Squeezing of atomic quantum projection noise

Abstract

We provide a framework for understanding recent experiments on squeezing of a collective atomic pseudo-spin, induced by a homodyne measurement on off-resonant probe light interrogating the atoms. The detection of light decimates the atomic state distribution and we discuss the conditions under which the resulting reduced quantum fluctuations are metrologically relevant. In particular, we consider a dual probe scheme which benefits from a cancelation of classical common mode noise sources such that quantum fluctuations from light and atoms are the main contributions to the detected signal.

Keywords:

• projection noise
• quantum noise squeezing
• quantum non-demolition measurement

Acknowledgements

This work was funded by the Danish National Research Foundation and the EU grants, COMPAS, EMALI, and QAP. N.K. acknowledges support from the Danish Natural Science Research Council through a Steno Fellowship.