Bulletin of the American Physical Society
41st Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 55, Number 5
Tuesday–Saturday, May 25–29, 2010; Houston, Texas
Session Q1: Focus Session: Rydberg Atoms and Molecules |
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Chair: James Shaffer, University of Oklahoma Room: Imperial East |
Friday, May 28, 2010 8:00AM - 8:12AM |
Q1.00001: Observation of Rydberg excitation blockade effects in strongly magnetized atom clouds E. Paradis, K.C. Younge, S. Zigo, G. Raithel We report on observations of a Rydberg excitation blockade within a strong magnetic field (B = 2.6 T). In this system, either permanent electric quadrupole moments or induced electric dipole moments can provide a strong interaction between neighboring Rydberg atoms, leading to an excitation blockade. The diamagnetic Rydberg states generated by the high-magnetic-field are well suited for this research because they are non-degenerate and have large oscillator strengths for photo-excitation. Rydberg states of laser-cooled Rb atoms are populated using narrow-band laser excitation ($<$ 5 MHz, variable pulse width). The blockade is measured through saturation of the observed number of Rydberg excitations as a function of laser power. The high-magnetic-field setup also affords high spatial resolution when reading out the Rydberg excitations present in the sample. This enables us to search for deviations of the spatial distribution of the detected Rydberg excitations from random ordering. [Preview Abstract] |
Friday, May 28, 2010 8:12AM - 8:42AM |
Q1.00002: Charge, density and electron temperature in a molecular ultracold plasma Invited Speaker: The double-resonant laser excitation of nitric oxide, cooled to 1 K in a seeded supersonic molecular beam, yields a gas of $\approx$10$^{12}$ molecules cm$^{-3}$ in a single selected Ryberg state. This population evolves to produce prompt free electrons and a durable cold quasineutral plasma of electrons and intact NO$^{+}$ ions. This system shows some properties of a correlated electron fluid. For example, the plasma expands at a small but measurable rate that accords with the Vlasov equations for an initial electron temperature of $T_{e} \approx$ 7~K. The laser-prepared population of Rydberg molecules releases electrons as it evolves to form an ultracold plasma. The size of this prompt signal, compared with one extracted from the plasma by the subsequent application of a pulsed electric field, determines the absolute magnitude of the plasma charge. This information, combined with the number-density of ions, supports a simple thermochemical model that explains the evolution of the plasma to an ultracold electron temperature. [Preview Abstract] |
Friday, May 28, 2010 8:42AM - 8:54AM |
Q1.00003: Observation of Controllable Excitation Suppression in Cold $^{87}$Rb Rydberg Atoms J.E. Johnson, I. Arakelyan, Tao Hong, S.L. Rolston Cold Rydberg atoms in ensembles and optical lattices offer the opportunity to study dipolar matter with controllable dipole-dipole interactions (DDIs). Varying an applied static electric field allows the excitation of Rydberg atoms ranging from those with no dipole moments to large permanent dipoles, which should greatly affect interactions within the sample. We have observed increased suppression of the CW excitation of a magneto-optical trap (MOT) of $^{87}$Rb atoms to the 56S$_{1/2}$ Rydberg state as an applied external static electric field is increased. As the field increases, the atom-atom interactions transition from Van der Waals to dipole-dipole. The longer-range dipolar interaction should be more effective in blockading excitation of closely space atom pairs, reducing the excitation rate as observed. [Preview Abstract] |
Friday, May 28, 2010 8:54AM - 9:06AM |
Q1.00004: Probing Coherence in a Cold Rydberg Gas M.R. Kutteruf, R.R. Jones We have used pulsed electric-field sequences to probe the coherence of dipole-dipole interactions in a MOT. Nanosecond dye lasers excite Rb atoms to the $\vert $25s$_{1/2}>$ and $\vert $33s$_{1/2}>$ states in an electric field. The field tunes the atoms so that the energy difference between $\vert $25s$_{1/2}>\vert $33s$_{1/2}>$ and $\vert $24p$_{1/2}>\vert $34p$_{3/2}>$ atom pairs is $\Delta $. For typical separations, the dipole-dipole coupling between atoms enables coherent population transfer from $\vert $25s$_{1/2}>\vert $33s$_{1/2}>$ to $\vert $24p$_{1/2}>\vert $34p$_{3/2}>$ at a rate comparable to $\Delta $.After a time T, an electric field step diabatically tunes the pair energy splitting to -$\Delta $. The atoms interact for an additional time T and the population in the $\vert $24p$_{1/2}>\vert $34p$_{3/2}>$ state is measured. The pulse sequence enhances the $\vert $24p$_{1/2}>\vert $34p$_{3/2}>$ population relative to that obtained in a time 2T at fixed detuning, +/-$\Delta $. Sequences involving multiple resonance traversals lead to further enhancement, indicating that this effect is due to the coherence of the dipole-dipole interaction rather than excitation of different sets of atoms in the ensemble. The enhancement decays as T approaches several microseconds. On this time scale, atomic motion may play a substantive role. This work is supported by NSF and AFOSR. [Preview Abstract] |
Friday, May 28, 2010 9:06AM - 9:18AM |
Q1.00005: Strong coherent coupling of many levels across the ionization limit via 17 and 36 GHz microwave fields Joshua Gurian, K. Richard Overstreet, Haruka Maeda, Thomas Gallagher It has recently been proposed that microwave ionization of Rydberg atoms at frequencies above the classical Kepler frequency can be described by a dynamic Anderson localization model crossing over to a Fermi's Golden Rule approach at the photoionization limit. Here we present results that indicate 17 and 36 GHz microwave ionization is instead best described by a strong coherent electric dipole coupling of levels both above and below the ionization limit. Below the ionization limit, the requisite fields for 50\% multiphoton ionization is similar to the single photon photoionization 50\% threshold field. The coherent coupling of states continues smoothly across the ionization limit, manifesting itself in above threshold ionization. The above threshold microwave recombination to bound Rydberg states can be well described by a simple classical model. [Preview Abstract] |
Friday, May 28, 2010 9:18AM - 9:48AM |
Q1.00006: Cooperative optical non-linearity using Rydberg atoms Invited Speaker: Strong dipole-dipole interactions between Rydberg atoms result in an energy level spacing that is anharmonic in the photon number (analogous to the strong coupling regime in cavity QED). This anharmonicity scales with the strength of the interactions and hence the interatomic spacing. This gives rise to a cooperative optical response where the state of each atom modifies the behaviour of its nearest neighbours in a significant way. Consequently the optical response becomes a non-linear function of both the incident optical field and the atomic density. We report on the experimental observation of this cooperative optical non-linearity [1] and discuss potential applications to single photon gates. \\[4pt] [1] J. D. Pritchard {\it et al}. arXiv0911:3523 [Preview Abstract] |
Friday, May 28, 2010 9:48AM - 10:00AM |
Q1.00007: Multiphoton population transfer in a kicked Rydberg atom: adiabatic rapid passage by separatrix crossing Turker Topcu, Francis Robicheaux Following an experimental observation [1], a recent simulation [2] has showed that efficient population transfer can be achieved through adiabatic chirping of a microwave pulse through a 10-photon resonance connecting two Rydberg states with $n=72$, $\ell=1$ and $n$$\sim$82. These simulations have revealed that this population transfer is essentially a classical transition caused by separatrix crossing in the classical phase space. Here we present results of our fully three dimensional quantum and classical simulations of coherent multiphoton population transfer in {\it kicked} Li atom in a Rydberg state. We were able to achieve $\sim$76\% population transfer from 40p to 46p state in Li through a 6-photon resonance condition and contrast our results with those when the transition is driven by microwaves. We further discuss the case when the atom starts out from a Stark state in conjunction with the $l$-distribution of the transferred population. We use a one-dimensional classical model to investigate the classical processes taking place in the phase space and find that the same separatrix crossing mechanism observed in microwave transitions is also responsible for the transition when the atom is kicked. \\[4pt] [1] H. Maeda {\it et al.}, Phys. Rev. Lett. {\bf 96}, 073002 (2006).\\[0pt] [2] T. Topcu and F. Robicheaux, J. Phys. B {\bf 42}, 044014 (2009). [Preview Abstract] |
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