1,353 research outputs found
Tripartite entanglement dynamics in a system of strongly driven qubits
We study the dynamics of tripartite entanglement in a system of two strongly
driven qubits individually coupled to a dissipative cavity. We aim at
explanation of the previously noted entanglement revival between two qubits in
this system. We show that the periods of entanglement loss correspond to the
strong tripartite entanglement between the qubits and the cavity and the
recovery has to do with an inverse process. We demonstrate that the overall
process of qubit-qubit entanglement loss is due to the second order coupling to
the external continuum which explains the exp[-g^2 t/2+g^2 k t^3/6+\cdot] for
of the entanglement loss reported previously.Comment: 9 pages, 5 figure
Re-entrant spin glass and magnetoresistance in Co_{0.2}Zn_{0.8}Fe_{1.6}Ti_{0.4}O_4 spinel oxide
We have investigated the static and dynamic response of magnetic clusters in
Co_{0.2}Zn_{0.8}Fe_{1.6}Ti_{0.4}O_4 spinel oxide, where a sequence of magnetic
phase transitions, i.e., paramagnetic (PM) to ferromagnetic at T_{C}
270K and ferromagnetic to canted spin glass state at T_f\leq$ 125K is
observed
A Nonperturbative Eliasson's Reducibility Theorem
This paper is concerned with discrete, one-dimensional Schr\"odinger
operators with real analytic potentials and one Diophantine frequency. Using
localization and duality we show that almost every point in the spectrum admits
a quasi-periodic Bloch wave if the potential is smaller than a certain constant
which does not depend on the precise Diophantine conditions. The associated
first-order system, a quasi-periodic skew-product, is shown to be reducible for
almost all values of the energy. This is a partial nonperturbative
generalization of a reducibility theorem by Eliasson. We also extend
nonperturbatively the genericity of Cantor spectrum for these Schr\"odinger
operators. Finally we prove that in our setting, Cantor spectrum implies the
existence of a -set of energies whose Schr\"odinger cocycle is not
reducible to constant coefficients
Coherent instabilities in a semiconductor laser with fast gain recovery
We report the observation of a coherent multimode instability in quantum
cascade lasers (QCLs), which is driven by the same fundamental mechanism of
Rabi oscillations as the elusive Risken-Nummedal-Graham-Haken (RNGH)
instability predicted 40 years ago for ring lasers. The threshold of the
observed instability is significantly lower than in the original RNGH
instability, which we attribute to saturable-absorption nonlinearity in the
laser. Coherent effects, which cannot be reproduced by standard laser rate
equations, can play therefore a key role in the multimode dynamics of QCLs, and
in lasers with fast gain recovery in general.Comment: 5 pages, 4 figure
On linearized gravity in the Randall-Sundrum scenario
In the literature about the Randall-Sundrum scenario one finds on one hand
that there exist (small) corrections to Newton's law of gravity on the brane,
and on another that the exact (and henceforth linearized) Einstein equations
can be recovered on the brane. The explanation for these seemingly
contradictory results is that the behaviour of the bulk far from the brane is
different in both models. We show that explicitely in this paper.Comment: 12 pages, plain TeX, no figure
Thermopower of Aharonov-Bohm Interferometer with a Quantum Dot
We report on the thermopower of an Aharonov-Bohm interferometer (AB) with a
quantum dot in the Kondo limit. The thermopower is anomalously enhanced due to
the Kondo effect as in heavy fermion systems. In contrast to the bulk systems,
the sign of the thermopower can be changed by adjusting the energy level scheme
or the particle-hole asymmetry of a dot with the gate voltage. Further the
magnitude and even the sign of the thermopower in the AB ring can be changed at
will with varying either magnetic fields or the gate voltages.Comment: 4 pages, 3 figures, accepted for publication in Physical Review
Letter
On the error term in Weyl's law for the Heisenberg manifolds (II)
In this paper we study the mean square of the error term in the Weyl's law of
an irrational -dimensional Heisenberg manifold . An asymptotic formula
is established
Suppression of current in transport through parallel double quantum dots
We report our study of the I-V curves in the transport through the quantum
dot when an additional quantum dot lying in the Kondo regime is side-connected
to it. Due to the Kondo scattering off the effective spin on a side-connected
quantum dot the conductance is suppressed at low temperatures and at low
source-drain bias voltages. This zero-bias anomaly is understood as enhanced
Kondo scattering with decreasing temperature.Comment: 14 pages, 8 figure
Cosmological thermodynamics and deflationary gas universe
We establish a general thermodynamic scheme for cosmic fluids with internal
self-interactions and discuss equilibrium and non-equilibrium aspects of such
systems in connection with (generalized) symmetry properties of the
cosmological dynamics. As an example we construct an exactly solvable gas
dynamical model of a ``deflationary'' transition from an initial de Sitter
phase to a subsequent Friedmann-Lema\^{\i}tre-Robertson-Walker (FLRW) period.
We demonstrate that this dynamics represents a manifestation of a conformal
symmetry of an ``optical'' metric, characterized by a specific effective
refraction index of the cosmic medium.Comment: 12 pages, to appear in PR
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