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Search Results: 1 - 10 of 479632 matches for " S. L. Rolston "
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Interactions Between Rydberg-Dressed Atoms
J. E. Johnson,S. L. Rolston
Physics , 2010, DOI: 10.1103/PhysRevA.82.033412
Abstract: We examine interactions between atoms continuously and coherently driven between the ground state and a Rydberg state, producing "Rydberg-dressed atoms." Because of the large dipolar coupling between two Rydberg atoms, a small admixture of Rydberg character into a ground state can produce an atom with a dipole moment of a few Debye, the appropriate size to observe interesting dipolar physics effects in cold atom systems. We have calculated the interaction energies for atoms that interact via the dipole-dipole interaction and find that due to blockade effects, the R-dependent two-atom interaction terms are limited in size, and can be R-independent up until the dipolar energy is equal to the detuning. This produces R-dependent interactions different from the expected 1/R^3 dipolar form, which have no direct analogy in condensed matter physics, and could lead to new quantum phases in trapped Rydberg systems.
Electron Evaporation from an Ultracold Plasma in a Uniform Electric Field
K. A. Twedt,S. L. Rolston
Physics , 2010, DOI: 10.1063/1.3466856
Abstract: Electrons in an expanding ultracold plasma are expected to be in quasi-equilibrium, since the collision times are short compared to the plasma lifetime, yet we observe electrons evaporating out as the ion density decreases during expansion. We observe that a small electric field that shifts the electron cloud with respect to the ions increases the evaporation rate. We have calculated the spatial distribution of a zero-temperature electron cloud as a function of applied field and ion density, which is assumed to be Gaussian at all times. This calculation allows us to predict the flux of cold electrons from the plasma at all times, and is in good agreement with our observed electron signal.
Electronic detection of collective modes of an ultracold plasma
K. A. Twedt,S. L. Rolston
Physics , 2011, DOI: 10.1103/PhysRevLett.108.065003
Abstract: Using a new technique to directly detect current induced on a nearby electrode, we measure plasma oscillations in ultracold plasmas, which are influenced by the inhomogeneous and time-varying density and changing neutrality. Electronic detection avoids heating and evaporation dynamics associated with previous measurements and allows us to test the importance of the plasma neutrality. We apply dc and pulsed electric fields to control the electron loss rate and find that the charge imbalance of the plasma has a significant effect on the resonant frequency, in excellent agreement with recent predictions suggesting coupling to an edge mode.
Using Charged Particle Imaging to Study Ultracold Plasma Expansion
X. L. Zhang,R. S. Fletcher,S. L. Rolston
Physics , 2008, DOI: 10.1063/1.3122273
Abstract: We develop a projection imaging technique to study ultracold plasma dynamics. We image the charged particle spatial distributions by extraction with a high-voltage pulse onto a position-sensitive detector. Measuring the 2D width of the ion image at later times (the ion image size in the first 20 $\mu$s is dominated by the Coulomb explosion of the dense ion cloud), we extract the plasma expansion velocity. These velocities at different initial electron temperatures match earlier results obtained by measuring the plasma oscillation frequency. The electron image size slowly decreases during the plasma lifetime because of the strong Coulomb force of the ion cloud on the electrons, electron loss and Coulomb explosion effects.
Observation of an ultracold plasma instability
X. L. Zhang,R. S. Fletcher,S. L. Rolston
Physics , 2008, DOI: 10.1103/PhysRevLett.101.195002
Abstract: We present the first observation of an instability in an expanding ultracold plasma. We observe periodic emission of electrons from an ultracold plasma in weak, crossed magnetic and electric fields, and a strongly perturbed electron density distribution in electron time-of-flight projection images. We identify this instability as a high-frequency electron drift instability due to the coupling between the electron drift wave and electron cyclotron harmonic, which has large wavenumbers corresponding to wavelengths close to the electron gyroradius.
Using Three-Body Recombination to Extract Electron Temperatures of Ultracold Plasmas
R. S. Fletcher,X. L. Zhang,S. L. Rolston
Physics , 2007, DOI: 10.1103/PhysRevLett.99.145001
Abstract: Three-body recombination, an important collisional process in plasmas, increases dramatically at low electron temperatures, with an accepted scaling of T_e^-9/2. We measure three-body recombination in an ultracold neutral xenon plasma by detecting recombination-created Rydberg atoms using a microwave-ionization technique. With the accepted theory (expected to be applicable for weakly-coupled plasmas) and our measured rates we extract the plasma temperatures, which are in reasonable agreement with previous measurements early in the plasma lifetime. The resulting electron temperatures indicate that the plasma continues to cool to temperatures below 1 K.
Manipulation of Single Neutral Atoms in Optical Lattices
Chuanwei Zhang,S. L. Rolston,S. Das Sarma
Physics , 2006, DOI: 10.1103/PhysRevA.74.042316
Abstract: We analyze a scheme to manipulate quantum states of neutral atoms at individual sites of optical lattices using focused laser beams. Spatial distributions of focused laser intensities induce position-dependent energy shifts of hyperfine states, which, combined with microwave radiation, allow selective manipulation of quantum states of individual target atoms. We show that various errors in the manipulation process are suppressed below $10^{-4} $ with properly chosen microwave pulse sequences and laser parameters. A similar idea is also applied to measure quantum states of single atoms in optical lattices.
Adiabaticity and localization in one-dimensional incommensurate lattices
E. E. Edwards,M. Beeler,Tao Hong,S. L. Rolston
Physics , 2008, DOI: 10.1103/PhysRevLett.101.260402
Abstract: We experimentally investigate the role of localization on the adiabaticity of loading a Bose-Einstein condensate into a one-dimensional optical potential comprised of a shallow primary lattice plus one or two perturbing lattice(s) of incommensurate period. We find that even a very weak perturbation causes dramatic changes in the momentum distribution and makes adiabatic loading of the combined lattice much more difficult than for a single period lattice. We interpret our results using a band structure model and the one-dimensional Gross-Pitaevskii equation.
A nanowaveguide platform for collective atom-light interaction
Y. Meng,J. Lee,M. Dagenais,S. L. Rolston
Physics , 2014, DOI: 10.1063/1.4929947
Abstract: We propose a nanowaveguide platform for collective atom-light interaction through evanescent field coupling. We have developed a 1cm-long silicon nitride nanowaveguide can use evanescent fields to trap and probe an ensemble of 87Rb atoms. The waveguide has a sub-micrometer square mode area and was designed with tapers for high fiber-to-waveguide coupling efficiencies at near-infrared wavelengths (750nm to 1100nm). Inverse tapers in the platform adiabatically transfer a weakly guided mode of fiber-coupled light into a strongly guided mode with an evanescent field to trap atoms and then back to a weakly guided mode at the other end of the waveguide. The coupling loss is -1dB per facet (~80% coupling efficiency) at 760nm and 1064nm, which is estimated by a propagation loss measurement with waveguides of different lengths. The proposed platform has good thermal conductance and can guide high optical powers for trapping atoms in ultra-high vacuum. As an intermediate step, we have observed thermal atom absorption of the evanescent component of a nanowaveguide, and have demonstrated the U-wire mirror magneto-optical trap that can transfer atoms to the proximity of the surface.
A single hollow beam optical trap for cold atoms
S. Kulin,S. Aubin,S. Christe,B. Peker,S. L. Rolston,L. A. Orozco
Physics , 2001, DOI: 10.1088/1464-4266/3/6/301
Abstract: We present an optical trap for atoms that we have developed for precision spectroscopy measurements. Cold atoms are captured in a dark region of space inside a blue-detuned hollow laser beam formed by an axicon. We analyze the light potential in a ray optics picture and experimentally demonstrate trapping of laser-cooled metastable xenon atoms.
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