10,625 research outputs found
Observation of a resonant four-body interaction in cold cesium Rydberg atoms
Cold Rydberg atoms subject to long-range dipole-dipole interactions represent
a particularly interesting system for exploring few-body interactions and
probing the transition from 2-body physics to the many-body regime. In this
work we report the direct observation of a resonant 4-body Rydberg interaction.
We exploit the occurrence of an accidental quasi-coincidence of a 2-body and a
4-body resonant Stark-tuned Forster process in cesium to observe a resonant
energy transfer requiring the simultaneous interaction of at least four
neighboring atoms. These results are relevant for the implementation of quantum
gates with Rydberg atoms and for further studies of many-body physics.Comment: 5 pages, 5 figure
Dynamical properties of dipolar Fermi gases
We investigate dynamical properties of a one-component Fermi gas with
dipole-dipole interaction between particles. Using a variational function based
on the Thomas-Fermi density distribution in phase space representation, the
total energy is described by a function of deformation parameters in both real
and momentum space. Various thermodynamic quantities of a uniform dipolar Fermi
gas are derived, and then instability of this system is discussed. For a
trapped dipolar Fermi gas, the collective oscillation frequencies are derived
with the energy-weighted sum rule method. The frequencies for the monopole and
quadrupole modes are calculated, and softening against collapse is shown as the
dipolar strength approaches the critical value. Finally, we investigate the
effects of the dipolar interaction on the expansion dynamics of the Fermi gas
and show how the dipolar effects manifest in an expanded cloud.Comment: 14 pages, 8 figures, submitted to New J. Phy
The Effects of Age on Red Giant Metallicities Derived from the Near-Infrared Ca II Triplet
We have obtained spectra with resolution 2.5 Angstroms in the region
7500-9500 Angstroms for 116 red giants in 5 Galactic globular clusters and 6
old open clusters (5 with published metallicities, and one previously
unmeasured). The signal-to-noise ranges from 20 to 85. We measure the
equivalent widths of the infrared Ca II triplet absorption lines in each stars
and compare to cluster metallicities taken from the literature. With globular
cluster abundances on the Carretta & Gratton scale, and open cluster abundances
taken from the compilation of Friel and collaborators, we find a linear
relation between [Fe/H] and Ca II line strength spanning the range -2 < [Fe/H]
< -0.2 and ages from 2.5 - 13 Gyr. No evidence for an age effect on the
metallicity calibration is observed. Using this calibration, we find the
metallicity of the old open cluster Trumpler 5 to be [Fe/H] = -0.56 +/-0.11.
Considering the 10 clusters of known metallicity shifted to a common distance
and reddening, we find that the additional metallicity error introduced by the
variation of horizontal branch/red clump magnitude with metallicity and age is
of order +/-0.05 dex, which can be neglected in comparison to the intrinsic
scatter in our method. The results are discussed in the context of abundance
determinations for red giants in Local Group galaxies.Comment: Accepted by MNRAS; 21 pages in LaTeX MNRAS style, 6 tables, 6 figure
Using Three-Body Recombination to Extract Electron Temperatures of Ultracold Plasmas
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.Comment: 5 pages, 3 figure
Effect of edge transmission and elastic scattering on the resistance of magnetic barriers
Strong magnetic barriers are defined in two-dimensional electron gases by
magnetizing dysprosium ferromagnetic platelets on top of a Ga[Al]As
heterostructure. A small resistance across the barrier is observed even deep
inside the closed regime. We have used semiclassical simulations to explain
this behavior quantitatively in terms of a combined effect of elastic electron
scattering inside the barrier region and E x B drift at the intersection of the
magnetic barrier with the edge of the Hall bar.Comment: 7 pages 4 figure
Spectral properties of a Rydberg atom immersed in a Bose-Einstein condensate
The electronic spectrum of a Rydberg atom immersed in a Bose-Einstein
condensate is investigated. The Heisenberg equations of motions for the
condensate and the Rydberg atom are derived. Neglecting the backaction of the
Rydberg atom onto the condensate decouples the equations describing the
condensate and Rydberg atom. In this case the spectral structure of the Rydberg
atom is completely determined by an effective potential which depends on the
density distribution of the condensate. We study the spectral properties for
the situation of an isotropic harmonic and anharmonic as well as axially
symmetric confinement. In the latter case an intriguing analogy with Rydberg
atoms in magnetic fields is encountered
Interactions Between Rydberg-Dressed Atoms
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.Comment: 5 pages, 7 figures; Accepted to Phys. Rev. A, 18 Aug. 201
Yosemite Conference on Ionospheric Plasma in the Magnetosphere: Sources, Mechanisms and Consequences, meeting report
The sixth biennial Yosemite topical conference and the first as a Chapman Conference was held on February 3 to 6, 1986. Due to the recent changes in our perception of the dynamics of the ionospheric/magnetospheric system, it was deemed timely to bring researchers together to discuss and contrast the relative importance of solar versus terrestrial sources of magnetospheric plasma. Although the solar wind was once thought to dominate the supply of plasma in the Earth's magnetosphere, it is now thought that the Earth's ionosphere is a significant contributor. Polar wind and other large volume outflows of plasma have been seen at relatively high altitudes over the polar cap and are now being correlated with outflows found in the magnetotail. The auroral ion fountain and cleft ion fountain are examples of ionospheric sources of plasma in the magnetosphere, observed by the Dynamics Explorer 1 (DE 1) spacecraft. The conference was organized into six sessions: four consisting of prepared oral presentations, one poster session, and one session for open forum discussion. The first three oral sessions dealt separately with the three major topics of the conference, i.e., the sources, mechanisms, and consequences of ionospheric plasma in the magnetosphere. A special session of invited oral presentations was held to discuss extraterrestrial ionospheric/magnetospheric plasma processes. The poster session was extended over two evenings during which presenters discussed their papers on a one-on-one basis. The last session of the conferences was reserved for open discussions of those topics or ideas considered most interesting or controversial
Resonant reflection at magnetic barriers in quantum wires
The conductance of a quantum wire containing a single magnetic barrier is
studied numerically by means of the recursive Greens function technique. For
sufficiently strong and localized barriers, Fano - type reflection resonances
are observed close to the pinch-off regime. They are attributed to a
magnetoelectric vortex-type quasibound state inside the magnetic barrier that
interferes with an extended mode outside. We furthermore show that disorder can
substantially modify the residual conductance around the pinch-off regime.Comment: 7 pages, 5 figure
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