1,593 research outputs found
Feshbach Molecules in a One-dimensional Optical Lattice
We present the theory of a pair of atoms in a one-dimensional optical lattice
interacting via a narrow Feshbach resonance. Using a two-channel description of
the resonance, we derive analytic results for the scattering states inside the
continuum band and the discrete bound states outside the band. We identify a
Fano resonance profile, and the survival probability of a molecule when swept
through the Bloch band of scattering states by varying an applied magnetic
field. We discuss how these results may be used to investigate the importance
of the structured nature of the continuum in experiments.Comment: 4 pages, 3 figure
Two-channel Feshbach physics in a structured continuum
We analyze the scattering and bound state physics of a pair of atoms in a
one-dimensional optical lattice interacting via a narrow Feshbach resonance.
The lattice provides a structured continuum allowing for the existence of bound
dimer states both below and above the continuum bands, with pairs above the
continuum stabilized by either repulsive interactions or their center of mass
motion. Inside the band the Feshbach coupling to a closed channel bound state
leads to a Fano resonance profile for the transmission, which may be mapped out
by RF- or photodissociative spectroscopy. We generalize the scattering length
concept to the one-dimensional lattice, where a scattering length may be
defined at both the lower and the upper continuum thresholds. As a function of
the applied magnetic field the scattering length at either band edge exhibits
the usual Feshbach divergence when a bound state enters or exits the continuum.
Near the scattering length divergences the binding energy and wavefunction of
the weakly bound dimer state acquires a universal form reminiscent of those of
free-space Feshbach molecules. We give numerical examples of our analytic
results for a specific Feshbach resonance, which has been studied
experimentally.Comment: 18 pages, 9 embedded figure
Scattering and binding of different atomic species in a one-dimensional optical lattice
The theory of scattering of atom pairs in a periodic potential is presented
for the case of different atoms. When the scattering dynamics is restricted to
the lowest Bloch band of the periodic potential, a separation in relative and
average discrete coordinates applies and makes the problem analytically
tractable, and we present a number of new results and features compared to the
case of identical atoms.Comment: 5 pages, 4 figure
Theory of Feshbach molecule formation in a dilute gas during a magnetic field ramp
Starting with coupled atom-molecule Boltzmann equations, we develop a
simplified model to understand molecule formation observed in recent
experiments. Our theory predicts several key features: (1) the effective
adiabatic rate constant is proportional to density; (2) in an adiabatic ramp,
the dependence of molecular fraction on magnetic field resembles an error
function whose width and centroid are related to the temperature; (3) the
molecular production efficiency is a universal function of the initial phase
space density, the specific form of which we derive for a classical gas. Our
predictions show qualitative agreement with the data from [Hodby et al, Phys.
Rev. Lett. {\bf{94}}, 120402 (2005)] without the use of adjustable parameters
Statistical mechanics of a Feshbach coupled Bose-Fermi gas in an optical lattice
We consider an atomic Fermi gas confined in a uniform optical lattice
potential, where the atoms can pair into molecules via a magnetic field
controlled narrow Feshbach resonance. The phase diagram of the resulting
atom-molecule mixture in chemical and thermal equilibrium is determined
numerically in the absence of interactions under the constraint of particle
conservation. In the limiting cases of vanishing or large lattice depth we
derive simple analytical results for important thermodynamic quantities. One
such quantity is the dissociation energy, defined as the detuning of the
molecular energy spectrum with respect to the atomic one for which half of the
atoms have been converted into dimers. Importantly we find that the
dissociation energy has a non-monotonic dependence on lattice depth.Comment: 9 pages, 5 figure
A Giant Sand Injection Complex: The Upper Jurassic Hareelv Formation of East Greenland
A major intrusive sandstone complex of Late Jurassic age is spectacularly exposed in Jameson land, East Greenland. It is probably the largest in the World, and covers an area of 55x70 km with a thickness of 200–400 m, and forms the Upper Oxfordian–Volgian Hareelv Formation. The complex consists of black basinal mudstones and highly irregular sandstone bodies, dykes and sills. The sand was derived from collapse of the front of sandy shelf-margin wedges, which triggered hyperconcentrated to concentrated density flows, and deposited massive sands further down the slope, at the base-of-slope and in the basin. The sand of some flows was loaded into the slope muds while elsewhere it flowed in steep-sided gullies formed by retrogressive slumping of the slope muds. All sand bodies were liquefied subsequent to burial and the sand was intruded into the surrounding black compacted muds and mudstones. Intrusion took place repeatedly over a long time interval, in environments ranging from very shallow to relatively deep burial, and the primary sediment structures of the sands were generally lost during these processes. It is rarely possible to determine the degree of post-burial remobilization but it ranges from rather small-scale modifications to wholesale liquefaction and out-of-place intrusion of the sand over many tens of metres. Sandstone dykes and sills occur ubiquitously and were emplaced by all combinations of stoping and dilation. The intrusive sand bodies range in dimensions from centimetres to many hundreds of metres. Deposition took place during the most important Mesozoic rift event in East Greenland and the pervasive remobilization and liquefaction of all sand bodies in the Hareelv Formation is interpreted as having been caused mainly by cyclic earthquake shocks. Additional important factors were slope shear stress, build up of pore pressure due to loading, slumping, upwards movement of pore waters expelled from the compacting muds, and also possibly of biogenic and thermogenic gas. The Hareelv Formation is an excellent field analogue for deeply buried hydrocarbon reservoirs, which have been modified by remobilization and injection of the sands
Angular momentum exchange between coherent light and matter fields
Full, three dimensional, time-dependent simulations are presented
demonstrating the quantized transfer of angular momentum to a Bose-Einstein
condensate from a laser carrying orbital angular momentum in a
Laguerre-Gaussian mode. The process is described in terms of coherent Bragg
scattering of atoms from a chiral optical lattice. The transfer efficiency and
the angular momentum content of the output coupled vortex state are analyzed
and compared with a recent experiment.Comment: 4 pages, 4 figure
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