1,842 research outputs found
Multifunction MMIC For Miniaturized Solid State Switch Matrix
This paper describes a new multifunction MMIC expressly designed for a reconfiguration matrix equipment.This MMIC has been developed using a standard PHEMT process and includes two switches,a totally switchable-off amplifier and a temperature compensation circuit.The complete circuit has also been designed to interface a standard CMOS control level. Performed simulations and obtained results demonstrate the effectiveness of this approach in reaching compactness and reliability of satellite equipment
Interplay among spin, orbital effects and localization in a GaAs two-dimensional electron gas in a strong in-plane magnetic field
The magnetoresistance of a low carrier density, disordered GaAs based
two-dimensional (2D) electron gas has been measured in parallel magnetic fields
up to 32 T. The feature in the resistance associated with the complete spin
polarization of the carriers shifts down by more than 20 T as the electron
density is reduced, consistent with recent theories taking into account the
enhancement of the electron-electron interactions at low densities.
Nevertheless, the magnetic field for complete polarization, Bp, remains 2-3
times smaller than predicted for a disorder free system. We show, in particular
by studying the temperature dependance of Bp to probe the effective size of the
Fermi sea, that localization plays an important role in determining the spin
polarization of a 2D electron gas.Comment: Published in the Physical Review
Effects of anisotropy in a nonlinear crystal for squeezed vacuum generation
Squeezed vacuum (SV) can be obtained by an optical parametric amplifier (OPA)
with the quantum vacuum state at the input. We are interested in a degenerate
type-I OPA based on parametric down-conversion (PDC) where due to phase
matching requirements, an extraordinary polarized pump must impinge onto a
birefringent crystal with a large \chi(2) nonlinearity. As a consequence of the
optical anisotropy of the medium, the direction of propagation of the pump
wavevector does not coincide with the direction of propagation of its energy,
an effect known as transverse walk-off. For certain pump sizes and crystal
lengths, the transverse walk-off has a strong influence on the spatial spectrum
of the generated radiation, which in turn affects the outcome of any experiment
in which this radiation is employed. In this work we propose a method that
reduces the distortions of the two-photon amplitude (TPA) of the states
considered, by using at least two consecutive crystals instead of one. We show
that after anisotropy compensation the TPA becomes symmetric, allowing for a
simple Schmidt expansion, a procedure that in practice requires states that
come from experimental systems free of anisotropy effects
Coherent Pion Production by Neutrinos
I concentrate in this article on the reaction--coherent pion production by
neutrinos incident on nuclei. A special effort is made in order to describe the
approximations entering the calculation. I conclude that the reaction is well
understood and with appropriate data for hadronic reactions is can be computed
for low and high energies. Because of shortage of space I omitted the resonance
analysis, which is described in articles with my collaborators.Comment: 4 pages. Proceedings of Conf. to be published by APS-Proceeding
Tuning Energy Relaxation along Quantum Hall Channels
The chiral edge channels in the quantum Hall regime are considered ideal
ballistic quantum channels, and have quantum information processing
potentialities. Here, we demonstrate experimentally, at filling factor 2, the
efficient tuning of the energy relaxation that limits quantum coherence and
permits the return toward equilibrium. Energy relaxation along an edge channel
is controllably enhanced by increasing its transmission toward a floating ohmic
contact, in quantitative agreement with predictions. Moreover, by forming a
closed inner edge channel loop, we freeze energy exchanges in the outer
channel. This result also elucidates the inelastic mechanisms at work at
filling factor 2, informing us in particular that those within the outer edge
channel are negligible.Comment: 8 pages including supplementary materia
Noise dephasing in the edge states of the Integer Quantum Hall regime
An electronic Mach Zehnder interferometer is used in the integer quantum hall
regime at filling factor 2, to study the dephasing of the interferences. This
is found to be induced by the electrical noise existing in the edge states
capacitively coupled to each others. Electrical shot noise created in one
channel leads to phase randomization in the other, which destroys the
interference pattern. These findings are extended to the dephasing induced by
thermal noise instead of shot noise: it explains the underlying mechanism
responsible for the finite temperature coherence time of the
edge states at filling factor 2, measured in a recent experiment. Finally, we
present here a theory of the dephasing based on Gaussian noise, which is found
in excellent agreement with our experimental results.Comment: ~4 pages, 4 figure
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