### Session U4: Focus Session: Cold Rydberg Gases

Chair: Michael Noel, Bryn Mawr College
Room: A704

 Friday, June 17, 2011 10:30AM - 11:00AM U4.00001: Rydberg-dressed Atoms Invited Speaker: Steve Rolston Rydberg atoms are showing promise to create quantum logic gates based on their long-range interactions that cause blockade and allow for conditional logic. They may also be useful for applications in many-body physics, creating systems with long-range, anisotropic interactions. Although typical Rydberg-Rydberg interactions are orders of magnitude too strong to be used in this application, atoms that are coherent admixtures of a ground state and a small amount of Rydberg character, Rydberg-dressed atoms,'' allow for suitably tunable long-range interactions. I will discuss challenges and prospects for creating and using Rydberg-dressed atoms. Friday, June 17, 2011 11:00AM - 11:30AM U4.00002: Coherent Rydberg Excitation in Thermal Microcells Invited Speaker: Robert Loew In order to create quantum devices based on the Rydberg blockade mechanism, it is necessary to have a confinement of the excitation volume to less than the blockade radius in a frozen gas of atoms; i.e. the excitation times need to be shorter than the timescales of the respective dephasing mechanisms. While ultracold gases seem to be the obvious choice, our approach utilizes thermal atomic vapor in small glass cells [1] which offer multiple advantages like good optical access and scalability. Such a system can be realized by confining the atoms to geometries in the micron regime. Decoherence effects like resonant interactions of the Rydberg atoms with polaritonic excitations in the glass have been studied and can be minimized by the appropriate choice of Rydberg states [2]. Using a bandwidth-limited pulsed laser system for the Rydberg excitation we observe coherent Rabi oscillations on the nanosecond timescale. In collaboration with Renate Daschner, Harald Kuebler, Bernhard Huber, Thomas Baluktsian, Andreas Koelle, James Shaffer, and Tilman Pfau. \\[4pt] [1] Baluktsian, T., et. al. Opt. Lett. 35, 1950 (2010) \\[0pt] [2] K\"{u}bler, H., et. al. Nature Photon. 4, 112-116 (2010) Friday, June 17, 2011 11:30AM - 11:42AM U4.00003: Enhancement of Rydberg-atom trapping efficiency in a ponderomotive optical lattice using lattice translations Sarah E. Anderson , Georg Raithel We present experimental results on the one-dimensional trapping of cold $^{85}$Rb Rydberg atoms in a ponderomotive optical lattice of laser wavelength 1064~nm. The challenge associated with this red-detuned lattice is that locations of potential minima in the ground state correspond to potential maxima in the Rydberg state. When ground state atoms in the lattice are excited to Rydberg states, they are located near potential maxima, and consequently trapping is limited. We present a method to overcome this difficulty by translating the lattice by $\lambda /4$ immediately after excitation, thus bringing the locations of the potential minima in the Rydberg state to the locations of the atoms. We report experimental microwave spectroscopy results that confirm this lattice phase-shift technique as an effective method to enhance the lattice's trapping efficiency. Friday, June 17, 2011 11:42AM - 11:54AM U4.00004: Dipole-dipole broadening of \textit{ns-np} Rydberg transitions Hyunwook Park , Tom Gallagher Using a microwave resonance technique we have measured the dipole-dipole broadening of \textit{ns-np} transitions of 300\textit{$\mu$K} Rb Rydberg atoms. The experiment has been done with $n$=28, 29, 34, 39, 44, and 50 states, all of which exhibit a linear increase in the linewidth with atomic density. The broadening rate varies as $n^{4}$, which is to be expected since \textit{$\mu$}$_{sp}\approx n^{2}$. The broadening is not Lorentzian, but results in asymmetric, cusp shaped resonances. To reproduce the observed resonances we have developed a molecular model in which pairs of atoms are driven from the \textit{nsns} to the \textit{nsnp/npns} states, which have a dipole-dipole energy splitting which scale as 1/R$^{3}$. We calculate the dipole-dipole splitting of the \textit{nsnp/npns} states, and the transition strengths from the nsns states with the spins of the two electrons included. The results, averaged over the density of Rydberg atoms, yield asymmetric cusp shaped resonances, which agree very well with the observations. Friday, June 17, 2011 11:54AM - 12:06PM U4.00005: Probing RF electric fields with Rydberg atoms Arne Schwettmann , Jonathon Sedlacek , Cale Gentry , James Shaffer Using an atom chip setup, we investigate the use of high-lying Rb Rydberg atoms (n$>$30) as sensitive electric field sensors. Rydberg atoms are sensitive to electric fields due to their large polarizability and the large transition dipole moments between nearby Rydberg states. We excite ultracold Rydberg atoms in a magnetic wire-trap. The magnetic trap is loaded from a mirror magneto-optical trap. We then probe the interaction of Rydberg atoms with small RF electric fields using an EIT scheme. The presence of very small external RF fields modifies the EIT line shape significantly, because the RF field couples strongly to the transitions between Rydberg levels. In future experiments, it will be possible to miniaturize this setup for use as a sensor, by using room temperature atoms in microcells. Friday, June 17, 2011 12:06PM - 12:18PM U4.00006: Rydberg Interactions On An Atom Chip Robert Spreeuw , Vanessa Leung , Atreju Tauschinsky , Ben van Linden van den Heuvell We report on our experiments aimed at developing a scalable quantum information platform based on a two-dimensional lattice of microscopic traps on a magnetic-film atom chip. Previously we have shown that a few hundred microtraps, each holding tens to several hundred $^{87}$Rb atoms, can be individually resolved, optically addressed, and spatially manipulated as a shift register [1]. Our current goal is to use the dipole blockade of Rydberg atoms to mediate switchable, long-range interaction between mesoscopic ensembles on the lattice. Through spectroscopic studies with electromagnetically induced transparency (EIT), we characterize the level shifts and broadenings of the Rydberg states in the proximity of the surface [2]. Our results open the way to studies of dipolar physics, collective excitations, quantum metrology, and quantum information processing involving interacting Rydberg excited atoms on atom chips. [1] Whitlock, S., R. Gerritsma, T. Fernholz, and R.J.C. Spreeuw, \textit{Two-dimensional array of micro-traps with atomic shift register on a chip}, New Journal of Physics \textbf{11}, 023021 (2009) [2] Tauschinsky, A., R. M. T. Thijssen, S. Whitlock, H. B. van Linden van den Heuvell, and R. J. C. Spreeuw, \textit{Spatially resolved excitation of Rydberg atoms and surface effects on an atom chip}, Phys. Rev. A \textbf{81}, 063411 (2010) Friday, June 17, 2011 12:18PM - 12:30PM U4.00007: Multi-grid experimental apparatus for the study of ultracold Rydberg-Rydberg interaction Joshua Gurian , Paul Huillery , Yoann Bruneau , Patrick Cheinet , Andrea Fioretti , Daniel Comparat , Pierre Pillet We have designed and constructed a new experimental setup for the study of ultracold Rydberg processes. A cold Cs MOT is centered between four parallel wire mesh grids, with two microchannel plate (MCP) detectors mounted perpendicular to the grids. Use of a phosphor screen behind one of the MCP detectors allows for spatial imaging of the ionized Rydberg atoms. This experimental apparatus allows for the study of both Rydberg many-body physics, as well as ion and electron imaging experiments. By controlling the voltages applied to the grids, ionized Rydberg atoms can be imaged on the MCP. Magnifications greater than ten have been observed, as well as strong focusing. We present initial results from this new experimental setup.