ABRACADABRA

The magnet's field circles inside the toroid (the copper arrows). The axion turns it into an effective current along the same circles, g √2ρ cos(mt) B, which threads an oscillating field through the hole, where the magnet has none, and so a flux through the pickup loop there (the vertical arrow and the loop's glow), slowed here from the axion's own frequency to one swing a second. Its size wanders as the halo's waves drift in and out of step.

The SQUID's spectrum near the last key struck, mixed down to its axion's frequency, in μΦ₀² per Hz against Hz above m c²/h (real Hz: the same as the note's), averaged over the seconds the key is held. The dashed line is the SQUID's noise floor and the curve what the Standard Halo Model predicts: the axion's line, a millionth of its frequency wide and one-sided, since every speed only adds. Averaging calms the noise, not the line: a buried axion climbs out, as in the experiment, as the square root of the time.

This universe's axion (the line, and a dot for each key sounding) on the plane every axion search plots: its coupling to photons against its mass. The keyboard spans 0.11 to 17 neV; ABRACADABRA-10 cm searched 0.41 to 8.3 neV and ruled out couplings down to 3.2×10⁻¹¹ GeV⁻¹ at its best; CAST and the stars allow 6.6×10⁻¹¹ at most. The QCD axion, the one that would also explain why the strong force keeps time reversal, lies far below, between its KSVZ and DFSZ lines.

Each note is a single line that brightens and fades on its own as its field wanders, the high notes faster (a million cycles is less time); the SQUID's noise is the haze around each, wider the higher the note.