297 research outputs found
Sub-Natural-Linewidth Quantum Interference Features Observed in Photoassociation of a Thermal Gas
By driving photoassociation transitions we form electronically excited
molecules (Na) from ultra-cold (50-300 K) Na atoms. Using a second
laser to drive transitions from the excited state to a level in the molecular
ground state, we are able to split the photoassociation line and observe
features with a width smaller than the natural linewidth of the excited
molecular state. The quantum interference which gives rise to this effect is
analogous to that which leads to electromagnetically induced transparency in
three level atomic systems, but here one of the ground states is a
pair of free atoms while the other is a bound molecule. The linewidth is
limited primarily by the finite temperature of the atoms.Comment: 4 pages, 5 figure
All-optical generation and photoassociative probing of sodium Bose-Einstein condensates
We demonsatrate an all optical technique to evaporatively produce sodium
Bose-Einstein condensates (BEC). We use a crossed-dipole trap formed from light
near 1060 nm, and a simple ramp of the intensity to force evaporation. In
addition, we introduce photoassociation as diagnostic of the trap loading
process, and show that it can be used to detect the onset of Bose-Einstein
condensation. Finally, we demonstrate the straightforward production of
multiple traps with condensates using this technique, and that some control
over the spinor state of the BEC is achieved by positioning the trap as well.Comment: 8 pages, 10 figure
Towards a guided atom interferometer based on a superconducting atom chip
We evaluate the realization of a novel geometry of a guided atom
interferometer based on a high temperature superconducting microstructure. The
interferometer type structure is obtained with a guiding potential realized by
two current carrying superconducting wires in combination with a closed
superconducting loop sustaining a persistent current. We present the layout and
realization of our superconducting atom chip. By employing simulations we
discuss the critical parameters of the interferometer guide in particular near
the splitting regions of the matter waves. Based on measurements of the
relevant chip properties we discuss the application of a compact and reliable
on-chip atom interferometer.Comment: 14 pages, 7 figures, accepted for New Journal of Physic
A Search for Extraplanar Dust in Nearby Edge-On Spirals
We present high resolution BV images of 12 edge-on spiral galaxies observed
with the WIYN 3.5-m telescope. These images were obtained to search for
extraplanar (|z| > 0.4 kpc) absorbing dust structures similar to those
previously found in NGC 891 (Howk & Savage 1997). Our imaged galaxies include a
sample of seven massive L_*-like spiral galaxies within D<25 Mpc that have
inclinations i > 87 deg from the plane of the sky. We find that five of these
seven systems show extraplanar dust, visible as highly-structured absorbing
clouds against the background stellar light of the galaxies. The more prominent
structures are estimated to have associated gas masses >10^5 M_sun; the implied
potential energies are > 10^(52) ergs. All of the galaxies in our sample that
show detectable halpha emission at large z also show extraplanar dust
structures. None of those galaxies for which extraplanar halpha searches were
negative show evidence for extensive high-z dust. The existence of extraplanar
dust is a common property of massive spiral galaxies. We discuss several
mechanisms for shaping the observed dust features, emphasizing the possibility
that these dusty clouds represent the dense phase of a multiphase medium at
high-z in spiral galaxies. The correlation between high-z dust and extraplanar
Halpha emission may simply suggest that both trace the high-z interstellar
medium in its various forms (or phases), the existence of which may ultimately
be driven by vigorous star formation in the underlying disk. (Abstract
abridged)Comment: 26 pages; 15 jpeg figures. To appear in The Astronomical Journal, May
1999. Gzipped tar files of high-resolution figures in postscript and jpeg
formats are available at
http://www.astro.wisc.edu/~howk/Papers/papers.html#surve
Wave Packet Echoes in the Motion of Trapped Atoms
We experimentally demonstrate and systematically study the stimulated revival
(echo) of motional wave packet oscillations. For this purpose, we prepare wave
packets in an optical lattice by non-adiabatically shifting the potential and
stimulate their reoccurence by a second shift after a variable time delay. This
technique, analogous to spin echoes, enables one even in the presence of strong
dephasing to determine the coherence time of the wave packets. We find that for
strongly bound atoms it is comparable to the cooling time and much longer than
the inverse of the photon scattering rate
Cubic optical nonlinearity of free electrons in bulk gold
A fast (τresponse <90 fs) free-electron spin-flipping frequency-degenerate nonlinearity with a significant value of |χ(3)xxyy(ω,ω,ω,-ω) χ(3)xyyx(ω,ω,ω,-ω)| ~ 10-8 esu has been observed in bulk gold at 1260 nm by use of a new pump-probe polarization-sensitive technique. <br/
Coherent manipulation of atomic qubits in optical micropotentials
We experimentally demonstrate the coherent manipulation of atomic states in
far-detuned dipole traps and registers of dipole traps based on two-dimensional
arrays of microlenses. By applying Rabi, Ramsey, and spin-echo techniques, we
systematically investigate the dephasing mechanisms and determine the coherence
time. Simultaneous Ramsey measurements in up to 16 dipole traps are performed
and proves the scalability of our approach. This represents an important step
in the application of scalable registers of atomic qubits for quantum
information processing. In addition, this system can serve as the basis for
novel atomic clocks making use of the parallel operation of a large number of
individual clocks each remaining separately addressable.Comment: to be published in Appl. Phys.
The Nature of Composite LINER/HII Galaxies, As Revealed from High-Resolution VLA Observations
A sample of 37 nearby galaxies displaying composite LINER/HII and pure HII
spectra was observed with the VLA in an investigation of the nature of their
weak radio emission. The resulting radio contour maps overlaid on optical
galaxy images are presented here, together with an extensive literature list
and discussion of the individual galaxies. Radio morphological data permit
assessment of the ``classical AGN'' contribution to the global activity
observed in these ``transition'' LINER galaxies. One in five of the latter
objects display clear AGN characteristics: these occur exclusively in
bulge-dominated hosts.Comment: 31 pages, 27 figures, accepted by ApJ
Radio continuum observations of the Virgo cluster spiral NGC 4522 The signature of ram pressure
Radio continuum observations at 20 and 6 cm of the highly inclined Virgo
spiral galaxy NGC 4522 are presented. Both, 20 and 6 cm total emission
distributions are asymmetric with an extended component to the west where
extraplanar atomic gas and Halpha emission are found. The 6 cm polarized
emission is located at the eastern edge of the galactic disk. Its peak is
located about 1 kpc to the east of the total emission peak. We argue that this
phenomena is a characteristic feature for cluster galaxies which are
experiencing significant pressure from the intracluster medium. The degree of
polarization decreases from the east to the west. The flattest spectral index
between 20 and 6 cm coincides with the peak of the 6 cm polarized emission.
These findings are consistent with a picture of a large scale shock due to ram
pressure located at the east of the galaxy where cosmic rays are accelerated.
We conclude that it is likely that the galaxy experiences active ram pressure.Comment: 11 pages, 11 figures. Accepted for publication in A
Image equalisation using an external brightness reference
After more than ten years in orbit at Mars, the coverage from the High
Resolution Stereo Camera (HRSC) on the European Space Agency’s Mars Express is
sufficient to begin constructing mosaic products on a global scale. We
describe our systematic processing procedure and, in particular, the technique
used to bring images affected by atmospheric dust into visual consistency with
the mosaic. We outline how the same method is used to produce a relative
colour mosaic which shows local colour differences. We demonstrate the results
and show that the techniques may also be applied to images from other orbital
cameras
- …