Sub-Shot-Noise Interferometry

Amplitude-squeezed light can enhance the sensitivity of interferometric measurements in the same way as it does for spectroscopy. The ultimate limits of a measurement are sought in many fundamental physics experiments which are trying to measure very weak interactions. One example of such difficult but exciting experiments is the detection of gravitational wave which has remained elusive since Einstein predicted the existence of a gravitational wave in general relativity theory. A very-large-scale optical interferometer is now considered as the most promising gravitational wave detector owing to the recent progress of lasers and other optical-component technologies [39]. Inoue, Yamamoto, and Bjork proposed a new scheme to realize sub-shotnoise interferometry using amplitude-squeezed light generated directly from a constant-current-driven semiconductor laser [107]. The idea was to inject the amplitude-squeezed light from an injection-locked semiconductor laser into the open port of a dark fringe interferometer. The output noise of the interferometer was reduced to the noise level of the squeezed laser when the interferometer was operated at a dark-fringe.