Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session A41: Localization, Cooling, Trapping and Clocks |
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Sponsoring Units: DAMOP Chair: Matthew Beeler, University of Maryland Room: 350 |
Monday, March 18, 2013 8:00AM - 8:12AM |
A41.00001: Theory of interaction-induced localization for mobile impurities Jian Li, Jin An, Chin-Sen Ting A phenomenological model is proposed for the interaction-induced localization of mobile impurities in the cold atomic systems. The fundamental properties of the transition between the extended and localized impurity state in one, two and three dimension are investigated with this model. We find that the transition is continuous in one and two dimension while discontinuous in three dimension. We show that the dynamics of single localized impurity is described by a soliton and predict the formation of bipolaron and Wigner lattices for many fermionic impurities. Our theory explains the essential features from specific models in a unified picture and can be used to realize several exotic phenomena with ultracold impurity atoms. [Preview Abstract] |
Monday, March 18, 2013 8:12AM - 8:24AM |
A41.00002: Single parameter scaling for 1d systems with scale-free long-range correlated disordered potentials Nancy Sandler, Greg Petersen Disordered optical lattices have renewed the interest in localization physics under power-law long-range correlated disorder potentials. For these systems, insight can be gained by combining numerical data and analytic expressions based on scaling laws. Thus, the absence of a transition in short-range correlated disordered systems can been proved by verifying the validity of the single parameter scaling (SPS) hypothesis for the distribution function of the dimensionless conductance. In this talk we discuss this hypothesis for a system with scale-free long-range correlated disorder potentials of the form $\sim 1/r^{\alpha}$ as a function of the correlation exponent $\alpha$. We present results for the $1^{st}$ (the $\beta$-function) and $2^{nd}$ (variance) cumulants of the distribution function, and show a violation of SPS at an energy scale $E_{SPS}$, that scales with an $\alpha$-renormalized disorder strength. Calculations for the localization length reveals the existence of a crossover scale $E_{cross}$ between two regions as correlations increase. An increased number of more extended-like states appear near the band-center while states near the band edges experience reduced localization lengths. We confirm previously predicted scaling behavior near the band edge and center. [Preview Abstract] |
Monday, March 18, 2013 8:24AM - 8:36AM |
A41.00003: Anderson localization of pairs in bichromatic optical lattices Giuliano Orso, Gabriel Dufour We investigate the formation of bound states made of two interacting atoms moving in a one dimensional quasi-periodic optical lattice. We derive the quantum phase diagram for Anderson localization of both attractively and repulsively bound pairs. We calculate the pair binding energy and show analytically that its behavior as a function of the interaction strength depends crucially on the nature -extended, multifractal, localized- of the single-particle atomic states. Experimental implications of our results are discussed. Reference: Phys. Rev. Lett. 109, 155306 (2012) [Preview Abstract] |
Monday, March 18, 2013 8:36AM - 8:48AM |
A41.00004: Many-body energy localization transition in periodically driven system Luca D'Alessio, Anatoli Polkovnikov According to the second law of thermodynamics the total entropy and energy of a system is increased during almost any dynamical process. Notable exceptions are known in noninteracting systems of particles moving in periodic potentials. Here the phenomenon of dynamical localization can prevent heating beyond certain threshold. However, it was believed that driven ergodic systems will always heat without bound. Here, on the contrary, we report strong evidence of dynamical localization transition in periodically driven ergodic systems in the thermodynamic limit. This phenomenon is reminiscent of many-body localization in energy space. We report numerical evidence based on exact diagonalization of small spin chains and theoretical arguments based on the Magnus expansion. Our findings are valid for both classical and quantum systems. [Preview Abstract] |
Monday, March 18, 2013 8:48AM - 9:00AM |
A41.00005: Many-Body Localization in a Quasiperiodic System Shankar Iyer, Gil Refael, Vadim Oganesyan, David Huse Recent theoretical and numerical evidence suggests that localization can survive the introduction of interactions in disordered many-body systems, giving rise to a so-called many-body localization transition. This dynamical phase transition is relevant to questions of thermalization in quantum systems. It separates a many-body localized phase, in which localization prevents thermalization, from an ``ergodic'' phase in which the usual assumptions of quantum statistical mechanics hold. Here, we present numerical evidence that many-body localization also occurs in models that omit true disorder in favor of a quasiperiodic potential. In one dimension, these systems already have a single-particle localization transition, and we show that this transition becomes a many-body localization transition upon the introduction of interactions. These issues are increasingly experimentally relevant, because quasiperiodic potentials have been used in place of true disorder in recent experiments with cold atoms and with photonic waveguides. [Preview Abstract] |
Monday, March 18, 2013 9:00AM - 9:12AM |
A41.00006: Dynamic Localization of Interacting Particles in an Anharmonic Potential Mark Herrera, Thomas Antonsen, Edward Ott, Shmuel Fishman We investigate the effect of anharmonicity and interactions on the dynamics of an initially Gaussian wavepacket in a weakly anharmonic potential. We note that depending on the strength and sign of interactions and anharmonicity, the quantum state can be either localized or delocalized in the potential. We formulate a classical model of this phenomenon and compare it to quantum simulations done for a self consistent potential given by the Gross-Pitaevskii Equation. [Preview Abstract] |
Monday, March 18, 2013 9:12AM - 9:24AM |
A41.00007: Anderson Localization of a non-interacting Bose-Einstein condensate with effective spin-orbit interaction in a quasiperiodic optical lattice Lu Zhou, Han Pu, Weiping Zhang We theoretically investigate the localization properties of a noninteracting atomic Bose-Einstein condensate moving in a one-dimensional quasiperiodic optical lattice potential in the tight-binding regime. The atoms are subject to effective spin-orbit coupling induced by external laser fields. We present the phase diagram in the parameter space of the disorder strength and those related to the effective spin-orbit coupling. The phase diagram are verified via multifractal analysis of the atomic wavefunctions. We found that spin-orbit coupling can lead to the spectra mixing (coexistence of extended and localized states) and the appearance of mobility edges. [Preview Abstract] |
Monday, March 18, 2013 9:24AM - 9:36AM |
A41.00008: Laser Controlled Rotational Cooling in Na$_2$ Based on Exceptional Points Adam Wearne, Viatcheslav Kokoouline, Osman Atabek, Roland Lefebvre In this study, we describe a computational simulation of the interaction of diatomic molecule with an applied laser field. It is known that for certain laser wavelengths and intensities, the wave functions and eigenenergies of two states become degenerate. Such locations in the laser parameter space are known as ``exceptional points.'' By applying a laser pulse which encircles one or more exceptional points in the parametric plane of wave length versus intensity, one can bring an ensemble of diatomic molecule into a pre-selected rovibrational state after the laser pulse is over. During this process, a fraction of the molecules dissociate, and those which remain, are brought to the chosen rovibrational state. Although this scheme can be applied more generally, here we use Na$_2$ as an illustrative example. We examine the locations in the parameteric space of exceptional points, which lead to the exchange of rotational states, and how the shape of laser pulse in the parametric plane affects the ``purification'' of the chosen rovibrational state and the dissociation of other states. [Preview Abstract] |
Monday, March 18, 2013 9:36AM - 9:48AM |
A41.00009: Dynamic dimer formation between superionic fluorines in CaF$_{2}$ Masashi Saito, Tomofumi Tasaka, Kazuo Tsumuraya Recently we have elucidated the formation of the dynamic dimers in the conductor $\alpha $-CuI through the analyses of the correlation peaks of the partial pair-distribution functions and the partial angle distribution functions with the first principles molecular dynamics (MD) method.(J. Phys. Soc. Jpn. 81,055603(2012).) The present study investigate the formation of the dynamic dimers and the migration paths of the dimers in the conductor CaF$_{2}$ with the MD method. The fluorines form the dynamic 32$f$-8$c$ dimers with the coordinate (x,x,x) x=0.300. These incommensurate dimers allow to decrease the migration barriers of the fluorines. [Preview Abstract] |
Monday, March 18, 2013 9:48AM - 10:00AM |
A41.00010: Laser cooling of Iron atoms Thierry Bastin, Nicolas Huet, Stephanie Krins We report on the first laser cooling of Iron atoms. Our laser cooling setup makes use of 2 UV laser radiation sent colinearly in a 0.8~m Zeeman slower. One laser is meant for optical pumping of the Iron atoms from the ground state to the lowest energy metastable state. The second laser cools down the atoms using a quasi-perfect closed transition from the optical pumped metastable state. The velocity distribution at the exit of the Zeeman slower is obtained from a probe laser crossing the atom beam at an angle of 50 degrees. The fluorescence light is detected using a photomultiplier tube coupled with a boxcar analyzer. The Iron atom beam is produced with a commercial effusion cell working at around 1950 K. Our laser radiations are stabilized using standard saturated-absorption signals in both an Iron hollow cathode absorption cell and an Iodine cell. We will present our experimental setup, as well as the first evidences of cooled down Iron atoms at the exit of the Zeeman slower. [Preview Abstract] |
Monday, March 18, 2013 10:00AM - 10:12AM |
A41.00011: Ytterbium in quantum gases and atomic clocks: van der Waals interactions and blackbody shifts S. G. Porsev, M. S. Safronova, Charles W. Clark We evaluated the $C_6$ coefficients of Yb-Yb and Yb-alkali/group II van der Waals interactions with 2\% uncertainty. The only existing results for such quantities are for the Yb-Yb dimer. Our value, $C_6 = 1929(39)$ a.u., is in excellent agreement with the recent experimental determination of 1932(35) a.u. [M. Kitagawa, {\em et al., Phys. Rev. A } {\bf 77}, 012719 (2008)]. We have also developed a new approach for the calculation of the dynamic correction to the blackbody radiation shift. We have calculated this quantity for the Yb $6s^2$ $^1{\rm S}_0 - 6s6p$ $^3{\rm P}^{\circ}_0$ clock transition with 3.5\% uncertainty. This reduces the fractional uncertainty due to the blackbody radiation shift in the Yb optical clock at 300 K to the $10^{-18}$ level. For further details, see http://arxiv.org/abs/1208.1456 [Preview Abstract] |
Monday, March 18, 2013 10:12AM - 10:24AM |
A41.00012: Blackbody radiation shift in the Sr optical atomic clock M.S. Safronova, S.G. Porsev, U.I. Safronova, M.G. Kozlov, Charles W. Clark We evaluated the static and dynamic polarizabilities of the $5s^2$ $^1$S$_0$ and $5s5p$ $^3{\rm P}^{\circ}_0$ states of Sr using the high-precision relativistic configuration interaction + all-order method. Our calculation explains the discrepancy between the recent experimental $5s^2$ $^1$S$_0$ - $5s5p$ $^3{\rm P}^{\circ}_0$ dc Stark shift measurement = 247.374(7) a.u. [T. Middelmann, S. Falke, C. Lisdat and U. Sterr, arXiv:1208.2848 (2012)] and the earlier theoretical result of 261(4) a.u. [S. G. Porsev and A. Derevianko, {\em Phys. Rev. A} {\bf 74}, 020502(R) (2006)]. Our present value of 247.5 a.u. is in excellent agreement with the experimental result. We also evaluated the dynamic correction to the BBR shift with 1\% uncertainty; -0.1492(16) Hz. The dynamic correction to the BBR shift is unusually large in the case of Sr (7\%) and it enters significantly into the uncertainty budget of the Sr optical lattice clock. We suggest future experiments that could further reduce the present uncertainties. For further information, see http://arxiv.org/abs/1210.7272 [Preview Abstract] |
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