1,074 research outputs found
Photon Self-Induced Spin to Orbital Conversion in TGG crystal at high laser power
In this paper, we present experimental evidence of a newly discovered
third-order nonlinear optical process Self-Induced Spin-to-Orbital Conversion
(SISTOC) of the photon angular momentum. This effect is the physical mechanism
at the origin of the depolarization of very intense laser beams propagating in
isotropic materials. The SISTOC process, like self-focusing, is triggered by
laser heating leading to a radial temperature gradient in the medium. In this
work we tested the occurrence of SISTOC in a terbium gallium garnet (TGG) rod
for an impinging laser power of about 100~W. To study the SISTOC process we
used different techniques: polarization analysis, interferometry and tomography
of the photon orbital angular momentum. Our results confirm, in particular,
that the apparent depolarization of the beam is due to the occurrence of
maximal entanglement between the spin and orbital angular momentum of the
photons undergoing the SISTOC process. This explanation of the true nature of
the depolarization mechanism could be of some help in finding novel methods to
reduce or to compensate for this usually unwanted depolarization effect in all
cases where very high laser power and good beam quality are required.Comment: 6 pages, 10 figures, submitte
COBE Observations of the Microwave Counterparts of Gamma Ray Bursts
We have used the data from the COBE satellite to search for delayed microwave
emission (31 - 90 GHz) from Gamma Ray Bursts (GRBs). The large beam
of COBE is well matched to the large positional uncertainties in the GRB
locations, although it also means that fluxes from (point source) GRB objects
will be diluted. In view of this we are doing a statistical search of the GRBs
which occurred during the currently released COBE DMR data (years 1990 and
1991), which overlap GRBs recorded by GRO. Here we concentrate on
just the top 10 GRBs (in peak counts/second). We obtain the limits on the
emission by comparing the COBE fluxes before and after the GRB at the GRB
location. Since it is thought that the microwave emission should lag the GRB
event, we have searched the GRB position for emission in the few months
following the GRB occurrence.Comment: 5 pages, LaTE
COMPASS: a 2.6m telescope for CMBR polarization studies
COMPASS (COsmic Microwave Polarization at Small Scale) is an experiment devoted to measuring the polarization of the CMBR. Its design and characteristics are presented
Spin-orbit hybrid entanglement of photons and quantum contextuality
We demonstrate electromagnetic quantum states of single photons and of
correlated photon pairs exhibiting "hybrid" entanglement between spin and
orbital angular momentum. These states are obtained from entangled photon pairs
emitted by spontaneous parametric down conversion, by employing a -plate for
coupling the spin and orbital degrees of freedom of a photon. Entanglement and
contextual quantum behavior (that is also non-local, in the case of photon
pairs) is demonstrated by the reported violation of the
Clauser-Horne-Shimony-Holt inequality. In addition a classical analog of the
hybrid spin-orbit photonic entanglement is reported and discussed.Comment: 5 pages, 3 figure
Detection of Zak phases and topological invariants in a chiral quantum walk of twisted photons
Topological insulators are fascinating states of matter exhibiting protected
edge states and robust quantized features in their bulk. Here, we propose and
validate experimentally a method to detect topological properties in the bulk
of one-dimensional chiral systems. We first introduce the mean chiral
displacement, and we show that it rapidly approaches a multiple of the Zak
phase in the long time limit. Then we measure the Zak phase in a photonic
quantum walk, by direct observation of the mean chiral displacement in its
bulk. Next, we measure the Zak phase in an alternative, inequivalent timeframe,
and combine the two windings to characterize the full phase diagram of this
Floquet system. Finally, we prove the robustness of the measure by introducing
dynamical disorder in the system. This detection method is extremely general,
as it can be applied to all one-dimensional platforms simulating static or
Floquet chiral systems.Comment: 10 pages, 7 color figures (incl. appendices) Close to the published
versio
Vortex and half-vortex dynamics in a spinor quantum fluid of interacting polaritons
Spinorial or multi-component Bose-Einstein condensates may sustain fractional
quanta of circulation, vorticant topological excitations with half integer
windings of phase and polarization. Matter-light quantum fluids, such as
microcavity polaritons, represent a unique test bed for realising strongly
interacting and out-of-equilibrium condensates. The direct access to the phase
of their wavefunction enables us to pursue the quest of whether half vortices
---rather than full integer vortices--- are the fundamental topological
excitations of a spinor polariton fluid. Here, we are able to directly generate
by resonant pulsed excitations, a polariton fluid carrying either the half or
full vortex states as initial condition, and to follow their coherent evolution
using ultrafast holography. Surprisingly we observe a rich phenomenology that
shows a stable evolution of a phase singularity in a single component as well
as in the full vortex state, spiraling, splitting and branching of the initial
cores under different regimes and the proliferation of many vortex anti-vortex
pairs in self generated circular ripples. This allows us to devise the
interplay of nonlinearity and sample disorder in shaping the fluid and driving
the phase singularities dynamicsComment: New version complete with revised modelization, discussion and added
material. 8 pages, 7 figures. Supplementary videos:
https://drive.google.com/folderview?id=0B0QCllnLqdyBfmc2ai0yVF9fa2g2VnZodGUwemVkLThBb3BoOVRKRDJMS2dUdjlZdkRTQk
SARS-CoV-2 and companion animals: sources of information and communication campaign during the COVID-19 pandemic in Italy
This study analyzed data on the sources and the level of Italiansâ awareness on the risk of infection by SARS-CoV-2 at the humanâanimal interface. Data were collected through a survey-type investigation on a representative sample of the Italian population. Forty-five percent of the interviewees were aware that companion animals could be infected by SARS-CoV-2. However, 29.8% were familiar with preventive measures to adopt to avoid viral transmission between infected humans and companion animals, and only 20.7% knew which companion animals could be at risk of infection. Higher awareness regarding the risk of SARS-CoV-2 transmission between animals and humans (51.7%) and the measures to prevent it (33.3%) was detected among companion animalsâ owners. Notably, 40.4% of interviewees were not informed at all. Television broadcasts (26.4%) represented the main source of information, while only 3.5% of the interviewees relied on veterinarians, of which 31.9% considered this source of information as the most trustworthy. Overall, 72.4% of Italians recognized that the communication campaign on COVID-19 and companion animals was inadequate. This survey highlights the need for increasing the public awareness of the risk of companion animals being infected with SARS-CoV-2 and the involvement of professionals in the public communication on zoonoses. © 2023 by the authors
Chirality effects on the IRMPD spectra of basket resorcinarene/nucleoside complexes
The IRMPD spectra of the
ESI-formed proton-bound complexes
of the R,R,R,R- and S,S,S,S-enantiomers
of a bis(diamido)-bridged basket
resorcin[4]arene (R and S) with cytosine
(1), cytidine (2), and cytarabine
(3) were measured in the region 2800â
3600 cm1. Comparison of the IRMPD
spectra with the corresponding
ONIOM (B3LYP/6-31(d):UFF)-calculated
absorption frequencies allowed
the assessment of the vibrational
modes that are responsible for the observed
spectroscopic features. All of
the complexes investigated, apart from
[R·H·3]+, showed similar IRMPD spectra,
which points to similar structural
and conformational landscapes. Their
IRMPD spectra agree with the formation
of several isomeric structures in
the ESI source, wherein the N(3)-protonated
guest establishes noncovalent
interactions with the host amidocarbonyl
groups that are either oriented
inside the host cavity or outside it between
one of the bridged side-chains
and the upper aromatic nucleus. The
IRMPD spectrum of the [R·H·3]+ complex
was clearly different from the
others. This difference is attributed to the effect of intramolecular hydrogen bonding interactions between the
C(2â)-OH group and the aglycone oxygen atom of the nucleosidic guest upon repulsive interactions between
the same oxygen atom and the aromatic rings of the host
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