A particle trapped in a light field behaves like a ball on a spring: give it a nudge and it starts to oscillate. If you suddenly stiffen the spring, the ball freezes for an instant at the very bottom, where its position is known most precisely. That's exactly the moment physicists exploited to turn a nanoparticle into an ultrasensitive accelerometer.
They cooled the particle to nearly absolute zero — the temperature at which thermal jitter nearly vanishes and quantum properties emerge. Then they abruptly changed the trap parameters (a move called a "quench," as if the spring were instantly made stiffer). In the first moments after such a jump, the particle's position uncertainty is squeezed, and it responds especially keenly to the slightest acceleration.
The measured sensitivity matched calculations based on the quantum Langevin equation and came close to the limit allowed by quantum physics (set by the so-called quantum Fisher information). This means the sensor operates almost perfectly, as well as nature permits.
Such a quantum accelerometer could find use in GPS-free navigation, seismometers, and gravitational-wave detectors. A tiny speck of dust, poised at the bottom of its optical well, turns out to be more precise than the bulkiest instruments.
At absolute zero (minus 273.15°C), atoms almost stop moving, but due to quantum laws they can never come to a complete halt: there is always a tiny residual "jitter."