2,085 research outputs found
Quantum-Statistical Current Correlations in Multi-Lead Chaotic Cavities
Quantum mechanics requires that identical particles are treated as
indistinguishable. This requirement leads to correlations in the fluctuating
properties of a system. Theoretical predictions are made for an experiment on a
multi-lead chaotic quantum dot which can identify exchange effects in
electronic current-current correlations. Interestingly, we find that the
ensemble averaged exchange effects are of the order of the channel number, and
are insensitive to dephasing.Comment: 4 pages REVTEX, including two figure
Reflection of light from a disordered medium backed by a phase-conjugating mirror
This is a theoretical study of the interplay of optical phase-conjugation and
multiple scattering. We calculate the intensity of light reflected by a
phase-conjugating mirror when it is placed behind a disordered medium. We
compare the results of a fully phase-coherent theory with those from the theory
of radiative transfer. Both methods are equivalent if the dwell time
\tau_{dwell} of a photon in the disordered medium is much larger than the
inverse of the frequency shift 2\Delta\omega acquired at the phase-conjugating
mirror. When \tau_{dwell} \Delta\omega < 1, in contrast, phase coherence
drastically affects the reflected intensity. In particular, a minimum in the
dependence of the reflectance on the disorder strength disappears when
\Delta\omega is reduced below 1/\tau_{dwell}. The analogies and differences
with Andreev reflection of electrons at the interface between a normal metal
and a superconductor are discussed.Comment: 27 pages RevTeX with 11 figures included with psfi
Non-perturbative calculation of the probability distribution of plane-wave transmission through a disordered waveguide
A non-perturbative random-matrix theory is applied to the transmission of a
monochromatic scalar wave through a disordered waveguide. The probability
distributions of the transmittances T_{mn} and T_n=\sum_m T_{mn} of an incident
mode n are calculated in the thick-waveguide limit, for broken time-reversal
symmetry. A crossover occurs from Rayleigh or Gaussian statistics in the
diffusive regime to lognormal statistics in the localized regime. A
qualitatively different crossover occurs if the disordered region is replaced
by a chaotic cavity. ***Submitted to Physical Review E.***Comment: 7 pages, REVTeX-3.0, 5 postscript figures appended as self-extracting
archive. A complete postscript file with figures and text (4 pages) is
available from http://rulgm4.LeidenUniv.nl/preprints.htm
Spontaneous Emission in Chaotic Cavities
The spontaneous emission rate \Gamma of a two-level atom inside a chaotic
cavity fluctuates strongly from one point to another because of fluctuations in
the local density of modes. For a cavity with perfectly conducting walls and an
opening containing N wavechannels, the distribution of \Gamma is given by
P(\Gamma) \propto \Gamma^{N/2-1}(\Gamma+\Gamma_0)^{-N-1}, where \Gamma_0 is the
free-space rate. For small N the most probable value of \Gamma is much smaller
than the mean value \Gamma_0.Comment: 4 pages, RevTeX, 1 figur
Shot noise in ferromagnet--normal metal systems
A semiclassical theory of the low frequency shot noise in ferromagnet -
normal metal systems is formulated. Non-collinear magnetization directions of
the ferromagnetic leads, arbitrary junctions and the elastic and inelastic
scattering regimes are considered. The shot noise is governed by a set of
mesoscopic parameters that are expressed in terms of the microscopic details of
the junctions in the circuit. Explicit results in the case of ballistic,
tunnel, and diffusive junctions are evaluated. The shot noise, the current and
the Fano factor are calculated for a double barrier ferromagnet - normal metal
- ferromagnet system. It is demonstrated that the shot noise can have a
non-monotonic behavior as a function of the relative angle between the
magnetizations of the ferromagnetic reservoirs.Comment: 17 pages, 7 figure
Random bond XXZ chains with modulated couplings
The magnetization behavior of q-periodic antiferromagnetic spin 1/2
Heisenberg chains under uniform magnetic fields is investigated in a background
of disorder exchange distributions. By means of both real space decimation
procedures and numerical diagonalizations in XX chains, it is found that for
binary disorder the magnetization exhibits wide plateaux at values of
1+2(p-1)/q, where p is the disorder strength. In contrast, no spin gaps are
observed in the presence of continuous exchange distributions. We also study
the magnetic susceptibility at low magnetic fields. For odd q-modulations the
susceptibility exhibits a universal singularity, whereas for q even it displays
a non-universal power law behavior depending on the parameters of the
distribution.Comment: 4 pages, 3 figures. Final version to appear in PR
Transmission through a many-channel random waveguide with absorption
We compute the statistical distribution of the transmittance of a random
waveguide with absorption in the limit of many propagating channels. We
consider the average and fluctuations of the conductance T = tr t^{\dagger} t,
where t is the transmission matrix, the density of transmission eigenvalues
\tau (the eigenvalues of t^{\dagger} t), and the distribution of the plane-wave
transmittances T_a and T_{ab}. For weak absorption (length L smaller than the
exponential absorption length \xi_a), we compute moments of the distributions,
while for strong absorption (L >> \xi_a), we can find the complete
distributions. Our findings explain recent experiments on the transmittance of
random waveguides by Stoytchev and Genack [Phys. Rev. Lett. 79, 309 (1997)].Comment: 13 pages, RevTeX; 9 figures include
Quantum interference and the formation of the proximity effect in chaotic normal-metal/superconducting structures
We discuss a number of basic physical mechanisms relevant to the formation of
the proximity effect in superconductor/normal metal (SN) systems. Specifically,
we review why the proximity effect sharply discriminates between systems with
integrable and chaotic dynamics, respectively, and how this feature can be
incorporated into theories of SN systems. Turning to less well investigated
terrain, we discuss the impact of quantum diffractive scattering on the
structure of the density of states in the normal region. We consider ballistic
systems weakly disordered by pointlike impurities as a test case and
demonstrate that diffractive processes akin to normal metal weak localization
lead to the formation of a hard spectral gap -- a hallmark of SN systems with
chaotic dynamics. Turning to the more difficult case of clean systems with
chaotic boundary scattering, we argue that semiclassical approaches, based on
classifications in terms of classical trajectories, cannot explain the gap
phenomenon. Employing an alternative formalism based on elements of
quasiclassics and the ballistic -model, we demonstrate that the inverse
of the so-called Ehrenfest time is the relevant energy scale in this context.
We discuss some fundamental difficulties related to the formulation of low
energy theories of mesoscopic chaotic systems in general and how they prevent
us from analysing the gap structure in a rigorous manner. Given these
difficulties, we argue that the proximity effect represents a basic and
challenging test phenomenon for theories of quantum chaotic systems.Comment: 21 pages (two-column), 6 figures; references adde
The value of genetic testing in the diagnosis and risk stratification of arrhythmogenic right ventricular cardiomyopathy
BACKGROUND: Arrhythmogenic right ventricular cardiomyopathy (ARVC) is characterized by risk of malignant ventricular arrhythmias (VA). ARVC is diagnosed using an array of clinical tests in the consensus-based task force criteria (TFC), one of which is genetic testing. OBJECTIVE: To investigate the value of genetic testing in diagnosing ARVC and its relation to the occurrence of first malignant VA. METHODS: A multicenter cohort of ARVC patients was scored using the revised 2010 TFC with and without genetic criterion, analyzing any resulting loss or delay of diagnosis. Malignant VA was defined as sustained ventricular arrhythmia (≥30s duration at ≥100 bpm or requiring intervention). RESULTS: We included 402 subjects (55% male, 54% proband, 40 [27-51] years old at presentation) who were diagnosed with definite ARVC. A total of 232 (58%) subjects fulfilled genetic testing criteria. Removing the genetic criterion caused loss of diagnosis in 18 (4%) patients (11/216 [5%] probands, 7/186 [4%] relatives), and delay of diagnosis ≥30 days in 22 (5%) patients (21/216 [10%] probands, 1/186 [0.5%] relative). A first malignant VA occurred in no patients who lost diagnosis and in 3 patients (3/216 [1%] probands and no relatives) during their diagnosis delay, none fatal. Time to event analysis showed no significant difference in time from diagnosis to malignant VA between pathogenic variant carriers and non-carriers. CONCLUSION: Disregarding the genetic criterion of the TFC caused loss or delay of diagnosis in 10% (n=40/402) of ARVC patients. Malignant VA occurred in 1% (n=3/402) of cases with lost or delayed diagnosis, none fatal
Charge densities and charge noise in mesoscopic conductors
We introduce a hierarchy of density of states to characterize the charge
distribution in a mesoscopic conductor. At the bottom of this hierarchy are the
partial density of states which represent the contribution to the local density
of states if both the incident and the out-going scattering channel is
prescribed. The partial density of states play a prominent role in measurements
with a scanning tunneling microscope on multiprobe conductors in the presence
of current flow. The partial density of states determine the degree of
dephasing generated by a weakly coupled voltage probe. In addition the partial
density of states determine the frequency-dependent response of mesoscopic
conductors in the presence of slowly oscillating voltages applied to the
contacts of the sample. The partial density of states permit the formulation of
a Friedel sum rule which can be applied locally. We introduce the off-diagonal
elements of the partial density of states matrix to describe charge fluctuation
processes. This generalization leads to a local Wigner-Smith life-time matrix.Comment: 10 pages, 2 figure
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