CASPEr@night

A search for dark matter in the noise of the world's idle NMR spectrometers.

The model is SETI@home — a search that runs on instruments the world already owns, during the hours nobody else wants, with the analysis centralized so that participating costs a facility almost nothing.

How it works

Every NMR receiver's noise floor conceals a measurement — of the spins, of the probe itself, and of any dark-matter field that couples to nuclear spins. Contributing takes one short session on an idle instrument.

Fill a tube with water. A standard 5 mm tube of plain water (~550 μL). Tap or distilled is fine — the software asks exactly what it is. A 90/10 H₂O/D₂O mix is better still: the field-stepped sweep steers the field through the deuterium lock, so a lockable sample covers a band of adjacent masses in one night instead of a single point.
Run one command. Type xpy spin_noise_run in TopSpin, answer six dialogs, and walk away. The default run is about 45 minutes wall clock — you are needed for roughly the first five. The field-stepped sweep is the same script with one extra word (xpy spin_noise_run sweep). Nothing pulses your sample at high power, and the script never changes instrument state silently.
Upload one zip. The run bundles data, calibrations, and metadata into a single file. You upload it with one command and keep the local copy — a failed upload never loses data. Consoles on isolated networks are fine: carry the zip out on a USB stick and upload from any machine.

What your facility gets back

A per-facility sensitivity report — your probe's measured spin-noise feature and its calibrated distance from the fundamental sensitivity ceiling of inductive detection. This is the number no vendor datasheet provides, and the number that settles whether a cryoprobe upgrade, a new preamplifier, or nothing at all is what your sensitivity budget actually wants.
Co-authorship on the network publications your data enter — both the fleet-scale spin-noise metrology papers and the dark-matter exclusion papers.
Participation in a fundamental-physics first — a coordinated, multi-site nuclear-spin search in an axion mass band no nuclear-spin experiment has reached, where each distinct magnet is a new mass point.

Short runs count

We know the queue is full — the best instruments book out weeks ahead, and not every facility has idle time. The physics is forgiving: sensitivity grows as the fourth root of measurement time, so a 15-minute wedge between queued experiments already delivers 40% of the reach of a full 10-hour overnight run, and a single hour delivers 56%. A full night is the ideal — a gap between runs is enough to participate.

The 2020 pilot result

In May 2020, seven 101-second receiver-open noise records were taken on a 600 MHz cryoprobe spectrometer to settle a disagreement about the fundamental sensitivity of inductively detected NMR. Our re-analysis found the ¹H spin-noise line at 2.30 ± 0.04 times the system noise floor — a 94σ combined detection. Reinterpreted as a resonant search for the axion wind, the same 12 minutes of noise yield a worst-case 90%-confidence exclusion on the axion–proton gradient coupling, g_ap < 5.1 × 10⁻⁵ GeV⁻¹ at m_a = 2.48 μeV — the first laboratory dark-matter constraint on this coupling at this mass, a 15× mass extension over the previous highest-mass nuclear-spin search. We state this plainly: the data are archival and opportunistic, and the limit is a deliberately worst-case construction — the full calibration envelope is taken against us and the entire observed line power is attributed to signal. Unpolarized thermal runs will not beat astrophysical bounds. The honest value is the unexplored mass coverage, the fleet-scale sensitivity metrology, and the multi-site coincidence infrastructure — with a hyperpolarization path toward far deeper reach.

Mass coverage

Each spectrometer's field strength corresponds to one axion mass point. The world's fleet of 300–1200 MHz instruments spans 1.24–4.96 μeV — coverage grows with every distinct magnet that joins, which is the respect in which your 750 is not redundant with someone else's 800. The same arithmetic means the network has no minimum size of institution: a 400 at a primarily-undergraduate department covers mass points a national lab literally cannot, with the same co-authorship.

One magnet, one mass point: m_a[μeV] ≈ 4.14 × 10⁻³ × ν_L[MHz]. Every point shown sits above the previous highest-mass nuclear-spin search at 0.166 μeV.

Where the network is

Each dot is a participating facility — shown only with the facility's consent, and only at city level. The map grows as the network does.

3 facilities · 4 distinct fields · updated 2026-09-03

Where the project stands

Status — September 2026

Version 0.6.0 of the acquisition and analysis software is released. The largest addition is spectral tiling: a spectrometer can now step its lock point across ±25 ppm of its field over a night, so each magnet covers a small band of axion masses instead of a single point. The release also adds a fluorine-19 channel — fluorine resonates at 94% of the proton frequency, so a participating magnet can contribute a second mass point — and a persistent line catalog, the bookkeeping needed to reuse the same nightly data for a dark-photon search.

Three facilities — in the United States, Finland, and Italy — have registered, spanning four distinct fields and therefore four distinct axion-mass bands; more are in conversation. The software passes every test we can run without a spectrometer, including reproducing the 2020 pilot analysis from the archival data, but it has not yet run on a real instrument — until the first supervised pilot run, now being scheduled, we call it a good start rather than a working system. Bruker/TopSpin is the primary target; JEOL and Magritek Spinsolve benchtop paths are in development in the public repository.

Join the network

One tube of water, one command, one upload — and your spectrometer spends a night doing physics it was never asked to do.

Not ready to commit a spectrometer? Join the low-volume announcements list. Or write directly: [email protected] — for the software bundle, a pilot-run slot, or questions about the physics.