41,194 research outputs found
Parametric Competition in non-autonomous Hamiltonian Systems
In this work we use the formalism of chord functions (\emph{i.e.}
characteristic functions) to analytically solve quadratic non-autonomous
Hamiltonians coupled to a reservoir composed by an infinity set of oscillators,
with Gaussian initial state. We analytically obtain a solution for the
characteristic function under dissipation, and therefore for the determinant of
the covariance matrix and the von Neumann entropy, where the latter is the
physical quantity of interest. We study in details two examples that are known
to show dynamical squeezing and instability effects: the inverted harmonic
oscillator and an oscillator with time dependent frequency. We show that it
will appear in both cases a clear competition between instability and
dissipation. If the dissipation is small when compared to the instability, the
squeezing generation is dominant and one can see an increasing in the von
Neumann entropy. When the dissipation is large enough, the dynamical squeezing
generation in one of the quadratures is retained, thence the growth in the von
Neumann entropy is contained
On statistical properties of traded volume in financial markets
In this article we study the dependence degree of the traded volume of the
Dow Jones 30 constituent equities by using a nonextensive generalised form of
the Kullback-Leibler information measure. Our results show a slow decay of the
dependence degree as a function of the lag. This feature is compatible with the
existence of non-linearities in this type time series. In addition, we
introduce a dynamical mechanism whose associated stationary probability density
function (PDF) presents a good agreement with the empirical results.Comment: 6 pages, 4 figures, 1 table. Based on the talk presented at "News,
Expectations and Trends in Statistical Physics, NEXT-SigmaPhi 3rd
International Conference. 13-18 August 2005, Kolymbari CRETE" Multi-fractal
analysis section remove
Thermal entanglement witness for materials with variable local spin lengths
We show that the thermal entanglement in a spin system using only magnetic
susceptibility measurements is restricted to the insulator materials. We
develop a generalization of the thermal entanglement witness that allows us to
get information about the system entanglement with variable local spin lengths
that can be used experimentally in conductor or insulator materials. As an
application, we study thermal entanglement for the half-filled Hubbard model
for linear, square and cubic clusters. We note that it is the itinerancy of
electrons that favors the entanglement. Our results suggest a weak dependence
between entanglement and external spin freedom degrees.Comment: 4 pages, 3 figure
Quantum-state transfer in staggered coupled-cavity arrays
We consider a coupled-cavity array, where each cavity interacts with an atom
under the rotating-wave approximation. For a staggered pattern of inter-cavity
couplings, a pair of field normal modes each bi-localized at the two array ends
arise. A rich structure of dynamical regimes can hence be addressed depending
on which resonance condition between the atom and field modes is set. We show
that this can be harnessed to carry out high-fidelity quantum-state transfer
(QST) of photonic, atomic or polaritonic states. Moreover, by partitioning the
array into coupled modules of smaller length, the QST time can be substantially
shortened without significantly affecting the fidelity.Comment: 12 pages, 8 figure
Wannier-based calculation of the orbital magnetization in crystals
We present a first-principles scheme that allows the orbital magnetization of
a magnetic crystal to be evaluated accurately and efficiently even in the
presence of complex Fermi surfaces. Starting from an initial
electronic-structure calculation with a coarse ab initio k-point mesh,
maximally localized Wannier functions are constructed and used to interpolate
the necessary k-space quantities on a fine mesh, in parallel to a
previously-developed formalism for the anomalous Hall conductivity [X.Wang, J.
Yates, I. Souza, and D. Vanderbilt, Phys. Rev. B 74, 195118 (2006)]. We
formulate our new approach in a manifestly gauge-invariant manner, expressing
the orbital magnetization in terms of traces over matrices in Wannier space.
Since only a few (e.g., of the order of 20) Wannier functions are typically
needed to describe the occupied and partially occupied bands, these Wannier
matrices are small, which makes the interpolation itself very efficient. The
method has been used to calculate the orbital magnetization of bcc Fe, hcp Co,
and fcc Ni. Unlike an approximate calculation based on integrating orbital
currents inside atomic spheres, our results nicely reproduce the experimentally
measured ordering of the orbital magnetization in these three materials.Comment: 13 pages, 3 figures, 4 table
New Algorithms for Computing a Single Component of the Discrete Fourier Transform
This paper introduces the theory and hardware implementation of two new
algorithms for computing a single component of the discrete Fourier transform.
In terms of multiplicative complexity, both algorithms are more efficient, in
general, than the well known Goertzel Algorithm.Comment: 4 pages, 3 figures, 1 table. In: 10th International Symposium on
Communication Theory and Applications, Ambleside, U
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