82 research outputs found
Atom lithography using MRI-type feature placement
We demonstrate the use of frequency-encoded light masks in neutral atom
lithography. We demonstrate that multiple features can be patterned across a
monotonic potential gradient. Features as narrow as 0.9 microns are fabricated
on silicon substrates with a metastable argon beam. Internal state manipulation
with such a mask enables continuously adjustable feature positions and feature
densities not limited by the optical wavelength, unlike previous light masks.Comment: 4 pages, 4 figure
Enhanced Pauli blocking of light scattering in a trapped Fermi gas
Pauli blocking of spontaneous emission by a single excited-state atom has
been predicted to be dramatic at low temperature when the Fermi energy
exceeds the recoil energy . The photon scattering
rate of a ground-state Fermi gas can also be suppressed by occupation of the
final states accessible to a recoiling atom, however suppression is diminished
by scattering events near the Fermi edge. We analyze two new approaches to
improve the visibility of Pauli blocking in a trapped Fermi gas. Focusing the
incident light to excite preferentially the high-density region of the cloud
can increase the blocking signature by 14%, and is most effective at
intermediate temperature. Spontaneous Raman scattering between imbalanced
internal states can be strongly suppressed at low temperature, and is
completely blocked for a final-state in the
high imbalance limit.Comment: 12 pages, 8 figures. v4: to appear in Journal of Physics B: Atomic,
Molecular, and Optical Physic
Spin Rotations in a Bose-Einstein Condensate Driven by Counterflow and Spin-independent Interactions
We observe spin rotations caused by atomic collisions in a non-equilibrium
Bose-condensed gas of Rb. Reflection from a pseudomagnetic barrier
creates counterflow in which forward- and backward-propagating matter waves
have partly transverse spin directions. Even though inter-atomic interaction
strengths are state-independent, the indistinguishability of parallel spins
leads to spin dynamics. A local magnetodynamic model, which captures the
salient features of the observed spin textures, highlights an essential
connection between four-wave mixing and collisional spin rotation. The observed
phenomenon has previously been thought to exist only in nondegenerate gases;
our observations and model clarify the nature of these effective-magnetic spin
rotations.Comment: 13 pages, 7 figure
Transverse Demagnetization Dynamics of a Unitary Fermi Gas
Understanding the quantum dynamics of strongly interacting fermions is a
problem relevant to diverse forms of matter, including high-temperature
superconductors, neutron stars, and quark-gluon plasma. An appealing benchmark
is offered by cold atomic gases in the unitary limit of strong interactions.
Here we study the dynamics of a transversely magnetized unitary Fermi gas in an
inhomogeneous magnetic field. We observe the demagnetization of the gas, caused
by diffusive spin transport. At low temperatures, the diffusion constant
saturates to the conjectured quantum-mechanical lower bound ,
where is the particle mass. The development of pair correlations,
indicating the transformation of the initially non-interacting gas towards a
unitary spin mixture, is observed by measuring Tan's contact parameter.Comment: 8 pages, 6 figures. Accepted versio
Intraosseous Hemangioma of the Left Parietal Bone
Background: A 26-year-old male presented with pain in his left tibia. Ultrasonography revealed no abnormalities. Tc-99m-bonescan was requested to rule out stress fracture. The scan confirmed the presence of a left tibial stress fracture, as well as an enhancing lesion in the left parietal bone. The patient had no neurological symptoms
Breakdown of time-dependent mean-field theory for a one-dimensional condensate of impenetrable bosons
We show that the time-dependent nonlinear Schrodinger equation of mean-field
theory has limited utility for a one-dimensional condensate of impenetrable
bosons. Mean-field theory with its associated order parameter predicts
interference between split condensates that are recombined, whereas an exact
many-body treatment shows minimal interference.Comment: 4 pages, 2 EPS figure
Spontaneous separation of two-component Fermi gases in a double-well trap
The two-component Fermi gas in a double-well trap is studied using the
density functional theory and the density profile of each component is
calculated within the Thomas-Fermi approximation. We show that the two
components are spatially separate in the two wells once the repulsive
interaction exceeds the Stoner point, signaling the occurrence of the
ferromagnetic transition. Therefore, the double-well trap helps to explore
itinerant ferromagnetism in atomic Fermi gases, since the spontaneous
separation can be examined by measuring component populations in one well.Comment: 6 pages, 6 figures, to appear in ep
Low-temperature, high-density magneto-optical trapping of potassium using the open 4S-5P transition at 405 nm
We report the laser cooling and trapping of neutral potassium on an open
transition. Fermionic 40K is captured using a magneto-optical trap (MOT) on the
closed 4S-4P transition at 767 nm and then transferred, with unit efficiency,
to a MOT on the open 4S-5P transition at 405 nm. Because the 5P state has a
smaller line width than the 4P state, the Doppler limit is reduced. We observe
temperatures as low as 63(6) microkelvin, the coldest potassium MOT reported to
date. The density of trapped atoms also increases, due to reduced temperature
and reduced expulsive light forces. We measure a two-body loss coefficient of 2
x 10^-10 cm^3/s, and estimate an upper bound of 8x10^-18 cm^2 for the
ionization cross section of the 5P state at 405 nm. The combined temperature
and density improvement in the 405 nm MOT is a twenty-fold increase in phase
space density over our 767 nm MOT, showing enhanced pre-cooling for quantum gas
experiments. A qualitatively similar enhancement is observed in a 405 nm MOT of
bosonic 41K.Comment: 8 pages, 8 figures, 1 tabl
Measurement of one-particle correlations and momentum distributions for trapped 1D gases
van Hove's theory of scattering of probe particles by a macroscopic target is
generalized so as to relate the differential cross section for atomic ejection
via stimulated Raman transitions to one-particle momentum-time correlations and
momentum distributions of 1D trapped gases. This method is well suited to
probing the longitudinal momentum distributions of 1D gases in situ, and
examples are given for bosonic and fermionic atoms.Comment: 4 pages, 2 .eps figure
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