120 research outputs found
Crossing of two Coulomb-Blockade Resonances
We investigate theoretically the transport of non--interacting electrons
through an Aharanov--Bohm (AB) interferometer with two quantum dots (QD)
embedded into its arms. In the Coulomb-blockade regime, transport through each
QD proceeds via a single resonance. The resonances are coupled through the arms
of the AB device but may also be coupled directly. In the framework of the
Landauer--Buttiker approach, we present expressions for the scattering matrix
which depend explicitly on the energies of the two resonances and on the AB
phase. We pay particular attention to the crossing of the two resonances.Comment: 15 pages, 1 figur
Photocount statistics of chaotic lasers
We derive the photocount statistics of the radiation emitted from a chaotic laser resonator in the regime of single-mode lasing. Random spatial variations of the resonator eigenfunctions lead to strong mode-to-mode fluctuations of the laser emission. The distribution of the mean photocount over an ensemble of modes changes qualitatively at the lasing transition, and displays up to three peaks above the lasing threshold
Interference Effects on Kondo-Assisted Transport through Double Quantum Dots
We systematically investigate electron transport through double quantum dots
with particular emphasis on interference induced via multiple paths of electron
propagation. By means of the slave-boson mean-field approximation, we calculate
the conductance, the local density of states, the transmission probability in
the Kondo regime at zero temperature. It is clarified how the Kondo-assisted
transport changes its properties when the system is continuously changed among
the serial, parallel and T-shaped double dots. The obtained results for the
conductance are explained in terms of the Kondo resonances influenced by
interference effects. We also discuss the impacts due to the spin-polarization
of ferromagnetic leads.Comment: 9 pages, 11 figures ; minor corrections and references adde
Friedel phases and phases of transmission amplitudes in quantum scattering systems
We illustrate the relation between the scattering phase appearing in the
Friedel sum rule and the phase of the transmission amplitude for quantum
scatterers connected to two one-dimensional leads. Transmission zero points
cause abrupt phase changes of the phase of the transmission amplitude.
In contrast the Friedel phase is a continuous function of energy. We
investigate these scattering phases for simple scattering problems and
illustrate the behavior of these models by following the path of the
transmission amplitude in the complex plane as a function of energy. We verify
the Friedel sum rule for these models by direct calculation of the scattering
phases and by direct calculation of the density of states.Comment: 12 pages, 12 figure
Scattering phases in quantum dots: an analysis based on lattice models
The properties of scattering phases in quantum dots are analyzed with the
help of lattice models. We first derive the expressions relating the different
scattering phases and the dot Green functions. We analyze in detail the Friedel
sum rule and discuss the deviation of the phase of the transmission amplitude
from the Friedel phase at the zeroes of the transmission. The occurrence of
such zeroes is related to the parity of the isolated dot levels. A statistical
analysis of the isolated dot wave-functions reveals the absence of significant
correlations in the parity for large disorder and the appearance, for weak
disorder, of certain dot states which are strongly coupled to the leads. It is
shown that large differences in the coupling to the leads give rise to an
anomalous charging of the dot levels. A mechanism for the phase lapse observed
experimentally based on this property is discussed and illustrated with model
calculations.Comment: 18 pages, 9 figures. to appear in Physical Review
A Mesoscopic Quantum Eraser
Motivated by a recent experiment by Buks et al. [Nature 391, 871 (1998)] we
consider electron transport through an Aharonov-Bohm interferometer with a
quantum dot in one of its arms. The quantum dot is coupled to a quantum system
with a finite number of states acting as a which-path detector. The
Aharonov-Bohm interference is calculated using a two-particle scattering
approach for the joint transitions in detector and quantum dot. Tracing over
the detector yields dephasing and a reduction of the interference amplitude. We
show that the interference can be restored by a suitable measurement on the
detector and propose a mesoscopic quantum eraser based on this principle.Comment: 7 pages, 2 figures, to appear in Europhys. Lett., uses EuroPhys.sty
and EuroMacro.tex (included
Classical orbit bifurcation and quantum interference in mesoscopic magnetoconductance
We study the magnetoconductance of electrons through a mesoscopic channel
with antidots. Through quantum interference effects, the conductance maxima as
functions of the magnetic field strength and the antidot radius (regulated by
the applied gate voltage) exhibit characteristic dislocations that have been
observed experimentally. Using the semiclassical periodic orbit theory, we
relate these dislocations directly to bifurcations of the leading classes of
periodic orbits.Comment: 4 pages, including 5 figures. Revised version with clarified
discussion and minor editorial change
Field quantization for chaotic resonators with overlapping modes
Feshbach's projector technique is employed to quantize the electromagnetic
field in optical resonators with an arbitray number of escape channels. We find
spectrally overlapping resonator modes coupled due to the damping and noise
inflicted by the external radiation field. For wave chaotic resonators the mode
dynamics is determined by a non--Hermitean random matrix. Upon including an
amplifying medium, our dynamics of open-resonator modes may serve as a starting
point for a quantum theory of random lasing.Comment: 4 pages, 1 figur
Quantum statistics of overlapping modes in open resonators
We study the quantum dynamics of optical fields in weakly confining
resonators with overlapping modes. Employing a recently developed quantization
scheme involving a discrete set of resonator modes and continua of external
modes we derive Langevin equations and a master equation for the resonator
modes. Langevin dynamics and the master equation are proved to be equivalent in
the Markovian limit. Our open-resonator dynamics may be used as a starting
point for a quantum theory of random lasers.Comment: 6 pages, corrected typo
Dephasing and Measurement Efficiency via a Quantum Dot Detector
We study charge detection and controlled dephasing of a mesoscopic system via
a quantum dot detector (QDD), where the mesoscopic system and the QDD are
capacitively coupled. The QDD is considered to have coherent resonant
tunnelling via a single level. It is found that the dephasing rate is
proportional to the square of the conductance of the QDD for the Breit-Wigner
model, showing that the dephasing is completely different from the shot noise
of the detector. The measurement rate, on the other hand, shows a dip near the
resonance. Our findings are peculiar especially for a symmetric detector in the
following aspect: The dephasing rate is maximum at resonance of the QDD where
the detector conductance is insensitive to the charge state of the mesoscopic
system. As a result, the efficiency of the detector shows a dip and vanishes at
resonance, in contrast to the single-channel symmetric non-resonant detector
that has always a maximum efficiency. We find that this difference originates
from a very general property of the scattering matrix: The abrupt phase change
exists in the scattering amplitudes in the presence of the symmetry, which is
insensitive to the detector current but {\em stores} the information of the
quantum state of the mesoscopic system.Comment: 7 pages, 3 figure
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