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arXiv:0806.1196 · Physical Review A

Creating ultracold molecules by collisions with ultracold rare-gas atoms in an optical trap

Paolo Barletta, Jonathan Tennyson, P. F. Barker

Published Nov 13, 2008• 26 citations
arXivHTMLPDF

Abstract

We study collisions of para-${\mathrm{H}}_{2}$ with five rare-gas atomic species (He, Ne, Ar, Kr, and Xe) over the range from $1\phantom{\rule{0.3em}{0ex}}\mathrm{K}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}1\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{K}$ and evaluate the feasibility of sympathetic cooling ${\mathrm{H}}_{2}$ with ultracold ground state rare-gas atoms co-trapped within a deep optical trap. Collision cross sections over this large temperature range show that all of these species could be used to cool ${\mathrm{H}}_{2}$ to ultracold temperatures and that argon and helium are the most promising species for future experiments. A simple yet accurate method for calculating the microscopic observables needed in the present analysis is also described, as well as the sensitivity of the calculated cross sections to the potential energy surface used.

DOI
10.1103/physreva.78.052707

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Ultracold matter offers a unique capability to reach the best high-precision spectroscopy measurements and leads to exciting perspectives in many different areas of science and technology. Molecules, thanks to their complex spectra, couple with a broader range of photons compared to atoms, so they are extremely attractive for fundamental science or to design new quantum technologies. However, to date, only a few molecular species have been brought to temperatures of the order of the microkelvin. This was done by laser cooling, a process that has been demonstrated only for species featuring an unpaired electron that does not participate to the chemical bond. \n \nA different approach, which is indifferent to the molecule electronic structure and thus potentially universal, is sympathetic cooling, where neutral molecules are cooled in a bath of ultracold atoms. However, inelastic collisions between molecules and the coolant is a major obstacle that has hindered the advances of this method thus far. Trapping the molecules in their absolute ground state would circumvent this problem or at least greatly simplify it. In this thesis we simulate the feasibility of an experiment in which metastable CO molecules are first slowed down to a few m/s with a microstructured Stark decelerator, then they are stopped by a strong DC electrical barrier and finally they are transferred irreversibly to their absolute ground state and captured in an optical trap. \nUnfortunately, the results of the simulations indicate that the total number of molecules that can be accumulated in the optical trap is rather low, far behind the observation threshold. Therefore, we concluded that other approaches to produce ultracold molecules must to be searched.
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