Fluctuations in atom interferometers as a new tool for dark matter

Abstract

We propose the use of the super-binomial variance in the count rate of an atom interferometer as a novel signature of dark matter. We show that the dark matter induced shift in this observable is enhanced by N, the number of atoms used per run of the interferometer, and therefore offers sensitivity that is enhanced by orders of magnitude relative to an independent-atom estimate. As an application, we consider dark matter that interacts with electrons, protons, and/or neutrons, via a long-range Yukawa interaction and new constraints on strongly interacting dark matter that thermalizes in the overburden of conventional direct detection experiments. We find that searches for super-binomial variance extend, and complement, existing atom interferometer observables; they are well suited to search for both short- and long-ranged forces.

Figures (2)

• Figure 1: Sensitivity projections for anomalous phase shift (dot-dashed curves) and super-binomial fluctuations (solid curves) searches with atom interferometers. For all curves, we take $T_{\rm exp} = 1~{\rm month}$, the dark matter coupling to the mediator to be $y_\chi = \sqrt{4\pi}$, an atomic species with $\text{A}= 87$ nucleons (e.g.,$^{87}\text{Rb}$ or $^{87}\text{Sr}$), and a subcomponent dark matter with $\rho_\chi = 0.05 \, \rho_{\rm DM}$ (in order to evade the strong self-interaction dark matter constraints at low dark matter masses). The black and red curves adopt the atom interferometer benchmarks quoted for the proposals AEDGE AEDGE:2019nxb and AICE Baynham:2025pzm, respectively. For AEDGE, a proposed space-based mission, a cloud of $N=10^{10}$ atoms is assumed, with $\mathcal{T}_{1/2}=600\text{ s}$, $\Delta x = 0.9 \text{ m}$, and $r_c = 4~{\rm mm}$. AICE, the proposal based at CERN, assumes $N=10^8$ atoms and $\mathcal{T}_{1/2}=1.5~{\rm s}$, $\Delta x = 50~{\rm m}$, and $r_c = 100~\mu{\rm m}$. The solid lines display the reach of the new observable proposed in this paper: super-binomial fluctuations of the atom interferometer. For comparison, we also indicate with dot-dashed curves the sensitivity of the coherently enhanced anomalous phase-shift following Ref. Murgui:2025unt. The inner plot zooms on a patch of parameter space and shows the sensitivity from super-binomial fluctuations adopting AICE as benchmark with different number of atoms and instrumental phase noises, as indicated in the figure. The gray shaded area shows the parameter space ruled out by fifth force searches Murata:2014nra. In several cold colors we show the excluded parameter space from the stellar astrophysical constraints on light mediators: bounds from SN1987 Hardy:2024gwy in green, from stellar evolution stages (red giant and horizontal branch stars Hardy:2016kme) in blue, and from stellar remnants (neutron stars Fiorillo:2025zzx and white dwarfs Bottaro:2023gep) in purple.
• Figure 2: Sensitivity curves for strongly interacting dark matter scattering off nucleons. Solid lines show the projected reach of the current Stanford atom fountain Overstreet:2021heaAsenbaum:2020era, located at the Earth’s surface, and of the proposed atom interferometer AICE Baynham:2025pzm, planned to operate about 100 m underground (at the PX46 access shaft to the LHC). Dashed lines show the projected sensitivity of prospective space-based atom interferometers, including the proposed AEDGE AEDGE:2019nxb and a space-based (fictitious) analogue of AICE Baynham:2025pzm. These sensitivities probe regions of parameter space not accessible to other direct-detection constraints, including underground nuclear-recoil experiments (shown in blue: DarkSide-50 DarkSide:2022dhx, CRESST CRESST:2019jnqCRESST:2019axxCRESST:2017ues, XENON-1T XENON:2017vdwPhysRevLett.123.251801, and CDEX-10 PhysRevLett.129.221802), and the rocket-based XQC experiment McCammon_2002 (orange). On the reinterpretation of the XQC data, we show with a dashed orange curve the interpreted bounds on $\sigma_{\chi N}$ assuming an optimistic $100\%$ efficiency for thermalization of the nuclear recoil energy in the sub-keV range Erickcek:2007jv, and with a solid orange curve the reinterpreted bounds adopting a more realistic thermalization efficiency Mahdawi:2018euy. For underground direct-detection experiments we adopt the upper bounds ( ceilings) from Refs. Emken:2018runKavanagh:2017cru, and estimate the ceiling for DarkSide-50. Areas covered with fainted beige indicate cosmological constraints Buen-Abad:2021mvc As discussed in the main text, these are model dependent and may be evaded, for example, if dark matter constitutes only a subcomponent or exhibits velocity-dependent scattering.