Varun Jorapur

Ultracold polar molecules, with their long-range dipolar interactions and rich internal structure, have emerged as a powerful platform for quantum information science, quantum simulation, and precision probes of fundamental physics. Techniques to directly laser cool molecules have developed rapidly in the past decade, with molecular magneto-optical traps (MOTs) demonstrated for several diatomic and polyatomic species. However, significant hurdles still remain to achieving higher densities and lower temperatures, as necessary to achieve quantum degeneracy. In this talk, we go over two key results that bring us closer to this goal. We first show that one can utilize the Λ-enhanced gray molasses technique to reach the low micro-Kelvin temperature regime, and that this can be used to load a conservative optical trap. We can greatly improve the trap loading and temperature by making use of the interplay of light shifts caused by the cooling and trapping beam. We next show that one can engineer a sub-Doppler trapping force by changing the light detuning to blue, and that this can reduce the trapped cloud size from 1 mm to around 200 μm. This leads to a 10x gain of molecules loaded in the optical trap and has allowed us to observe molecule-molecule collisions for the first time in a bulk gas of directly laser cooled molecules. This step is crucial for understanding the requirements to implement collisional cooling towards degeneracy.