854 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
Quantum Nondemolition Measurement of a Kicked Qubit
We propose a quantum nondemolition measurement using a kicked two-state
system (qubit). By tuning the waiting time between kicks to be the qubit
oscillation period, the kicking apparatus performs a nondemolition measurement.
While dephasing is unavoidable, the nondemolition measurement can (1) slow
relaxation of diagonal density matrix elements, (2) avoid detector back-action,
and (3) allow for a large signal-to-noise ratio. Deviations from the ideal
behavior are studied by allowing for detuning of the waiting time, as well as
finite-time, noisy pulses. The scheme is illustrated with a double-dot qubit
measured by a gate-pulsed quantum point contact.Comment: 7 pages, 1 figur
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
Low frequency admittance of a quantum point contact
We present a current and charge conserving theory for the low frequency
admittance of a quantum point contact. We derive expressions for the
electrochemical capacitance and the displacement current. The latter is
determined by the {\em emittance} which equals the capacitance only in the
limit of vanishing transmission. With the opening of channels the capacitance
and the emittance decrease in a step-like manner in synchronism with the
conductance steps. For vanishing reflection, the capacitance vanishes and the
emittance is negative.Comment: 11 pages, revtex file, 2 ps figure
Optimal energy quanta to current conversion
We present a microscopic discussion of a nano-sized structure which uses the
quantization of energy levels and the physics of single charge Coulomb
interaction to achieve an optimal conversion of heat flow to directed current.
In our structure the quantization of energy levels and the Coulomb blockade
lead to the transfer of quantized packets of energy from a hot source into an
electric conductor to which it is capacitively coupled. The fluctuation
generated transfer of a single energy quantum translates into the directed
motion of a single electron. Thus in our structure the ratio of the charge
current to the heat current is determined by the ratio of the charge quantum to
the energy quantum. An important novel aspect of our approach is that the
direction of energy flow and the direction of electron motion are decoupled.Comment: 9 pages, 6 figure
Magnetic-field asymmetry of nonlinear mesoscopic transport
We investigate departures of the Onsager relations in the nonlinear regime of
electronic transport through mesoscopic systems. We show that the nonlinear
current--voltage characteristic is not an even function of the magnetic field
due only to the magnetic-field dependence of the screening potential within the
conductor. We illustrate this result for two types of conductors: A quantum
Hall bar with an antidot and a chaotic cavity connected to quantum point
contacts. For the chaotic cavity we obtain through random matrix theory an
asymmetry in the fluctuations of the nonlinear conductance that vanishes
rapidly with the size of the contacts.Comment: 4 pages, 2 figures. Published versio
Effect of incoherent scattering on shot noise correlations in the quantum Hall regime
We investigate the effect of incoherent scattering in a Hanbury Brown and
Twiss situation with electrons in edge states of a three-terminal conductor
submitted to a strong perpendicular magnetic field. The modelization of
incoherent scattering is performed by introducing an additional voltage probe
through which the current is kept equal to zero which causes voltage
fluctuations at this probe. It is shown that inelastic scattering can lead in
this framework to positive correlations, whereas correlations remain always
negative for quasi-elastic scattering.Comment: 5 pages latex, 5 eps figure
Theory of conductance and noise additivity in parallel mesoscopic conductors
We present a theory of conductance and noise in generic mesoscopic conductors
connected in parallel, and we demonstrate that the additivity of conductance
and of shot noise arises as a sole property of the junctions connecting the two
(or more) conductors in parallel. Consequences on the functionality of devices
based on the Aharonov-Bohm effect are also drawn.Comment: 4 pages, 2 figure
Pion-Pion Scattering in Chiral Perturbation and Dispersion Relation Theories
Chiral perturbation theory, the low energy effective theory of the strong
interactions for the light pseudoscalar degrees of freedom, is based on
effective Lagrangian techniques and is an expansion in the powers of the
external momenta and the powers of the quark masses, which correct the
soft-pion theorems. Our primary emphasis will be on the problem of
scattering. After briefly reviewing these features and some results, we review
some features of scattering.Comment: Invited talk at the "Frontiers of Fundamental Physics" Symposium, B.
M. Birla Science Centre, Hyderabad, India, December 30, 1998- January 1,
1999, Plain latex (to be run twice), 20 page
Weakly nonlinear quantum transport: an exactly solvable model
We have studied the weakly non-linear quantum transport properties of a
two-dimensional quantum wire which can be solved exactly. The non-linear
transport coefficients have been calculated and interesting physical properties
revealed. In particular we found that as the incoming electron energy
approaches a resonant point given by energy , where the transport is
characterized by a complete reflection, the second order non-linear conductance
changes its sign. This has interesting implications to the current-voltage
characteristics. We have also investigated the establishment of the gauge
invariance condition. We found that for systems with a finite scattering
region, correction terms to the theoretical formalism are needed to preserve
the gauge invariance. These corrections were derived analytically for this
model.Comment: 15 pages, LaTeX, submitted to Phys. Rev.
- …