Ultracold hydrogen atoms: a versatile coolant for producing microkelvin molecules

Jeremy M. Hutson (Durham University, UK)
Event Date and Time: 
Fri, 2013-07-05 16:00 - 17:00
Chem D-215
Intended Audience: 

There are several experimental methods that are capable of producing samples of molecules such as ND3, OH and NH at temperatures of 10 to 100 mK in electrostatic or magnetic traps. These include helium buffer-gas cooling and molecular beam deceleration. However, there is so far no way to transfer these cold molecules to the ultracold regime below 1 mK. Ultracold molecules would offer a wide range of opportunities for quantum simulation, quantum information processing, and the development of a controlled molecular assembly in which chemical transformations are carried out coherently on an entire sample of molecules.

Sympathetic cooling, in which cold species are cooled further by thermal contact with ultracold atoms, usually alkali metals, has been used successfully for atoms and molecular ions but has not yet been achieved for neutral molecules. The difficulty is that molecules are usually trapped in states that are not the lowest in the field used to trap the molecules, and can undergo inelastic (deexcitation) collisions that release kinetic energy and eject both collision partners from the trap.

We have explored sympathetic cooling theoretically in many different systems, in order to find collision partners that do not have this problem. We have found that, in general, light collision partners are favourable for sympathetic cooling because inelastic collisions are suppressed by centrifugal barriers at low fields and low collision energies. However, even atoms such as Li [1] and Mg [2] are predicted to succeed only at temperatures below about 10 mK, which is on the edge of what is experimentally achievable.

We have recently discovered [3] that ultracold hydrogen atoms, which can be produced at very high densities at temperatures down to 50 μK, have very favourable properties for sympathetic cooling. The potential energy surfaces for (spin-polarised) interactions of H with NH and OH are quite weakly anisotropic and the centrifugal barriers are very high. We predict that sympathetic cooling with ultracold H atoms can succeed from starting temperatures as high as 1 K, which are much easier to achieve.


[1] A. O. G. Wallis, E. J. J. Longdon, P. S. Żuchowski and J. M. Hutson, Eur. Phys. J. D, 2011, 65, 151.

[2] A. O. G. Wallis and J. M. Hutson, Phys. Rev. Lett., 2009, 103, 183201.

[3] M. L. González-Martínez and J. M. Hutson, http://arxiv.org/abs/1305.6282

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