Toward Ultracold CaF
B. Hemmerling1,2, H.-I Lu2,3, E. Chae1,2, G. K. Drayna1,2,4, I. Kozyryev1,2, A. Ravi1,2
and J. M. Doyle1,2,*
1Department
of Physics, Harvard University, Cambridge, MA 02138, USA
Center for Ultracold Atoms, Cambridge, MA 02138, USA
2Harvard-MIT
3School
of Engineering and Applied Sciences, Harvard University, Cambridge, MA
02138, USA
4Department of Chemistry, Harvard University, Cambridge, MA 02138, USA
*E-mail: doyle@physics.harvard.edu
The prospects of novel physics employing polar cold molecules encompass
quantum computing and simulations, controlled ultra-cold chemistry and precision
measurements. However, a method liable to bring a general class of chemically
diverse molecules to the ultracold regime still needs to be developed. We report on
the progress of experiments to bring a sample of CaF molecules to the milli-Kelvin
regime. A cryogenic Helium buffer-gas cell [1,2] serves as a versatile and flexible
source for molecules (e.g. CaF, CaH, ThO, SrF, YO, … ), producing cold, slow and
bright molecular beams with typical forward velocities of ~150m/s (single-stage cell)
and ~70m/s (two-stage cell) with ~10^9 molecules/sr/ablation pulse.
In a first experiment, a cold molecular beam of CaF will be loaded into a few
Tesla deep magnetic trap using optical loading techniques. Since the scattering of a
few photons is sufficient for optical pumping, this method does not rely on cycling
transitions, which are in general absent in molecules. Simulations indicate loading
efficiencies on the order of ~0.1%. Once CaF is trapped, a second atomic species,
namely Li, will be simultaneously loaded to study collisions and the feasibility of its
use for sympathetic cooling of CaF [2].
We also discuss the implementation, in a second experiment, of a magnetooptical trap (MOT) of CaF. We plan to load the trap directly from the buffer-gas
source, which provides a portion of molecules below the capture velocity. As a
precursor, we successfully implemented the first buffer-gas loaded MOT of Yb using
only an additional slowing laser; its lifetime was measured to be ~40 ms. We further
propose a scheme for the laser cooling and confinement of CaF molecules, following
an approach similar to those used in the cooling of SrF and YO [3,4].
References
[1] H.-I Lu, et al., Phys. Chem. Chem. Phys. 13, 18986 (2011)
[2] N.R. Hutzler, et al., Chem. Rev. 112, 4803 (2012)
[3] T. V. Tscherbul, et al., Phys. Rev. A 84, 040701(R) (2011)
[4] E.F. Shuman, et al., Nature 467, 820 (2010).
[5] M.T. Hummon, et al., arXiv:1209.4069 [physics.atom-ph] (2012)