  Quantum measurements of mechanical systems can produce optical squeezing via
ponderomotive forces. Its observation requires high environmental isolation and
efficient detection, typically achieved by using optical cavities and cryogenic
cooling. Here we realize these conditions by measuring the position of an
optically levitated nanoparticle at room temperature and without the overhead
of an optical cavity. We use a fast heterodyne detection to reconstruct
simultaneously orthogonal optical quadratures, and observe a noise reduction of
$9\%\pm0.5\%$ below shot noise. Our experiment offers a novel, cavity-less
platform for squeezed-light enhanced sensing. At the same time it delineates a
clear and simple strategy towards observation of stationary optomechanical
entanglement.
