Levitated nanoparticles — silica spheres trapped in focused laser beams — oscillate thermally. Cooling their motion toward the quantum ground state requires damping the oscillation without introducing noise. Electrical feedback (measuring the particle's position and applying corrective electric fields) is the standard approach, but it requires charged particles and electrical infrastructure that complicates the experiment.
Interference between a weak auxiliary laser and the trapping beam creates optical damping forces without electrical actuation (arXiv:2603.11976). The auxiliary beam interferes with the trapping field, producing an intensity gradient that depends on the particle's position. When the particle moves, it shifts within this gradient, experiencing a force proportional to its velocity — a damping force. Tuning the auxiliary beam's phase and intensity shapes the interference pattern to produce damping along all three axes simultaneously.
A 142-nanometer silica particle is cooled to 19.9 millikelvin along the beam axis. The cooling is all-optical: no electrodes, no charged particles, no feedback electronics. The damping emerges from the physics of interference — the same constructive and destructive patterns that produce fringes in a double-slit experiment, repurposed to slow a mechanical oscillator.
The pathway to quantum ground-state preparation is direct. Lower the auxiliary beam's noise floor, improve the phase stability, and the cooling deepens. The interference pattern is the mechanism, the laser is the actuator, and the particle is the oscillator. The brake is made of light.