1,255 research outputs found
Dephasing at Low Temperatures
We discuss the significance and the calculation of dephasing at low
temperatures. The particle is moving diffusively due to a static disorder
configuration, while the interference between classical paths is suppressed due
to the interaction with a dynamical environment. At high temperatures we may
use the `white noise approximation' (WNA), while at low temperatures we
distinguish the contribution of `zero point fluctuations' (ZPF) from the
`thermal noise contribution' (TNC). We study the limitations of the above
semiclassical approach and suggest the required modifications. In particular we
find that the ZPF contribution becomes irrelevant for thermal motion.Comment: 4 pages, 1 figure, clearer presentatio
Aharonov-Bohm oscillations of a particle coupled to dissipative environments
The amplitude of the Bohm-Aharonov oscillations of a particle moving around a
ring threaded by a magnetic flux and coupled to different dissipative
environments is studied. The decay of the oscillations when increasing the
radius of the ring is shown to depend on the spatial features of the coupling.
When the environment is modelled by the Caldeira-Leggett bath of oscillators,
or the particle is coupled by the Coulomb potential to a dirty electron gas,
interference effects are suppressed beyond a finite length, even at zero
temperature. A finite renormalization of the Aharonov-Bohm oscillations is
found for other models of the environment.Comment: 6 page
Percolation Critical Exponents in Scale-Free Networks
We study the behavior of scale-free networks, having connectivity
distribution P(k) k^-a, close to the percolation threshold. We show that for
networks with 3<a<4, known to undergo a transition at a finite threshold of
dilution, the critical exponents are different than the expected mean-field
values of regular percolation in infinite dimensions. Networks with 2<a<3
possess only a percolative phase. Nevertheless, we show that in this case
percolation critical exponents are well defined, near the limit of extreme
dilution (where all sites are removed), and that also then the exponents bear a
strong a-dependence. The regular mean-field values are recovered only for a>4.Comment: Latex, 4 page
Aharonov-Bohm ring with fluctuating flux
We consider a non-interacting system of electrons on a clean one-channel
Aharonov-Bohm ring which is threaded by a fluctuating magnetic flux. The flux
derives from a Caldeira-Leggett bath of harmonic oscillators. We address the
influence of the bath on the following properties: one- and two-particle
Green's functions, dephasing, persistent current and visibility of the
Aharonov-Bohm effect in cotunneling transport through the ring. For the bath
spectra considered here (including Nyquist noise of an external coil), we find
no dephasing in the linear transport regime at zero temperature.
PACS numbers: 73.23.-b, 73.23.Hk, 73.23.Ra, 03.65.YzComment: 17 pages, 8 figures. To be published in PRB. New version contains
minor corrections and additional discussion suggested by referee. A simple
introduction to the basics of dephasing can be found at
http://iff.physik.unibas.ch/~florian/dephasing/dephasing.htm
Saturation induced coherence loss in coherent backscattering of light
We use coherent backscattering (CBS) of light by cold Strontium atoms to
study the mutual coherence of light waves in the multiple scattering regime. As
the probe light intensity is increased, the atomic optical transition starts to
be saturated. Nonlinearities and inelastic scattering then occur. In our
experiment, we observe a strongly reduced enhancement factor of the coherent
backscattering cone when the intensity of the probe laser is increased,
indicating a partial loss of coherence in multiple scattering
Quantum pumping and dissipation: from closed to open systems
Current can be pumped through a closed system by changing parameters (or
fields) in time. The Kubo formula allows to distinguish between dissipative and
non-dissipative contributions to the current. We obtain a Green function
expression and an matrix formula for the associated terms in the
generalized conductance matrix: the "geometric magnetism" term that corresponds
to adiabatic transport; and the "Fermi golden rule" term which is responsible
to the irreversible absorption of energy. We explain the subtle limit of an
infinite system, and demonstrate the consistency with the formulas by Landauer
and Buttiker, Pretre and Thomas. We also discuss the generalization of the
fluctuation-dissipation relation, and the implications of the Onsager
reciprocity.Comment: 4 page paper, 1 figure (published version) + 2 page appendi
A Parameterization Invariant Approach to the Statistical Estimation of the CKM Phase
In contrast to previous analyses, we demonstrate a Bayesian approach to the
estimation of the CKM phase that is invariant to parameterization. We
also show that in addition to {\em computing} the marginal posterior in a
Bayesian manner, the distribution must also be {\em interpreted} from a
subjective Bayesian viewpoint. Doing so gives a very natural interpretation to
the distribution. We also comment on the effect of removing information about
.Comment: 14 pages, 3 figures, 1 table, minor revision; to appear in JHE
Percolation in Directed Scale-Free Networks
Many complex networks in nature have directed links, a property that affects
the network's navigability and large-scale topology. Here we study the
percolation properties of such directed scale-free networks with correlated in-
and out-degree distributions. We derive a phase diagram that indicates the
existence of three regimes, determined by the values of the degree exponents.
In the first regime we regain the known directed percolation mean field
exponents. In contrast, the second and third regimes are characterized by
anomalous exponents, which we calculate analytically. In the third regime the
network is resilient to random dilution, i.e., the percolation threshold is
p_c->1.Comment: Latex, 5 pages, 2 fig
Classical and quantum pumping in closed systems
Pumping of charge (Q) in a closed ring geometry is not quantized even in the
strict adiabatic limit. The deviation form exact quantization can be related to
the Thouless conductance. We use Kubo formalism as a starting point for the
calculation of both the dissipative and the adiabatic contributions to Q. As an
application we bring examples for classical dissipative pumping, classical
adiabatic pumping, and in particular we make an explicit calculation for
quantum pumping in case of the simplest pumping device, which is a 3 site
lattice model.Comment: 5 pages, 3 figures. The long published version is cond-mat/0307619.
This is the short unpublished versio
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