AION-10: 10m Atom Interferometer for Dark Matter

• AION-10 is a 10-meter atom interferometer using ultracold 87Sr in a vertical gradiometer configuration designed for dark matter searches and precision tests.
• It employs a single-photon clock transition method to minimize laser phase noise, serving as a demonstrator for future advanced detectors.
• The instrument integrates modular ultra-high vacuum, precise magnetic shielding, and vibration isolation to validate technologies for larger gravitational-wave observatories.

Searching arXiv for recent and foundational papers on AION-10. I’ll gather the most relevant atom-interferometer AION-10 papers and use them to write the article. AION-10 is the 10-meter stage of AION, the Atom Interferometer Observatory and Network, and is the Oxford University implementation of the program’s first long-baseline terrestrial detector. In the literature it is described both as a standalone precision instrument, built around ultracold fermionic $^{87}$Sr atoms in a vertical gradiometer geometry, and as the prototype platform for later AION-100, AION-km, and space-based AEDGE concepts (Bongs et al., 5 Aug 2025, Badurina et al., 2019). Its scientific role is correspondingly dual: immediate searches for ultralight dark matter and related beyond-Standard-Model signatures at 10 m scale, and technology validation for the mid-frequency gravitational-wave program pursued more aggressively by the longer-baseline AION stages (Badurina et al., 2021).

1. Definition and staged role within AION

AION is a staged cold-atom interferometry program. The foundational roadmap defines four steps: Stage 1, AION-10; Stage 2, AION-100; Stage 3, AION-km; and a later satellite-based detector at thousands-of-kilometres scale (Badurina et al., 2019). Within that structure, AION-10 is the first operational detector and the first full-scale vertical implementation of the platform.

The stage structure in the literature is summarized below.

Stage	Baseline	Role in the program
AION-10	10 m	First detector; science plus technology development
AION-100	100 m	Intermediate terrestrial stage
AION-km	kilometre scale / 2000 m in the 2019 roadmap	Main terrestrial gravitational-wave instrument
AEDGE	space-based	Future long-baseline extension

The 2019 program paper distinguishes two AION-10 performance scenarios. “AION-10-initial” assumes $L=10$ m, $T=1.4$ s, $\delta\phi_{\rm noise}\sim 10^{-3}/\sqrt{\rm Hz}$, and $n=100$, while “AION-10-goal” keeps $L=10$ m and $T=1.4$ s but targets $\delta\phi_{\rm noise}=10^{-4}/\sqrt{\rm Hz}$ and $n=1000$ (Badurina et al., 2019). Later programmatic work sharpens the interpretation of this stage: AION-10 is “primarily a dark-matter/technology demonstrator” and is “not expected to detect GWs,” whereas AION-100 and especially AION-km are the stages emphasized for gravitational-wave astronomy (Badurina et al., 2021). The 2025 Technical Design Report nonetheless describes AION-10 as a “versatile scientific instrument” with science drivers that include gravitational-wave detection, ultralight dark matter, equivalence-principle tests, dark-energy and fifth-force probes, and broader quantum-sensing applications (Bongs et al., 5 Aug 2025).

This apparent tension is resolved by the staged logic of the program. The published record treats AION-10 as scientifically meaningful in its own right, but also as the platform on which the experimental methods required for the longer-baseline gravitational-wave observatories are to be established (Badurina et al., 2021, Bongs et al., 5 Aug 2025).

2. Architecture and interferometric operating principle

AION-10 is a vertical atom-interferometric gradiometer. The 2025 design report specifies a 10 m vertical tower in the Beecroft building stairwell in Oxford, containing two vertically aligned 5 m atom interferometers inside a 10 m XHV/UHV beam-pipe system (Bongs et al., 5 Aug 2025). The atoms are launched upward from two separate sidearms, and the differential phase is read out by camera assemblies at the bottom of the interferometers (Bongs et al., 5 Aug 2025).

The broader AION concept uses several atom interferometers placed at different heights inside the same vertical vacuum system and interrogated by a shared laser source. Because the same laser field addresses multiple interferometers, common laser phase noise can be strongly suppressed by differencing the measured phases (Badurina et al., 2019). The 2025 prototype paper presents the same idea in gradiometer language: two simultaneous atom interferometers, separated vertically and interrogated by a common clock laser, with the phase difference as the signal (Baynham et al., 12 Apr 2025).

The atom-optical basis of the instrument is the single-photon clock transition in strontium. AION is explicitly built around strontium and the 698 nm clock line, rather than Raman-based schemes, because the single-photon architecture reduces sensitivity to laser phase noise over long baselines (Badurina et al., 2019). The design report and prototype work both identify fermionic $^{87}$Sr as the target species; the reasons given are the extremely narrow 698 nm clock transition and the precision enabled by it (Bongs et al., 5 Aug 2025, Baynham et al., 12 Apr 2025).

For gravitational waves, the 2019 AION paper gives the low-frequency differential response between two interferometers separated by $L=10$0 as

$L=10$1

This displays the basic scaling with strain $L=10$2, baseline $L=10$3, optical wave number $L=10$4, and interrogation time $L=10$5 (Badurina et al., 2019). The same paper also describes a resonant mode, implemented with a $L=10$6 sequence containing $L=10$7 intermediate $L=10$8 pulses, with resonance frequency

$L=10$9

and low-frequency resonant enhancement

$T=1.4$0

In this formulation, $T=1.4$1 provides large-momentum-transfer enhancement and $T=1.4$2 provides resonant enhancement (Badurina et al., 2019).

The technical report expresses the sensitivity logic in detector-engineering form through the best-case individual interferometer scaling

$T=1.4$3

where $T=1.4$4 is the number of large-momentum-transfer pulses and $T=1.4$5 is the atom number (Bongs et al., 5 Aug 2025). This connects the scientific reach of AION-10 directly to atom source performance and LMT capability.

3. Physics program at 10 m scale

The most consistently emphasized direct physics target of AION-10 is ultralight scalar dark matter. The 2019 AION overview states that the AION-10 goal sensitivity can improve constraints on scalar dark-matter–electron coupling around $T=1.4$6 eV by about an order of magnitude relative to MICROSCOPE (Badurina et al., 2019). The 2021 sensitivity survey generalizes the target region, stating that AION and AEDGE could explore unconstrained ultralight scalar dark matter parameter space for

$T=1.4$7

and that AION-10 is expected to approach or even surpass existing constraints, while AION-100 and AION-km push to smaller couplings (Badurina et al., 2021).

The dark-matter signal mechanism is an oscillatory modulation of atomic transition energies induced by time-dependent shifts in $T=1.4$8 and $T=1.4$9. In the 2021 survey this is summarized as

$\delta\phi_{\rm noise}\sim 10^{-3}/\sqrt{\rm Hz}$0

leading to a coherent sinusoidal modulation

$\delta\phi_{\rm noise}\sim 10^{-3}/\sqrt{\rm Hz}$1

with frequency set by the dark-matter mass (Badurina et al., 2021). The earlier AION paper gives the corresponding linear interaction Lagrangian for scalar dark matter and explicitly notes $\delta\phi_{\rm noise}\sim 10^{-3}/\sqrt{\rm Hz}$2 for the Sr clock transition used by AION (Badurina et al., 2019).

Recent theory proposals extend the 10 m science case. One paper proposes equipping a 10 m-scale vertical atom gradiometer with an annular planar source mass to search for screened scalar fifth forces and states that the proposal is “directly applicable to forthcoming experiments, such as AION-10 or VLBAI” (Banks et al., 12 Nov 2025). The configuration uses a 10.1 m baseline gradiometer with $\delta\phi_{\rm noise}\sim 10^{-3}/\sqrt{\rm Hz}$3Sr atoms, an upper interferometer passing near a 1 cm-thick annular stainless-steel plate mounted at the top of the chamber, and a lower interferometer as reference (Banks et al., 12 Nov 2025). Its central experimental novelty is the “$\delta\phi_{\rm noise}\sim 10^{-3}/\sqrt{\rm Hz}$4-flip protocol,” which alternates between a resonant $\delta\phi_{\rm noise}\sim 10^{-3}/\sqrt{\rm Hz}$5 sequence and a butterfly sequence so that a static fifth-force signal appears as a modulated signal at a chosen frequency (Banks et al., 12 Nov 2025). The paper states that this setup could improve existing chameleon and symmetron bounds by about 1 to 1.5 orders of magnitude (Banks et al., 12 Nov 2025).

A further proposal argues that MAGIS- and AION-like long-baseline atom interferometers, including the staged AION-10 concept, can test supersymmetric hidden sectors if ultralight moduli, dilatons, or hidden scalars induce coherent oscillatory phase shifts. The signal is written as

$\delta\phi_{\rm noise}\sim 10^{-3}/\sqrt{\rm Hz}$6

with the measured effective coupling related to derivatives of gauge kinetic functions, Kähler metrics, Yukawa couplings, Higgs-sector parameters, and the QCD scale (Trivedi, 8 Jun 2026). This suggests a broader interpretation of AION-10 as a narrow-band phase spectrometer for coherent ultralight fields, not only as a dark-matter detector in the narrower phenomenological sense.

4. Engineering design and subsystem requirements

The 2025 Technical Design Report gives the first fully integrated engineering specification for AION-10. The optical path begins with the laser entering from the laboratory through an input arm, then passing through a beam conditioning pipe, a beam transfer pipe that turns the beam upward, and a Keplerian telescope at the top that expands the beam to about a 1 cm waist through the interferometry region. The beam then propagates through the two 5 m interferometer beam pipes and is reflected by a bottom retroreflecting mirror on the phase-shear detection platform (Bongs et al., 5 Aug 2025).

A defining design choice is modular assembly. The tower is built from five modules: two beam-pipe modules, one lower interconnect/phase-shear module, one upper interconnect chamber module, and one telescope module (Bongs et al., 5 Aug 2025). The vacuum system is designed so that these parts can be built and capped off separately, then connected after the structural tower is in place, which reduces contamination risk and simplifies installation in the stairwell environment (Bongs et al., 5 Aug 2025).

The principal engineering constraints are vibration, magnetics, and vacuum. For vibration, the report states that phase-shear detection with a typical 1000 $\delta\phi_{\rm noise}\sim 10^{-3}/\sqrt{\rm Hz}$7m fringe spacing implies that a resolution of $\delta\phi_{\rm noise}\sim 10^{-3}/\sqrt{\rm Hz}$8 corresponds to a fringe displacement of about 100 nm; camera assemblies must therefore be stable to this scale or monitored at that precision (Bongs et al., 5 Aug 2025). For the main telescope, keeping pointing fluctuations below 35 nrad requires lens 1 transverse shift below 40 nm, lens 2 transverse shift below 70 nm, and lens tilts below 1.8 $\delta\phi_{\rm noise}\sim 10^{-3}/\sqrt{\rm Hz}$9rad for lens 1 and 70 nrad for lens 2 (Bongs et al., 5 Aug 2025).

For magnetic control with $n=100$0Sr, the report specifies a horizontal bias magnetic field up to 10 G, field homogeneity better than 5 mG, angular alignment better than 5 mrad, and field noise below $n=100$1 (Bongs et al., 5 Aug 2025). The report also notes that a 10 mrad misalignment between magnetic field and light polarization would create a $n=100$2 ratio of Rabi frequencies between undesired and desired transitions, corresponding to a $n=100$3 pulse infidelity (Bongs et al., 5 Aug 2025).

For vacuum, the interferometry region is required to operate in the extreme-high-vacuum regime, ideally near

$n=100$4

while the beam conditioning and input sections can relax to

$n=100$5

The Molflow+ simulations reported in the TDR show that three 300 l/s pumping ports yield average pressures in the $n=100$6 mbar range, meeting the minimum AION-10 requirement (Bongs et al., 5 Aug 2025).

The magnetic shielding solution converges on a double-layer octagonal mu-metal shield in which each layer is built from three 0.8 mm mu-metal sheets, for total thickness 2.4 mm per layer, separated by a 15 mm gap (Bongs et al., 5 Aug 2025). Under a 0.6 G external field, the single-layer shield reduces the field at the center to about 4.4 mG, while the double-layer shield reduces it further to about 0.5 mG and field gradients below 0.01 G/m (Bongs et al., 5 Aug 2025). The guide-field assembly is a 4.6 m long semi-cylindrical coil shell that produces about 10.8 G while keeping field inhomogeneity within the required 5 mG in the center region (Bongs et al., 5 Aug 2025).

5. Experimental validation and prototype evidence

The design report is complemented by a laboratory prototype that directly addresses one of the key risks of long-baseline atom interferometry: laser phase noise. The prototype is a tabletop single-photon long-baseline atom interferometer using the $n=100$7Sr clock transition, operated as a differential gradiometer (Baynham et al., 12 Apr 2025). Each interferometer uses a Mach–Zehnder sequence

$n=100$8

with 698 nm light, $n=100$9-pulse duration about 40–44 $L=10$0s, and dark time $L=10$1s (Baynham et al., 12 Apr 2025). The atoms are cooled to about $L=10$2K and trapped in two crossed optical dipole traps separated vertically by 1 mm (Baynham et al., 12 Apr 2025).

The core result is that the differential readout remains at the Standard Quantum Limit even when large artificial laser phase noise is injected. The abstract states that the detector “operates at the Standard Quantum Limit (SQL), producing a signal with no unexpected noise beyond atom shot noise,” and that it remains at the SQL even when additional laser phase noise is introduced to emulate long-baseline conditions (Baynham et al., 12 Apr 2025). This is experimentally important because, for a single interferometer, the laser phase-noise contribution scales as

$L=10$3

and for a thermal-noise-limited cavity-stabilized laser the estimated RMS phase noise in a km-scale detector with $L=10$4 s is about 730 mrad, far above the final target phase resolution (Baynham et al., 12 Apr 2025). The prototype demonstrates that the gradiometer configuration can reject this common-mode noise to the experimental resolution.

The 2025 TDR reports additional subsystem validation. Critical optical components remain within specification 97% of the time under realistic operating conditions (Bongs et al., 5 Aug 2025). For the bottom retroreflecting mirror and phase-shear platform, the prototype subsystem achieved a PZT settling time of 65 ms to a 100 nm error threshold, satisfying the $L=10$5 ms requirement, and angular stability of 33 nrad rms over about 10 s, better than the $L=10$6 nrad goal (Bongs et al., 5 Aug 2025). The structural model of the full tower yields a fundamental mode at 24.0 Hz with the selected 100 × 100 × 10 mm box sections and single diagonal bracing (Bongs et al., 5 Aug 2025). Building-vibration data collected in June 2022 give input displacement RMS values of 33.1–40.8 nm and relative lens-motion RMS values of 7.1–17.0 nm, which the report judges acceptable, though the upper lens is close to the maximum transverse-shift specification (Bongs et al., 5 Aug 2025).

Taken together, these prototype and subsystem results do not yet demonstrate full 10 m physics performance, but they do validate the central experimental claim that long-baseline clock-transition atom interferometry with differential common-mode rejection is technically plausible in the required noise regime (Baynham et al., 12 Apr 2025, Bongs et al., 5 Aug 2025).

6. Scientific position, scope, and common misconceptions

A recurring source of confusion in the literature is the distinction between AION-10 and the broader AION detector family. Many of the most prominent gravitational-wave forecasts associated with “AION” are in fact forecasts for AION-100 or AION-km rather than for the 10 m stage. The 2021 survey is explicit that AION-10 “is primarily a dark-matter/technology demonstrator” and “is not expected to detect GWs” (Badurina et al., 2021). Likewise, published forecasts for improved direct bounds on the graviton mass, for sensitivity to Lorentz-violating dispersion, and for intermediate-mass black-hole population studies are framed around the 1 km stage, with only limited discussion of the 10 m stage as part of the overall roadmap (Ellis et al., 2020, Ellis et al., 2023).

This distinction matters for interpreting gravitational-wave methodology papers. For example, work on broadband and resonant operation of AION-like atom interferometers shows that an early-inspiral broadband observation followed by a resonant-mode merger observation can improve signal-to-noise ratio and parameter estimation for intermediate-mass black-hole binaries, but those quantitative forecasts are based on AION-1km / “short AION” noise assumptions rather than the Oxford 10 m instrument (Torres-Orjuela, 2023). Similarly, the main AION mid-band astrophysics forecasts in the detector-sensitivity literature are attached to AION-100 and especially AION-km (Badurina et al., 2021).

The correct encyclopedic interpretation is therefore layered. AION-10 is the first realized long-baseline instrument of the AION program, with a direct 10 m-scale science case centered on ultralight dark matter and closely related precision measurements, while the strongest published gravitational-wave discovery forecasts belong to later AION stages (Badurina et al., 2019, Badurina et al., 2021). At the same time, the technical principles validated at 10 m scale—single-photon strontium interferometry, long-baseline gradiometry, differential laser-noise rejection, modular vacuum construction, magnetic shielding, and vibration isolation—are precisely the principles required for the larger observatories (Baynham et al., 12 Apr 2025, Bongs et al., 5 Aug 2025).

In that sense, AION-10 occupies a specific and technically important niche. It is neither merely a benchtop demonstrator nor yet the full gravitational-wave observatory envisioned in the AION roadmap. It is the first instrument in that hierarchy: a 10 m strontium atom interferometer designed to produce its own precision-physics results while establishing the experimental basis for the longer-baseline atom-interferometric observatories that follow (Bongs et al., 5 Aug 2025, Badurina et al., 2019).