A broadband squeezed light source for table-top interferometry

Abstract We report on the characterisation of one of two broadband squeezed light sources (SLSs) developed for the quantum enhanced space-time (QUEST) experiment, using balanced homodyne detection. QUEST consists of a pair of co-located, table-top, power-recycled Michelson interferometers designed to probe stationary space-time fluctuations. The interferometers are designed to be shot-noise limited in the frequency range from 1 to 200 MHz, and squeezed light will be employed with the goal to reduce the shot noise by 6 dB at frequencies inside the linewidth of the optical parametric amplifier (OPA). We directly observed up to 6.8 dB of squeezing and maintained at least 3 dB of squeezing across the full 100 MHz measurement bandwidth. After accounting for the dark noise contribution, the inferred squeezing level increased to 8.6 dB. Our SLS is based on a hemilithic OPA with a 43.6 mm round-trip optical length and a linewidth of 138(2) MHz, making it the broadest-linewidth device to date among those suitable for long-term integration with interferometers operating at a wavelength of 1064 nm.