• Sep 20 2011

    WITS Seminar

    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