INTERFEROMETERS AND MINIMUM-UNCERTAINTY STATES

Minimum-uncertainty states in variables which are quadratic in mode cr eation and annihilation operators can be used to increase the accuracy of interferometric measurements. For a general interferometer we show how to find the relevant uncertainty relation. We consider two specif ic examples, a Mach-Zehnder interferometer and a Mach-Zehnder interfer ometer in which the first beam splitter has been replaced by a four-wa ve mixer. For both devices su(2) squeezed minimum-uncertainty states c an be used to achieve phase-measurement accuracies of 1/N, where N is the total photon number at the input. We also describe a method of pro ducing approximate versions of these states.