We present the observation of optical fields carrying squeezed vacuum states at sideband frequencies from 10Hz to above 35MHz. The field was generated with type-I optical parametric oscillation below threshold at 1064nm. A coherent, unbalanced classical modulation field at 40MHz 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 -4dB 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.
@article{arxiv.0704.3796,
title = {Coherent control of broadband vacuum squeezing},
author = {Simon Chelkowski and Henning Vahlbruch and Karsten Danzmann and Roman Schnabel},
journal= {arXiv preprint arXiv:0704.3796},
year = {2007}
}