6,092 research outputs found
A polarisation modulation scheme for measuring vacuum magnetic birefringence with static fields
A novel polarisation modulation scheme for polarimeters based on Fabry-Perot
cavities is presented. The application to the proposed HERA-X experiment aiming
to measuring the magnetic birefringence of vacuum with the HERA superconducting
magnets is discussed
Scattering of accelerated wave packets
Wave-packet scattering from a stationary potential is significantly modified
when the wave-packet is subject to an external time-dependent force during the
interaction. In the semiclassical limit, wave--packet motion is simply
described by Newtonian equations and the external force can, for example,
cancel the potential force making a potential barrier transparent. Here we
consider wave-packet scattering from reflectionless potentials, where in
general the potential becomes reflective when probed by an accelerated
wave-packet. In the particular case of the recently-introduced class of complex
Kramers-Kronig potentials we show that a broad class of time dependent forces
can be applied without inducing any scattering, while there is a breakdown of
the reflectionless property when there is a broadband distribution of initial
particle momentum, involving both positive and negative components.Comment: 13 pages, 4 figures, to appear in Phys. Rev.
Observation of surface states with algebraic localization
We introduce and experimentally demonstrate a class of surface bound states
with algebraic decay in a one-dimensional tight-binding lattice. Such states
have an energy embedded in the spectrum of scattered states and are
structurally stable against perturbations of lattice parameters. Experimental
demonstration of surface states with algebraic localization is presented in an
array of evanescently-coupled optical waveguides with tailored coupling rates.Comment: revised version with Supplemental Material, to appear in Phys. Rev.
Let
Erratum to: A polarisation modulation scheme for measuring vacuum magnetic birefringence with static fields
In the original article unfortunately we missed two typos in the equation for at the top of the fourth page of the article
Ultrafast hot electron dynamics in plasmonic nanostructures: Experiments, modelling, design
Metallic nanostructures exhibit localized surface plasmons (LSPs), which offer unprecedented opportunities for advanced photonic materials and devices. Following resonant photoexcitation, LSPs quickly dephase, giving rise to a distribution of energetic ‘hot’ electrons in the metal. These out-of-equilibrium carriers undergo ultrafast internal relaxation processes, nowadays pivotal in a variety of applications, from photodetection and sensing to the driving of photochemical reactions and ultrafast all-optical modulation of light. Despite the intense research activity, exploitation of hot carriers for real-world nanophotonic devices remains extremely challenging. This is due to the com- plexity inherent to hot carrier relaxation phenomena at the nanoscale, involving short-lived out-of-equilibrium electronic states over a very broad range of energies, in interaction with thermal electronic and phononic baths. These issues call for a comprehensive understanding of ultrafast hot electron dynamics in plasmonic nanostructures. This paper aims to review our contribution to the field: starting from the fundamental physics of plasmonic nanostructures, we first describe the experimental techniques used to probe hot electrons; we then introduce a numerical model of ultrafast nanoscale relaxation processes, and present examples in which experiments and modelling are combined, with the aim of designing novel optical functionalities enabled by ultrafast hot-electron dynamics
The PVLAS experiment: measuring vacuum magnetic birefringence and dichroism with a birefringent Fabry-Perot cavity
Vacuum magnetic birefringence was predicted long time ago and is still
lacking a direct experimental confirmation. Several experimental efforts are
striving to reach this goal, and the sequence of results promises a success in
the next few years. This measurement generally is accompanied by the search for
hypothetical light particles that couple to two photons. The PVLAS experiment
employs a sensitive polarimeter based on a high finesse Fabry-Perot cavity. In
this paper we report on the latest experimental results of this experiment. The
data are analysed taking into account the intrinsic birefringence of the
dielectric mirrors of the cavity. Besides the limit on the vacuum magnetic
birefringence, the measurements also allow the model-independent exclusion of
new regions in the parameter space of axion-like and milli-charged particles.
In particular, these last limits hold also for all types of neutrinos,
resulting in a laboratory limit on their charge
The local stellar population of nova regions in the Large Magellanic Cloud
This study aims at identifying and understanding the parent population of
novae in the Large Magellanic Cloud (LMC) by studying the local, projected,
stellar population. The star formation history of the local environment around
novae is studied based on photometric data of stars and star clusters in the
nova neighbourhood, available in the OGLE II survey and star cluster
catalogues. The ages of stellar population within a few arcmin around novae
regions are estimated using isochrone fits to the V vs (V-I) colour-magnitude
diagrams. The fraction of stars in various evolutionary states are compared
using luminosity functions of the main-sequence stars and the red giant stars.
The age, density and luminosity function of the stellar population are
estimated around 15 novae. The upper limit of the age of the intermediate
stellar population is found to be 4 Gyr in all the regions, excepting the
region around the slow nova LMC 1948. Star formation in these regions is found
to have started between 4 - 2.0 Gyr, with a majority of the regions starting
the star formation at 3.2 Gyr. This star formation event lasted until 1.6 - 0.8
Gyr The star formation history of the underlying population of both the fast
and moderately fast novae indicate their parent population to be similar and
likely to be in the age range 3.2 - 1.0 Gyr. This is in good agreement with the
theoretical age estimates for Galactic cataclysmic variables. The region around
the slow nova shows a stellar population in the age range 1 - 10 Gyr, with a
good fraction belonging to an older population, consistent with the idea that
the progenitors of slow novae belong to older population.Comment: to appear in A&A (final version - error analysis included, typos
corrected, figures 17 and 18 changed
First results from the new PVLAS apparatus: a new limit on vacuum magnetic birefringence
Several groups are carrying out experiments to observe and measure vacuum
magnetic birefringence, predicted by Quantum Electrodynamics (QED). We have
started running the new PVLAS apparatus installed in Ferrara, Italy, and have
measured a noise floor value for the unitary field magnetic birefringence of
vacuum T (the error
represents a 1 deviation). This measurement is compatible with zero and
hence represents a new limit on vacuum magnetic birefringence deriving from non
linear electrodynamics. This result reduces to a factor 50 the gap to be
overcome to measure for the first time the value of predicted by QED:
~T. These birefringence measurements also yield improved
model-independent bounds on the coupling constant of axion-like particles to
two photons, for masses greater than 1 meV, along with a factor two improvement
of the fractional charge limit on millicharged particles (fermions and
scalars), including neutrinos
New PVLAS model independent limit for the axion coupling to for axion masses above 1meV
During 2014 the PVLAS experiment has started data taking with a new apparatus
installed at the INFN Section of Ferrara, Italy. The main target of the
experiment is the observation of magnetic birefringence of vacuum. According to
QED, the ellipticity generated by the magnetic birefringence of vacuum in the
experimental apparatus is expected to be . No ellipticity signal is present so far with a noise floor
after 210 hours of data taking.
The resulting ellipticity limit provides the best model independent upper limit
on the coupling of axions to for axion masses above eV
Classical realization of two-site Fermi-Hubbard systems
A classical wave optics realization of the two-site Hubbard model, describing
the dynamics of interacting fermions in a double-well potential, is proposed
based on light transport in evanescently-coupled optical waveguides.Comment: 4 page
- …