A silicon sphere 166 nanometers in diameter floats in a beam of infrared laser light. The pressure is below 10⁻⁸ mbar, and the motional temperature is about 10 millikelvin. That is colder than the cosmic microwave background. The sphere is a microscopic seismograph, sensing quantum jolts from invisible particles.

Each impact from a dark matter particle transfers momentum to the sphere. The sphere flinches. Its position is tracked via scattered light with precision limited by quantum fluctuations. The sensitivity reached 65 keV/c, only 2.7 times worse than the standard quantum limit for such an oscillator. It is like hearing a mouse's footstep at the other end of a bridge.

Over 26.1 days, events with amplitudes of 1–4 MeV/c accumulated. Their origin is unclear. A conservative analysis treated them as possible signal or background. As a result, upper limits were set on the dark matter–neutron coupling: for virialized dark matter, up to 10⁻⁷ per 1 GeV/c² mass; for thermalized dark matter, constraints for masses above 10³ GeV/c². For composite dark matter with a constituent mass of 1 keV/c², the limits on the neutron scattering cross section are two orders of magnitude stronger than those from fifth-force and stellar cooling experiments.

The method paves the way for arrays of nanospheres. A 10×10 grid would improve sensitivity by several orders of magnitude. Three-dimensional momentum measurement would allow reconstruction of the recoil direction and use of the daily modulation to confirm the galactic origin of the signal. Detection of individual neutrinos emitted in radioactive decays inside the sphere may be possible. The seismograph becomes a telescope.