25,882 research outputs found
Determination of spin polarization in InAs/GaAs self-assembled quantum dots
The spin polarization of electrons trapped in InAs self-assembled quantum dot
ensembles is investigated. A statistical approach for the population of the
spin levels allows one to infer the spin polarization from the measure values
of the addition energies. From the magneto-capacitance spectroscopy data, the
authors found a fully polarized ensemble of electronic spins above 10 T when
and at 2.8 K. Finally, by including the g-tensor
anisotropy the angular dependence of spin polarization with the magnetic field
orientation and strength could be determined.Comment: 3 pages, 2 figures, Accepted Appl. Phys. Let
Microstrip resonator for microwaves with controllable polarization
In this work the authors implemented a resonator based upon microstrip
cavities that permits the generation of microwaves with arbitrary polarization.
Design, simulation, and implementation of the resonators were performed using
standard printed circuit boards. The electric field distribution was mapped
using a scanning probe cavity perturbation technique. Electron spin resonance
using a standard marker was carried out in order to verify the polarization
control from linear to circular.Comment: 3 pages, 3 figures, submitted to Appl. Phys. Let
Lande g-tensor in semiconductor nanostructures
Understanding the electronic structure of semiconductor nanostructures is not
complete without a detailed description of their corresponding spin-related
properties. Here we explore the response of the shell structure of InAs
self-assembled quantum dots to magnetic fields oriented in several directions,
allowing the mapping of the g-tensor modulus for the s and p shells. We found
that the g-tensors for the s and p shells show a very different behavior. The
s-state in being more localized allows the probing of the confining potential
details by sweeping the magnetic field orientation from the growth direction
towards the in-plane direction. As for the p-state, we found that the g-tensor
modulus is closer to that of the surrounding GaAs, consistent with a larger
delocalization. These results reveal further details of the confining
potentials of self-assembled quantum dots that have not yet been probed, in
addition to the assessment of the g-tensor, which is of fundamental importance
for the implementation of spin related applications.Comment: 4 pages, 4 figure
Dynamic heterogeneities in critical coarsening: Exact results for correlation and response fluctuations in finite-sized spherical models
We study dynamic heterogeneities in the out-of-equilibrium coarsening
dynamics of the spherical ferromagnet after a quench from infinite temperature
to its critical point. A standard way of probing such heterogeneities is by
monitoring the fluctuations of correlation and susceptibility, coarse-grained
over mesoscopic regions. We discuss how to define fluctuating coarse-grained
correlations (C) and susceptibilities (Chi) in models where no quenched
disorder is present. Our focus for the spherical model is on coarse-graining
over the whole volume of spins, which requires accounting for N^{-1/2}
non-Gaussian fluctuations of the spin. The latter are treated as a perturbation
about the leading order Gaussian statistics. We obtain exact results for these
quantities, which enable us to characterise the joint distribution of C and Chi
fluctuations. We find that this distribution is qualitatively different, even
for equilibrium above criticality, from the spin-glass scenario where C and Chi
fluctuations are linked in a manner akin to the fluctuation-dissipation
relation between the average C and Chi. Our results show that coarsening at
criticality is clearly heterogeneous for d>4 and suggest that, as in other
glassy systems, there is a well-defined timescale on which fluctuations across
thermal histories are largest. Surprisingly, however, neither this timescale
nor the amplitude of the heterogeneities increase with the age of the system,
as would be expected from the growing correlation length. For d<4, the strength
of the fluctuations varies on a timescale proportional to the age of the
system; the corresponding amplitude also grows with age, but does not scale
with the correlation volume as might have been expected naively.Comment: 39 pages, 9 figures, version for publication in J. Stat. Mech.
Shortened by cutting all technical details in section 6, with minor
corrections elsewher
Polarization-selective excitation of N-V centers in diamond
The nitrogen-vacancy (N-V) center in diamond is promising as an electron spin
qubit due to its long-lived coherence and optical addressability. The ground
state is a spin triplet with two levels () degenerate at zero
magnetic field. Polarization-selective microwave excitation is an attractive
method to address the spin transitions independently, since this allows
operation down to zero magnetic field. Using a resonator designed to produce
circularly polarized microwaves, we have investigated the polarization
selection rules of the N-V center. We first apply this technique to N-V
ensembles in [100] and [111]-oriented samples. Next, we demonstrate an imaging
technique, based on optical polarization dependence, that allows rapid
identification of the orientations of many single N-V centers. Finally, we test
the microwave polarization selection rules of individual N-V centers of known
orientation
On the spectrum of Farey and Gauss maps
In this paper we introduce Hilbert spaces of holomorphic functions given by
generalized Borel and Laplace transforms which are left invariant by the
transfer operators of the Farey map and its induced version, the Gauss map,
respectively. By means of a suitable operator-valued power series we are able
to study simultaneously the spectrum of both these operators along with the
analytic properties of the associated dynamical zeta functions.Comment: 23 page
Local estimates for entropy densities in coupled map lattices
We present a method to derive an upper bound for the entropy density of
coupled map lattices with local interactions from local observations. To do
this, we use an embedding technique being a combination of time delay and
spatial embedding. This embedding allows us to identify the local character of
the equations of motion. Based on this method we present an approximate
estimate of the entropy density by the correlation integral.Comment: 4 pages, 5 figures include
Rational Trust Modeling
Trust models are widely used in various computer science disciplines. The
main purpose of a trust model is to continuously measure trustworthiness of a
set of entities based on their behaviors. In this article, the novel notion of
"rational trust modeling" is introduced by bridging trust management and game
theory. Note that trust models/reputation systems have been used in game theory
(e.g., repeated games) for a long time, however, game theory has not been
utilized in the process of trust model construction; this is where the novelty
of our approach comes from. In our proposed setting, the designer of a trust
model assumes that the players who intend to utilize the model are
rational/selfish, i.e., they decide to become trustworthy or untrustworthy
based on the utility that they can gain. In other words, the players are
incentivized (or penalized) by the model itself to act properly. The problem of
trust management can be then approached by game theoretical analyses and
solution concepts such as Nash equilibrium. Although rationality might be
built-in in some existing trust models, we intend to formalize the notion of
rational trust modeling from the designer's perspective. This approach will
result in two fascinating outcomes. First of all, the designer of a trust model
can incentivise trustworthiness in the first place by incorporating proper
parameters into the trust function, which can be later utilized among selfish
players in strategic trust-based interactions (e.g., e-commerce scenarios).
Furthermore, using a rational trust model, we can prevent many well-known
attacks on trust models. These two prominent properties also help us to predict
behavior of the players in subsequent steps by game theoretical analyses
Escape configuration lattice near the nematic-isotropic transition: Tilt analogue of blue phases
We predict the possible existence of a new phase of liquid crystals near the
nematic-isotropic () transition. This phase is an achiral, tilt-analogue
of the blue phase and is composed of a lattice of {\em double-tilt},
escape-configuration cylinders. We discuss the structure and the stability of
this phase and provide an estimate of the lattice parameter.Comment: 5 pages, 6 figures (major revision, typos corrected, references
added
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