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Durham Seminar, Wednesday 12 December 2018

12:00 - 13:00

CM 221

Goulven Quéméner

Goulven Quéméner

Controlling the scattering length of ultracold dipolar molecules

Ultracold dipolar molecules are excellent candidates for engineering quantum applications and controlled chemistry [1]. Therefore a lot of effort is devoted nowadays to produce ground state ultracold molecules in high densities as well as to understand their properties [2]. One of a main goal is to create a quantum degenerate gas of dipolar molecules such as a Bose-Einstein condensate or a degenerate Fermi gas. This is for now a major missing step for ultracold molecules. Unfortunately, when the molecules start to collide, whether they are chemically reactive or not, a lot of molecules are lost in the process. Hoping for a long-lived quantum degenerate gas is then compromised unless to shield the molecules from collisional losses. This can be achieved by using a static electric field [3] but also by using microwaves [4]. By applying a circularly polarized and slightly blue-detuned microwave field with respect to the first excited rotational state of a dipolar molecule, one can [5]: (i) bring the ratio good to bad collisions γ = βel / βqu (elastic over quenching rate coefficient) to high values such that evaporative cooling techniques can be successful, (ii) suppress the imaginary part of the scattering length and shield the molecules against losses, (iii) tune the real part of the scattering length to small or large values, positive or negative and control the interaction strength of an ultracold molecular gas. We adopt in our theoretical formalism an adimensional approach, where all the molecules are characterized by a unique parameter. This theoretical proposal might be a necessary requirement for successful evaporative cooling of molecules and for reaching quantum degeneracy. The ability to control the molecular scattering length opens the door for a rich, strongly correlated, many-body physics for ultracold molecules, similar than that for ultracold atoms. I acknowledge the financial support of the FEW2MANY-SHIELD project (#ANR-17-CE30-0015), the COPOMOL project (#ANR-13-IS04-0004) and the BLUESHIELD project (#ANR-14-CE34-0006) from Agence Nationale de la Recherche in France. [1] L. Carr et al., New J. Phys. 11, 055049 (2009) ; J. L. Bohn et al., Science 357, 1002 (2017) [2] G. Quéméner, P. Julienne, Chem. Rev. 112, 4949 (2012) [3] M. L. González-Martínez, J. L. Bohn, G. Quéméner, Phys. Rev. A 96, 032718 (2017) [4] A. Micheli et al., Phys. Rev. A 76, 043604 (2007) [5] L. Lassablière, G. Quéméner, Phys. Rev. Lett. 121, 163402 (2018)