Bulletin of the American Physical Society
46th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 60, Number 7
Monday–Friday, June 8–12, 2015; Columbus, Ohio
Session C3: Few-body Physics in Cold Atoms |
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Sponsoring Units: GFB Chair: Doerte Blume, Washington State University Room: Franklin AB |
Tuesday, June 9, 2015 2:00PM - 2:12PM |
C3.00001: Trapped unitary two-component Fermi gases with up to ten particles X.Y. Yin, D. Blume The properties of two-component Fermi gases with zero-range interactions are universal. We use an explicitly correlated Gaussian basis set expansion approach to investigate small equal-mass two-component Fermi gases under spherically symmetric external harmonic confinement. At unitarity, we determine the ground state energy for systems with up to ten particles interacting through finite-range two-body potentials for both even and odd number of particles. We extrapolate the energies to the zero-range limit using a novel scheme that removes the linear and quadratic dependence of the ground state energies on the two-body range. Our extrapolated zero-range energies are compared with results from the literature. We also calculate structural properties and the two-body Tan contact. [Preview Abstract] |
Tuesday, June 9, 2015 2:12PM - 2:24PM |
C3.00002: Magneto-association of atoms near an atom-dimer resonance Jason H.V. Nguyen, De Luo, Randall G. Hulet Ultracold atomic gases provide an environment to study few body physics in a regime where universal properties, such as the scaling laws of Efimov trimers, can be explored. In our work, Efimov trimers and Feshbach dimers are created in a condensate of $^7$Li atoms by RF-field modulation. The molecular binding energies are tunable using the broad Feshbach resonance for atoms in the $|1,1\rangle$ state. We find that the rate of dimer formation is sharply peaked at the atom-dimer resonance, where the trimer merges with the dimer plus free-atom continuum. The origins of this enhancement are unclear, but may be related to our previous observation of enhanced three-body loss at the atom-dimer resonance.\footnote{S.E. Pollack, D. Dries, \& R.G. Hulet, Science, 326, 1683 (2009).} [Preview Abstract] |
Tuesday, June 9, 2015 2:24PM - 2:36PM |
C3.00003: Efimov Physics in a $^6$Li-$^{133}$Cs Atomic Mixture Jacob Johansen, Lei Feng, Colin Parker, Cheng Chin, Yujun Wang We investigate Efimov physics based on three-body recombination in an atomic mixture of $^6$Li and $^{133}$Cs in the vicinity of interspecies Feshbach resonances at 843 and 889 G. This allows us to compare the loss spectra near different resonances and test the universality of Efimov states. Theoretically the Efimov spectrum near 889 G is expected to be similar to that near 843 G, except that the first resonance is absent near the former Feshbach resonance. This is due to the difference in the Cs-Cs scattering length near the two resonances: At 843 G it is negative, whereas at 889 G it is positive. Although it is primarily the Li-Cs interactions that lead to Efimov resonances, the Cs-Cs scattering length is expected to influence the spectrum. This work is supported by NSF and Chicago MRSEC. [Preview Abstract] |
Tuesday, June 9, 2015 2:36PM - 2:48PM |
C3.00004: A Unified View of Finite Range Effects in Efimov Trimers Lucas Platter, Chen Ji, Eric Braaten, Daniel Phillips Three-body recombination in ultracold atoms is a process that can demonstrate the appearance of discrete scale invariance due to the Efimov effect. Different features in the scattering length dependent recombination rate are related by universal relations in the so-called zero-range limit. However, experiments are usually carried out with systems that display non-neglible corrections due to the finite range of interatomic interaction. We explain the origin of recently constructed universal relations for systems of three identical bosons interacting through a large scattering length [1]. Range corrected universal relations are calculated using first order perturbation theory and are benchmarked against microcopic calculations that by construction contain finite range effects [2-4]. We relate our results to work done in other frameworks and explain differences and similarities. We present also relations that are crucial for analyzing experiments in the future.\\[4pt] [1] C. Ji, D. R. Phillips and L. Platter, Annals Phys. 327, 1803 (2012).\\[0pt] [2] A. Deltuva, Phys. Rev. A85, 012708 (2012).\\[0pt] [3] E. Garrido, M. Gattobigio and A. Kievsky, Phys. Rev. A88, 032701 (2013).\\[0pt] [4] R. Schmidt, S. P. Rath and W. Zwerger, Eur. Phys. J. B85, 386 (2012). [Preview Abstract] |
Tuesday, June 9, 2015 2:48PM - 3:00PM |
C3.00005: Ultracold nonreactive molecules in an optical lattice Andris Docaj, Michael Wall, Kaden Hazzard Nonreactive (NR) ultracold molecules in optical lattices are free from the two-body losses that occur in other ultracold molecules, opening up new possibilities for quantum many-body physics. Despite the absence of chemical reactions, NR molecules scatter in extremely complex ways -- not captured by a delta function pseudopotential -- due to the enormous number of rotational and vibrational states. We calculate the eigenstates and energies of two NR molecules confined to a single site of an optical lattice, as a first step towards deriving an effective lattice model that can describe many molecules in a lattice. To describe the short-range collisional properties, which are presently experimentally unknown, we employ random matrix theory. However, our formalism is capable of handling arbitrary short-range collisional physics. [Preview Abstract] |
Tuesday, June 9, 2015 3:00PM - 3:12PM |
C3.00006: Few-body systems in the adiabatic hyperspherical representation Kevin Daily, Chris H. Greene We study few-body systems using the adiabatic hyperspherical representation. We use a correlated Gaussian basis at a fixed hyperradius with efficiently calculated matrix elements [1] to generate the adiabatic potentials and non-adiabatic couplings as a function of the hyperradius. We consider different dimensions with neutral or charged particles. \\[4pt] [1] K. M. Daily and Chris H. Greene, Phys. Rev. A {\bf 89}, 012503 (2014). [Preview Abstract] |
Tuesday, June 9, 2015 3:12PM - 3:24PM |
C3.00007: Loss of Cold Atoms from Inelastic Collisions with Large Energy Release Eric Braaten Many of the most important loss processes for ultracold atoms involve inelastic collisions with large energy release. The large energy release implies that the loss process is local, so it should be describable by a local rate equation for the number density of the low energy atoms. In few-body physics, the effects of the inelastic collisions on the low-energy atoms can be reproduced by adding a local anti-Hermitian term to the Hamiltonian density. For example, if the inelastic scattering process is a two-atom collision, the anti-Hermitian term is the contact density multiplied by an imaginary constant. If the anti-Hermitian term is included in the time-evolution equation for the density matrix of a many-body system, it predicts a completely wrong time dependence for the number density. This puzzle can be resolved by including an additional term in the evolution equation for the density matrix that transforms it into a Lindblad equation with local Lindblad operators. The Lindblad equation guarantees that the trace of the density matrix is conserved and that its time evolution is Markovian. [Preview Abstract] |
Tuesday, June 9, 2015 3:24PM - 3:36PM |
C3.00008: Approaching the universal loss regime in cold and ultracold molecular collisions Paul S. Julienne, Matthew D. Frye, Jeremy M. Hutson We investigate properties of single-channel quantum defect models of cold atomic and molecular collisions that take account of inelastic and reactive processes using a single parameter to represent short-range inelastic or reactive loss. We present plots of the resulting energy-dependence of elastic and inelastic cross sections over the full parameter space of loss parameters and short-range phase shifts. We then test the single-channel model by comparing it with the results of coupled-channel calculations of rotationally inelastic collisions between vibrational ground state LiH molecules and Li atoms. We find that the range of cross sections predicted by the single-channel model becomes increasingly accurate as the initial LiH rotational quantum number increases, with a corresponding increase in the number of open loss channels. The results suggest that coupled-channel calculations at very low energy (in the s-wave regime) could in some cases be used to estimate a loss parameter and then to predict the range of possible loss rates at higher energy without the need for explicit coupled-channel calculations for higher partial waves. [Preview Abstract] |
Tuesday, June 9, 2015 3:36PM - 3:48PM |
C3.00009: Three-body scattering hypervolume for ultracold atoms with a model two-body potential Shangguo Zhu, Shina Tan It has been known that the three-boson low energy effective interaction influences the dynamic and the static properties of many bosons, including the ground state energies of dilute Bose-Einstein condensates. The three-body scattering hypervolume, which is a three-body analogue of the two-body scattering length, characterizes this effective interaction. Surprisingly, knowledge of this fundamental quantity has still been lacking, except for hard sphere bosons and bosons with large scattering length. For bosons with a soft-ball potential - the repulsive Gaussian potential, we determine the scattering hypervolume by solving the three-body Schr\"{o}dinger equation numerically, and matching the solution with the asymptotic expansions for the wave function at large hyperradii. Our analyses of the three-body scattering hypervolume can be extended to the long-range Van der Waals potential. They will be necessary in the precise understanding of the energetics and dynamics of three, more, or many ultracold bosonic atoms. [Preview Abstract] |
Tuesday, June 9, 2015 3:48PM - 4:00PM |
C3.00010: Inducing Resonant Interactions in Ultracold Atoms with an Oscillating Magnetic Field D. Hudson Smith In systems of ultracold atoms, two-atom interactions can be resonantly enhanced by a new mechanism which does not rely upon the presence of a Feshbach resonance. In this mechanism, interactions are controlled by tuning the frequency of an applied oscillating magnetic field near the Bohr frequency corresponding to the energy gap between a pair of low-energy atoms and a two-atom bound state. Near the resonance, the s-wave scattering length is a simple function of the oscillation frequency whose asymmetric line-shape is similar to that of Feshbach resonances. Atom pairs can absorb (emit) quanta from (to) the oscillating field leading to inelastic losses. This mechanism for inducing resonant interactions is illustrated using two simple models, from which the dependencies of the resonance parameters on the strength of oscillating field are extracted. This mechanism gives experimental access to strongly interacting systems of atoms that have no convenient Feshbach resonance. [Preview Abstract] |
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