Mechanical sensors have advanced scientific understanding by detecting minute motions from gravitational waves to molecular vibrations. Their performance has nevertheless been constrained by quantum mechanics. Researchers at ETH Zurich, led by Lukas Novotny, demonstrated a method using quantum squeezing to surpass this barrier, as reported in Physical Review Letters. Sensors convert mechanical motion into electrical signals and can register nanoscale displacements caused by various subtle phenomena. At very small scales, however, Heisenberg’s uncertainty principle produces unavoidable fluctuations known as zero-point noise that restrict detection thresholds. Squeezing redistributes uncertainty between position and momentum while keeping their product above the required minimum. In the experiment, a 100-nanometer silica particle was held in an optical trap inside an ultrahigh-vacuum chamber and cooled near absolute zero. Briefly weakening the trap reduced momentum uncertainty. An electrical pulse then simulated a weak force, after which the trap was restored and the squeezing reversed, amplifying the signal above the noise level. Without this protocol, hundreds of averaged measurements were needed to observe the effect. With squeezing applied, a single measurement sufficed to register forces below the particle’s intrinsic quantum noise. The approach could enable detection of previously inaccessible signals such as dark-matter collisions. Further gains are expected as squeezing efficiency improves.
