Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session D31: Molecular and Dipolar Quantum Gases |
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Sponsoring Units: DAMOP Chair: Kadan Hazzard, Cornell University Room: E141 |
Monday, March 15, 2010 2:30PM - 2:42PM |
D31.00001: Magnetoassociation of KRb Feshbach molecules Tyler Cumby, John Perreault, Ruth Shewmon, Deborah Jin I will discuss experiments in which we study the creation of $^{40}$K$^{87}$Rb Feshbach molecules via magnetoassociation. We measure the molecule number as a function of the magnetic-field sweep rate through the interspecies Feshbach resonance and explore the dependence of association on the initial atom gas conditions. This study of the Feshbach molecule creation process may be relevant to the production of ultracold polar molecules, where magnetoassociated Feshbach molecules can be a crucial first step [1].\\[4pt] [1] K.-K. Ni, S. Ospelkaus, M. H. G. de Miranda, A. Peer, B. Neyenhuis, J. J. Zirbel, S. Kotochigova, P. S. Julienne, D. S. Jin, and J. Ye, Science, 2008, 322, 231-235. [Preview Abstract] |
Monday, March 15, 2010 2:42PM - 2:54PM |
D31.00002: Polar molecules with strong three-body repulsions on two-dimensional hexagonal lattice Lars Bonnes, Hanspeter B\"uchler, Stefan Wessel Motivated by a recent proposal on using polar molecules in optical lattices driven by microwave fields to induce strong three-body interactions (H. P. B\"uchler et al., Nature Physics 3, 726 (2007)), we analyze the quantum phase diagram of the hard-core boson Hubbard model with competing two- and three-body interactions. In particular, we consider the case of the honeycomb lattice. The rich phase diagram, which we access using quantum Monte Carlo simulations, shows a variety of complex valence bond crystal phases, emerging out of classical ground-states of extensive degeneracies. We obtain effective description of these phases in terms of local resonances and quantum dimer models. Cascading transitions result from the competition of the two types of interaction terms. Furthermore, we revisit the bose Hubbard model on the triangular lattice, and consider the nature and stability of its supersolid phases in the presence of three-body repulsions. [Preview Abstract] |
Monday, March 15, 2010 2:54PM - 3:06PM |
D31.00003: Accumulating NH molecules in a magnetic trap Steven Hoekstra, Fabian Gr\"atz, Jens Riedel, Wolfgang J\"ager, Gerard Meijer We work on the trapping of stark-decelerated neutral molecules. In the last few years we have electrostatically trapped OH and OD, metastable NH and metastable CO molecules. We have investigated trap loss mechanisms, and found that room-temperature blackbody radiation is a limiting factor for the trapping time, which is typically a few seconds. If the molecule is decelerated and trapped in a state that is short-lived compared to the trapping time, the metastable-state lifetime can be accurately obtained from the observed fluorescence decay.\\ Currenty we aim to increasing the density of the trapped NH molecules. The decelerated NH(a$^{1}\Delta )$ molecules can be optically pumped to the electronic ground state. A magnetic trap is used to trap the produced groundstate molecules. Since the groundstate is decoupled through a spontaneous emission step from the metastable state, this scheme enables a phase-space increase by accumulating multiple packets of Stark-declerated molecules. We will present our results on the reloading of NH using a trap made of permanent magnets. [Preview Abstract] |
Monday, March 15, 2010 3:06PM - 3:18PM |
D31.00004: Kinematic production and study of cold atoms and molecules Kevin Strecker, David Chandler, Jeffery Kay We have produced measurable amounts of cold molecules using a unique crossed molecular beam scattering technique, Kinematic Cooling. This technique allows for the production of cold molecules in either their absolute ro-vibrational ground state via elastic scattering with a near equal mass atom, or produced in rotationally, vibrationally or electronically exited states via inelastic collisions with an atom of a dissimilar mass. We have demonstrate this technique using inelastic collisions between NO molecules and Ar atoms, specifically NO($^{2}\Pi _{1/2}$,j=0.5) + Ar $\to $NO($^{2}\Pi _{1/2}$,j'=7.5) + Ar. We have performed new measurements on this system, utilizing vastly different experimental conditions, such that now we can report observation of samples of NO$_{7.5}$ that persist in our observation volume for over 150 microseconds. This observation time has been shown to be limited by diffusion of the unconfined molecules from our observation region. Monte-Carlo modeling of the diffusion of the molecules from the interaction volume convoluted with the detection volume yields a final average temperature for the NO$_{7.5}$ to be near 30mK. The Kinematic cooling technique has recently been extended to cooling of ND$_{3}$, NH$_{3}$ and Kr. [Preview Abstract] |
Monday, March 15, 2010 3:18PM - 3:30PM |
D31.00005: Simultaneous Optical Trapping of Lithium and Ytterbium Atoms Anders Hansen, Alexander Khramov, William Dowd, Vladyslav Ivanov, Subhadeep Gupta Simultaneous trapping of different atomic species forms the starting point for experiments probing strong interactions and aspects of superfluidity in mass-imbalanced ultracold mixtures, as well as the synthesis of dipolar molecules through interspecies scattering resonances. Our choice of lithium (Li) and ytterbium (Yb) atoms as the two constituent species is based on several reasons. Both Li and Yb possess stable bosonic and fermionic isotopes which have previously been brought to quantum degeneracy in separate single-species experiments. Li is a one-electron atom and Yb is a two-electron atom, allowing species-selective trapping techniques using external magnetic fields are realizable, magnetic trapping of diatomic molecules of LiYb, and a large electric dipole moment in the molecular ground state allowing for studies of strongly dipolar gases. Ultracold polar LiYb is also a promising candidate for a sensitive electron EDM measurement. We have achieved simultaneous magneto-optical trapping of lithium and ytterbium atoms by loading from Zeeman slowed atomic beams from two separate beamlines. We will report on our experimental setup and latest experiments on trapping and cooling of both species in a far off resonance optical trap. [Preview Abstract] |
Monday, March 15, 2010 3:30PM - 3:42PM |
D31.00006: Collective excitations of the pairing states in multi-component dipolar Fermi gases Yi Li, Congjun Wu The multi-component ultra-cold dipolar Fermi gases exhibit competing singlet and triplet Cooper pairings. We investigate collective excitations in such states, including the gapless phonon and spin-wave Goldstone modes with anisotropic dispersions due to the anisotropic nature of the dipolar interaction. An excitonic mode in the p-wave triplet channel is predicted as a low energy resonance mode between the singlet and triplet pairing states. [Preview Abstract] |
Monday, March 15, 2010 3:42PM - 3:54PM |
D31.00007: Supersolid phases in two-dimensional dipolar Bose liquids Chris Laumann, David Huse, Roderich Moessner, Shivaji Sondhi, Boris Spivak We consider a system of Bose molecules confined in a two-dimensional trapping potential with repulsive dipolar interactions. We show that in between the usual superfluid and crystalline phases there are necessarily other phases which may be viewed as mesoscale mixtures of the two. The particular stable microemulsions vary with microscopic details but they generically feature superfluidity in conjunction with the breaking of translational symmetry and thus are supersolids. We discuss the stability of these phases to thermal and quantum fluctuations and consider the particular mesoscale phases arising in the limit of a weak underlying first order transition. [Preview Abstract] |
Monday, March 15, 2010 3:54PM - 4:06PM |
D31.00008: Ferronematic phase in ultracold dipolar Fermi gases Benjamin Munoz Fregoso, Eduardo Fradkin We show [1] that a homogeneous two-component Fermi gas with long range dipolar and short-range isotropic interactions has a {\em ferronematic} phase for suitable values of the dipolar and short- range coupling constant. The ferronematic phase is characterized by having a non-zero magnetization and long range orientational uniaxial order. The Fermi surface of the mayority component is elongated while the Fermi surface for the minority component is compressed along the direction of the magnetization. \\[4pt] [1] B.M. Fregoso and E. Fradkin, Phys. Rev. Lett. 103, 205301 (2009) [Preview Abstract] |
Monday, March 15, 2010 4:06PM - 4:18PM |
D31.00009: Collective modes in two dimensional dipolar systems Qiuzi Li, Euyheon Hwang, Sankar Das Sarma Motivated by recent experimental progress in producing and manipulating ultracold polar molecules with a net electric dipole moment, we theoretically consider the many body effects of two-dimensional dipolar systems with the anisotropic and long-range dipole-dipole interactions. We calculate the collective modes in 2D dipolar systems, and also consider spatially separated bilayer and superlattice dipolar systems. Our aim is to obtain characteristic features of these dipolar systems. We also consider the detailed quantitative comparison between these dipolar systems and the extensively studied usual parabolic two-dimensional electron systems. [Preview Abstract] |
Monday, March 15, 2010 4:18PM - 4:30PM |
D31.00010: Nonmonotonic temperature dependence of dipolar compressibility Jason Kestner, Sankar Das Sarma We calculate the compressibility of a two-dimensional gas of fermionic dipolar molecules within the Hartree-Fock approximation at finite temperature. The compressibility is nonmonotonic in the reduced temperature, $T/T_F$, exhibiting a local maximum. This effect may be detectable at currently attainable densities and temperatures, providing the possibility of direct observation of a quantum degenerate many- body effect in the ultracold polar molecule system. [Preview Abstract] |
Monday, March 15, 2010 4:30PM - 4:42PM |
D31.00011: Dipolar Fermions in Layered Systems Nikolaj Zinner, Bernard Wunsch, David Pekker, Eugene Demler A system of fermions confined to a stack of two-dimensional layers interacting through the long-range dipole-dipole force is expected to have a rich phase diagram with several different types of superfluid states and possible crystallization. We first study this system from the few-body perspective in order to determine what kind of bound structures are possible. Next, we use a mean-field approach to understand the imprint of these structures on many-body states as a function of the densities in the layers. [Preview Abstract] |
Monday, March 15, 2010 4:42PM - 4:54PM |
D31.00012: Stripe glass and stripe supersolid of two-dimensional dipolar bosons in an optical lattice Tommaso Roscilde, Massimo Boninsegni Making use of mean-field theory and quantum Monte Carlo simulations, we investigate the zero-temperature phase diagram of dipolar bosons (with hardcore on-site interactions) on a square and triangular lattice. We consider dipoles forming an angle of 45 degrees with respect to the lattice plane, so that the dipolar interaction takes a spatially anisotropic nature, and it is attractive along the dipole direction and repulsive perpendicular to it. In the case of the square lattice, the attractive part of the interaction leads to the collapse of the dipolar gas and phase separation. On the contrary, in the case of the triangular lattice a stripe crystal is stabilized at most commensurate fillings of the form n/L, where 1 $<$ n $<$ L and L is the linear size. Yet, dislocations in the stripe crystal give rise to highly metastable states, which can be systematically studied at the mean-field level. Metastability is most pronounced close to half filling, and it leads to a strong tendency towards the formation of a ``stripe glass,'' which exhibits a characteristic signature in the structure factor. For higher fillings crystal phase exhibits strong quantum fluctuations, and it hosts a superfluid fraction for sufficiently low strength of the dipolar potential, resulting in a stripe supersolid phase. [Preview Abstract] |
Monday, March 15, 2010 4:54PM - 5:06PM |
D31.00013: Competing instabilities of cold atoms on self-assembled dipolar lattices Chuntai Shi, Shan-Wen Tsai Cold atoms moving on a self-assembled lattice of dipolar molecules can be created with the motion of the (dressed) atoms being described by extended Hubbard~models with tunable long-range interactions with repulsive and attractive components [1]. Motivated by this proposal, we investigate the phase diagram of the extended fermionic Hubbard model with an off-site interaction V between nearest-neighbor pairs in addition to the usual on-site interaction U and hopping amplitude t. We study this model close to half filling, where a rich set of phases, including (charge or spin) density waves and (s-wave, p-wave or d-wave) superconductivities, can be realized via tuning of the strength of the components of the interaction and of the chemical potential. We employ a one-loop functional renormalization-group approach which takes into account all the scattering processes around the Fermi surface systematically, and enable us to investigate the competing orders on an equal basis. \\[4pt] [1] G. Pupillo {\it et al.}, Phys. Rev. Lett. {\bf 100}, 050402 (2008) [Preview Abstract] |
Monday, March 15, 2010 5:06PM - 5:18PM |
D31.00014: Liquid crystal phases of ultracold dipolar fermions on a lattice Chungwei Lin, Erhai Zhao, Vincent Liu Motivated by the search for quantum liquid crystal phases in a gas of ultracold atoms and molecules, we study the density wave and nematic instabilities of dipolar fermions on the two-dimensional square lattice (in the $x-y$ plane) with dipoles pointing to the $z$ direction. We determine the phase diagram using two complimentary methods, the Hatree-Fock mean field theory and the linear response analysis of compressibility. Both give consistent results. In addition to the staggered ($\pi$, $\pi$) density wave, over a finite range of densities and hopping parameters, the ground state of the system first becomes nematic and then smectic, when the dipolar interaction strength is increased. Both phases are characterized by the same broken four-fold (C$_4$) rotational symmetry. The difference is that the nematic phase has a closed Fermi surface but the smectic does not. The transition from the nematic to the smectic phase is associated with a jump in the nematic order parameter. This jump is closely related to the van Hove singularities. We derive the kinetic equation for collective excitations in the normal isotropic phase and find that the zero sound mode is strongly Landau damped and thus is not a well defined excitation. Experimental implications of our results are discussed. [Preview Abstract] |
Monday, March 15, 2010 5:18PM - 5:30PM |
D31.00015: Bose-Einstein crystal phase of cold gases with momentum dependent interaction Xiaopeng Li, W. Vincent Liu, Chungwei Lin Motivated by the experiments of dipolar quantum gases, we study a system of bosons with long range interaction in the regime between superfluid and Wigner crystal phases. From the analysis of low energy fluctuations based on effective field theory and Bogoliubov approaches, the uniform Bose-Einstein state is found unstable toward crystalline order for a class of potentials which has minima at finite values in momentum space. Further variational calculation shows that a new phase, Bose-Einstein crystal, is of lower energy than both uniform BEC and Wigner crystal states. [Preview Abstract] |
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