Coherent control of broadband vacuum squeezing

We present the observation of optical fields carrying squeezed vacuum states at sideband frequencies from 10 Hz to above 35 MHz. The field was generated with type-I optical parametric oscillation below threshold at 1064 nm. A coherent, unbalanced classical modulation field at 40 MHz enabled the generation of error signals for stable phase control of the squeezed vacuum field with respect to a strong local oscillator. Broadband squeezing of approximately -4 dB was measured with balanced homodyne detection. The spectrum of the squeezed field allows a quantum noise reduction of ground-based gravitational wave detectors over their full detection band, regardless of whether homodyne readout or radio-frequency heterodyne readout is used.