Quantum interference of ultrastable twin optical beams

Phys Rev Lett. 2004 May 21;92(20):203601. doi: 10.1103/PhysRevLett.92.203601. Epub 2004 May 21.

Abstract

We report the first measurement of the quantum phase-difference noise of an ultrastable nondegenerate optical parametric oscillator that emits twin beams classically phase locked at exact frequency degeneracy. The measurement illustrates the property of a lossless balanced beam splitter to convert number-difference squeezing into phase-difference squeezing, and thus provides indirect evidence for Heisenberg-limited interferometry using twin beams. This experiment is a generalization of the Hong-Ou-Mandel interference effect for continuous variables and constitutes a milestone towards continuous-variable entanglement of bright, ultrastable nondegenerate beams.