Creating a Dense Sample of Ultracold YO Molecules in an Optical Lattice

Wu, Yewei (Ph.D., Physics)
Creating a dense sample of ultracold YO molecules in an optical lattice
Thesis directed by Prof. Jun Ye

Ultracold molecules offer a new platform for quantum chemistry, strongly correlated quantum
systems, quantum information processing, and precision tests of fundamental physics. Their rich
internal structure and strong anisotropic dipolar interaction provide the tools for new physics and
chemistry studies. However, due to the additional ro-vibrational degrees of freedom, controlling of
molecules becomes very challenging. The past few years have witnessed a rapid progress of laser
cooling and trapping of molecules realized by several groups around the world.
In this thesis, we show an enhanced slowing efficiency for YO molecular beams by an improved
laser coupling regime. With enough number of slowed molecules, we demonstrate the first creation
of RF and DC MOT of YO, which makes YO the first oxide molecule trapped in MOT. We
systematically study various types of MOT and the gray molasses cooling of YO, achieving a
temperature of 4 μK, 25 times colder than the Doppler limit. The robust cooling against large
magnetic field allows us to develop a novel scheme to significantly compress the molecular cloud
below mm. With a compressed cloud, we are able to efficiently load molecules into a 1D optical
lattice for further cooling and compression. A factor of 220 and 95 increase in density and phase
space density are realized compared to the cloud before loading, creating a molecular sample with
the highest phase space density to date by direct laser cooling. By adiabatically ramping down the
lattice depth, 1.0(2) μK is achieved, which is the lowest temperature realized by direct laser cooling
of molecules. With a long lattice lifetime of 850(70) ms, the study of YO-YO interaction is within
reach.