1,618 research outputs found
Parallel Implementation of the Discrete Green's Function Formulation of the FDTD Method on a Multicore Central Processing Unit
Parallel implementation of the discrete Green's function formulation of the finite-difference time-domain (DGF-FDTD) method was developed on a multicore central processing unit. DGF-FDTD avoids computations of the electromagnetic field in free-space cells and does not require domain termination by absorbing boundary conditions. Computed DGF-FDTD solutions are compatible with the FDTD grid enabling the perfect hybridization of FDTD with the use of time-domain integral equation methods. The developed implementation can be applied to simulations of antenna characteristics. For the sake of example, arrays of Yagi-Uda antennas were simulated with the use of parallel DGF-FDTD. The efficiency of parallel computations was investigated as a function of the number of current elements in the FDTD grid. Although the developed method does not apply the fast Fourier transform for convolution computations, advantages stemming from the application of DGF-FDTD instead of FDTD can be demonstrated for one-dimensional wire antennas when simulation results are post-processed by the near-to-far-field transformation
Applications of Integrated Magnetic Microtraps
Lithographically fabricated circuit patterns can provide magnetic guides and
microtraps for cold neutral atoms. By combining several such structures on the
same ceramic substrate, we have realized the first ``atom chips'' that permit
complex manipulations of ultracold trapped atoms or de Broglie wavepackets. We
show how to design magnetic potentials from simple conductor patterns and we
describe an efficient trap loading procedure in detail. Applying the design
guide, we describe some new microtrap potentials, including a trap which
reaches the Lamb-Dicke regime for rubidium atoms in all three dimensions, and a
rotatable Ioffe-Pritchard trap, which we also demonstrate experimentally.
Finally, we demonstrate a device allowing independent linear positioning of two
atomic clouds which are very tightly confined laterally. This device is well
suited for the study of one-dimensional collisions.Comment: 10 pages, 17 figure
Trapped-Atom-Interferometer in a Magnetic Microtrap
We propose a configuration of a magnetic microtrap which can be used as an
interferometer for three-dimensionally trapped atoms. The interferometer is
realized via a dynamic splitting potential that transforms from a single well
into two separate wells and back. The ports of the interferometer are
neighboring vibrational states in the single well potential. We present a
one-dimensional model of this interferometer and compute the probability of
unwanted vibrational excitations for a realistic magnetic potential. We
optimize the speed of the splitting process in order suppress these excitations
and conclude that such interferometer device should be feasible with currently
available microtrap technique.Comment: 6 pages, 6 figures, submitted to PR
Program user's manual for optimizing the design of a liquid or gaseous propellant rocket engine with the automated combustor design code AUTOCOM
This computer program manual describes in two parts the automated combustor design optimization code AUTOCOM. The program code is written in the FORTRAN 4 language. The input data setup and the program outputs are described, and a sample engine case is discussed. The program structure and programming techniques are also described, along with AUTOCOM program analysis
Coherence in Microchip Traps
We report the coherent manipulation of internal states of neutral atoms in a
magnetic microchip trap. Coherence lifetimes exceeding 1 s are observed with
atoms at distances of m from the microchip surface. The coherence
lifetime in the chip trap is independent of atom-surface distance within our
measurement accuracy, and agrees well with the results of similar measurements
in macroscopic magnetic traps. Due to the absence of surface-induced
decoherence, a miniaturized atomic clock with a relative stability in the
range can be realized. For applications in quantum information
processing, we propose to use microwave near-fields in the proximity of chip
wires to create potentials that depend on the internal state of the atoms.Comment: Revised version, accepted for publication in Phys. Rev. Lett., 4
pages, 4 figure
Quantitative study of quasi-one-dimensional Bose gas experiments via the stochastic Gross-Pitaevskii equation
The stochastic Gross-Pitaevskii equation is shown to be an excellent model
for quasi-one-dimensional Bose gas experiments, accurately reproducing the in
situ density profiles recently obtained in the experiments of Trebbia et al.
[Phys. Rev. Lett. 97, 250403 (2006)] and van Amerongen et al. [Phys. Rev. Lett.
100, 090402 (2008)], and the density fluctuation data reported by Armijo et al.
[Phys. Rev. Lett. 105, 230402 (2010)]. To facilitate such agreement, we propose
and implement a quasi-one-dimensional stochastic equation for the low-energy,
axial modes, while atoms in excited transverse modes are treated as independent
ideal Bose gases.Comment: 10 pages, 5 figures; updated figures with experimental dat
Creating Ioffe-Pritchard micro-traps from permanent magnetic film with in-plane magnetization
We present designs for Ioffe-Pritchard type magnetic traps using planar
patterns of hard magnetic material. Two samples with different pattern designs
were produced by spark erosion of 40 m thick FePt foil. The pattern on the
first sample yields calculated axial and radial trap frequencies of 51 Hz and
6.8 kHz, respectively. For the second sample the calculated frequencies are 34
Hz and 11 kHz. The structures were used successfully as a magneto-optical trap
for Rb and loaded as a magnetic trap. A third design, based on
lithographically patterned 250 nm thick FePt film on a Si substrate, yields an
array of 19 traps with calculated axial and radial trap frequencies of 1.5 kHz
and 110 kHz, respectively.Comment: 8 pages, 5 figures Revised and accepted for EPJD, improved picture
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