Squeezed-light–enhanced polarization interferometer

Enhancement of the sensitivity of a polarization interferometer beyond the limit set by vacuum fluctuations of the electromagnetic field has been obtained with use of squeezed light generated by a ${\mathrm{KTiOPO}}_4$ optical parametric amplifier. The increase in signal-to-noise ratio relative to the shot-noise limit is 2 dB. The corresponding improvement in the response time of the interferometer is measured to be a factor of 1.6.