Interferometric Measurements Beyond the Shot-Noise Limit.

The fundamental "shot-noise" limit of interferometric measurement is studied for a polarization interferometer with squeezed light entering the normally dark port. Noise reduction 2 dB below the shot-noise limit is obtained using squeezed light from parametric downconversion in a KTP crystal. Polarization rotation angles as small as 300 nanoradians can be measured with a 1 KHz bandwidth and 2 mv entering the excitation port of the interferometer.