1,061 research outputs found
Comparison of Pion-Kaon Scattering in SU(3) Chiral Perturbation Theory and Dispersion Relations
We establish the framework for the comparison of scattering
amplitudes from SU(3) chiral perturbation theory with suitable dispersive
representations which result from the combination of certain fixed-t dispersion
relations with dispersion relations on hyperbolic curves. This allows for
predictions for some combinations of low energy constants appearing in higher
order calculations of chiral perturbation theory. Using a simple
parametrization for the lowest partial waves, first estimates for some
combinations are presented.Comment: 20 pages, LaTeX2e; replaced with version to appear in European
Physical Journal C; typographical errors removed, minor stylistic change
Persistent current magnification in a double quantum-ring system
The electronic transport in a system of two quantum rings side-coupled to a
quantum wire is studied via a single-band tunneling tight-binding Hamiltonian.
We derived analytical expressions for the conductance, density of states and
the persistent current when the rings are threaded by magnetic fluxes. We found
a clear manifestation of the presence of bound states in each one of those
physical quantities when either the flux difference or the sum of the fluxes
are zero or integer multiples of a quantum of flux. These bound states play an
important role in the magnification of the persistent current in the rings. We
also found that the persistent current keeps a large amplitude even for strong
ring-wire coupling.Comment: 15 pages, 10 figures. Submitted to PR
Full counting statistics for voltage and dephasing probes
We present a stochastic path integral method to calculate the full counting
statistics of conductors with energy conserving dephasing probes and
dissipative voltage probes. The approach is explained for the experimentally
important case of a Mach-Zehnder interferometer, but is easily generalized to
more complicated setups. For all geometries where dephasing may be modeled by a
single one-channel dephasing probe we prove that our method yields the same
full counting statistics as phase averaging of the cumulant generating
function.Comment: 4 pages, 2 figure
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
Quantum pump driven fermionic Mach-Zehnder interferometer
We have investigated the characteristics of the currents in a pump-driven
fermionic Mach-Zehnder interferometer. The system is implemented in a conductor
in the quantum Hall regime, with the two interferometer arms enclosing an
Aharonov-Bohm flux . Two quantum point contacts with transparency
modulated periodically in time drive the current and act as beam-splitters. The
current has a flux dependent part as well as a flux independent
part . Both current parts show oscillations as a function of frequency
on the two scales determined by the lengths of the interferometer arms. In the
non-adiabatic, high frequency regime oscillates with a constant
amplitude while the amplitude of the oscillations of increases
linearly with frequency. The flux independent part is insensitive to
temperature while the flux dependent part is exponentially
suppressed with increasing temperature. We also find that for low amplitude,
adiabatic pumping rectification effects are absent for semitransparent
beam-splitters. Inelastic dephasing is introduced by coupling one of the
interferometer arms to a voltage probe. For a long charge relaxation time of
the voltage probe, giving a constant probe potential, and the part
of flowing in the arm connected to the probe are suppressed with
increased coupling to the probe. For a short relaxation time, with the
potential of the probe adjusting instantaneously to give zero time dependent
current at the probe, only is suppressed by the coupling to the
probe.Comment: 10 pages, 4 figure
Entangled Hanbury Brown Twiss effects with edge states
Electronic Hanbury Brown Twiss correlations are discussed for geometries in
which transport is along adiabatically guided edge channels. We briefly discuss
partition noise experiments and discuss the effect of inelastic scattering and
dephasing on current correlations. We then consider a two-source Hanbury Brown
Twiss experiment which demonstrates strikingly that even in geometries without
an Aharonov-Bohm effect in the conductance matrix (second-order interference),
correlation functions can (due to fourth-order interference) be sensitive to a
flux. Interestingly we find that this fourth-order interference effect is
closely related to orbital entanglement. The entanglement can be detected via
violation of a Bell Inequality in this geometry even so particles emanate from
uncorrelated sources.Comment: International Symposium "Quantum Hall Effect: Past, Present and
Future
Time-Dependent Current Partition in Mesoscopic Conductors
The currents at the terminals of a mesoscopic conductor are evaluated in the
presence of slowly oscillating potentials applied to the contacts of the
sample. The need to find a charge and current conserving solution to this
dynamic current partition problem is emphasized. We present results for the
electro-chemical admittance describing the long range Coulomb interaction in a
Hartree approach. For multiply connected samples we discuss the symmetry of the
admittance under reversal of an Aharonov-Bohm flux.Comment: 22 pages, 3 figures upon request, IBM RC 1971
Time dependence of evanescent quantum waves
The time dependence of quantum evanescent waves generated by a point source
with an infinite or a limited frequency band is analyzed. The evanescent wave
is characterized by a forerunner (transient) related to the precise way the
source is switched on. It is followed by an asymptotic, monochromatic wave
which at long times reveals the oscillation frequency of the source. For a
source with a sharp onset the forerunner is exponentially larger than the
monochromatic solution and a transition from the transient regime to the
asymtotic regime occurs only at asymptotically large times. In this case, the
traversal time for tunneling plays already a role only in the transient regime.
To enhance the monochromatic solution compared to the forerunner we investigate
(a) frequency band limited sources and (b) the short time Fourier analysis (the
spectrogram) corresponding to a detector which is frequency band limited.
Neither of these two methods leads to a precise determination of the traversal
time. However, if they are limited to determine the traversal time only with a
precision of the traversal time itself both methods are successful: In this
case the transient behavior of the evanescent waves is at a time of the order
of the traversal time followed by a monochromatic wave which reveals the
frequency of the source.Comment: 16 text pages and 9 postscript figure
Charge Fluctuations in Quantum Point Contacts and Chaotic Cavities in the Presence of Transport
We analyze the frequency-dependent current fluctuations induced into a gate
near a quantum point contact or a quantum chaotic cavity. We use a current and
charge conserving, effective scattering approach in which interactions are
treated in random phase approximation. The current fluctuations measured at a
nearby gate, coupled capacitively to the conductor, are determined by the
screened charge fluctuations of the conductor. Both the equilibrium and the
non-equilibrium current noise at the gate can be expressed with the help of
resistances which are related to the charge dynamics on the conductor. We
evaluate these resistances for a point contact and determine their
distributions for an ensemble of chaotic cavities. For a quantum point contact
these resistances exhibit pronounced oscillations with the opening of new
channels. For a chaotic cavity coupled to one channel point contacts the charge
relaxation resistance shows a broad distribution between 1/4 and 1/2 of a
resistance quantum. The non-equilibrium resistance exhibits a broad
distribution between zero and 1/4 of a resistance quantum.Comment: 9 pages, two-column Revtex, 6 figures include
Zero-point fluctuations in the ground state of a mesoscopic normal ring
We investigate the persistent current of a ring with an in-line quantum dot
capacitively coupled to an external circuit. Of special interest is the
magnitude of the persistent current as a function of the external impedance in
the zero temperature limit when the only fluctuations in the external circuit
are zero-point fluctuations. These are time-dependent fluctuations which
polarize the ring-dot structure and we discuss in detail the contribution of
displacement currents to the persistent current. We have earlier discussed an
exact solution for the persistent current and its fluctuations based on a Bethe
ansatz. In this work, we emphasize a physically more intuitive approach using a
Langevin description of the external circuit. This approach is limited to weak
coupling between the ring and the external circuit. We show that the zero
temperature persistent current obtained in this approach is consistent with the
persistent current calculated from a Bethe ansatz solution. In the absence of
coupling our system is a two level system consisting of the ground state and
the first excited state. In the presence of coupling we investigate the
projection of the actual state on the ground state and the first exited state
of the decoupled ring. With each of these projections we can associate a phase
diffusion time. In the zero temperature limit we find that the phase diffusion
time of the excited state projection saturates, whereas the phase diffusion
time of the ground state projection diverges.Comment: 12 pages, 5 figure
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