Bulletin of the American Physical Society
43rd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 57, Number 5
Monday–Friday, June 4–8, 2012; Orange County, California
Session B5: Cold Collisions and Ultracold Molecules |
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Chair: Phillip Gould, University of Connecticut Room: Garden 3 |
Tuesday, June 5, 2012 10:30AM - 10:42AM |
B5.00001: Travelling wave deceleration of heavy polar molecules in weak-field seeking states Richard Hendricks, Nicholas Bulleid, Sarah Skoff, Daniel Segal, Ben Sauer, Michael Tarbutt, Edward Hinds, Samuel Meek, Andreas Osterwalder, Maxwell Parsons, Gabriele Santambrogio, Gerard Meijer Electrostatic forces can be used to decelerate neutral molecules via the Stark interaction. Most Stark decelerators to date use switched dc electric fields to manipulate light molecules in weak field seeking states. More massive molecules have smaller rotational constants and greater kinetic energies at a given velocity, and would require very long decelerators to bring them to rest. We have combined a new cryogenic source of YbF molecules, based on a pulsed solenoid valve cooled to 4K, with a 48cm long travelling wave Stark decelerator that is suitable for decelerating heavy molecules in weak-field seeking states. This decelerator uses continuously modulated sinusoidal electric fields to produce a series of moving 3-dimensional traps that can be continuously slowed to decelerate the molecules within them. We have decelerated YbF molecules from 300m/s to 276m/s. This implies that a 3 metre long decelerator could produce trapped YbF molecules at rest. In a different configuration, our source produces broader pulses of YbF molecules with speeds of 200m/s or less that could be brought to rest with a decelerator that is just 1 metre in length. [Preview Abstract] |
Tuesday, June 5, 2012 10:42AM - 10:54AM |
B5.00002: Continuous Production of Rovibrational Ground State RbCs via Photoassociation Colin Bruzewicz, Mattias Gustavsson, Toshihiko Shimasaki, David DeMille We photoassociate electronically-excited RbCs molecules into a deeply-bound vibrational level of the $\Omega=0^{+}$ component of the (2)$^{3}\Pi$ state. Following spontaneous decay of the excited molecules, we measure the vibrational levels populated in the $X^{1}\Sigma^{+}$ state using resonance-enhanced multiphoton ionization through the well-characterized (2)$^{1}\Pi$ state. For photoassociation on the $J=1$ level of the $\Omega=0^{+}$ component, selection rules from the spontaneous decay constrain the ground state molecules to the $J=0, 2$ rotational levels. We are currently investigating methods for the continuous accumulation of rovibrational ground state RbCs in an optical trap. We also intend to purify the molecular sample by exploiting trap loss due to inelastic scattering, which is predicted to remove only excited RbCs and hence yield a large, trapped sample of polar $v=J=0$ molecules. [Preview Abstract] |
Tuesday, June 5, 2012 10:54AM - 11:06AM |
B5.00003: Enhanced creation efficiency of polar molecules with a species-selective dipole trap Bo Yan, Brian Neyenhuis, Steven Moses, Jacob Covey, Deborah Jin, Jun Ye Quantum degenerate ultracold polar molecules offer the possibility to study many-body physics and exotic phases of matter. In our experiment, we create ultracold fermionic ground-state KRb molecules near quantum degeneracy. A high atom-molecule conversion efficiency at very low temperatures should enable us to create a quantum degenerate dipolar gas. However, the efficiency of molecule creation has two main challenges at very low temperatures. First, the mass and polarizability differences between K and Rb result in a gravitational sag between the two atomic clouds. Second, the differing quantum statistics (bosonic Rb vs. fermionic K) cause a size mismatch between the two clouds when T/Tc$<$1 for Rb. To overcome these issues, we have implemented a species-selective dipole trap around 790 nm that has a trapping force on K but not Rb, in addition to the original dipole trap at 1064nm. This new dipole trap allows us to adjust the size and position of the K cloud for optimal spatial overlap with Rb, which can significantly increase the molecule creation efficiency at very low temperatures. This should lead to a colder, denser gas of ground-state molecules and should allow us to create a degenerate dipolar gas. [Preview Abstract] |
Tuesday, June 5, 2012 11:06AM - 11:18AM |
B5.00004: Cold Collisions in a K-Rb two species dipole trap Carlos Menegatti, Bruno Marangoni, Luis Marcassa Several experiments involving cold collisions and cold heteronuclear molecules rely on large and dense atomic samples. In our experiment, we have trapped cold K atoms and Rb atoms in a two species crossed broadband optical dipole trap. Our crossed beam configuration uses 25 W of power (at 1064 n, bandwidth of 2 nm) in each beam with about 50 $\mu $m waist radius at the focus and a depth of about 700 $\mu $K. The dipole trap is loaded from a standard mixed species MOT. In the dipole trap, we have about 2 x 10$^{6}$ K atoms, 7 x 10$^{6}$ Rb atoms, and an average temperature of 20 $\mu $K and a density of about 10$^{12}$ atoms/cm$^{3}$ for both species. We have observed that the K atom population presents an exponential decay with a lifetime of about 200 ms in the absence of Rb atoms. When we add the Rb population in the dipole trap, the K atom population presents a non-exponential decay. We believe that such observation suggests that the mixed sample is photoassociated by the 1064 nm laser, forming an excited state KRb molecule, which further decays forming KRb in the electronic ground state. More results will be discussed during the presentation. [Preview Abstract] |
Tuesday, June 5, 2012 11:18AM - 11:30AM |
B5.00005: Non-universal binding energies of weakly bound Feshbach molecules Paul Julienne, Jeremy Hutson, Gerhard Zurn, Andre N. Wenz, Thomas Lompe, Selim Jochim It is well-known that two atoms weakly bound into a Feshbach molecule have a universal binding energy proportional to 1/$a^{2}$ when the $s$-wave scattering length $a$ becomes large compared to a characteristic scale length of the long range potential. Analytic formulas giving the correction to universality in terms of the ratio of $a$ to the scale length for a van der Waals potential have been given by Gribakin and Flambaum [1] and by Gao [2]. We examine the domain of validity of such corrections for several species with different potentials and masses using accurate numerical quantum mechanical calculations for single and coupled channels representations of the interatomic interactions. In particular, we examine Feshbach molecules comprised of two $^{6}$Li fermionic atoms in different spin states. We use new measurements with the two lowest spin states of this species to construct an improved model for very weak binding energies down to a few kHz and consequently obtain a more accurate value of the precise magnetic field at which the s-wave scattering length has its singularity. \\[4pt] [1] G. F. Gribakin and V. V. Flambaum, Phys. Rev. A 48, 546 (1993).\\[0pt] [2] B. Gao, J. Phys. B 37, 4273 (2004). [Preview Abstract] |
Tuesday, June 5, 2012 11:30AM - 11:42AM |
B5.00006: Resolved-sideband RF spectroscopy on weakly bound $^6$Li$_2$ molecules S. Jochim, G. Z{\"u}rn, A.N. Wenz, T. Lompe, P.S. Julienne, J.M. Hutson In a unitary Fermi gas, the scattering length is tuned to infinity, leaving the interparticle spacing as the only length scale remaining. Recent measurements of the equation of state in an ultracold gas of $^6$Li at a Feshbach resonance are so precise that the derivation of universal constants such as the Bertsch parameter is limited by the present knowledge of the resonance position [1]. We have performed RF spectroscopy measurements of the binding energies of weakly bound $^6$Li$_2$ molecules near the broad Feshbach resonance at $\sim$834\,G. To avoid density dependent shifts we start from thermal samples of 30-60 molecules. Resolving sidebands resulting from the quantized relative motion of the dissociated molecules in a cigar-shaped trap with a radial trap frequency of about 349\,Hz allows us to measure binding energies with an unprecedented precision of $\sim$60\,Hz. Our results allow for a much more accurate determination of the Feshbach resonance position compared to previous measurements.\\[4pt] [1] M. Bartenstein et al., PRL {\bf94}, 103201 (2005) [Preview Abstract] |
Tuesday, June 5, 2012 11:42AM - 11:54AM |
B5.00007: Towards ultracold RbCa molecules Michaela Kleinert, Hayley Whitson, Alexandria Parsagian Ultracold heteronuclear molecules have seen increasing interest in the scientific community over the last few years. By controlling their ro-vibrational energy levels, ultracold molecules can be used for high precision spectroscopy, to study cold collisions with rich internal dynamics, as model systems for condensed matter physics, and as qubits in quantum information processing. We study the novel combination RbCa. In addition to a permanent electric dipole moment, it also possesses a permanent magnetic dipole moment. This makes it an ideal candidate to study strong long-range dipole-dipole interactions. We are currently in the process of adding a Ca MOT to our existing Rb MOT and will discuss our current and future efforts toward our goal of creating, for the first time, ultracold RbCa molecules. Molecules, once created, will be detected through resonantly enhanced multi-photon ionization (REMPI). We have also performed \textit{ab initio} calculations to determine the electronic energy levels of RbCa, and calculated Franck-Condon factors between the ground and several excited states [Preview Abstract] |
Tuesday, June 5, 2012 11:54AM - 12:06PM |
B5.00008: Lifetimes of three particles in an isotropic harmonic trap Edmund Meyer, B.D. Esry We present an analytic calculation of the energy levels and lifetimes of particles confined by an isotropic harmonic trap. Using a single adiabatic hyperspherical channel, we derive a transcendental equation whose solutions give the energy levels and lifetimes of the trapped states. To obtain a more physical interpretation of the results, we examine two regimes: the oscillator length much greater, and much less than, the two-body $s$-wave scattering length. For the case of large oscillator length, we find explicit analytical expressions for the lifetime of the trapped states. In particular we find that the lifetime for three identical bosons scales as $|a|^4$, in agreement with previous studies of free-space recombination. Moreover, the decay rate shows resonant enhancements due to Efimov physics just as free space rates do. [Preview Abstract] |
Tuesday, June 5, 2012 12:06PM - 12:18PM |
B5.00009: Production of Ultracold Strontium Dimers in Optical Lattices for Precision Measurements and Metrology Christopher Osborn, Gael Reinaudi, Tanya Zelevinsky Ultracold diatomic molecules offer exciting possibilities for studies of novel states of matter, quantum information, and precision measurements. We present recent results on the photoassociation of ultracold strontium dimers in optical lattices of various dimensions, including the coherent two-photon production of stable ground state molecules. We discuss features of this two-photon transfer, including the frequencies and strengths of the relevant transitions, and the associated Autler-Townes splitting. Further, we present results on the molecular lifetime, and its dependence on the dimensionality of the lattice. In addition, we highlight further work toward the development of deeply bound (10's of THz) molecules for use in a molecular clock. [Preview Abstract] |
Tuesday, June 5, 2012 12:18PM - 12:30PM |
B5.00010: Quantum control of ultracold Rb Svetlana Malinovskaya, Thomas Collins, Spencer Horton Ultracold control has originated on the base of latest developments in the field of ultracold gases. Control of electron dynamics within the hyperfine structure in the ultracold Rb atom using chirped pulses aimed to induce the desired excitations and create predetermined non-equilibrium states will be discussed. We show population inversion within the hyperfine levels of $5^{2}S_{1/2}$ state through Raman transitions by making use of a single ns chirped pulse having $kW/cm^2$ beam intensity. Satisfying the one-photon resonance condition with a hyperfine state of the $5^{2}P_{1/2}$ or $5^{2}P_{3/2}$ state allows us to enter the adiabatic region at field intensities such that the corresponding Rabi frequencies are less than or equal to the hyperfine splitting. We will highlight the studies of the impact of decoherence through the process of cooling of internal degrees of freedom in KRb from the Feshbach state by implementation of optical frequency combs in a framework of a semiclassical model. [Preview Abstract] |
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