Bulletin of the American Physical Society
41st Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 55, Number 5
Tuesday–Saturday, May 25–29, 2010; Houston, Texas
Session S6: Ultracold Dipoles |
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Chair: Robert Forrey, Pennsylvania State University Room: Arboretum IV-V |
Friday, May 28, 2010 2:00PM - 2:12PM |
S6.00001: Ultracold dipoles on a ring Sascha Zoellner, Georg M. Bruun, Stephanie M. Reimann Dipolar bosons and fermions in a quasi-one-dimensional (1D) ring potential have the interesting feature of combining the physics of 1D gases with anisotropic effects. Depending on the orientation of their dipole moments and the dipolar interaction strength, there may be a competition between repulsive and attractive regions on the ring. We identify three basic phases based on simulations in a few-body system: (i) a repulsive regime resembling an inhomogeneous 1D Bose (Fermi) gas, (ii) a Wigner-crystal-like state with a non-equidistant spatial distribution, and (iii) bound states of identical bosons (fermions) localized in the strongly attractive regions on the ring. We discuss how these states arise in a crossover from weak to strong dipolar interactions, with an emphasis on the particle-number dependence. [Preview Abstract] |
Friday, May 28, 2010 2:12PM - 2:24PM |
S6.00002: Controllable stability of dipolar gases in 1-D geometry Robin C\^ot\'e, John Montgomery, Jason Byrd We present results of the long-range interaction of dipolar molecules, considering in particular the case of KRb+KRb. The potential energy surface for this system has been obtained by {\it ab initio} calculations for various orientations of the dimers, and fitted to a long-range potential function which includes electrostatic, dispersion and induction terms. We found that, in addition to the dipole-dipole interaction between the dimers, which can be attractive (colinear) or repulsive (parallel), repulsive quadrupolar interactions result in barriers that can prevent molecules to approach each other at short distance, and thus stabilize ultracold samples. For the colinear geometry, the combination of attractive dipolar and repulsive quadrupolar interactions lead to long-range wells that can support several bound states. We explore how these wells can be controlled by external electric fields. Finally, we discuss the prospects of forming bound polymer chains of KRb molecules at ultra-cold temperatures as well as implications for controllable phase transitions such as 1-D gas to Luttinger liquid transitions. [Preview Abstract] |
Friday, May 28, 2010 2:24PM - 2:36PM |
S6.00003: ABSTRACT WITHDRAWN |
Friday, May 28, 2010 2:36PM - 2:48PM |
S6.00004: Controlling collective rotational excitations of polar molecules in optical lattices Felipe Herrera, Marina Litinskaya, Roman Krems We consider a two-species mixture of ultracold LiCs and LiRb molecules in the ground rotational state trapped on an optical lattice with one molecule per site. Rotational excitation of LiCs molecules gives rise to rotational excitons that undergo multiple collisions with LiRb molecules. This leads to localization of excitons. We present the results of numerical simulations demonstrating that the localization of excitons as well as interference patterns due to multiple scattering events can be controlled by applying an external electric field or varying the concentration and distribution of the LiRb molecules. The two-species mixture of polar molecules trapped on an optical lattice can thus be used as a quantum simulator of localization phenomena in disordered media. Our results show that the localization of excitons in the proposed system can be studied in real time. [Preview Abstract] |
Friday, May 28, 2010 2:48PM - 3:00PM |
S6.00005: Observation of dipolar collisions in a near quantum-degenerate gas of polar molecules Dajun Wang, K.-K. Ni, S. Ospelkaus, G. Qu\`{e}m\`{e}ner, B. Neyenhuis, M.H.G. de Miranda, J.L. Bohn, J. Ye, D.S. Jin We have studied dipolar collisions in an ultracold molecular gas prepared close to quantum degeneracy [1]. By applying a modest external electric field to fermionic KRb molecules produced in a single quantum state, we tune the dipolar interaction strength in the molecular gas. We observe a steep power law dependence of the chemical reaction rate on the induced dipole moment. In addition, we directly observe the spatial anisotropy of the dipolar interactions manifested in measurements of the thermodynamics of the dipolar gas.\\[4pt] [1] K-K. Ni et al., arXiv:1001.2809 (2010) [Preview Abstract] |
Friday, May 28, 2010 3:00PM - 3:12PM |
S6.00006: Bosonic and fermionic dipolar collisions in confined geometries Jose P. D'Incao, Brett D. Esry, Chris H. Greene We study ultracold collisions of point dipoles in quasi-1D and quasi-2D geometries. We explore the fundamental aspects that dictate the collisional properties of both bosonic and fermionic dipoles when exposed to an external electric field. We also discuss the possible effects that the confined geometry might have for both species and explore interference effects which might prove useful in achieving stable samples of ultracold dipolar molecules. [Preview Abstract] |
Friday, May 28, 2010 3:12PM - 3:24PM |
S6.00007: Towards dipolar collisions between magnetically trapped OH and buffer gas cooled ND$_{3}$ Mark Yeo, Brian Sawyer, Benjamin Stuhl, David Patterson, John Doyle, Jun Ye Cold molecule research has been progressing at a rapid pace with many new and exciting topics being developed. The long range dipole-dipole interaction between cold polar molecules allows us to exquisitely control their collisional dynamics using an external electric field. We have successfully trapped Stark decelerated OH molecules in a permanent magnetic trap at a temperature of $70$ $mK$ and a density of $10^{6}$ $cm^{-3}$. We have also developed a cold, bright continuous beam of polar molecules by buffer gas cooling and electrostatically guiding ND$_{3}$. This yields a flux of $10^{10}$ molecules per second at a temperature of $\sim$ $5$ $K$. Harnessing these two techniques, we report progress towards the observation of collisions between these two dipolar species. Furthermore, we investigate the tuning of the collision cross sections via a variable external electric field superposed on the magnetic trap. [Preview Abstract] |
Friday, May 28, 2010 3:24PM - 3:36PM |
S6.00008: Ultracold dipolar collisions of KRb molecules in a 2D confined geometry Goulven Quemener, John Bohn Ultracold fermionic polar molecules of $^{40}$K$^{87}$Rb in their absolute rovibronic and hyperfine ground state [1] have been recently created and pave the way to probe ultracold chemistry of polar molecules [2]. When an electric field is applied, KRb + KRb $\to$ K$_2$ + Rb$_2$ chemical rates increase as the sixth power of the molecule induced dipole moment [3], due dominantly to head-to-tail collisions. As a consequence, chemical reactions are enhanced in an electric field and are unfavorable to long lifetimes of polar molecules. To prevent these collisions, an additional optical lattice can be used to confine the molecules in two dimensions. In this talk, we will present a theoretical investigation of ultracold dipolar collisions of indistinguishable KRb molecules in a presence of an electric field in a 2D confined geometry. We will present expected chemical rates as a function of the electric field and discuss if this will be favorable to achieve evaporative cooling of a dense sample of KRb molecules. [1] Ni et al., Science 322, 231 (2008) ; Ospelkaus et al., Phys. Rev. Lett. 104, 030402 (2010). [2] Ospelkaus et al., arXiv:0912.3854, Science, in press (2010). [3] Qu{\'e}m{\'e}ner et al., Phys. Rev. A, in press (2010) ; Ni et al., arXiv:1001.2809, submitted (2010). [Preview Abstract] |
Friday, May 28, 2010 3:36PM - 3:48PM |
S6.00009: Simple treatment of ultracold polar molecule collisions John Bohn, Goulven Qu\'{e}m\'{e}ner, Zbigniew Idziaszek, Paul Julienne Collisions of polar molecules at ultracold ($< \mu K$) temperatures open the way for prospects of manipulating collision dynamics, including chemical reactions, by by varying an electric field. To understand such processes, one needs a scattering theory that accounts sufficiently accurately for the long-range van der Waals and dipolar forces acting between the molecules, but that also has a reasonable parametrization of the short-range physics when the molecules actually encounter one another. In this presentation we discuss a theory that marries a quantum-defect-theory parametrization of short-range physics \footnotemark[2], to a modified Langevin-like model that has successfully estimated the effect of electric fields \footnotemark[3]. We discuss the character of the resulting scattering, including field-dependent chemical reaction rates and resonances. \footnotetext[2]{Z. Idziaszek and P. S. Julienne, e-print arXiv:0912.0370 (2009).} \footnotetext[3]{ G. Qu\'{e}m\'{e}ner and J. L. Bohn, Phys. Rev. A, to appear (2009). } [Preview Abstract] |
Friday, May 28, 2010 3:48PM - 4:00PM |
S6.00010: Mixed triplet and singlet pairing in multicomponent fermion systems with dipolar interactions Congjun Wu, Jorge Hirsch The symmetry properties of the Cooper pairing problem for multi-component ultra-cold dipolar molecular systems are investigated. The dipolar anisotropy provides a natural and robust mechanism for both triplet and singlet Cooper pairing to first order in the interaction strength. With a purely dipolar interaction, the triplet $p_z$-like polar pairing is the most dominant. A short-range attractive interaction can enhance the singlet pairing to be nearly degenerate with the triplet pairing. We point out that these two pairing channels can mix by developing a relative phase of $\pm\frac{\pi}{2}$, thus spontaneously breaking time-reversal symmetry. We also suggest the possibility of such mixing of triplet and singlet pairing in other systems. [Preview Abstract] |
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