NITheP - National Institute For Theoretical Physics

The National Institute for Theoretical Physics, and the Centre for Theoretical Physics, School of Physics, would like to invite to its coming talk in the theory seminar series, entitled:

"Dipolar collisions of ultracold polar molecules in a microwave field"

to be presented by Dr. Alexander Avdeenkov (NITheP - Stellenbosch)

Abstract: Collisions at ultracold temperatures between $^1Sigma$ state diatomic polar molecules in a circularly polarized microwave field(mw) are theoretically analysed. We demonstrate that elastic and inelastic collisions of polar molecules at ultracold temperatures are affected by an external microwave field and that they are enhanced at resonance frequencies. We show that the collision dynamics of polar molecules in a microwave field is largely determined by the long-range
dipole--dipole(DD) interaction. Through this interaction, two polar molecules can resonantly exchange internal energy by undergoing a transition between neighbouring rotational levels. This process may stabilize the system and enable the successive evaporative cooling of molecules. We mainly discuss fermionic polar molecules at ultralow temperatures (mu K$).

We also analyze the temporal evolution of the ultracold molecular population in a microwave field with. Our calculations show that the behavior of populations dynamics is defined by the ratio of the mw- field Rabi frequency and the magnitude of the dipole-dipole
interaction(V_DD) . At large enough
distances, V_DD is too weak and we have the case of two independent molecules dressed by the mw- field, which is characterized by the typical Rabi oscillations in the bare states populations and no change in time in the dressed states populations. As the density of the molecular gas increases, the DD interaction becomes significant and causes beatings in the evolution of the bare states, while the dressed states start to slightly oscillate.
At a given
distance, V_{ DD} becomes comparable to Rabi frequency and the dressed states oscillate rapidly, while beating and oscillations occur in the
bare states time-development. A three- peak structure appears in the
populations of the bare and dressed states. Upon calculating the eigenvalues of the system, we associate the origin of these peaks with the existence of three avoided crossings in the eigenvalue spectrum. The latter occurs at a certain value of the DD interaction when it becomes equal to the absolute value of the mw field detuning.

Date: Tuesday, 20th September 2011
Venue: Frank Nabarro Lecture Theatre P216
Time: 13.20 - 14.10

For more information please contact:

Alan S. Cornell

School of Physics
University of the Witwatersrand
Private Bag 3
Wits 2050
South Africa

Tel.:+27-11-717-6819