Bulletin of the American Physical Society
2006 37th Meeting of the Division of Atomic, Molecular and Optical Physics
Tuesday–Saturday, May 16–20, 2006; Knoxville, TN
Session Z1: Hot Topics |
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Chair: Anthony Starace, University of Nebraska Room: Knoxville Convention Center Lecture Hall |
Saturday, May 20, 2006 9:00AM - 9:36AM |
Z1.00001: Experimental evidence for Efimov quantum states Invited Speaker: Three interacting particles form a system which is well known for its complex physical behavior. A landmark theoretical result in few-body quantum physics is Efimov's prediction of a universal set of weakly bound trimer states appearing for three identical bosons with a resonant two-body interaction [1]. Surprisingly, these states even exist in the absence of a corresponding two-body bound state and their precise nature is largely independent of the concrete type of the two-body interaction potential. Efimov's scenario has attracted great interest in many areas of physics; an experimental test however has not been achieved. We report the observation of an Efimov resonance in an ultracold thermal gas of cesium atoms [2]. The resonance occurs in the range of large negative two-body scattering lengths and arises from the coupling of three free atoms to an Efimov trimer. We observe its signature as a giant three-body recombination loss when the strength of the two-body interaction is varied near a Feshbach resonance. We also report on a minimum in the recombination loss for positive scattering lengths, indicating destructive interference of decay pathways. Our results confirm central theoretical predictions of Efimov physics and represent a starting point with which to explore the universal properties of resonantly interacting few-body systems. [1] V. Efimov, Phys. Lett. 33B, 563 (1970). [2] T. Kraemer, M. Mark, P. Waldburger, J. G. Danzl, C. Chin, B. Engeser, A. D. Lange, K. Pilch, A. Jaakkola, H.-C. N\"{a}gerl, R. Grimm, accepted for publication in Nature, cond-mat/0512394. [Preview Abstract] |
Saturday, May 20, 2006 9:36AM - 10:12AM |
Z1.00002: Ultracold three-body collisions and their influence on ultracold quantum gases Invited Speaker: In this talk we will discuss general properties of three-body collisions and their influence on ultracold quantum gases in the regime where the interatomic interactions are strongly affected by a Feshbach resonance. We have developed a simple and unifying picture [1] capable of predicting the energy, mass, and scattering length dependence of the three-body collision rates for all systems relevant for current experiments on ultracold quantum gases. As it turns out, this picture reveals that the scattering length dependence of the three-body rates is strongly influenced by so-called Efimov physics [2]. Efimov's original work in nuclear physics was published roughly 35 years ago, but the first experimental evidence was only recently found using ultracold quantum gases [3]. We will discuss conditions favorable for extending such experiments to enable even more definitive observations of Efimov physics. We will also discuss other processes that might be of interest experimentally such as the formation of long-lived weakly bound boson-fermion molecules. We hope that our results will help experimentalists find ways to take advantage of three-body collisions in their experiments and to encourage them to look for manifestations of few-body physics in this interesting regime. [1] J. P. D'Incao and B. D. Esry, Phys. Rev. Lett. {\bf 94}, 213201 (2005); physics/0508119. [2] V. Efimov, Phys. Lett. {\bf 33}, 563 (1970). [3] T. Kraemer, {\em et al.}, cond-mat/0512394. [Preview Abstract] |
Saturday, May 20, 2006 10:12AM - 10:48AM |
Z1.00003: Phase Engineering of Entangled Number States (aka Schr\"{o}dinger cats) in Gaseous Bose-Einstein Condensates in ``Two," and ``Many" Wells Invited Speaker: It has been demonstrated that a phase offset may be imprinted on ``part'' of a single ground state Bose-Einstein condensate (BEC), and that such a phase imprint can then, via the natural subsequent dynamics of the condensate, generate both solitons and vortices. A similar phase imprint on one or more wells of a coherently connected (Josephson regime) set of BECs yields, again simply from the natural time evolution of the condensate ground state following the phase imprinting, highly entangled number states, the extreme version of which would be the macroscopic N-body superposition state: $\vert $N,0,0,0{\ldots}$>+\vert $0,N,0,0{\ldots}$>+\vert $0,0,N,0{\ldots}$>+\vert $0,0,0N,{\ldots}.$>$ +{\ldots} with appropriate normalization. The notation is intended to indicate that all N particles are in all wells simultaneously. A simple physical model is introduced for the two well case allowing control of both the extremity and sharpness of the number entangled states. Less extreme states are rather more robust than the extreme superposition illustrated above. Similar results are found in systems with 3,4, and 8 wells indicating the generality of the proposed methods, although visualization of the results becomes progressively more difficult, and the computations become intractable surprisingly quickly. Extension of the Bose-Hubbard model where fully coupled GP wavefuctions are combined with exact solution of the correlation problem for the two mode system shows the importance of strong mean-field effects in the understanding and modeling of such systems. Time allowing, a discussion of ``detection'' of such states may be included. The author delightedly acknowledges collaboration with Heidi Perry, Khan Mahmud, Mary Ann Leung and David Masiello. [Preview Abstract] |
Saturday, May 20, 2006 10:48AM - 11:24AM |
Z1.00004: Generation and Applications of Femtosecond Optical Vortices Invited Speaker: An optical vortex is a singularity point in a (scalar) electric field where the amplitude vanishes and the phase is undetermined. Laguerre-Gaussian modes are examples of modes containing an optical vortex. Our interest in vortex modes stems from the fact that their photons possess optical orbital angular momentum (OAM).$^{2}$ Our goal is to make strong ultrashort pulses with a vortex, so we can study the influence of optical OAM on intense-field ionization. Our motivation is the role of the photon's \textit{spin} angular momentum: in its manifestation as polarization, this affects intense-field ionization. Notable are electron recollision processes, central to many schemes to generate attosecond pulses. What role optical \textit{orbital} angular momentum plays in intense-field processes is to the best of our knowledge experimentally unexplored territory. In 2005, we were the first to report the generation of a pure femtosecond vortex.$^{3}$ Our setup uses holographic diffraction and properly deals with bandwidth (tens of nm). We now use a programmable hologram.$^{4}$ We are currently increasing the intensity of our fs vortices to reach ionization levels so we can image focused vortices with our spatially-resolved ion detector. Recent progress will be discussed. Refs: $^{2}$Allen L \textit{et al.} 2003 \textit{Optical Angular Momentum} (Bristol: IoP Publ.); $^{3}$Mariyenko I \textit{et al.} 2005 \textit{Opt. Expr.} \textbf{13} 7599; $^{4}$Strohaber J \textit{et al.} 2006 \textit{J. Phys B}. subm. [Preview Abstract] |
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