The sensitivity of a mechanical transducer is ultimately limited by its inherent quantum fluctuations. Here, we use an optically levitated nanoparticle to measure impulsive forces smaller than the particle’s zero-point momentum uncertainty. Our approach relies on reversibly squeezing the levitated particle’s center-of-mass motion to coherently amplify the perturbation. We demonstrate an impulsive-force resolution as small as $6.9\mathrm{keV}/\mathrm{c}$, a value 0.6 dB below the sensor’s zero-point value.

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• Optomechanics
• Optical lattices & traps