Phase-sensitive amplification and SU(1,1) interferometry via multimode four-wave mixing*

We demonstrate a useful phase dependence in a multi-pump four-wave mixing configuration. We find that, for certain phase values, the intensity noise of an output mode is lower than that of its phase-insensitive counterpart. This lower-noise amplification has been demonstrated previously in atomic four wave mixing, but only with the use of significantly more complex experimental configurations, e.g. dual homodyne detection or cascaded vapor cells. Additionally, our method naturally results in four beams that can be quantum correlated with one another.
These findings have obvious applications in the simplification of quantum optical experiments that involve the generation or amplification of more than two correlated modes. Additionally, we describe how this result may be employed in a “touchless” or interaction-free SU(1,1) interferometry scheme, wherein a phase measurement may be made remotely on a pair of modes without introducing loss or destroying any squeezing between them.