Bulletin of the American Physical Society
2007 APS April Meeting
Volume 52, Number 3
Saturday–Tuesday, April 14–17, 2007; Jacksonville, Florida
Session B8: Efimov Effect Observed! |
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Sponsoring Units: GFB Chair: William Reinhardt, University of Washington Room: Hyatt Regency Jacksonville Riverfront City Terrace 4 |
Saturday, April 14, 2007 10:45AM - 11:21AM |
B8.00001: Manifestations of Efimov states in three-body bound levels and continua Invited Speaker: In 1969, Vitaly Efimov stunned nuclear physicists with a paper that made a bizarre prediction: that a system of 3 uncharged particles can possess an infinite number of weakly bound states, even when none of its 2-particle subsystems are sufficiently attracted to one another to form even one bound state. This counterintuitive effect was initially controversial, but subsequent theoretical studies of 3-body nuclear states as well as analogous states for atoms and molecules confirmed Efimov's universal prediction. Until last year, these states had little or no experimental evidence, but their first confirmation has now been reported.[1] In the meantime theoretical understanding of Efimov states and their implications for seemingly unrelated observables like 3-body recombination has been making exciting advances.[2] This invited talk will summarize our present understanding and recent generalizations, describe an intuitive way of visualizing the Efimov effect, and review its implications for modern day experiments in ultracold quantum gases that manipulate Fano-Feshbach resonances. \newline \newline [1] T. Kraemer {\it et al.}, Nature {\bf 440}, 315 (2006). \newline [2] B. D. Esry and C. H. Greene, Nature {\bf 440}, 289 (2006). [Preview Abstract] |
Saturday, April 14, 2007 11:21AM - 11:57AM |
B8.00002: Beller Lectureship Award: Evidence for Efimov quantum states in an ultracold gas of cesium atoms Invited Speaker: A landmark theoretical result in few-body quantum physics is Efimov's prediction of a universal set of bound trimer states appearing for three identical bosons with a resonant two-body interaction. Since the formulation of Efimov's problem in the context of nuclear physics 37 years ago, it has attracted great interest in many areas of physics. However, the observation of Efimov trimer states has remained an elusive goal. In an ultracold gas of cesium atoms cooled to temperatures in the nanokelvin range, we observe signatures of Efimov states. Exploiting the special interaction properties of ultracold cesium, we control the two-body scattering length by application of a variable magnetic field. In three-body collisions at large negative scattering lengths, we observe a pronounced decay resonance. This resonance results from three free atoms coupling to an Efimov trimer state. At a positive two-body scattering length, we observe a scattering resonance in atom-dimer collisions, which we interpret as atoms colliding with dimers to couple to a trimer state. Our results confirm central theoretical predictions of Efimov physics and represent a starting point to explore the universal properties of resonantly interacting few-body systems. We discuss further prospects of Efimov physics in ultracold gases. [Preview Abstract] |
Saturday, April 14, 2007 11:57AM - 12:33PM |
B8.00003: Efimov effect and the quest for a theory of Nuclear Forces Invited Speaker: The force between two nucleons or two atoms is well understood at large distances (pion exchange or Van der Waals force) but, at short distances, they are much complex. These are examples of a common problem in physics: how can we understand long distance properties of a system when they seem to depend on short distance details that are unknown? Effective field theories and the renormalization group techniques have been developed primarily to deal with this situation. The application of these ideas to the nuclear force problem or to atoms close to a Feshbach resonance shows the full power of these techniques and allow the derivation of a host of results equally applicable in nuclear and atomic physics. In particular, the study of three-particle systems provides a startling example of a limit cycle in the renormalization flow -- a theoretical possibility not previously realized in Nature. [Preview Abstract] |
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