  Continuous measurements of the position of an oscillator become projective on
position eigenstates when the measurements are made faster than the coherent
evolution. We evidence an effect of this transition on a spin oscillator within
an ensemble of $2\times10^{10}$ room-temperature atoms by observing
correlations between the quadratures of the meter light field. These
correlations squeeze the fluctuations of the light quadratures below the vacuum
level. When the measurement is slower than the oscillation, we generate 11.5 dB
and detect 8.5 dB of squeezing in a tunable band that is a fraction of the
resonance frequency. When the measurement is as fast as the oscillation, we
detect 4.7 dB of squeezing that spans more than one decade of frequencies below
the resonance. Our results demonstrate a new regime of continuous quantum
measurements on material oscillators, and set a new benchmark for the
performance of a linear quantum sensor.
