220 research outputs found
Coherent response of a low T_c Josephson junction to an ultrafast laser pulse
By irradiating with a single ultrafast laser pulse a superconducting
electrode of a Josephson junction it is possible to drive the quasiparticles
(qp's) distribution strongly out of equilibrium. The behavior of the Josephson
device can, thus, be modified on a fast time scale, shorter than the qp's
relaxation time. This could be very useful, in that it allows fast control of
Josephson charge qubits and, in general, of all Josephson devices. If the
energy released to the top layer contact of the junction is of the order
of , the coherence is not degradated, because the perturbation is
very fast. Within the framework of the quasiclassical Keldysh Green's function
theory, we find that the order parameter of decreases. We study the
perturbed dynamics of the junction, when the current bias is close to the
critical current, by integrating numerically its classical equation of motion.
The optical ultrafast pulse can produce switchings of the junction from the
Josephson state to the voltage state. The switches can be controlled by tuning
the laser light intensity and the pulse duration of the Josephson junction.Comment: 17 pages, 5 figure
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
General theory of electromagnetic fluctuations near a homogeneous surface, in terms of its reflection amplitudes
We derive new general expressions for the fluctuating electromagnetic field
outside a homogeneous material surface. The analysis is based on general
results from the thermodynamics of irreversible processes, and requires no
consideration of the material interior, as it only uses knowledge of the
reflection amplitudes for its surface. Therefore, our results are valid for all
homogeneous surfaces, including layered systems and metamaterials, at all
temperatures. In particular, we obtain new formulae for the near-field region,
which are important for interpreting the numerous current experiments probing
proximity effects for macroscopic and/or microscopic bodies separated by small
empty gaps. By use of Onsager's reciprocity relations, we obtain also the
general symmetry properties that must be satisfied by the reflection matrix of
any material.Comment: 5 page
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
Postmodern String Theory: Stochastic Formulation
In this paper we study the dynamics of a statistical ensemble of strings,
building on a recently proposed gauge theory of the string geodesic field. We
show that this stochastic approach is equivalent to the Carath\'eodory
formulation of the Nambu-Goto action, supplemented by an averaging procedure
over the family of classical string world-sheets which are solutions of the
equation of motion. In this new framework, the string geodesic field is
reinterpreted as the Gibbs current density associated with the string
statistical ensemble. Next, we show that the classical field equations derived
from the string gauge action, can be obtained as the semi-classical limit of
the string functional wave equation. For closed strings, the wave equation
itself is completely analogous to the Wheeler-DeWitt equation used in quantum
cosmology. Thus, in the string case, the wave function has support on the space
of all possible spatial loop configurations. Finally, we show that the string
distribution induces a multi-phase, or {\it cellular} structure on the
spacetime manifold characterized by domains with a purely Riemannian geometry
separated by domain walls over which there exists a predominantly Weyl
geometry.Comment: 24pages, ReVTe
Optical measurement of torque exerted on an elongated object by a non-circular laser beam
We have developed a scheme to measure the optical torque, exerted by a laser
beam on a phase object, by measuring the orbital angular momentum of the
transmitted beam. The experiment is a macroscopic simulation of a situation in
optical tweezers, as orbital angular momentum has been widely used to apply
torque to microscopic objects. A hologram designed to generate LG02 modes and a
CCD camera are used to detect the orbital component of the beam. Experimental
results agree with theoretical numerical calculations, and the strength of the
orbital component suggest its usefulness in optical tweezers for
micromanipulation.Comment: 6 pages, 7 figures, v2: minor typographical correction
Quantum many particle systems in ring-shaped optical lattices
In the present work we demonstrate how to realize 1d-optical closed lattice
experimentally, including a {\it tunable} boundary phase-twist. The latter may
induce ``persistent currents'', visible by studing the atoms' momentum
distribution. We show how important phenomena in 1d-physics can be studied by
physical realization of systems of trapped atoms in ring-shaped optical
lattices. A mixture of bosonic and/or fermionic atoms can be loaded into the
lattice, realizing a generic quantum system of many interacting particles.Comment: 10 pages, 5 figures. To be published in PR
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
Optical microrheology using rotating laser-trapped particles
We demonstrate an optical system that can apply and accurately measure the
torque exerted by the trapping beam on a rotating birefringent probe particle.
This allows the viscosity and surface effects within liquid media to be
measured quantitatively on a micron-size scale using a trapped rotating
spherical probe particle. We use the system to measure the viscosity inside a
prototype cellular structure.Comment: 5 pages, 4 figures. v2: bibliographic details, minor text correction
Serologic diagnosis of celiac disease: May it be suitable for adults?
The diagnosis of coeliac disease (CD) in adult patients requires the simultaneous assessment of clinical presentation, serology, and typical histological picture of villous atrophy. However, several years ago, the European Society of Pediatric Gastroenterology, Hepatology, and Nutrition guidelines approved new criteria for the diagnosis in children: Biopsy could be avoided when anti-transglutaminase antibody (TGA) values exceed the cut-off of × 10 upper limit of normal (ULN) and anti-endomysium antibodies are positive, independently from value. This “no biopsy” approach is a decisive need for pediatric population, allowing to avoid stressful endoscopic procedures in children, if unnecessary. This approach relies on the correlation existing in children between TGA levels and assessment of mucosal atrophy according to Marsh’s classification. Several lines of evidence have shown that patients with villous atrophy have markedly elevated TGA levels. Therefore, we aim to perform a narrative review on the topic in adults. Despite that some studies confirmed that the × 10 ULN threshold value has a very good diagnostic performance, several lines of evidence in adults suggest that TGA cut off should be different from that of pediatric population for reaching a good correlation with histological picture. In conclusion, the heterogeneity of study reports as well as some conditions, which may hamper the serological diagnosis of CD (such as seronegative CD and non-celiac villous atrophy) and are much more common in adults than in children, could represent a limitation for the “no biopsy” approach to CD diagnosis in patients outside the pediatric age
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