Session C1: Invited Session: Dipolar Quantum Gases

Quantum degenerate Bose and Fermi gases of dysprosium

Advances in the quantum manipulation of ultracold atomic gases are opening a new frontier in the quest to better understand strongly correlated matter. By exploiting the long-range and anisotropic character of the dipole-dipole interaction, we hope to create novel forms of soft quantum matter, phases intermediate between canonical states of order and disorder. Our group recently created Bose and Fermi degenerate gases of the most magnetic atom, dysprosium, which should allow investigations of quantum liquid crystals, analogs to the electron nematics and smectics thought to exist in, e.g., high-Tc cuprate superconductors. We present details of recent experiments that created the first degenerate dipolar Fermi gas as well as the first strongly dipolar BEC in low field.   

Dipolar Chromium BECs

Bose-Einstein condensates (BECs) made of 52Cr atoms reveal new phenomena, due to the presence of the long-range and anisotropic dipole-dipole interactions (see for example [1]). In this talk, I will describe the effect of dipolar interactions on the properties of multi-component (spinor) Cr condensates at extremely low magnetic fields. Due to its anisotropy, the dipolar interaction introduces magnetization-changing collisions, which dynamically frees the magnetization of the gas. We have thus observed a demagnetization of the BEC when the magnetic field is quenched below a critical value Bc corresponding to a phase transition between a ferromagnetic and a non-polarized ground state. The phase transition is due to an inter-play between spin-dependent interactions and the linear Zeeman effect [2]. We have also studied the thermodynamic properties of spinor Cr atoms, and we have observed that above the critical field Bc, the ferromagnetic nature of BECs leads to the spontaneous magnetization of the cloud when BEC is reached [3]. I will also describe the control of magnetization-changing collisions in optical lattices. We investigate a scheme in which dipolar relaxation is resonant when the energy released in dipolar relaxation matches a band excitation resonance [4]. This scheme, which may produce correlated pairs of rotating states in each lattice site, can be viewed as the equivalent of the Einstein-de-Haas effect. Although rotation is not yet produced in our experiment, I will present first experimental results of these dipolar resonances, which show a pronounced anisotropic behaviour. \\[4pt] [1] T. Lahaye et al., Rep. Prog. Phys. 72, 126401 (2009), G. Bismut, et al., Phys. Rev. Lett. 105, 040404 (2010) \\[0pt] [2] B. Pasquiou et al., Phys. Rev. Lett. 106, 255303 (2011) \\[0pt] [3] B. Pasquiou, arXiv:1110.0786, to be published in Phys. Rev. Lett. (2012) \\[0pt] [4] B. Pasquiou et al., Phys. Rev. Lett. 106, 015301 (2011)   

Ultracold Polar Molecules

Ultracold gases are powerful model systems for exploring interesting quantum many-body phenomena, and ultracold polar molecules open the possibility of studying systems with long-range interactions. At JILA, we make fermionic KRb molecules starting from an ultracold gas mixture of K and Rb atoms. We have observed and investigated atom-exchange chemical reactions in the ultracold polar molecule gas, and we are exploring polar molecules in optical lattice traps.   

Quantum phases of bosonic polar molecules in optical lattice geometries

In this talk I will address properties of a gas of polar bosonic molecules confined within single-, bi-, and multi-layer geometries --- the molecular dipole moments are aligned perpendicularly to the layers. The results presented are based on Quantum Monte Carlo simulations. I will discuss phases and phase transitions displayed by such systems --- with emphasis on solids and supersolids ---, and the experimental conditions required to observe such phases. In the single layer geometry, I will focus on how the presence of atoms affects molecular solid phases stabilized by dipolar interactions, while in bi- and multi-layer geometries, my focus will be on the formation of pairs and multimers.