79 research outputs found
Whispering gallery quantum well exciton polaritons in an Indium Gallium Arsenide microdisk cavity
Despite appealing high-symmetry properties that enable high quality factor
and strong confinement, whispering gallery modes of spherical and circular
resonators have been absent from the field of quantum-well exciton polaritons.
Here we observe whispering gallery exciton polaritons in a Gallium Arsenide
microdisk cavity filled with Indium Gallium Arsenide quantum wells, the testbed
materials of polaritonics. Strong coupling is evidenced in photoluminescence
and resonant spectroscopy, accessed through concomitant confocal microscopy and
near-field optical techniques. Excitonic and optical resonances are tuned by
varying temperature and disk radius, revealing Rabi splittings between 5 and 10
meV. A dedicated analytical quantum model for such circular polaritons is
developed, which reproduces the measured values. At high power, lasing is
observed and accompanied by a blueshift of the emission that points to the
regime of polariton lasing
Efficient optical coupling to gallium arsenide nano-waveguides and resonators with etched conical fibers
We explore new methods for coupling light to on-chip gallium arsenide
nanophotonic structures using etched conical optical fibers. With a
single-sided conical fiber taper, we demonstrate efficient coupling to an
on-chip photonic bus waveguide in a liquid environment. We then show that it is
possible to replace such on-chip bus waveguide by two joined conical fibers in
order to directly couple light into a target whispering gallery disk resonator.
This latter approach proves compliant with demanding environments, such as a
vibrating pulse tube cryostat operating at low temperature, and it is
demonstrated both in the telecom band and in the near infrared close to 900 nm
of wavelength. The versatility, stability, and high coupling efficiency of this
method are promising for quantum optics and sensing experiments in constrained
environments, where obtaining high signal-to-noise ratio remains a challenge
Fundamental limitations of time measurement precision in Hong-Ou-Mandel interferometry
In quantum mechanics, the precision achieved in parameter estimation using a
quantum state as a probe is determined by the measurement strategy employed.
The ultimate quantum limit of precision is bounded by a value set by the state
and its dynamics. Theoretical results have revealed that in interference
measurements with two possible outcomes, this limit can be reached under ideal
conditions of perfect visibility and zero losses. However, in practice, this
cannot be achieved, so precision {\it never} reaches the quantum limit. But how
do experimental setups approach precision limits under realistic circumstances?
In this work we provide a general model for precision limits in two-photon
Hong-Ou-Mandel interferometry for non-perfect visibility. We show that the
scaling of precision with visibility depends on the effective area in
time-frequency phase space occupied by the state used as a probe, and we find
that an optimal scaling exists. We demonstrate our results experimentally for
different states in a set-up where the visibility can be controlled and reaches
up to . In the optimal scenario, a ratio of is observed between
the experimental precision and the quantum limit, establishing a new benchmark
in the field
Alix is required for activity-dependent bulk endocytosis at brain synapses
In chemical synapses undergoing high frequency stimulation, vesicle components can be
retrieved from the plasma membrane via a clathrin-independent process called activitydependent bulk endocytosis (ADBE). Alix (ALG-2-interacting protein X/PDCD6IP) is an
adaptor protein binding to ESCRT and endophilin-A proteins which is required for clathrinindependent endocytosis in fibroblasts. Alix is expressed in neurons and concentrates at
synapses during epileptic seizures. Here, we used cultured neurons to show that Alix is
recruited to presynapses where it interacts with and concentrates endophilin-A during conditions triggering ADBE. Using Alix knockout (ko) neurons, we showed that this recruitment,
which requires interaction with the calcium-binding protein ALG-2, is necessary for ADBE.
We also found that presynaptic compartments of Alix ko hippocampi display subtle morphological defects compatible with flawed synaptic activity and plasticity detected electrophysiologically. Furthermore, mice lacking Alix in the forebrain undergo less seizures during
kainate-induced status epilepticus and reduced propagation of the epileptiform activity.
These results thus show that impairment of ADBE due to the lack of neuronal Alix leads to
abnormal synaptic recovery during physiological or pathological repeated stimulations
Antibiotic Therapy of Plague: A Review
International audiencePlague-a deadly disease caused by the bacterium Yersinia pestis-is still an international public health concern. There are three main clinical forms: bubonic plague, septicemic plague, and pulmonary plague. In all three forms, the symptoms appear suddenly and progress very rapidly. Early antibiotic therapy is essential for countering the disease. Several classes of antibiotics (e.g., tetracyclines, fluoroquinolones, aminoglycosides, sulfonamides, chloramphenicol, rifamycin, and beta-lactams) are active in vitro against the majority of Y. pestis strains and have demonstrated efficacy in various animal models. However, some discrepancies have been reported. Hence, health authorities have approved and recommended several drugs for prophylactic or curative use. Only monotherapy is currently recommended; combination therapy has not shown any benefits in preclinical studies or case reports. Concerns about the emergence of multidrug-resistant strains of Y. pestis have led to the development of new classes of antibiotics and other therapeutics (e.g., LpxC inhibitors, cationic peptides, antivirulence drugs, predatory bacteria, phages, immunotherapy, host-directed therapy, and nutritional immunity). It is difficult to know which of the currently available treatments or therapeutics in development will be most effective for a given form of plague. This is due to the lack of standardization in preclinical studies, conflicting data from case reports, and the small number of clinical trials performed to date
Les amphores dans la ville antique de Durocorturum. Apport des fouilles récentes depuis 2007
International audienc
Semi-analytical theory of mean orbital motion for geosynchronous space debris under gravitational influence
Les amphores dans la ville antique de Durocorturum. Apport des fouilles récentes depuis 2007
International audienc
Semi-analytical theory of mean orbital motion for geosynchronous space debris under gravitational influence
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