8,567 research outputs found
Driven activation versus thermal activation
Activated dynamics in a glassy system undergoing steady shear deformation is
studied by numerical simulations. Our results show that the external driving
force has a strong influence on the barrier crossing rate, even though the
reaction coordinate is only weakly coupled to the nonequilibrium system. This
"driven activation" can be quantified by introducing in the Arrhenius
expression an effective temperature, which is close to the one determined from
the fluctuation-dissipation relation. This conclusion is supported by
analytical results for a simplified model system.Comment: 5 pages, 3 figure
Accurate measurement of a 96% input coupling into a cavity using polarization tomography
Pillar microcavities are excellent light-matter interfaces providing an
electromagnetic confinement in small mode volumes with high quality factors.
They also allow the efficient injection and extraction of photons, into and
from the cavity, with potentially near-unity input and output-coupling
efficiencies. Optimizing the input and output coupling is essential, in
particular, in the development of solid-state quantum networks where artificial
atoms are manipulated with single incoming photons. Here we propose a technique
to accurately measure input and output coupling efficiencies using polarization
tomography of the light reflected by the cavity. We use the residual
birefringence of pillar microcavities to distinguish the light coupled to the
cavity from the uncoupled light: the former participates to rotating the
polarization of the reflected beam, while the latter decreases the polarization
purity. Applying this technique to a micropillar cavity, we measure a output coupling and a input coupling with unprecedented
precision.Comment: 6 pages, 3 figure
Sketching sound with voice and gesture
Voice and gestures are natural sketching tools that can be exploited to communicate sonic interactions. In product and interaction design, sounds should be included in the early stages of the design process. Scientists of human motion have shown that auditory stimuli are important in the performance of difficult tasks and can elicit anticipatory postural adjustments in athletes. These findings justify the attention given to sound in interaction design for gaming, especially in action and sports games that afford the development of levels of virtuosity. The sonic manifestations of objects can be designed by acting on their mechanical qualities and by augmenting the objects with synthetic and responsive sound
Genericity aspects in gravitational collapse to black holes and naked singularities
We investigate here the genericity and stability aspects for naked
singularities and black holes that arise as the final states for a complete
gravitational collapse of a spherical massive matter cloud. The form of the
matter considered is a general Type I matter field, which includes most of the
physically reasonable matter fields such as dust, perfect fluids and such other
physically interesting forms of matter widely used in gravitation theory. We
first study here in some detail the effects of small pressure perturbations in
an otherwise pressure-free collapse scenario, and examine how a collapse
evolution that was going to the black hole endstate would be modified and go to
a naked singularity, once small pressures are introduced in the initial data.
This allows us to understand the distribution of black holes and naked
singularities in the initial data space. Collapse is examined in terms of the
evolutions allowed by Einstein equations, under suitable physical conditions
and as evolving from a regular initial data. We then show that both black holes
and naked singularities are generic outcomes of a complete collapse, when
genericity is defined in a suitable sense in an appropriate space.Comment: 24 pages, 6 figures, some changes in text and figures to match the
version accepted for publication by IJMP
Controlled light-matter coupling for a single quantum dot embedded in a pillar microcavity using far-field optical lithography
Using far field optical lithography, a single quantum dot is positioned
within a pillar microcavity with a 50 nm accuracy. The lithography is performed
in-situ at 10 K while measuring the quantum dot emission. Deterministic
spectral and spatial matching of the cavity-dot system is achieved in a single
step process and evidenced by the observation of strong Purcell effect.
Deterministic coupling of two quantum dots to the same optical mode is
achieved, a milestone for quantum computing.Comment: Modified version: new title, additional experimental data in figure
Bistability of the Nuclear Polarisation created through optical pumping in InGaAs Quantum Dots
We show that optical pumping of electron spins in individual InGaAs quantum
dots leads to strong nuclear polarisation that we measure via the Overhauser
shift (OHS) in magneto-photoluminescence experiments between 0 and 4T. We find
a strongly non-monotonous dependence of the OHS on the applied magnetic field,
with a maximum nuclear polarisation of 40% for intermediate magnetic fields. We
observe that the OHS is larger for nuclear fields anti-parallel to the external
field than in the parallel configuration. A bistability in the dependence of
the OHS on the spin polarization of the optically injected electrons is found.
All our findings are qualitatively understood with a model based on a simple
perturbative approach.Comment: Phys Rev B (in press
Dark Matter Prediction from Canonical Quantum Gravity with Frame Fixing
We show how, in canonical quantum cosmology, the frame fixing induces a new
energy density contribution having features compatible with the (actual) cold
dark matter component of the Universe. First we quantize the closed
Friedmann-Robertson-Walker (FRW) model in a sinchronous reference and determine
the spectrum of the super-Hamiltonian in the presence of ultra-relativistic
matter and a perfect gas contribution. Then we include in this model small
inhomogeneous (spherical) perturbations in the spirit of the Lemaitre-Tolman
cosmology. The main issue of our analysis consists in outlining that, in the
classical limit, the non-zero eigenvalue of the super-Hamiltonian can make
account for the present value of the dark matter critical parameter.
Furthermore we obtain a direct correlation between the inhomogeneities in our
dark matter candidate and those one appearing in the ultra-relativistic matter.Comment: 5 pages, to appear on Modern Physics Letters
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