5,060 research outputs found
Stable Quantum Resonances in Atom Optics
A theory for stabilization of quantum resonances by a mechanism similar to
one leading to classical resonances in nonlinear systems is presented. It
explains recent surprising experimental results, obtained for cold Cesium atoms
when driven in the presence of gravity, and leads to further predictions. The
theory makes use of invariance properties of the system, that are similar to
those of solids, allowing for separation into independent kicked rotor
problems. The analysis relies on a fictitious classical limit where the small
parameter is {\em not} Planck's constant, but rather the detuning from the
frequency that is resonant in absence of gravity.Comment: 5 pages, 3 figure
Dynamical Mean-Field Study of the Ferromagnetic Transition Temperature of a Two-Band Model for Colossal Magnetoresistance Materials
The ferromagnetic (FM) transition temperature (Tc) of a two-band
Double-Exchange (DE) model for colossal magnetoresistance (CMR) materials is
studied using dynamical mean-field theory (DMFT), in wide ranges of coupling
constants, hopping parameters, and carrier densities. The results are shown to
be in excellent agreement with Monte Carlo simulations. When the bands overlap,
the value of Tc is found to be much larger than in the one-band case, for all
values of the chemical potential within the energy overlap interval. A nonzero
interband hopping produces an additional substantial increase of Tc, showing
the importance of these nondiagonal terms, and the concomitant use of multiband
models, to boost up the critical temperatures in DE-based theories.Comment: 4 pages, 4 eps figure
Short-Range Ordered Phase of the Double-Exchange Model in Infinite Dimensions
Using dynamical mean-field theory, we have evaluated the magnetic
instabilities and T=0 phase diagram of the double-exchange model on a Bethe
lattice in infinite dimensions. In addition to ferromagnetic (FM) and
antiferromagnetic (AF) phases, we also study a class of disordered phases with
magnetic short-range order (SRO). In the weak-coupling limit, a SRO phase has a
higher transition temperature than the AF phase for all fillings p below 1 and
can even have a higher transition temperature than the FM phase. At T=0 and for
small Hund's coupling J_H, a SRO state has lower energy than either the FM or
AF phases for 0.26\le p 0 limit
but appears for any non-zero value of J_H.Comment: 11 pages, 3 figures, published versio
A classical scaling theory of quantum resonances
The quantum resonances occurring with delta-kicked particles are studied with
the help of a fictitious classical limit, establishing a direct correspondence
between the nearly resonant quantum motion and the classical resonances of a
related system. A scaling law which characterizes the structure of the resonant
peaks is derived and numerically demonstrated.Comment: 4 pages, 2 Fig
Faster Methods for Contracting Infinite 2D Tensor Networks
We revisit the corner transfer matrix renormalization group (CTMRG) method of
Nishino and Okunishi for contracting two-dimensional (2D) tensor networks and
demonstrate that its performance can be substantially improved by determining
the tensors using an eigenvalue solver as opposed to the power method used in
CTMRG. We also generalize the variational uniform matrix product state (VUMPS)
ansatz for diagonalizing 1D quantum Hamiltonians to the case of 2D transfer
matrices and discuss similarities with the corner methods. These two new
algorithms will be crucial to improving the performance of variational infinite
projected entangled pair state (PEPS) methods.Comment: 20 pages, 5 figures, V. Zauner-Stauber previously also published
under the name V. Zaune
Effect of noise for two interacting particles in a random potential
We investigated the effect of noise on propagation of two interacting
particles pairs in a quasi one--dimensional random potential. It is shown that
pair diffusion is strongly enhanced by short range interaction comparing with
the non--interacting case.Comment: 8 Latex pages + 3 postscript figures uu- compressed submitted to
Europhysics Letter
Polymers for spacecraft hardware materials specifications and engineering information Monthly technical progress report no. 18, Nov. 10 - Dec. 9, 1965
Chemical test procedures for analyzing potting compound bases for spacecraft construction material
Polymers for spacecraft hardware materials specifications and engineering information Monthly technical progress report no. 19, Dec. 10, 1965 - Jan. 9, 1966
Thermal vacuum weight loss determinations of polymers for spacecraft construction material application
Pseudo-classical theory for fidelity of nearly resonant quantum rotors
Using a semiclassical ansatz we analytically predict for the fidelity of
delta-kicked rotors the occurrence of revivals and the disappearance of
intermediate revival peaks arising from the breaking of a symmetry in the
initial conditions. A numerical verification of the predicted effects is given
and experimental ramifications are discussed.Comment: Shortened and improved versio
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