2,528 research outputs found
Magnetically generated spin-orbit coupling for ultracold atoms
We present a new technique for producing two- and three-dimensional
Rashba-type spin-orbit couplings for ultracold atoms without involving light.
The method relies on a sequence of pulsed inhomogeneous magnetic fields
imprinting suitable phase gradients on the atoms. For sufficiently short pulse
durations, the time-averaged Hamiltonian well approximates the Rashba
Hamiltonian. Higher order corrections to the energy spectrum are calculated
exactly for spin-1/2 and perturbatively for higher spins. The pulse sequence
does not modify the form of rotationally symmetric atom-atom interactions.
Finally, we present a straightforward implementation of this pulse sequence on
an atom chip
Small ball probability for the condition number of random matrices
Let be an random matrix with i.i.d. entries of zero mean,
unit variance and a bounded subgaussian moment. We show that the condition
number satisfies the small ball probability estimate
where may only depend on the subgaussian moment.
Although the estimate can be obtained as a combination of known results and
techniques, it was not noticed in the literature before. As a key step of the
proof, we apply estimates for the singular values of , obtained (under some additional assumptions) by Nguyen.Comment: Some changes according to the Referee's comment
Smoothed Complexity Theory
Smoothed analysis is a new way of analyzing algorithms introduced by Spielman
and Teng (J. ACM, 2004). Classical methods like worst-case or average-case
analysis have accompanying complexity classes, like P and AvgP, respectively.
While worst-case or average-case analysis give us a means to talk about the
running time of a particular algorithm, complexity classes allows us to talk
about the inherent difficulty of problems.
Smoothed analysis is a hybrid of worst-case and average-case analysis and
compensates some of their drawbacks. Despite its success for the analysis of
single algorithms and problems, there is no embedding of smoothed analysis into
computational complexity theory, which is necessary to classify problems
according to their intrinsic difficulty.
We propose a framework for smoothed complexity theory, define the relevant
classes, and prove some first hardness results (of bounded halting and tiling)
and tractability results (binary optimization problems, graph coloring,
satisfiability). Furthermore, we discuss extensions and shortcomings of our
model and relate it to semi-random models.Comment: to be presented at MFCS 201
Synthetic 3D Spin-Orbit Coupling
We describe a method for creating a three-dimensional analogue to Rashba
spin-orbit coupling in systems of ultracold atoms. This laser induced coupling
uses Raman transitions to link four internal atomic states with a tetrahedral
geometry, and gives rise to a Dirac point that is robust against environmental
perturbations. We present an exact result showing that such a spin-orbit
coupling in a fermionic system always rise to a molecular bound state.Comment: 4 pages, 6 figure
A New Linear Inductive Voltage Adder Driver for the Saturn Accelerator
Saturn is a dual-purpose accelerator. It can be operated as a large-area
flash x-ray source for simulation testing or as a Z-pinch driver especially for
K-line x-ray production. In the first mode, the accelerator is fitted with
three concentric-ring 2-MV electron diodes, while in the Z-pinch mode the
current of all the modules is combined via a post-hole convolute arrangement
and driven through a cylindrical array of very fine wires. We present here a
point design for a new Saturn class driver based on a number of linear
inductive voltage adders connected in parallel. A technology recently
implemented at the Institute of High Current Electronics in Tomsk (Russia) is
being utilized[1].
In the present design we eliminate Marx generators and pulse-forming
networks. Each inductive voltage adder cavity is directly fed by a number of
fast 100-kV small-size capacitors arranged in a circular array around each
accelerating gap. The number of capacitors connected in parallel to each cavity
defines the total maximum current. By selecting low inductance switches,
voltage pulses as short as 30-50-ns FWHM can be directly achieved.Comment: 3 pages, 4 figures. This paper is submitted for the 20th Linear
Accelerator Conference LINAC2000, Monterey, C
Evidence for 2k_F Electron-Electron Scattering Processes in Coulomb Drag
Measurements and calculations of Coulomb drag between two low density,
closely spaced, two-dimensional electron systems are reported. The
experimentally measured drag exceeds that calculated in the random phase
approximation by a significant, and density dependent, factor. Studies of the
dependence of the measured drag on the difference in density between the two
layers clearly demonstrate that previously ignored q=2k_F scattering processes
can be very important to the drag at low densities and small layer separations.Comment: 5 pages, 5 figure
Thin-film GaAs photovoltaic solar energy cells Final report
Thin film gallium arsenide photovoltaic solar cell
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