In the laser cooling lab, we seek to study ultracold molecules by first loading molecules into a magneto-optical trap (MOT) and then transferring these molecules to a magnetic trap for further cooling. Interesting later experiments could involve studying atom-molecule or molecule-molecule collisions, as well as using the ultracold sample of diatomic molecules for quantum simulation or precision measurement experiments.
The goal of this experiment is to load a magneto-optical trap (MOT) with the diatomic radical calcium monofluoride (CaF) using a two-stage buffer-gas beam source (for details on buffer-gas cells see [1-3]). We first ablate a solid precursor of atomic Ca with a pulsed Nd:YAG laser. We simultaneously flow sulfur hexafluoride (SF6) into the buffer-gas cell, leading to a chemical reaction which produces CaF. The hot molecular gas then thermalizes with ~1 K Helium buffer-gas and is extracted into a beam. The molecular beam has an average forward velocity of 50-60 m/s out of our two-stage cell. While such velocities are low enough to load conventional atomic MOTs (see our previous work on lanthanide atoms), the estimated capture velocity for a MOT of CaF is less than 10 m/s. A slowing stage is thus required to bring a sufficient number of molecules to below the capture velocity. We use a white-light slowing technique for this beam deceleration, as was demonstrated in our recent paper . An additional challenge to trapping molecules is the existence of magnetic dark states in molecules, which arise due to the fact that we trap the molecules on a transition with "inverted" angular momentum structure. We address this problem by switching the polarization and the magnetic field of the MOT very rapidly (~1 MHz) to depopulate those dark states.
- N. R. Hutzler, H.-I Lu, and J. M. Doyle, The Buffer Gas Beam: An Intense, Cold, and Slow Source for Atoms and Molecules, Chem. Rev., 112, 4803 (2012)
- H.-I Lu, J. Rasmussen, M. J. Wright, D. Patterson, and J. M. Doyle, A cold and slow molecular beam, Phys. Chem. Chem. Phys. 13, 18986 (2011)
- D. Patterson and J. M. Doyle, Bright, Guided, molecular beam with hydrodynamic enhancement, J. Chem. Phys. 126, 154307 (2007)
- E. S. Shuman, J. F. Barry, D. R. Glenn, and D. DeMille, Radiative Force from Optical Cycling on a Diatomic Molecule, Phys. Rev. Lett. 103, 223001 (2009)
- E. S. Shuman, J. F. Barry, and D. DeMille, Laser cooling of a diatomic molecule, Nature 467, 820 (2010)
- M. T. Hummon, M. Yeo, B. K. Stuhl, A. L. Collopy, Y. Xia, and J. Ye, 2D Magneto-Optical Trapping of Diatomic Molecules, Phys. Rev. Lett. 110, 143001 (2013)
- M. Harvey, A. J. Murray, Cold Atom Trap with Zero Residual Magnetic Field: The ac Magneto-Optical Trap , Phys. Rev. Lett. 101, 173201 (2008)
- V. Zhelyazkova, A. Cournol, T. E. Wall, A. Matsushima, J. J. Hudson, E. A. Hinds, M. R. Tarbutt, and B. E. Sauer, Laser cooling and slowing of CaF molecules , Phys. Rev. A. 89, 053416 (2014)
- B. Hemmerling, G. K. Drayna, E. Chae, A. Ravi, J. M. Doyle, Buffer gas loaded magneto-optical traps for Yb, Tm, Er and Ho, New J. Phys. 16, 063070 (2014)
- J. F. Barry, D. J. McCarron, E. B. Norrgard, M. H. Steinecker, and D. DeMille, Magneto-optical trapping of a diatomic molecule, Nature 512, 286 (2014)
- D. J. McCarron, E. B. Norrgard, M. H. Steinecker, D. DeMille, Improved magneto-optical trapping of a diatomic molecule, New J. Phys. 17, 035014 (2015)
- M. Yeo, M. T. Hummon, A. L. Collopy, B. Yan, B. Hemmerling, E. Chae, J. M. Doyle, J. Ye, Rotational state microwave mixing for laser cooling of complex diatomic molecules, Phys. Rev. Lett. 114, 223003 (2015)
- E. B. Norrgard, D. J. McCarron, M. H. Steinecker, M. R. Tarbutt, and D. DeMille, Submillikelvin Dipolar Molecules in a Radio-Frequency Magneto-Optical Trap, Phys. Rev. Lett. 116, 063004 (2016)
- B. Hemmerling, E. Chae, A. Ravi, L. Anderegg, G. K. Drayna, N. R. Hutzler, A. L. Collopy, J. Ye, W. Ketterle and J. M. Doyle, Laser slowing of CaF molecules to near the capture velocity of a molecular MOT, J. Phys. B 49, 17 (2016)