4 mois (Mars 2020 - Juin 2020)

Control of ultracold quantum gases with shielded interactions


The research field of cold (T<1K) and ultracold (T<<1mK) molecules is continuously expanding in many directions, involving an increasing number of groups throughout the world. This research field actually has initiated a “revolution in molecular physics” similar to the one induced by laser-cooling of atoms and Bose-Einstein Condensation (BEC) in dilute gases of weakly interacting ultracold atoms. Due to their much richer internal structure than atoms, ultracold molecules have opened the way towards fascinating researches and new possibilities for controlling quantum systems. A few examples are:

(i) High-resolution molecular spectroscopy;
(ii) Precision measurements for testing fundamental theories;
(iii) Quantum information devices;
(iv) Elementary chemical reactions and Many-body physics.

Those last years a major breakthrough has recently been achieved, as molecules in the lowest vibrational level of their absolute ground state have been formed. While paving the way towards a new kind of ultracold chemistry, collisions, in particular inelastic collisions (molecule-molecule and atom-molecule collisions), in general limit the possibility to use such ultracold molecular samples for other purposes. Soon came the desire of suppressing collisions using electromagnetic fields. The basic idea is to couple the initial molecular state of the colliding atom-molecule to a repulsive excited trimer state using laser light detuned to the blue of a resonant atomic transition, preventing molecules to come close to residual atoms.

The goal of this project is to identify  repulsive excited channels appropriate for optical shielding and to
describe their coupling with the initial state of  the colliding atom-molecule (for example Na and Rb atoms with NaRb molecules) in the framework of the dressed-state picture where the coupling of the involved molecular states is induced by the blue-detuned laser light with Rabi frequency and treated under the rotating wave approximation.
During the internship period the problem will be treated in the framework of a semiclassical Landau-Zener model whose robustnes has been assessed which would readily provide an indication of the shielding efficiency usable in the experiments. If continued by a PhD thesis a full quantum treatment using close coupling methods will be implemented and the role of spontaneous emission will also be investigated as it may become a limit of the shielding process due to the very weak relative velocities of the atoms and molecules at ultralow temperatures. Good knowledge of Atomic and Molecular Physics is required. Good programming skills (e.g., Fortran, Mathematica) are desirable.

Nadia BOULOUFA-MAAFA - Contacter
Laboratoire Aimé cotton, bât 221, Campus d'ORSAY, 91405 Orsay Cedex