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arXiv:2610.36044

An open EFT for dark matter searches with matter-wave interferometers

Leonardo Badurina, Kathryn M. Zurek

hep-phhep-thquant-phSubmitted Oct 26, 2026• Announced Oct 28, 2026
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Abstract

Matter-wave interferometers (MWIs) are a genuine quantum probe of dark matter (DM), being sensitive to DM-induced phase shifts and loss of contrast. Treating the interferometer as an open quantum system and the dark sector as its environment, we derive an open EFT to study these signatures using the Schwinger-Keldysh formalism. Starting from a microscopic theory, we derive the interferometer's effective action, which we then project onto the many-body worldline sectors relevant for atom interferometers and MWIs employing mesoscopic objects, i.e., composite-particle interferometers (CPIs). This construction clarifies the heavy-probe limit and organizes phase shifts and decoherence as distinct real-time components of the influence action: the retarded kernel controls the causal response of the environment, while the Keldysh kernel controls environmental fluctuations and hence loss of contrast. At leading order, these kernels reduce to: (i) DM bubble diagrams in the case of four-point interactions, and (ii) dressed in-medium mediator propagators in the case of long-range interactions, where the dressing is provided by the DM environment. Within this framework, we study the signatures of elastic spin-independent sub-GeV DM scattering off nucleons and find that: (i) owing to Bose enhancements below the DM wave-particle boundary, ambitious CPIs could probe Higgs-portal DM with mass below 1 eV in an unexplored region of model space; (ii) for DM coupled to nucleons via a light hadrophilic scalar, the DM background can drive the mediator's in-medium mass tachyonic over much of parameter space; outside these regions, CPIs could probe provide powerful probes of light DM.

AI Summary

Matter-wave interferometers can register dark matter (DM) through phase shifts and contrast loss without resolving recoil or deposited energy. This paper develops an open effective field theory connecting microscopic DM–matter interactions to these observables across particle-like and wave-like DM regimes. Using the Schwinger–Keldysh formalism, it traces out the dark sector and projects the resulting influence action onto single-atom and many-body worldlines. In the heavy-probe limit, environmental retarded and Keldysh kernels determine phase shifts and decoherence, respectively. The construction recovers known coherent enhancements: both signals can scale as $N_{\rm at}^2$ for bound composite-particle interferometers (CPIs), whereas, for initially uncorrelated atom clouds, only the per-atom phase receives an $N_{\rm at}$ enhancement. Finite-time expressions retain non-Markovian effects; recoil corrections are controlled by the probe-to-DM mass ratio and probe momentum spread. For spin-independent contact interactions, DM bubble diagrams produce Bose-enhanced decoherence below the wave–particle boundary, without a corresponding phase enhancement. Ambitious CPI projections reach unexplored Higgs-portal parameter space below $1\,\mathrm{eV}$. For light scalar mediation, resummed DM polarization corrections can make the mediator’s effective mass squared negative, invalidating homogeneous plane-wave projections over substantial parameter regions. Outside these regions, CPI benchmarks can probe unexplored parameter space, including a $5\%$ DM subcomponent with masses roughly $10\,\mathrm{eV}$–$10\,\mathrm{MeV}$. The calculations assume a stationary, homogeneous, initially Gaussian dark environment and weak probe coupling. Sensitivities assume shot-noise-limited readout; terrestrial refraction can modify some projections. Phonon excitation channels, dynamics after the instability, and realistic environmental backgrounds are not evaluated.

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50 pages + appendices, 8 figures

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Matter-wave interferometers (MWIs) are a genuine quantum probe of dark matter (DM), being sensitive to DM-induced phase shifts and loss of contrast. Treating the interferometer as an open quantum system and the dark sector as its environment, we derive an open EFT to study these signatures using the Schwinger-Keldysh formalism. Starting from a microscopic theory, we derive the interferometer's effective action, which we then project onto the many-body worldline sectors relevant for atom interferometers and MWIs employing mesoscopic objects, i.e., composite-particle interferometers (CPIs). This construction clarifies the heavy-probe limit and organizes phase shifts and decoherence as distinct real-time components of the influence action: the retarded kernel controls the causal response of the environment, while the Keldysh kernel controls environmental fluctuations and hence loss of contrast. At leading order, these kernels reduce to: (i) DM bubble diagrams in the case of four-point interactions, and (ii) dressed in-medium mediator propagators in the case of long-range interactions, where the dressing is provided by the DM environment. Within this framework, we study the signatures of elastic spin-independent sub-GeV DM scattering off nucleons and find that: (i) owing to Bose enhancements below the DM wave-particle boundary, ambitious CPIs could probe Higgs-portal DM with mass below 1 eV in an unexplored region of model space; (ii) for DM coupled to nucleons via a light hadrophilic scalar, the DM background can drive the mediator's in-medium mass tachyonic over much of parameter space; outside these regions, CPIs could probe provide powerful probes of light DM.
Matter-wave interferometers can register dark matter (DM) through phase shifts and contrast loss without resolving recoil or deposited energy. This paper develops an open effective field theory connecting microscopic DM–matter interactions to these observables across particle-like and wave-like DM regimes.
Using the Schwinger–Keldysh formalism, it traces out the dark sector and projects the resulting influence action onto single-atom and many-body worldlines. In the heavy-probe limit, environmental retarded and Keldysh kernels determine phase shifts and decoherence, respectively. The construction recovers known coherent enhancements: both signals can scale as Nat2N_{\rm at}^2Nat2​ for bound composite-particle interferometers (CPIs), whereas, for initially uncorrelated atom clouds, only the per-atom phase receives an NatN_{\rm at}Nat​ enhancement. Finite-time expressions retain non-Markovian effects; recoil corrections are controlled by the probe-to-DM mass ratio and probe momentum spread.
For spin-independent contact interactions, DM bubble diagrams produce Bose-enhanced decoherence below the wave–particle boundary, without a corresponding phase enhancement. Ambitious CPI projections reach unexplored Higgs-portal parameter space below 1 eV1\,\mathrm{eV}1eV. For light scalar mediation, resummed DM polarization corrections can make the mediator’s effective mass squared negative, invalidating homogeneous plane-wave projections over substantial parameter regions. Outside these regions, CPI benchmarks can probe unexplored parameter space, including a 5%5\%5% DM subcomponent with masses roughly 10 eV10\,\mathrm{eV}10eV–10 MeV10\,\mathrm{MeV}10MeV.
The calculations assume a stationary, homogeneous, initially Gaussian dark environment and weak probe coupling. Sensitivities assume shot-noise-limited readout; terrestrial refraction can modify some projections. Phonon excitation channels, dynamics after the instability, and realistic environmental backgrounds are not evaluated.
Matter-wave interferometers (MWIs) offer a uniquely quantum route to dark matter (DM) detection: DM can reveal itself through phase and decoherence between spatially separated wavepackets, even when negligible energy deposition or resolvable recoil occurs. We formulate these effects in an open effective field theory for MWIs using the Schwinger-Keldysh formalism, which highlights a structural asymmetry between the two detection channels. For elastic spin-independent DM scattering, decoherence inherits novel Bose enhancement or Pauli blocking factors, while the phase is at most linear in the DM occupation number. By retaining the DM's coherence time, this framework spans Markovian and non-Markovian dynamics across a wide range of DM masses, and systematically organizes corrections beyond the heavy-probe limit.
A new frontier in the search for dark matter (DM) is based on the idea of detecting the decoherence caused by DM scattering against a mesoscopic superposition of normal matter. Such superpositions are uniquely sensitive to very small momentum transfers from new particles and forces, especially DM with a mass below 100 MeV. Here we investigate what sorts of dark sectors are inaccessible with existing methods but would induce noticeable decoherence in the next generation of matter interferometers. We show that very soft but medium range ($0.1\text{ }\mathrm{nm}--1\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$) elastic interactions between nuclei and DM are particularly suitable. We construct toy models for such interactions, discuss existing constraints, and delineate the expected sensitivity of forthcoming experiments. The first hints of DM in these devices would appear as small variations in the anomalous decoherence rate with a period of one sidereal day. This is a generic signature of interstellar sources of decoherence, clearly distinguishing it from terrestrial backgrounds. The OTIMA experiment under development in Vienna will begin to probe Earth-thermalizing DM once sidereal variations in the background decoherence rate are pushed below one part in a hundred for superposed 5-nm gold nanoparticles. The proposals by Bateman et al. and Geraci et al. could be similarly sensitive although they would require at least a month of data taking. DM that is absorbed or elastically reflected by the Earth, and so avoids a greenhouse density enhancement, would not be detectable by those three experiments. On the other hand, the aggressive proposals of the MAQRO collaboration and Pino et al. would immediately open up many orders of magnitude in DM mass, interaction range, and coupling strength, regardless of how DM behaves in bulk matter.
Atom interferometers measure quantum interference patterns in the wave functions of cold atoms that follow superpositions of different space-time trajectories. These can be sensitive to phase shifts induced by fundamental physics processes such as interactions with ultralight dark matter or the passage of gravitational waves. The capabilities of large-scale atom interferometers are illustrated by their estimated sensitivities to the possible interactions of ultralight dark matter with electrons and photons, and to gravitational waves in the frequency range around 1 Hz, intermediate between the peak sensitivities of the LIGO and LISA experiments. Atom interferometers can probe ultralight scalar couplings with much greater sensitivity than is currently available from probes of the Equivalence Principle. Their sensitivity to mid-frequency gravitational waves may open a window on mergers of masses intermediate between those discovered by the LIGO and Virgo experiments and the supermassive black holes present in the cores of galaxies, as well as fundamental physics processes in the early Universe such as first-order phase transitions and the evolution of networks of cosmic strings.
We explore how recent advances in the manipulation of single-ion wave packets open new avenues for detecting weak magnetic fields sourced by ultralight dark matter. A trapped ion in a “Schrödinger’s cat” state can be prepared with its spin and motional degrees of freedom entangled and be used as a matter-wave interferometer that is sensitive to the Aharonov-Bohm-like phase shift accumulated by the ion over its trajectory. The result of the spin-motion entanglement is a parametrically enhanced sensitivity to weak magnetic fields as compared with an unentangled ion in a trap. Taking into account the relevant boundary conditions, we demonstrate that a single trapped ion can probe unexplored regions of kinetically mixed dark-photon dark matter parameter space in the 10 − 15 eV ≲ m A ′ ≲ 10 − 14 eV mass window. We also show how such a table-top quantum device will also serve as a complementary probe of axionlike particle dark matter in the same mass window.
The wave-particle duality is a key concept of quantum physics and extending quantum superpositions to bodies of increasing mass and complexity has become a key goal to numerous research groups. Such experiments are motivated by the desire to probe and better understand the quantum-classical interface in advanced tests of spontaneous or gravity-induced wave function collapse and in the search for non-linear modifications of quantum theory. High mass interferometry has been proposed to serve in the search for light dark matter via weak recoil decoherence as well as in tests of the weak equivalence principle by comparing a large variety of quantum systems with very distinct internal composition, excitation, mass, shape or angular momentum. Here we discuss the experimental state of the art in high-mass matter-wave interferometry, as well as new perspectives from cluster and nanoparticle physics to push quantum superpositions by 3 to 4 orders of magnitude in mass or up to 6 orders of magnitude in 'macroscopicity'. We discuss different near-field interferometer configurations that shall become useful in near-future demonstrations of quantum phenomena with objects as diverse as proteins, metal clusters and dielectric nanoparticles.
Atom and matter interferometers are precise quantum sensing experiments that can probe differential forces along separated spacetime paths. Various atom and matter interferometer experiments have been proposed to study dark matter, gravitational waves, and exotic new physics. Increasingly, these experimental concepts have proposed space-based designs to maximize interrogation times and baselines. However, decoherence and phase shifts caused by astrophysical backgrounds could largely undermine or destroy the target sensitivity of the experiments. We calculate the decoherence effects induced by solar photons, the solar wind, cosmic rays, solar neutrinos and zodiacal dust on space-based atom and matter interferometers. We find that, in future space-based atom and matter interferometers, the solar wind generically produces decoherence beyond the quantum noise limit, without proper shielding. In addition, solar photons are also an important background for matter interferometers.