Squeezed Vacuum Enhanced Interferometry at the Dark Fringe

An experimental study of enhancement of interferometric sensitivity using squeezed vacuum fluctuations will be described. By operating an interferometer at the dark fringe, large laser powers can be used for high sensitivity. It is possible to enhance the interferometric sensitivity beyond the shot-noise limit in the dark fringe arrangement by using an electrooptic modulator in the interferometer to vary the phase periodically away from the dark fringe. A detector at the dark output port can then operate at the shot-noise limit and detect phase imbalance at the sensitivity determined by power level at the bright output port.