonances of the cavity. We present experimental result of such an experiment and report no evidence of DM for masses in the [$4.1\times 10^{-11}$, $8.3\times 10^{-10}$]~eV region. In addition, we improve constraints on the involved coupling constants by one order of magnitude in a standard galactic DM model, at the mass corresponding to the resonant frequency of our cavity. Furthermore, in the model of relaxion DM, we improve on existing constraints over the whole DM mass range by about one order of magnitude, and up to six orders of magnitude at resonance.