Bulletin of the American Physical Society
43rd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 57, Number 5
Monday–Friday, June 4–8, 2012; Orange County, California
Session T1: Invited Session: Rydberg Gases and Ultracold Plasmas |
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Chair: Charles Adams, Durham University Room: Grand Ballroom BCD |
Friday, June 8, 2012 8:00AM - 8:30AM |
T1.00001: Ultracold Neutral Plasma Density Waves Invited Speaker: Thomas Killian Ultracold neutral plasmas, which are created by photoionizing laser cooled atoms near the ionization threshold, have been extensively studied in order to probe strong Coulomb coupling effects, low-energy atomic processes, equilibration, and collective phenomena [1]. The experimental study of collective modes, however, has previously been limited to phenomena involving electrons. By spatially modulating the intensity pattern of the photoionizing laser, we are now able to create controlled density perturbations on the plasma, which enables study of ion collective behavior. Periodic modulation excites ion acoustic waves [2]. We have also created two distinct plasmas that stream into each other. In the hydrodynamic regime, the central gap between the two plasmas splits into two density ``holes'' that propagate away from the plasma center at the ion acoustic velocity. At lower densities and higher particle velocities, plasmas are less collisional, and we observe kinetic effects such as plasma streams penetrating each other, with a penetration depth that reflects the ion stopping power. This general technique for sculpting the density opens many new possibilities, such as investigation of non-linear phenomena, instabilities, and shock waves in the ultracold regime, and determination of the effects of strong coupling on dispersion relations. The low temperature, small size, plasma expansion, and strongly coupled nature of ultracold plasmas make these studies fundamentally interesting. They may also shed light on similar phenomena in high energy density, laser-produced plasmas that can be near the strongly coupled regime. \\[4pt] [1] T. C. Killian, T. Pattard, Thomas Pohl, and J. M. Rost, Phys. Rep., 449, 77 (2007).\\[0pt] [2] J. Castro, P. McQuillen, and T. C. Killian, Phys. Rev. Lett. 105, 065004 (2010). [Preview Abstract] |
Friday, June 8, 2012 8:30AM - 9:00AM |
T1.00002: Trilobites and other molecular animals: How Rydberg-electrons catch ground state atoms Invited Speaker: Tilman Pfau We report on laser spectroscopy results obtained in a dense and frozen Rydberg gas. Novel molecular bonds resulting in ultralong-range Rydberg dimers were predicted [1] and dimers as well as trimers in different vibrational states were found [2]. Some of these states are predicted to be bound by quantum reflection. Lifetime measurements confirm this prediction. Coherent superposition between free and bound states have been investigated [3]. Recently we have also confirmed that in an electric field these homonuclear molecules develop a permanent dipole moment [4]. \\[4pt] [1] C. H. Greene, A. S. Dickinson, and H. R. Sadeghpour, \textit{Phys. Rev. Lett.} \textbf{85}, 2458 (2000). \\[0pt] [2] V. Bendkowsky, B. Butscher, J. Nipper, J. P. Shaffer, R. L\"{o}w, T. Pfau, \textit{Nature }\textbf{458}, 1005 (2009), V. Bendkowsky, B. Butscher, J. Nipper, J. Balewski, J. P. Shaffer, R. L\"{o}w, T. Pfau, W. Li, J. Stanojevic, T. Pohl, and J. M. Rost, \textit{Phys. Rev. Lett. }\textbf{105}, 163201 (2010). \\[0pt] [3] B. Butscher, J. Nipper, J. B. Balewski, L. Kukota, V. Bendkowsky, R. L\"{o}w, and T. Pfau \textit{Nature Physics }\textbf{6}, 970--974 (2010). \\[0pt] [4] W. Li, T. Pohl, J. M. Rost, Seth T. Rittenhouse, H. R. Sadeghpour, J. Nipper, B. Butscher, J. B. Balewski, V. Bendkowsky, R. L\"{o}w, T. Pfau, \textit{Science }\textbf{334}, 1110 (2011). [Preview Abstract] |
Friday, June 8, 2012 9:00AM - 9:30AM |
T1.00003: How electron collisions shape an ultracold plasma Invited Speaker: Edward Grant Excitation of diatomic nitric oxide in a supersonic molecular beam forms a Rydberg gas with a temperature less than 1 K in the moving frame. This system relaxes to a molecular ultracold plasma with properties very comparable to plasmas formed by Rydberg excitation or threshold photoionization of atoms in a MOT. While, both MOT and molecular beam plasmas expand on a microsecond timescale with velocities determined by the electron temperature and the mass of the positive ions, molecular beam plasmas appear to expand slower than MOT plasmas suggesting a state of strong coupling. This observation challenges the conventional understanding of these systems. The nitric oxide plasma differs from MOT plasmas in one very important fundamental respect. Molecular cations carry the positive charge, and when a diatomic NO$^+$ ion recombines with an electron, it can dissociate to neutral atoms. The spatial distribution of ions and electrons in a quasi-neutral plasma determines the driving force for expansion. Dissociative recombination occurs fastest in the core of the plasma. This loss channel flattens the charged-particle density distribution in the centre. Model calculations show that this suppresses the expansion of the core, channeling the thermal energy of the electrons to flow instead to the hydrodynamic motion of the peripheral ions. [Preview Abstract] |
Friday, June 8, 2012 9:30AM - 10:00AM |
T1.00004: Nonlocal light-matter interactions in cold Rydberg gases Invited Speaker: Thomas Pohl By virtue of their exaggerated properties, cold Rydberg atoms are considered to be promising systems for exploring quantum phenomena on a few- and many-body level. In this talk we discuss different facets of the laser-driven excitation dynamics in ultracold Rydberg gases. The evolution of both the atoms as well as the applied light-field displays profound effects of the strong van der Waals interactions between Rydberg atoms. On the one hand, they gives rise to long-range and collective atomic interactions that induce nonlocal matter-wave dynamics and the formation of exotic quantum phases. On the other hand, this system provides a well-controllable nonlocal optical medium with enormous nonlinearities. We discuss the resulting nonlinear light propagation and possible applications to photonic quantum computation. [Preview Abstract] |
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