Using nuclear demagnetization—a method that extracts energy by removing a magnetic field—a 1.5-nanogram plate was passively cooled to 6.1 millikelvin. The residual jittering neatly obeyed the laws of thermodynamics. The record paves the way for gravitational wave detectors and testing quantum mechan
arXiv:2510.24199 · 2025-10-28