Efficient Separation of Four-wave Mixing Twin Beams Using Dove Prisms*

Four-wave mixing (FWM) is a non-linear process that can produce quantum correlated twin beams of light with noise properties below the shot noise limit. This makes them useful for quantum-enhanced sensing, as has been shown for example by experiments at the LIGO interferometer. We are interested in squeezed light at 589 nm to enhance density measurements of our sodium Bose-Einstein condensate. We generate twin beams of light in a double-lambda configuration via a FWM process in hot sodium vapor. The hot sodium vapor is produced in a custom-designed hot stainless-steel vacuum chamber that allows temperatures of up to 400 degrees Celsius. To satisfy conservation of energy and momentum, we generate the twin beams at a small angle between the probe/conjugate beams and the pump beam of approximately 0.08 degrees. At this small angle, the beams need to travel a long optical path before they can be separated via conventional means. Since the beam diameter increases at the same time, a small overlap is caused between the pump beam and the probe and conjugate beams. To eliminate this overlap, we use two Dove prisms to separate the probe and conjugate beams from the pump beam more efficiently in a shorter optical path. We also present other improvements to our setup to reduce amplitude noise in our measurements. We present the design of our modified setup and results on the dependence of the FWM gain on temperature, pump beam intensity, detunings, and other experimental parameters.

 

We gratefully acknowledge funding from the NSF through Grant No. PHY-1846965