27 research outputs found
Ultra-coherent single photon source
We present a novel type of single photon source in solid state, based on the
coherent laser light scattering by a single InAs quantum dot. We demonstrate
that the coherence of the emitted single photons is tailored by the resonant
excitation with a spectral linewidth below the radiative limit. Our
ultra-coherent source opens the way for integrated quantum devices dedicated to
the generation of single photons with high degrees of indistinguishability
Optically-gated resonant emission in single quantum dots
We report on the resonant emission in coherently-driven single semiconductor
quantum dots. We demonstrate that an ultra-weak non-resonant laser acts as an
optical gate for the quantum dot resonant response. We show that the gate laser
suppresses Coulomb blockade at the origin of a resonant emission quenching, and
that the optically-gated quantum dots systematically behave as ideal two-level
systems in both regimes of coherent and incoherent resonant emission
Periodic squeezing in a polariton Josephson junction
The use of a Kerr nonlinearity to generate squeezed light is a well-known way
to surpass the quantum noise limit along a given field quadrature.
Nevertheless, in the most common regime of weak nonlinearity, a single Kerr
resonator is unable to provide the proper interrelation between the field
amplitude and squeezing required to induce a sizable deviation from Poissonian
statistics. We demonstrate experimentally that weakly coupled bosonic modes
allow exploration of the interplay between squeezing and displacement, which
can give rise to strong deviations from the Poissonian statistics. In
particular, we report on the periodic bunching in a Josephson junction formed
by two coupled exciton-polariton modes. Quantum modeling traces the bunching
back to the presence of quadrature squeezing. Our results, linking the light
statistics to squeezing, are a precursor to the study of nonclassical features
in semiconductor microcavities and other weakly nonlinear bosonic systems.Comment: 6 pages, 4 figure
Effect of a noisy driving field on a bistable polariton system
International audienceWe report on the effect of noise on the characteristics of the bistable polariton emission system. The present experiment provides a time-resolved access to the polariton emission intensity. We evidence the noise-induced transitions between the two stable states of the bistable polaritons. It is shown that the external noise specifications, intensity and correlation time, can efficiently modify the polariton Kramers time and residence time. We find that there is a threshold noise strength that provokes the collapse of the hysteresis loop. The experimental results are reproduced by numerical simulations using Gross-Pitaevskii equation driven by a stochastic excitation
De-Confinement in high multiplicity proton-proton collisions at LHC energies
Recently, the CMS Collaboration has published identified particle transverse
momentum spectra in high multiplicity events at LHC energies =
0.9-13 TeV. In the present work the transverse momentum spectra have been
analyzed in the framework of the color fields inside the clusters of
overlapping strings, which are produced in high energy hadronic collisions. The
non-Abelian nature is reflected in the coherence sum of the color fields which
as a consequence gives rise to an enhancement of the transverse momentum and a
suppression of the multiplicities relative to the non overlapping strings.
The initial temperature and shear viscosity to entropy density ratio
are obtained. For the higher multiplicity events at =7 and 13 TeV
the initial temperature is above the universal hadronization temperature and is
consistent with the creation of de-confined matter. In these small systems it
can be argued that the thermalization is a consequence of the quantum tunneling
through the event horizon introduced by the confining color fields, in analogy
to the Hawking-Unruh effect. The small shear viscosity to entropy density ratio
near the critical temperature suggests that the matter is a strongly
coupled Quark Gluon Plasma.Comment: 5 pages, 4 figure
Photoneutralization and slow capture of carriers in quantum dots probed by resonant excitation spectroscopy
International audienceWe investigate experimentally and theoretically the resonant emission of single InAs/GaAs quantum dots in a planar microcavity. Due to the presence of at least one residual charge in the quantum dots, the resonant excitation of the neutral exciton is blocked. The influence of the residual doping on the initial quantum dots charge state is analyzed, and the resonant emission quenching is interpreted as a Coulomb blockade effect. The use of an additional non-resonant laser in a specific low power regime leads to the carrier draining in quantum dots and allows an efficient optical gating of the exciton resonant emission. A detailed population evolution model, developed to describe the carrier draining and the optical gate effect, perfectly fits the experimental results in the steady state and dynamical regimes of the optical gate with a single set of parameters. We deduce that ultra-slow Auger- and phonon-assisted capture processes govern the carrier draining in quantum dots with relaxation times in the 1 - 100 microsecond range. We conclude that the optical gate acts as a very sensitive probe of the quantum dots population relaxation in an unprecedented slow-capture regime
Photon correlation spectroscopy on a single quantum dot embedded in a nanowire
We have observed strong photoluminescence from a single CdSe quantum dot
embedded in a ZnSe nanowire. Exciton, biexciton and charged exciton lines have
been identified unambiguously using photon correlation spectroscopy. This
technique has provided a detailed picture of the dynamics of this new system.
This type of semi conducting quantum dot turns out to be a very efficient
single photon source in the visible. Its particular growth technique opens new
possibilities as compared to the usual self-asssembled quantum dots
Dark exciton optical spectroscopy of a semiconducting quantum dot embedded in a nanowire
Photoluminescence of a single CdSe quantum dot embedded in a ZnSe nanowire has been investigated. It has been found that the dark exciton has a strong influence on the optical properties. The most visible influence is the strongly reduced excitonic emission compared to the biexcitonic one. Temperature dependent lifetime measurements have allowed us to measure a large splitting of meV between the dark and the bright exciton as well as the spin flip rates between these two states
Listeria pathogenesis and molecular virulence determinants
The gram-positive bacterium Listeria monocytogenes is the causative agent of listeriosis, a highly fatal opportunistic foodborne infection. Pregnant women, neonates, the elderly, and debilitated or immunocompromised patients in general are predominantly affected, although the disease can also develop in normal individuals. Clinical manifestations of invasive listeriosis are usually severe and include abortion, sepsis, and meningoencephalitis. Listeriosis can also manifest as a febrile gastroenteritis syndrome. In addition to humans, L. monocytogenes affects many vertebrate species, including birds. Listeria ivanovii, a second pathogenic species of the genus, is specific for ruminants. Our current view of the pathophysiology of listeriosis derives largely from studies with the mouse infection model. Pathogenic listeriae enter the host primarily through the intestine. The liver is thought to be their first target organ after intestinal translocation. In the liver, listeriae actively multiply until the infection is controlled by a cell-mediated immune response. This initial, subclinical step of listeriosis is thought to be common due to the frequent presence of pathogenic L. monocytogenes in food. In normal indivuals, the continual exposure to listerial antigens probably contributes to the maintenance of anti-Listeria memory T cells. However, in debilitated and immunocompromised patients, the unrestricted proliferation of listeriae in the liver may result in prolonged low-level bacteremia, leading to invasion of the preferred secondary target organs (the brain and the gravid uterus) and to overt clinical disease. L. monocytogenes and L. ivanovii are facultative intracellular parasites able to survive in macrophages and to invade a variety of normally nonphagocytic cells, such as epithelial cells, hepatocytes, and endothelial cells. In all these cell types, pathogenic listeriae go through an intracellular life cycle involving early escape from the phagocytic vacuole, rapid intracytoplasmic multiplication, bacterially induced actin-based motility, and direct spread to neighboring cells, in which they reinitiate the cycle. In this way, listeriae disseminate in host tissues sheltered from the humoral arm of the immune system. Over the last 15 years, a number of virulence factors involved in key steps of this intracellular life cycle have been identified. This review describes in detail the molecular determinants of Listeria virulence and their mechanism of action and summarizes the current knowledge on the pathophysiology of listeriosis and the cell biology and host cell responses to Listeria infection. This article provides an updated perspective of the development of our understanding of Listeria pathogenesis from the first molecular genetic analyses of virulence mechanisms reported in 1985 until the start of the genomic era of Listeria research