Bulletin of the American Physical Society
47th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 61, Number 8
Monday–Friday, May 23–27, 2016; Providence, Rhode Island
Session U3: Focus Session: Long Range InteractionsFocus

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Sponsoring Units: GFB Chair: Jose DIncao, JILA Room: Ballroom D 
Friday, May 27, 2016 10:30AM  11:00AM 
U3.00001: Coherent and incoherent dipoledipole interactions between atoms Invited Speaker: Francis Robicheaux Results will be presented on the collective interaction between atoms due to the electric dipoledipole coupling between states of different parity on two different atoms. A canonical example of this effect is when the electronic state of one atom has Scharacter and the state of another atom has Pcharacter. The energy difference between the two states plays an important role in the interaction since the change in energy determines the wave number of a photon that would cause a transition between the states. If the atoms are much closer than the wave length of this photon, then the dipoledipole interaction is in the near field and has a $1/r^3$ dependence on atomic separation. If the atoms are farther apart than the wave length, then the interaction is in the far field and has a $1/r$ dependence. When many atoms interact, collective effects can dominate the system with the character of the collective effect depending on whether the atomic separation leads to near field or far field coupling. As an example of the case where the atoms are in the far field, the line broadening of transitions and strong deviations from the BeerLambert law in a diffuse gas will be presented. As an example of near field collective behavior, the radiative properties of a Rydberg gas will be presented. [Preview Abstract] 
Friday, May 27, 2016 11:00AM  11:12AM 
U3.00002: Effect of the band structure in a rigorous twobody model with longrange interactions in 1D optical lattices Tom Kristensen, Andrea Simoni, JeanMichel Launay We compute scattering and bound state properties for two ultracold molecules in a pure 1D optical lattice. We introduce reference functions with complex quasimomentum that naturally account for the effect of excited energy bands. Our exact results for a shortrange interaction are first compared with the simplest version of the standard BoseHubbard (BH) model. Such comparison allows us to highlight the effect of the excited bands, of the nononsite interaction and of tunneling with distant neighbor, that are not taken into account in the BH model. The effective interaction can depend strongly on the particle quasimomenta and can present a resonant behavior even in a deep lattice. As a second step, we study scattering of two polar particles in the optical lattice. Peculiar Wigner threshold laws stem from the interplay of the long range dipolar interaction and the presence of the energy bands. We finally assess the validity of an extended BoseHubbard model for dipolar gases based on our exact twobody calculations. [Preview Abstract] 
Friday, May 27, 2016 11:12AM  11:24AM 
U3.00003: Quantum localization of particles with dipolar tunnelling in threedimensional lattices of finite size Joshua T. Cantin, Tianrui Xu, Roman V. Krems It is generally assumed that quantum particles with dipolar longrange hopping do not undergo Anderson localization in 3D disordered lattices. However, this is valid only for lattices of infinite size. The delocalization of particles with longrange hopping occurs through resonant couplings between sites with the same onsite energy. As the lattice size grows, the energy for each lattice site within a finite volume has a nonzero probability to be equal to the energy of a site outside this volume. The number of such resonances diverges with the system size. If the lattice size is finite, the number of resonances is finite and may not be sufficiently large to cause delocalization. This raises the question: can quantum transport be suppressed by reducing the size of the system? To answer this, we compute the localizationdiffusion phase diagram for a quantum particle with dipolar longrange hopping in a finitesize threedimensional lattice with diagonal and offdiagonal disorder. We characterize the diffusionlocalization transition as a function of the system size and the amount of diagonal and offdiagonal disorder. Our calculations show that the diffusionlocalization transition could be detected using excitations of polar molecules in an optical lattice as probe particles. [Preview Abstract] 
Friday, May 27, 2016 11:24AM  11:36AM 
U3.00004: A detailed analysis of threshold behavior for the Efimov effect R. C\^ot\'e, i. simbotin, d. shu We analyze the energy dependence of the threebody recombination rate $K_3$ for systems which possess Efimov states, and we identify a new regime of energies, characterized by a simple behavior of $K_3(E)$. Using a model which captures the key features of the Efimov problem, we confirm the oscillatory behavior at high energy found by Esry et al. However, we find that in the ultracold limit, the oscillatory behavior does not transition directly into the Wigner type behavior. We uncovered a domain of intermediate energies between the Wigner and the oscillatory regimes. The extent of the new energy regime is determined by the Efimov state nearest to the threshold, or by an Efimov resonance just above the threshold. [Preview Abstract] 
Friday, May 27, 2016 11:36AM  11:48AM 
U3.00005: A novel approach for Milne's phaseamplitude method I. Simbotin, D. Shu, R. C\^ot\'e We have uncovered a linear equation for the envelope functionfully equivalent with the original nonlinear equation of Milne'sand have implemented a highly accurate and efficient numerical method for computing the envelope and the associated phase. Consequently, we obtain a high precision parametrization of the wavefunction, within a very economical approach. The key ingredients are: (i) straightforward optimization for smoothness, and (ii) Chebyshev polynomials as the workhorse for solving integro/differential equations. The latter also give a builtin interpolation, and allow for developing numerical tools that are robust, accurate, and convenient. [Preview Abstract] 
Friday, May 27, 2016 11:48AM  12:00PM 
U3.00006: Quantum phases from competing short and longrange interactions in an optical lattice Lorenz Hruby, Renate Landig, Nishant Dogra, Manuele Landini, Rafael Mottl, Tobias Donner, Tilman Esslinger Quantum simulations with ultracold atoms are mostly limited to shortrange collisional interactions, while longer ranged interactions have proven to be difficult to implement so far. Here we experimentally realize a bosonic lattice model with competing short and infiniterange interactions, and observe the appearance of four distinct phases  a superfluid, a supersolid, a Mott insulator and a charge density wave. Our system is based on an atomic quantum gas trapped in an optical lattice inside a high finesse optical cavity. The strength of the shortranged onsite interactions is controlled by means of the optical lattice depth. The infiniterange interaction potential is mediated by a vacuum mode of the cavity and is independently controlled by tuning the cavity resonance. [Preview Abstract] 
Friday, May 27, 2016 12:00PM  12:30PM 
U3.00007: Quantum dynamics and topological excitations in interacting dipolar particles Invited Speaker: Ana Rey Dipoledipole interactions, longrange and anisotropic interactions that arise due to the virtual exchange of photons, are of fundamental importance in optical physics, and are enabling a range of new quantum technologies including quantum networks and optical lattice atomic clocks. In this talk I will first discuss how arrays of dipolar particles with a simple J$=$0J$=$1 internal level structure can naturally host topological and chiral excitations including Weyl quasiparticles [1]. Weyl fermions were first predicted to exist in the context of high energy physics but only recently have been observed in solid state systems. I will discuss a proposal of using Mott insulators of Sr atoms to observe and probe the Weyl excitation spectrum and its nontrivial chirality. Finally I will report on a recent experiment done at JILA [2] which validates the underlying microscopic model that predicts the existence of these excitations. The experiment measured the collective emission from a coherently driven gas of ultracold $^{\mathrm{88}}$Sr atoms and observed a highly directional and anisotropic emission intensity and a substantial broadening of the atomic spectral lines. All of the measurements are well reproduced by the theoretical model. These investigations open the door for the exploration of novel quantum manybody systems involving strongly interacting atoms and photons, and are useful guides for further developments of optical atomic clocks and other applications involving dense atomic ensembles. [1] S. V. Syzranov \textit{et al}, Emergent Weyl quasiparticles in threedimensional dipolar arrays, arXiv:1512.08723 [2]S. L. Bromley \textit{et al}, Collective atomic scattering and motional effects in a dense coherent medium, arXiv:1601.05322 [Preview Abstract] 
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