Quantum squeezing of a levitated nanomechanical oscillator

Manipulating the motions of macroscopic objects near their quantum mechanical uncertainties has been desired in diverse fields, including fundamental physics, sensing, and transducers. Despite significant progresses in ground-state cooling of a levitated solid particle, realizing non-classical states of its motion has been elusive. Here, we demonstrate quantum squeezing of the motion of a single nanoparticle by rapidly varying its oscillation frequency. We reveal significant narrowing of the velocity variance to $-4.9(1)$~dB of that of the ground state via free-expansion measurements. To quantitatively confirm our finding, we develop a method to accurately measure the displacement of the nanoparticle by referencing an optical standing wave. Our work shows that a levitated nanoparticle offers an ideal platform for studying non-classical states of its motion and paves the way for its applications in quantum sensing, as well as for exploring quantum mechanics at a macroscopic scale.