Teaching a laser beam to go straight

Abstract

In classical physics a beam of light propagates in a perfectly straight line and this means that we can measure small displacements with unlimited accuracy. However, this is not correct for real laser beams when we take the quantum properties of light into account. Spatial measurements will be limited by quantum noise, similar to the limitations for optical communication and sensing. Here we derive the spatial quantum noise limit and show how to measure it. Next we demonstrate that we can use specially prepared light with quantum correlations, so-called squeezed light, to improve spatial measurements to below this quantum limit. In this way we prepare a beam which goes in a straighter line than the output of any conventional laser.

Acknowledgments

We would like to thank Magnus Hsu, Vincent Delaubert, Charles Harb, Agnes Maitre, Sylvain Gigan, Nicolai Grosse and Warwick Bowen for the many contributions to experiments and theory and Max Colla for the excellent graphics and technical support. The work presented here was made possible through funding by the Australian Research Council and CNRS France.