Squeezed light from an oscillator measured at the rate of oscillation

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.