7,525 research outputs found
Decoherence of interacting electrons in disordered conductors: on the relation between influence functional and diagrammatic approaches
We establish a connection between the influence functional approach of
Golubev and Zaikin (GZ) and Keldysh diagrammatic perturbation theory for
calculating the decoherence time of interacting electrons in disordered metals;
we show how the standard diagrams for the Cooperon self energy can be recovered
from GZ's influence functional . This allows us to shed
light on GZ's claim that is irrelevant for decoherence: generates
as many important self energy diagrams as ; GZ's neglect of is
permissible only at high temperatures ().Comment: 6 pages LaTeX, 2 figures, for conference proceedings: "Quantum
Transport and Quantum Coherence" -- Localisation 2002 Sophia University,
Tokyo, August 16-19, 2002, to be published in a supplement of the Journal of
Physical Society of Japa
Electron transport and current fluctuations in short coherent conductors
Employing a real time effective action formalism we analyze electron
transport and current fluctuations in comparatively short coherent conductors
in the presence of electron-electron interactions. We demonstrate that, while
Coulomb interaction tends to suppress electron transport, it may {\it strongly
enhance} shot noise in scatterers with highly transparent conducting channels.
This effect of excess noise is governed by the Coulomb gap observed in the
current-voltage characteristics of such scatterers. We also analyze the
frequency dispersion of higher current cumulants and emphasize a direct
relation between electron-electron interaction effects and current fluctuations
in disordered mesoscopic conductors.Comment: 16 pages, 4 figure
Effect of Nyquist Noise on the Nyquist Dephasing Rate in 2d Electron Systems
We measure the effect of externally applied broadband Nyquist noise on the
intrinsic Nyquist dephasing rate of electrons in a two-dimensional electron gas
at low temperatures. Within the measurement error, the phase coherence time is
unaffected by the externally applied Nyquist noise, including applied noise
temperatures of up to 300 K. The amplitude of the applied Nyquist noise from
100 MHz to 10 GHz is quantitatively determined in the same experiment using a
microwave network analyzer.Comment: 5 pages, 4 figures. Author affiliation clarified; acknowledgements
modified. Replacement reason clarifie
Universal scaling of current fluctuations in disordered graphene
We analyze the full transport statistics of graphene with smooth disorder at
low dopings. First we consider the case of 1D disorder for which the
transmission probability distribution is given analytically in terms of the
graphene-specific mean free path. All current cumulants are shown to scale with
system parameters (doping, size, disorder strength and correlation length) in
an identical fashion for large enough systems. In the case of 2D disorder,
numerical evidence is given for the same kind of identical scaling of all
current cumulants, so that the ratio of any two such cumulants is universal.
Specific universal values are given for the Fano factor, which is smaller than
the pseudodiffusive value of ballistic graphene (F=1/3) both for 1D (F=0.243)
and 2D (F=0.295) disorder. On the other hand, conductivity in wide samples is
shown to grow without saturation as \sqrt{L} and Log L with system length L in
the 1D and 2D cases respectively.Comment: 9 pages, 7 figures. Published version, includes corrected figure for
Fano facto
Quantum parallel dense coding of optical images
We propose quantum dense coding protocol for optical images. This protocol
extends the earlier proposed dense coding scheme for continuous variables
[S.L.Braunstein and H.J.Kimble, Phys.Rev.A 61, 042302 (2000)] to an essentially
multimode in space and time optical quantum communication channel. This new
scheme allows, in particular, for parallel dense coding of non-stationary
optical images. Similar to some other quantum dense coding protocols, our
scheme exploits the possibility of sending a classical message through only one
of the two entangled spatially-multimode beams, using the other one as a
reference system. We evaluate the Shannon mutual information for our protocol
and find that it is superior to the standard quantum limit. Finally, we show
how to optimize the performance of our scheme as a function of the
spatio-temporal parameters of the multimode entangled light and of the input
images.Comment: 15 pages, 4 figures, RevTeX4. Submitted to the Special Issue on
Quantum Imaging in Journal of Modern Optic
New Examples of Systems of the Kowalevski Type
A new examples of integrable dynamical systems are constructed. An
integration procedure leading to genus two theta-functions is presented. It is
based on a recent notion of discriminantly separable polynomials. They have
appeared in a recent reconsideration of the celebrated Kowalevski top, and
their role here is analogue to the situation with the classical Kowalevski
integration procedure.Comment: 17 page
Structure of natural impact glasses on AFM data
This work was supported by the RSF (project No. 17-17-01080)
Detection of a new methanol maser line with the Kitt Peak 12-m telescope by remote observing from Moscow
A new methanol maser line 6(-1)-5(0)E at 133 GHz was detected with the 12-m
Kitt Peak radio telescope using remote observation mode from Moscow. Moderately
strong, narrow maser lines were found in DR21(OH), DR21-W, OMC-2, M8E, NGC2264,
L379, W33-Met. The masers have similar spectral features in other transitions
of methanol-E at 36 and 84 GHz, and in transitions of methanol-A at 44 and 95
GHz. All these are Class I transitions, and the new masers also belong to Class
I. In two other methanol transitions near 133 GHz, 5(-2)-6(-1)E and
6(2)-7(1)A+, only thermal emission was detected in some sources. Several other
sources with wider lines in the transition 6(-1)-5(0)E also may be masers,
since they do not show any emission at the two other methanol transitons near
133 GHz. These are NGC2071, S231, S255, GGD27, also known as Class I masers.
The ratio of intensities and line widths of the 133 GHz masers and 44 GHz
masers is consistent with the saturated maser model, in which the line
rebroadening with respect to unsaturated masers is suppressed by cross
relaxation due to elastic collisions.Comment: 4 pages, AASTeX text, uses aasms4.sty, 2 Postscript figures, to be
published in Ap
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