Ultracold Molecules: The Effect of Electromagnetic Fields

Abstract

There is great interest within the physics and chemistry communities in the properties of ultracold molecules.
Electromagnetic fields can be used to create, trap, and modify the collisional dynamics of ultracold molecules, and thus the properties of ultracold molecules in electromagnetic fields is of growing importance.

This thesis examines some of the effects of externally applied electromagnetic fields on ultracold molecules. Initially, magnetic Feshbach resonances in combined electric and magnetic fields are examined in the collisions of He()+SO().
Through detailed quantum scattering calculations, it is then shown that the sympathetic cooling of NH() molecules with Mg atoms has a good prospect of success, a first for a neutral molecular system. Detailed quantum scattering calculations are performed for a wide range of collision energies and magnetic field strengths and it is found that the ratio of elastic to inelastic collisions is large for temperatures below 10 mK, and increases as the collision energy and magnetic field strength decrease. The near threshold collision properties of Mg+NH have been examined using a multichannel quantum defect theory approach.

A new type of conical intersection, that is a function of applied electromagnetic fields only, is also demonstrated. For states of opposite parity, brought into degeneracy with a magnetic field, the degeneracy can be resolved by the addition of an electric field, forming a conical intersection. A suitable arrangement of fields could thus be used to create a conical intersection in laboratory coordinates within an ultracold trapped gas.
For a Bose-Einstein condensate, in the mean-field approximation, the resultant geometric phase effect induces stable states of persistent superfluid flow that are characterized by half-integer quantized angular momentum.