Physicists at the University of Tokyo have demonstrated a technique for measuring extraordinarily small accelerations acting on a nanoparticle suspended in vacuum, operating in a regime where quantum fluctuations would normally drown the signal. The team trapped a particle around 300 nanometres across in a laser-generated potential and cooled its motion close to the quantum ground state, the lowest energy a confined object can possess.
Ordinarily, zero-point oscillation, the residual jitter that quantum mechanics imposes even at absolute rest, masks the tiny displacements caused by weak forces. By precisely varying the intensity of the trapping laser, the researchers amplified the particle's acceleration-induced displacement and measured the weak gravitational acceleration acting on it. Detection sensitivity improved by two orders of magnitude over conventional methods, and the observed dynamics matched theoretical simulations based on the quantum Langevin equation.
The work, published in Physical Review Letters with collaborators in the university's Graduate School of Engineering, is described as the first demonstration of sensing that exploits dynamics near the quantum ground state. Beyond precision metrology, the authors point to applications in next-generation quantum sensing, including searches for dark matter and neutrinos, detection of high-frequency gravitational waves, and fundamental experiments probing how gravity and electromagnetic forces interact for objects of macroscopic scale.