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 T5: Rydberg Atoms and Wave Packets |
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Chair: Francis Robicheaux, Auburn University Room: Knoxville Convention Center 301 AB |
Friday, May 19, 2006 10:30AM - 10:42AM |
T5.00001: High-Resolution Rydberg-spectroscopy on ultracold Rubidium atoms Tilman Pfau, Rolf Heidemann, Axel Grabowski, Vera Bendkowsky, Eva Kuhnle, Juergen Stuhler Rydberg atoms can have huge static electric dipole moments. We are working on the investigation of electric dipole-dipole interaction between them as well as the interaction between Rydberg atoms and ground-state atoms of a BEC. The starting point of our Rydberg spectroscopy measurements is a cloud of magneto-optically trapped $^{87}$Rb-atoms. Using two narrow band, frequency stabilized cw laser systems, we perform two-photon excitation via the 5P$_{3/2}$-level of ground state (5S$_{1/2}$) Rb atoms to high lying Rydberg states with linewidths below 1 MHz. For the coherent control of the excitation, we need high spectral resolution and precise control of the Rabi-frequencies on both of the transitions. To demonstrate the spectral resolution and stability of our system, we investigated the Stark splitting of the two 41D-finestructure-states by measuring the number of Rydberg atoms as a function of the excitation frequency for different electric fields. We found it to be in excellent agreement with our calculations using perturbation theory on the Rubidium-wavefunctions. The Rabi-frequencies were measured by observation of the Autler-Townes-splitting while driving one of the transitions strongly and probing the other one. A line broadening mechnism due to ionic background charges is discussed. [Preview Abstract] |
Friday, May 19, 2006 10:42AM - 10:54AM |
T5.00002: Superradiance in ultracold Rydberg atoms Tun Wang, Robin Cote, Edward Eyler, S. Farooqi, Philip Gould, Marijan Kostrun, David Tong, Daniel Vrinceanu, Susanne Yelin Experiments in dense, ultracold Rydberg atoms show a considerable decrease of excited state lifetimes compared to dilute gases. We show, using a novel formalism, that this behaviour can be modeled and explained as superradiance-type decay. In addition, we find that the tendency to decay into the highest-possible frequency channel is reversed as the density increases, and thus long-wavelength decay into the closest lying level is the most probable. [Preview Abstract] |
Friday, May 19, 2006 10:54AM - 11:06AM |
T5.00003: Quadrupole Transitions to Rydberg States in an Ultracold $^{85}$Rb Gas D. Tong, S.M. Farooqi, E.G.M van Kempen, E.E. Eyler, P.L. Gould We report the observation of dipole-forbidden, but quadrupole-allowed, transitions to Rydberg states in $^{85}$Rb. Using pulsed UV excitation ($\lambda$ = 297 nm) of ultracold atoms in a MOT, we are able to drive 5$s \rightarrow nd$ quadrupole (E2) transitions. We show that these transitions are one-photon excitations and give evidence that they are not caused by stray-field induced Stark-mixing. These transitions are observed over the range $n$=28 to $n$=50. We will give the measured E1/E2 transition strength ratio strength at various principal quantum numbers $n$. We will also report our experimental measurements of the $np$ fine-structure transition strength ratio for principal quantum number up to $n$=70. [Preview Abstract] |
Friday, May 19, 2006 11:06AM - 11:18AM |
T5.00004: Van-der-Waals shifts of rubidium Rydberg states Tara Cubel Liebisch, Aaron Reinhard, Brenton Knuffman, Paul Berman, Georg Raithel We present calculations of van der Waals energy shifts of Rb Rydberg-atom pairs for different quantum numbers n, l, j and m$_{\rm j}$, taking into account a large number of perturbing states. For D$_{5/2}$-states we find that over the range of 54 $<$ n $<$ 86 the van-der-Waals shift scaled by $R^6/n^{11}$ is nearly constant, and that the shift does not vary by more than $50\%$ as a function of the relative atomic orientation. This result is consistent with recent experimental work, in which we have studied the effect of a Rydberg-excitation blockade on the probability distribution of the number of Rydberg atoms detected in small atomic ensembles. In these experiments it was found that the counting statistics is sub-poissonian, and that its Mandel Q-parameter exhibits a smooth dependence on n. The calculations further show that the shifts of the D$_{5/2}$, D$_{3/2}$, P$_{3/2}$, P$_{1/2}$ and S$_{1/2}$-levels exhibit qualitatively different behavior. How these differences might effect future experiments will be discussed. [Preview Abstract] |
Friday, May 19, 2006 11:18AM - 11:30AM |
T5.00005: Ionization of an Highly Excited Hydrogen atom in parallel Electric and Magnetic fields T\"urker Top\c cu, Francis Robicheaux In a recent paper, Mitchell {\it et al} [Phys. Rev. Lett. {\bf 92}, 073001 (2004)] investigated the ionization of a classical hydrogen atom in parallel electric and magnetic fields. They reported epistrophic self- similar pulse trains of ionized electrons attributed to the classical chaos induced by the magnetic field. We study hydrogen atom in an excited state with $n\sim 80$ in parallel external fields as an example of an open, chaotic {\it quantum} system in the time domain. We investigate the effect of interference between the outgoing pulse trains which is absent in the classical picture. We look at interference effect as a function of the energy since Schr\"odinger equation does not scale as the classical equations of motion do. We compare and contrast our quantum results with the classical results of Mitchell {\it et al}. [Preview Abstract] |
Friday, May 19, 2006 11:30AM - 11:42AM |
T5.00006: Microwave Ionization of Sodium at High Scaled Frequency Xiaodong Zhang, Thomas Gallagher Microwave ionization at high-scaled frequency (n$^{3}\omega )$ is very interesting because it is the connection between field ionization via MPI (Multi-photon Ionization) to photoionization. We measure the ionization rates for sodium with 12.54GHz and 25.15GHz linearly polarized microwave. With a stray field presented we can only go scaled frequency up to 20 with different field amplitudes and microwave pulse lengths. In general the 50{\%} ionization fields increase with the scaled frequency. There are some persistent structures at scaled-frequency around 7, and the thresholds no longer decrease monotonically with binding energy. These measurements will help us to understand the basic mechanism of microwave ionization at high scaled-frequency. [Preview Abstract] |
Friday, May 19, 2006 11:42AM - 11:54AM |
T5.00007: Probing Time-Dependent Electron Interactions in Double-Rydberg Wavepackets X. Zhang, R.R. Jones Subpicosecond half-cycle electric field pulses (HCPs) have been used as a time-resolved probe of interactions between electrons in a 3-body Coulomb system.We produce double-Rydberg wavepackets (DRWs) using a multi-step, ultrafast, isolated core excitation of ground-state barium atoms.Two laser pulses first create a 5dnd radial wavepacket. At some time within the first Kepler period of the nd Rydberg electron's motion, additional laser pulses excite the 5d core-electron into a superposition of Ba$^{+}$ Ng Rydberg states. Initially, the two electrons in the Ngnd DRW have well defined energies, momenta, and radial positions as they move in singly and doubly-charged Coulomb potentials, respectively.However, the electrons soon become highly correlated as they exchange energy and angular momentum. If left unaltered, the atom eventually autoionizes, creating a free electron and an N'L ionic wavepacket (N' $<$ N).We probe the evolution of the DRW using a HCP that has sufficient strength to impulsively ionize both the initial Ng (ionic) and nd (neutral) wavepackets individually, but insufficient amplitude to efficiently ionize the N'L ions that result from autoionization. We monitor the production of Ba++ ions as a function of the delay between the HCP and the launch of the Ng ionic wavepacket to probe the time-dependent energy-exchange between the two electrons. Classical trajectory Monte Carlo simulations aid in the interpretation of our experimental results. This work has been supported by the NSF. [Preview Abstract] |
Friday, May 19, 2006 11:54AM - 12:06PM |
T5.00008: Orbital dynamics of two-electron atoms in a static electric field probed by scaled energy spectroscopy J. Murray-Krezan, J. Kelly, M.R. Kutteruf, R.R. Jones Photoabsorption spectra for Ba and Ca Rydberg atoms are measured as a continuous function of electric field strength and electron energy. In both Ba and Ca, the singly-excited $msnd$ series are strongly perturbed by doubly-excited configurations. Using scaled energy recurrence spectroscopy, we investigate the dynamical signatures associated with the spectral variations observed in perturbed Rydberg series, namely oscillator strength modulation and energy-dependent quantum defects. In Ca, small shifts in the Kepler period, conspicuous at large action are attributed to the broad $3d5s$ and $3d3d$ perturbing resonances. In Ba, splittings in the primary recurrence peaks are observed only if the recurrence spectra are measured at energies near the narrow $5d7d$ perturber. These splittings reflect the time delay between electron scattering into and back out of the doubly-excited configuration and are consistent with measurements by Bates \textit{et al.}[Phys. Rev. A \textbf{64}, 033409 (2001)]. Our observations suggest that, in general, the dynamical consequences of interactions between low angular momentum. This work has been supported by the NSF. [Preview Abstract] |
Friday, May 19, 2006 12:06PM - 12:18PM |
T5.00009: Coherent population transfer by multiphoton adiabatic rapid pasasage H. Maeda, J.H. Gurian, D.V.L. Norum, T.F. Gallagher Coherent population transfer in an atom through a range of states using a sequence of adiabatic rapid passage by single-photon resonances is well known, and it requires the frequency sweep match the changing the frequencies of the atomic transition [1]. The same population transfer can be effected via single multiphoton adiabatic rapid passage, which requires only a small frequency sweep if it is possible to select desired multiphoton transition from the many possible other transitions. In the present study we report observation of population transfer between Rydberg states of atomic Li in the range of $n=70\sim 90$ by high order ($\geq 11$) multiphoton adiabatic rapid passage using a frequency chirped microwave pulse. This work has been supported by the NSF. [1] H. Maeda, D.V.L. Norum, and T.F. Gallagher, Science {\bf 307}, 1757 (2005). [Preview Abstract] |
Friday, May 19, 2006 12:18PM - 12:30PM |
T5.00010: Observing angular precession of a Rydberg wave packet due to spin-orbit coupling by orthogonal polarized half-cycle pulses Haidan Wen, Santosh Pisharody, Joel Murray, Philip Bucksbaum We investigate the response of an $np$ Rydberg wave packet to orthogonal polarized half-cycle pulses(HCPs) over the course of its field free evolution. The population redistribution from $p$ to $s$ states is highly sensitive to the polarization of HCPs and changes with the precession of the electron orbits due to spin-orbit coupling. The selection rules of HCP redistribution are obtained and an intuitive classical interpretation is given. [Preview Abstract] |
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