Bulletin of the American Physical Society
42nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 56, Number 5
Monday–Friday, June 13–17, 2011; Atlanta, Georgia
Session T3: Low Temperature Plasmas and Rydberg Atoms |
Hide Abstracts |
Chair: Steve Rolston, JQI and University of Maryland Room: A703 |
Friday, June 17, 2011 8:00AM - 8:12AM |
T3.00001: On characterization of an ultracold ion source N. Debernardi, W.J. Engelen, R.W.L. van Vliembergen, P.H.A. Mutsaers, E.J.D. Vredenbregt, O.J. Luiten The ultracold ion source (UCIS) is based on creating very cold ion beams (T $<$ 1 mK) by near-threshold photo-ionization of a laser-cooled and trapped $^{85}$Rb gas. The UCIS has the potential of producing ion beams with a brightness and current comparable to the liquid-metal ion source (LMIS), which is the current state-of-art for focused ion beam (FIB) technology. The brightness characterizes the source and is proportional to the ion current, the source temperature and the energy spread. We have already shown that the UCIS can provide much lower energy spread than LMIS, and may therefore offer a route toward 1-nm ion beam milling. The ultra low temperature of the source permits collimated bunches to be created at a low energy (down to few eV), which allows using time-dependent fields for accelerating and focusing. With this lens, a source temperature of (3 $\pm $ 2) mK has been measured. A dynamic model of the source describing its properties under pulsed operation has been developed and experiments have been started in order to validate it. The extracted current is the missing ingredient needed to characterize the brightness of the UCIS. [Preview Abstract] |
Friday, June 17, 2011 8:12AM - 8:24AM |
T3.00002: High resolution ionization of ultracold neutral plasmas P. McQuillen, J.A. Castro, T.C. Killian Collective effects, such as waves and instabilities, are integral to our understanding of most plasma phenomenon. We have been able to study these in a new regime, ultracold neutral plasmas, by effectively shaping the initial density distribution through spatial modulation of the ionizing laser. This technique has allowed us to excite ion acoustic waves (IAW) and measure the dispersion relation in the long wavelength limit. We have produced streaming plasmas and measured the evolution of a possible instability. To overcome resolution limits imposed by diffraction of the modulated ionizing beam, we have developed and implemented a high resolution 1:1 optical relay with CTF100 $>$ 80 cyc./mm. This unlocks a wide range of studies in both linear and nonlinear phenomenon at length scales comparable to Debye shielding lengths on both sides of the strongly coupled crossover. The latest results from these studies will be presented. [Preview Abstract] |
Friday, June 17, 2011 8:24AM - 8:36AM |
T3.00003: Ion-ion thermalization rate in ultracold neutral plasmas Jose Castro, Patrick McQuillen, Thomas Killian We measured the ion-ion thermalization rate in strontium ultracold neutral plasmas (UNP) in a regime of strong ion coupling. Traditional plasma descriptions, based on the Landau-Spitzer collision time, fail to describe collisions in this regime of strong coupling where interaction energies between the ions become comparable to their kinetic energies. The thermalization rates were determined by measuring the relaxation time of an initially perturbed velocity distribution of Sr$^+$ ions into a Maxwellian. The initial velocity distribution of one of the spin ground states of S$_{1/2}$ level is perturbed by optically pumping the ions with circularly polarized light. The resulting, perturbed velocity distribution is then measured at a variable time until relaxation. Optical pumping and the subsequent relaxation of the velocity distribution are strongly affected by collisions between the ions. We modeled the measured spectra and their evolution with a system of coupled rate equations and a simple collisional term to determine the ion-ion thermalization rate and compare these to theory. [Preview Abstract] |
Friday, June 17, 2011 8:36AM - 8:48AM |
T3.00004: Disorder-induced heating and early time dynamics in ultracold neutral plasmas Mary Lyon, Scott Bergeson, Francis Robicheaux Disorder-induced heating (DIH) is a nonequilibrium, ultrafast relaxation process that occurs when laser-cooled atoms are photo-ionized to make an ultracold plasma. Its effects dominate the ion motion during the first 100 ns of the plasma evolution. We measure DIH using laser-induced fluorescence on the ions. By changing the frequency of the probe laser beam we map out the time evolution of the velocity distribution with ns time resolution. We compare to a fluorescence simulation to more clearly determine the relationship between the fluorescence signal and the velocity distribution. This allows us to characterize ion heating and (quasi-)equilibration in a wide range of plasma conditions. [Preview Abstract] |
Friday, June 17, 2011 8:48AM - 9:00AM |
T3.00005: Radio-frequency detection of electron oscillations in ultracold plasmas K.A. Twedt, S.L. Rolston Electron oscillations in ultracold plasmas were previously observed through the enhanced electron emission from the plasma due to resonant rf heating. Both simple Langmuir and Tonks-Dattner resonances were detected in this manner. Recent theoretical work [1] predicts that the resonant energy absorption occurs primarily at the edge of the electron distribution and thus the resonant frequency depends on the charge imbalance of the plasma. To aid in investigating this claim, we have developed a new technique to observe electron resonances by directly monitoring the amplitude and phase changes of the rf field capacitively coupled onto a grid located near the plasma. This technique provides a direct measure of the rf absorption that does not depend on the dynamics of electron evaporation, and can be used in experiments where electron detection is not possible. In addition to studying Langmuir waves, we have also excited and observed an upper hybrid oscillation of the electrons in the presence of a perpendicular magnetic field.\\[4pt] [1] A. Lyubonko, T. Pohl, and J.-M. Rost, arXiv:1011.5937 (2010). Supported by NSF PHY-1004242. [Preview Abstract] |
Friday, June 17, 2011 9:00AM - 9:12AM |
T3.00006: Evolution of Rydberg atom clouds in a linear magnetic trap Mallory Traxler, Georg Raithel A linear magnetic guide provides a unique environment in which to perform studies on dense, elongated Rydberg atom samples. In our setup, we utilize a long, high-gradient atom guide for $^{87}$Rb atoms with a transverse temperature of 400 $\mu $K, a longitudinal temperature of 1~mK, and a flux of 3x10$^{7}$ atoms/s. We measure the spatial and temporal evolution of elongated Rydberg atom samples excited in the guiding potential. The evolution is monitored by detecting ions that arise from Penning ionization and from black-body-induced thermal ionization of the Rydberg atoms. As such, the signal exhibits two main components. We present detailed numerical simulations that indicate a well-localized, early-time, high-density component is due to an initial collapse of the Rydberg atom distribution in the guiding potential and Penning ionization. The diffuse, long-lived, low-density component is due to slow thermal ionization of the remaining, magnetically guided Rydberg atoms. [Preview Abstract] |
Friday, June 17, 2011 9:12AM - 9:24AM |
T3.00007: Atom-molecule coherence and Ramsey interferometry in ultracold Rydberg gases Robert Loew, Jonathan Balewski, Johannes Nipper, Bjoern Butscher, Tilman Pfau Ultralong-range Rydberg molecules are bound states of a Rydberg atom with ground state atoms [1]. We report on experiments studying the coherence properties of this new class of molecular bond. We demonstrate the coherent transfer of initially free pairs of rubidium ground-state atoms to ultralong-range Rydberg molecules using rotary echo and Ramsey-pulse sequences. The coherent evolution of the molecular system is characterized by measuring the timescales for the energy-conserving dephasing rate, T2, and for non-energy-conserving decay processes, T1 [2]. Furthermore, these Ramsey experiments can be viewed as an atom-molecule interferometer where the unbound ground state atoms and the ultalong-range Ryberg molecules form two branches. The relative phase in the arms of such an interferometer can be precisely controlled and varied over a wide range using additional electric field pulses. Besides this proof of principle, this technique provides a phase sensitive tool to measure interactions between Rydberg atoms or molecules. \\[4pt] [1] V. Bendkowsky et al., Nature 458, 1005 (2009) \\[0pt] [2] B. Butscher et al., Nature Physics, nphys1828 (2010) [Preview Abstract] |
Friday, June 17, 2011 9:24AM - 9:36AM |
T3.00008: Interactions between cold rubidium Rydberg atoms with external control J.E. Johnson, S.L. Rolston We explore the interactions in an ensemble of $^{87}$Rb atoms at temperatures ~500 $\mu$K excited to the 50S$_{1/2}$ Rydberg state. The atoms interact with an externally-controlled static electric field, producing a Stark-shifted energy level and an induced electric dipole moment. Changes in this induced dipole moment give rise to increased interactions between the atoms, as evidenced by a suppression of the excitation to the Rydberg state. We model this excitation suppression with a simple Monte Carlo simulation and show that the suppression of excitation is fully explained by a dipole-dipole interaction between the induced dipoles along with the van der Waals interaction. Additionally, we investigate a perturbative approach to calculate the full interactions by using Stark-perturbed wavefunctions in a calculation of the van der Waals interaction through Forster processes. [Preview Abstract] |
Friday, June 17, 2011 9:36AM - 9:48AM |
T3.00009: Dipolar Bose-Einstein condensate of Stationary-Light Dark-state Polaritons Gor Nikoghosyan, Frank Zimmer, Martin Plenio We put forward and discuss in detail a scheme to achieve BEC of stationary-light dark-state polaritons with dipolar interaction. We extend the works on Bose-Einstein condensation of photons and polaritonic quasiparticles, to the regime of dipolar quantum gases. To this end we introduce a diamond-like coupling scheme in a vapor of Rydberg atoms under the frozen gas approximation. To determine the system's dynamics we employ normal modes and identify the dark-state polariton corresponding to one of the modes. We show that these polaritonic quasiparticles behave in adiabatic limit like Schr\"{o}dinger particles with a purely dipolar inter-particle interaction. Moreover, we could show, by analyzing the Bogoliubov spectrum of a homogeneous dipolar BEC, that for a special choice of the dipolar interaction parameter the considered dipolar BEC is, in contrast to usual dipolar BEC, very stable. [Preview Abstract] |
Friday, June 17, 2011 9:48AM - 10:00AM |
T3.00010: Dark-State Polaritons with Rydberg Interactions Johannes Otterbach, Alexey V. Gorshkov, Thomas Pohl, Mikhail D. Lukin, Michael Fleischhauer Due to their strong long-range interaction and high level of controllability Rydberg-atoms are especially well suited for applications in quantum-information [1]. We study the interaction of single- or few-photon pulses in a coherently driven ensemble of Rydberg atoms exhibiting a ladder-like linkage pattern. Under conditions of electromagnetically induced transparency the photons form quasi-particles, so-called dark-state polaritons [2]. We investigate the effect of the strong Rydberg interactions on the polaritons. In particular we discuss two-particle correlations which are shown to decay very quickly to zero within the so-called blockade radius if the lower transition is close to resonance. Away from resonance temporary two-polariton bound states are formed. On length scales large compared to the blockade radius the Rydberg polaritons experience a repulsive interaction. \\[4pt] [1] M. Saffman et al., Rev. Mod. Phys. 82, 2313 (2010).\\[0pt] [2] M. Fleischhauer et al., Rev. Mod. Phys. 77, 633 (2005). [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700