32,461 research outputs found
State Transfer and Spin Measurement
We present a Hamiltonian that can be used for amplifying the signal from a
quantum state, enabling the measurement of a macroscopic observable to
determine the state of a single spin. We prove a general mapping between this
Hamiltonian and an exchange Hamiltonian for arbitrary coupling strengths and
local magnetic fields. This facilitates the use of existing schemes for perfect
state transfer to give perfect amplification. We further prove a link between
the evolution of this fixed Hamiltonian and classical Cellular Automata,
thereby unifying previous approaches to this amplification task.
Finally, we show how to use the new Hamiltonian for perfect state transfer in
the, to date, unique scenario where total spin is not conserved during the
evolution, and demonstrate that this yields a significantly different response
in the presence of decoherence.Comment: 4 pages, 2 figure
Resonance absolute quantum reflection at selected energies
The possibility of the resonance reflection (100 % at maximum) is revealed.
The corresponding exactly solvable models with the controllable numbers of
resonances, their positions and widths are presented.Comment: 5 pages, 2 figure
Self-energy flows in the two-dimensional repulsive Hubbard model
We study the two-dimensional repulsive Hubbard model by functional RG
methods, using our recently proposed channel decomposition of the interaction
vertex. The main technical advance of this work is that we calculate the full
Matsubara frequency dependence of the self-energy and the interaction vertex in
the whole frequency range without simplifying assumptions on its functional
form, and that the effects of the self-energy are fully taken into account in
the equations for the flow of the two-body vertex function. At Van Hove
filling, we find that the Fermi surface deformations remain small at fixed
particle density and have a minor impact on the structure of the interaction
vertex. The frequency dependence of the self-energy, however, turns out to be
important, especially at a transition from ferromagnetism to d-wave
superconductivity. We determine non-Fermi-liquid exponents at this transition
point.Comment: 48 pages, 18 figure
The generic character table of a Sylow -subgroup of a finite Chevalley group of type
Let be a Sylow -subgroup of the finite Chevalley group of type
over the field of elements, where is a power of a prime . We
describe a construction of the generic character table of
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