On April 12, Varun Jorapur successfully defended the thesis “Towards a Bose-Einstein Condensate of SrF molecules” (advisor: Steve Lamoreaux, work under the direction of David DeMille at the University of Chicago).
Varun explained, “Ultracold polar molecules offer a lot of exciting opportunities to study fundamental physics as well as quantum simulation. However, direct laser cooling of molecules is complicated and it has been an outstanding challenge in the field to produce dense enough ensembles of such molecules that one may see collisions between them. In my thesis work, we demonstrated techniques to achieve ultracold temperatures, while also very high densities in an optical trap, which led to the first observation of collisions between directly laser cooled molecules in a bulk gas. This paves the way for future experiments to try and achieve quantum degeneracy.”
He will be joining Argonne National Laboratory as a postdoctoral appointee.
Thesis abstract:
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.