Abstract

The sensitivity limit of interferometric phase measurements using normal laser light is $\Delta {\text{θ}}_{{\text{q}}_{SQL}}=1/\surd N$, where N is the total number of photons detected in the measurement time interval. This sensitivity limit is set by a vacuum fluctuation that enters the open port of the interferometer input beamsplitter. The straightforward way to improve the sensitivity is to replace the vacuum fluctuation with a squeezed vacuum state [1]. However, we can improve the sensitivity by replacing the vacuum fluctuation with amplitude squeezed light generated directly from a constant-current-driven semiconductor laser when the interferometer is operated at a “dark-fringe” [2].