  We present the measurement of squeezed light generation using an engineered
optomechanical system fabricated from a silicon microchip and composed of a
micromechanical resonator coupled to a nanophotonic cavity. Laser light is used
to measure the fluctuations in the position of the mechanical resonator at a
measurement rate comparable to the free dynamics of the mechanical resonator,
and greater than its thermal decoherence rate. By approaching the strong
continuous measurement regime we observe, through homodyne detection,
non-trivial modifications of the reflected light's vacuum fluctuation spectrum.
In spite of the mechanical resonator's highly excited thermal state ($10,000$
phonons), we observe squeezing at the level of $4.5 \pm 0.5%$ below that of
shot-noise over a few MHz bandwidth around the mechanical resonance frequency
of 28 MHz. This squeezing is interpreted as an unambiguous quantum signature of
radiation pressure shot-noise.
