Bulletin of the American Physical Society
38th Annual Meeting of the Division of Atomic, Molecular, and Optical Physics
Volume 52, Number 7
Tuesday–Saturday, June 5–9, 2007; Calgary, Alberta, Canada
Session B6: Rydberg Atoms and Molecules |
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Chair: J. Shaffer, University of Oklahoma Room: TELUS Convention Centre Olde Scotch Room |
Wednesday, June 6, 2007 10:30AM - 10:42AM |
B6.00001: Rydberg Multipole Transitions in Time-Dependent Ponderomotive Potentials B. Knuffman, G. Raithel We consider multipole transitions in Rydberg atoms driven by amplitude modulation of an applied standing-wave ponderomotive potential. Using experimentally realizable parameters, we calculate Rabi frequencies of tens of kHz. Dipole selection rules are not applicable to these transitions, which can occur between states whose angular momentum quantum numbers can differ up to about five. Experimental schemes to measure the quantum defects of high angular momentum states using this technique are discussed. [Preview Abstract] |
Wednesday, June 6, 2007 10:42AM - 10:54AM |
B6.00002: Enhancement of Rydberg atom interactions using ac Stark shifts Joseph Petrus, Parisa Bohlouli-Zanjani, James Martin A microwave dressing field was used to induce resonant energy transfer in translationally cold Rydberg atoms. The $^{85}$Rb Rydberg atoms were obtained by laser excitation of cold atoms in a magneto-optical trap. When the amplitude of a $1.356$ GHz dressing field was scanned, the two-atom dipole-dipole process $43d_{5/2} + 43d_{5/2} \rightarrow 45p_{3/2} + 41f_{5/2,7/2}$ was enhanced due to the induced degeneracy of the initial and final states. The resulting spectrum had a series of resonant field amplitudes corresponding to different magnetic sublevels possible for the states involved. The scanned field amplitude was calibrated using microwave spectroscopy of the $43d_{5/2}-41f$ transition under the influence of non-resonant dressing fields. The calibrated resonant field amplitudes agree well with ac Stark shift calculations performed using the Floquet approach. This method for enhancing interactions is complementary to dc electric field induced resonant energy transfer, but benefits from the ability to shift energy levels in either direction by choice of frequency. [Preview Abstract] |
Wednesday, June 6, 2007 10:54AM - 11:06AM |
B6.00003: Resonant enhancement of state-mixing and ionizing collisions in Rb Rydberg states Aaron Reinhard, Tara Cubel Liebisch, Paul Berman, Georg Raithel In rubidium Rydberg states, the binary collision $2 \times nD_{5/2} \rightarrow (n-2) F_{7/2} + (n+2) P_{3/2}$ is nearly resonant in the vicinity of $n=43$. As a result, over a short range of $n$ centered around $n \approx 43$ the two-particle interaction potential is quite large and turns from repulsive to attractive. This behavior has interesting consequences for the rates of Penning-ionizing and state-changing collisions in Rydberg-atom gases and for Rydberg-excitation blockades. In this talk, we report the use of state-selective field ionization to investigate the effect of this resonance on coherent excitation of mixed two-particle states, state-mixing collisions, and Penning-ionization. In particular, we excite superpositions of the two-particle states $2 \times nD_{5/2}$ and $(n-2) F_{7/2} + (n+2) P_{3/2}$ and show that the cross section for subsequent state-changing collisions is a strong function of $n$ near $n=43$. We find that the dynamics of state-mixing collisions and the evolution of the Rydberg gas to a cold plasma depend sensitively on the sign of the interaction potential, and thus on $n$ near the resonance. We compare these results with cases where the atoms are initially excited into states of different $\ell$ and $j$. [Preview Abstract] |
Wednesday, June 6, 2007 11:06AM - 11:18AM |
B6.00004: Spatially resolved observation of dipole-dipole interaction between Rydberg atoms Carolijn van Ditzhuijzen, Femius Koenderink, Atreju Tauschinsky, Bart Noordam, Ben van Linden van den Heuvell We have observed resonant energy transfer between cold Rydberg atoms in separate volumes. Two pulsed laser beams are focused in a $^{85}$Rb MOT, with waists of $\sim$~10~$\mu$m. In one laser focus $\sim$~10 atoms are excited to the $49\mathrm{s}$ state and in the other $\sim$~60 atoms are excited to the $41\mathrm{d}$ state. At a field of 0.4~V/cm a resonant dipole-dipole coupling occurs with a wavelength of 1~cm: $41\mathrm{d} + 49\mathrm{s} \rightarrow 42\mathrm{p} + 49\mathrm{p}$. We have measured the production of the $49\mathrm{p}$ state as a function of laser focus separation (0~-~80~$\mu$m) and interaction time (0~-~50~$\mu$s). The procedure can be understood as writing a 0 bit ($49\mathrm{s}$) in volume A and a 1 bit ($41\mathrm{d}$) in volume B. The bit in A goes from 0 to 1 ($49\mathrm{p}$) and the bit in B from 1 to 0 ($42\mathrm{p}$), due to the dipole-dipole energy transfer from B to A. [Preview Abstract] |
Wednesday, June 6, 2007 11:18AM - 11:30AM |
B6.00005: Investigation into the Dipole-Dipole Interaction between Two Localized Groups of Rydberg Atoms Peter D. Maenner, Thomas J. Carroll, Michael W. Noel Atoms in a highly excited, ultracold sample are coupled through the dipole-dipole interaction. The interactions in such a sample are complicated, and an effort has been made to understand and control them. In our experiment, we have investigated how the spatial arrangement of highly excited atoms affects the dipole-dipole interaction strength. Two tunable dye-lasers were focused into a magneto-optical trap, producing a sample consisting of two localized groups of Rydberg atoms. Each group was excited to a different state, such that the only interactions possible were between the different groups of atoms. The dipole-dipole interaction was tuned into resonance with a static electric field. Varying the beam separation, we measured the number of interacting atoms and width of the field tuned resonance peaks. [Preview Abstract] |
Wednesday, June 6, 2007 11:30AM - 11:42AM |
B6.00006: Coherent many-body dynamics in cold Rydberg gases Thomas Pohl, Mikhail D. Lukin Recent realizations of ultra-cold ensembles of Rydberg atoms opens up unique possibilities for exploring non-equilibrium quantum dynamics of many body system with strong, long-range interactions. Here we will report on theoretical progress in describing the evolution of Rydberg populations in cold gases for various types of interactions. Special emphasis will be placed on excitation schemes that provide a more intuitive understanding of the gas evolution and reveal effects of atomic disorder and quantum correlations on the collective excitation dynamics. [Preview Abstract] |
Wednesday, June 6, 2007 11:42AM - 11:54AM |
B6.00007: Radiative lifetime measurements of high-$n$ Rb Rydberg states Duncan Tate, Mao Zheng, Drew Branden, Tamas Juhasz, Andrew Kortyna We have measured the radiative lifetimes of $S$, $P$, and $D$ states of rubidium in the range $30 \le n \le 50$ using cold atoms in a MOT. Two experimental techniques have been adopted to reduce random and systematic errors. First, a frequency doubled, pulse amplified diode laser is used to excite the target $n\ell$ Rydberg state. The output from this laser has a Fourier-transform linewidth of $\approx 100$ MHz at 480 nm, and results in minimal shot-to-shot variation in the Rydberg state population when it is used to drive the $5p_{3/2}$ $\rightarrow$ $n\ell$ transition. Second, we monitor the target state population as a function of time delay from the 480 nm laser pulse using a short mm-wave pulse that is resonant with the two-photon transition $n\ell$ $\rightarrow$ $(n+1)\ell$. We then selectively field ionize the $(n+1)\ell$ state, and detect the resulting electrons with a microchannel plate (MCP). We step the time delay between the laser pulse and the mm-wave pulse and acquire the MCP signal as a function of the delay. This signal is an accurate mirror of the $n\ell$ population, which we fit to an exponential decay to recover the $n\ell$ state lifetime. [Preview Abstract] |
Wednesday, June 6, 2007 11:54AM - 12:06PM |
B6.00008: Resonant collision processes in a Cs Rydberg gas K. Richard Overstreet, Arne Schwettmann, Jonathan Tallant, James P. Shaffer Experimental studies of high principle quantum number Cs Rydberg atom interactions will be described. Ultracold samples of Rydberg atoms provide a unique opportunity to study inelastic collisions where the dynamics are the result of strong multipole interactions. Photoassociative collision resonances that occur in the cold Rydberg gas are a sensitive probe of theoretical pair potential energy curves. We present measurements of the product state recoil energy after photoassociation to identify the collision process taking place in the Cs Rydberg gas. Our results are compared to theoretical pair potential energy curves that account for both dipole and quadrupole long range interactions between Rydberg atoms in a background electric field. The pair nature of the process is confirmed by measurements of the laser intensity dependence and product state charge distribution after pulsed field ionization of the photoassociation collision resonance. [Preview Abstract] |
Wednesday, June 6, 2007 12:06PM - 12:18PM |
B6.00009: Long-range Cs Rydberg molecules Arne Schwettmann, K. Richard Overstreet, Jonathan Tallant, James P. Shaffer We present calculations of high-lying cold long-range Cs Rydberg molecules. We show bound molecular states at large interatomic distances of up to $\sim$5 microns, entirely due to avoided crossings of the Van der Waals pair-interaction potentials. These wells were found in the full set of long- range multipole Rydberg-Rydberg pair interaction potential curves calculated by our group via matrix diagonalization. The well-depths are enhanced by the application of a small (mV) background electric field. Corresponding bound state wavefunctions are analyzed. Methods to excite and observe these long-lived ($\tau >\mu$s) molecular states will be discussed. Experimental progress toward observing these novel molecular states will also be presented. [Preview Abstract] |
Wednesday, June 6, 2007 12:18PM - 12:30PM |
B6.00010: Measurements in high-L, n=17 and 20 Rydberg states of barium: An investigation of ion core properties of Ba$^{+}$. Erica L. Snow, Stephen R. Lundeen Microwave spectroscopy studies with selective laser excitation for detection of Rydberg levels by Stark ionization have been used to measure the fine structure intervals of n=17 and 20 for a range of angular momentum states,$7\ge L\ge 11$. Measurement of the energy splittings in the fine structure levels, due largely to interactions of the Rydberg electron's angular momentum with the ion core spin, are also reported. The implications of these measurements on the determination of the ion core properties, such as the polarizability and lifetimes, and associated matrix elements is investigated. [Preview Abstract] |
Wednesday, June 6, 2007 12:30PM - 12:42PM |
B6.00011: Higher-order contributions to fine structure in high-L Rydberg states of Si$^{2+}$. Erica L. Snow, Stephen R. Lundeen Measured fine structure patterns of high-L Rydberg states have often been used to extract measurements of both dipole and quadrupole polarizabilities of their positive ion cores. Dipole polarizabilities deduced in this way are apparently quite accurate, judging by comparison with calculated values, but the accuracy of quadrupole polarizabilities is questionable. The polarizabilites of Na-like Silicon are a good example. Recent fine structure measurements seem to imply a quadrupole polarizability in clear disagreement with calculations. This apparent discrepancy is due to misinterpretation of the experimental data, neglecting the effects of higher-order terms in the polarization potential that can significantly alter the slope of the traditional polarization plots. When these terms are calculated, and their magnitude estimated, the discrepancy is eliminated. The implications of the higher order terms for analysis of high-L fine structure patterns are discussed. [Preview Abstract] |
Wednesday, June 6, 2007 12:42PM - 12:54PM |
B6.00012: Polarizability of Kr$^{6+}$ from High-L Kr$^{5+}$ Fine Structure Measurements S.R. Lundeen, C.W. Fehrenbach The transition between n=55 and n=109 Rydberg levels of Kr$^{5+}$ has been studied at high resolution using the RESIS method. Resolved excitation of L = 6, 7, 8, and 9 levels in n=55 lead to a determination of the fine structure energies of these levels. Interpreted with the long-range polarization model, this leads to a measurement of the dipole polarizability of Zn-like Kr$^{6+}$, $\alpha _{d}$ = 2.53(2) a$_{0}^{3}$. Considerations involved in deducing a value of the quadrupole polarizability from the data and factors contributing to the signal and noise levels in measurements of this type will be discussed. [Preview Abstract] |
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