6,299 research outputs found
Analysis of an F.M. Discriminator with Fading Signal plus Additive Gaussian Noise
Fading signal plus additive Gaussian noise applied to frequency modulation discriminator for determining fading effects on threshol
The effects of disorder in dimerized quantum magnets in mean field approximations
We study theoretically the effects of disorder on Bose-Einstein condensates
(BEC) of bosonic triplon quasiparticles in doped dimerized quantum magnets. The
condensation occurs in a strong enough magnetic field Hc, where the
concentration of bosons in the random potential is sufficient to form the
condensate. The effect of doping is partly modeled by delta - correlated
disorder potential, which (i) leads to the uniform renormalization of the
system parameters and (ii) produces disorder in the system with renormalized
parameters. These approaches can explain qualitatively the available
magnetization data in the Tl_(1-x)K_(x)CuCl_3 compound taken as an example. In
addition to the magnetization, we found that the speed of the Bogoliubov mode
has a peak as a function of doping parameter, x. No evidence of the pure Bose
glass phase has been obtained in the BEC regime.Comment: Includes 19 pages, 5 figure
Asymptotic energy profile of a wavepacket in disordered chains
We investigate the long time behavior of a wavepacket initially localized at
a single site in translationally invariant harmonic and anharmonic chains
with random interactions. In the harmonic case, the energy profile averaged on time and disorder decays for large as a power
law where and 3/2 for
initial displacement and momentum excitations, respectively. The prefactor
depends on the probability distribution of the harmonic coupling constants and
diverges in the limit of weak disorder. As a consequence, the moments of the energy distribution averaged with respect to disorder
diverge in time as for , where
for . Molecular dynamics simulations yield good agreement with
these theoretical predictions. Therefore, in this system, the second moment of
the wavepacket diverges as a function of time despite the wavepacket is not
spreading. Thus, this only criteria often considered earlier as proving the
spreading of a wave packet, cannot be considered as sufficient in any model.
The anharmonic case is investigated numerically. It is found for intermediate
disorder, that the tail of the energy profile becomes very close to those of
the harmonic case. For weak and strong disorder, our results suggest that the
crossover to the harmonic behavior occurs at much larger and larger
time.Comment: To appear in Phys. Rev.
A generalization of the q-Saalschutz sum and the Burge transform
A generalization of the q-(Pfaff)-Saalschutz summation formula is proved.
This implies a generalization of the Burge transform, resulting in an
additional dimension of the ``Burge tree''. Limiting cases of our summation
formula imply the (higher-level) Bailey lemma, provide a new decomposition of
the q-multinomial coefficients, and can be used to prove the Lepowsky and Primc
formula for the A_1^{(1)} string functions.Comment: 18 pages, AMSLaTe
Regular-to-chaotic tunneling rates using a fictitious integrable system
We derive a formula predicting dynamical tunneling rates from regular states
to the chaotic sea in systems with a mixed phase space. Our approach is based
on the introduction of a fictitious integrable system that resembles the
regular dynamics within the island. For the standard map and other kicked
systems we find agreement with numerical results for all regular states in a
regime where resonance-assisted tunneling is not relevant.Comment: 4 pages, 4 figure
Generation of Total Angular Momentum Eigenstates in Remote Qubits
We propose a scheme enabling the universal coupling of angular momentum of
remote noninteracting qubits using linear optical tools only. Our system
consists of single-photon emitters in a -configuration that are
entangled among their long-lived ground-state qubits through suitably designed
measurements of the emitted photons. In this manner, we present an
experimentally feasible algorithm that is able to generate any of the
symmetric and nonsymmetric total angular momentum eigenstates spanning the
Hilbert space of the -qubit compound.Comment: 5 pages, 4 figures, improved presentation. Accepted in Physical
Review
Unquenching the Quark Model and Screened Potentials
The low-lying spectrum of the quark model is shown to be robust under the
effects of `unquenching'. In contrast, the use of screened potentials is shown
to be of limited use in models of hadrons. Applications to unquenching the
lattice Wilson loop potential and to glueball mixing in the adiabatic hybrid
spectrum are also presented.Comment: 6 pages, 3 ps figures, revtex. Version to appear in J. Phys.
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