Session N6: Ultracold Molecules

Quantum Phases of Dipolar Molecules

I will discuss possible quantum phases of dipolar molecules focusing primarily on dipolar bosons in optical lattices and continuum systems in the two-dimensional regime. For the optical lattice case, I will discuss a few low temperature phases that emerge out of the dipolar superfluid. These phases include checkerboard supersolids, striped supersolids and collapsed [1]. The emergence of a striped supersolid is particularly interesting because the anisotropy of the dipolar interaction can be controlled externally. In the case of dipolar bosons in continuum systems, I will discuss the finite temperature phase diagram of purely repulsive interactions and show that for large dipolar repulsions a dipolar Wigner crystal appears at low temperatures and melts at intermediate temperatures into a dipolar hexatic fluid, before becoming a normal dipolar fluid at higher temperatures [2,3]. In addition, an intermediate dipolar supersolid phase is possible at low temperatures, which can also melt into a dipolar hexatic superfluid, before becoming a normal dipolar fluid at high temperatures [2,3]. Furthermore, I will discuss a generalization of Feynman's nodal theorem for interacting bosons and apply it to the ground state wavefunction of dipolar bosons to highlight the theorem's relevance to the quantum phases described [3]. Lastly, I will emphasize that the experimental characterization of theses phases may be possible via Bragg scattering and other experimental techniques. \\[4pt] [1] I. Danshita and C. A. R. Sa de Melo, Phys. Rev. Lett. 103, 225301 (2009).\\[0pt] [2] K. Mitra, C. J. Williams, and C. A. R. Sa de Melo, Arxiv 0903.4655v1.\\[0pt] [3] D. M. Kurkcuoglu and C. A. R. Sa de Melo, in preparation (2011).   

A quantitative analysis of small atomic and molecular systems

Ultracold atoms in an optical lattice provide a unique toolbox for emulating the prototypical models of condensed matter physics. Before the optical lattice system can be trusted as a quantum simulator however, it needs to be validated and benchmarked against known results, for which quantum Monte Carlo simulations are ideally suited. In the first part of this talk, an overview of recent numerical studies of ultracold bosonic and fermionic systems in an optical lattice will be given, starting with a full comparison based on experimental time-of-flight images of bosons in an optical lattice and ab-initio simulations. Next, the temperature and entropy in present experiments on fermions in an optical lattice will be estimated, and the full thermodynamics on approach to the Neel temperature will be presented. In the second part of the talk, a similar numerical analysis will be given for polar bosonic molecules. Special emphasis will be given on the feasibility of observing supersolid phases.   

Laser cooling of a diatomic molecule

We report the experimental demonstration of laser cooling applied to a diatomic molecule. Using an optical cycling scheme requiring only three lasers, we observe both Sisyphus and Doppler cooling forces acting on the transverse velocity distribution of a beam of the polar molecule strontium monofluoride (SrF). This results in substantial reduction of the transverse temperature of the beam to as low as $\sim 300 \mu$K, limited by finite interaction time with the laser. The properties of a new type of cryogenic molecular beam source, which made observation of laser cooling possible, will be discussed. Possible scientific applications and recent progress towards longitudinal cooling and slowing of the SrF beam will be discussed.   

Dipolar Effects in an Ultracold Gas of LiCs Molecules

Recently, there has been important progress in the investigation of ultracold polar molecules in the absolute ground state, thus opening intriguing perspectives for strongly correlated quantum systems under the influence of long-range dipolar forces. We have studied the formation of LiCs molecules via photoassociation (PA) in a double-species magneto-optical trap. The LiCs dimer is a particularly promising candidate for observing dipolar effects, as it possesses the largest dipole moment of all alkali dimers (5.5 Debye in the ground state). Ultracold LiCs molecules in the absolute rovibrational ground state are formed by a single photo-association step. The dipole moment of ground state levels is determined by Stark spectroscopy and was found to be in excellent agreement with the theoretical predictions. Vibrational redistribution due to spontaneous emission and blackbody radiation is observed and compared a rate-equation model.\\[4pt] In collaboration with Johannes Deiglmayr, Marc Repp, University of Heidelberg; Roland Wester, University of Innsbruck; and Olivier Dulieu, Laboratoire Aime Cotton.