Making it with molecules

Paul S. Julienne, Eite Tiesinga, Thorsten Köhler

Pairs of trapped atoms can be associated to make a diatomic molecule using a time-dependent magnetic field to ramp the energy of a scattering resonance state from above to below the scattering threshold. A relatively simple model, parametrized in terms of the background scattering length and resonance width and magnetic moment, can be used to predict conversion probabilities from atoms to molecules. The model and its Landau-Zener interpretation are described and illustrated by specific calculations for 23Na, 87Rb and 133Cs resonances. The model can be readily adapted to Bose-Einstein condensates. Comparison with full many-body calculations for the condensate case shows that the model is very useful for making simple estimates of molecule conversion efficiencies.

Heather J. Lewandowski

Paul S. Julienne

Luigi De Marco, Giacomo Valtolina, Kyle Matsuda +3 more

Experimental realization of a quantum degenerate gas of molecules would provide access to a wide range of phenomena in molecular and quantum sciences. However, the very complexity that makes ultracold molecules so enticing has made reaching degeneracy an outstanding experimental challenge over the past decade. We now report the production of a degenerate Fermi gas of ultracold polar molecules of potassium-rubidium. Through coherent adiabatic association in a deeply degenerate mixture of a rubidium Bose-Einstein condensate and a potassium Fermi gas, we produce molecules at temperatures below 0.3 times the Fermi temperature. We explore the properties of this reactive gas and demonstrate how degeneracy suppresses chemical reactions, making a long-lived degenerate gas of polar molecules a reality.

Otto Robert Frisch

G. M. Svishchev

A method of selective (with respect to the Stark effect) burning of a spectral hole in the 0-0 absorption band of zero-dipole impurity molecules is suggested. It is shown that in combination with the Stark modulation of the optical density of a sample, this method makes it possible to determine that contribution to the total absorption and luminescence of the sample that the impurity molecules with a preset magnitude of the matrix-induced Stark moment (provided this magnitude exceeds the mean value for the entire ensemble) make. This allows one to experimentally study both the distribution of impurity molecules over the magnitude of the Stark moment and the correlation of the Stark moment with other parameters of impurity molecules.