172 research outputs found
Optimal antibunching in passive photonic devices based on coupled nonlinear resonators
We propose the use of weakly nonlinear passive materials for prospective
applications in integrated quantum photonics. It is shown that strong
enhancement of native optical nonlinearities by electromagnetic field
confinement in photonic crystal resonators can lead to single-photon generation
only exploiting the quantum interference of two coupled modes and the effect of
photon blockade under resonant coherent driving. For realistic system
parameters in state of the art microcavities, the efficiency of such
single-photon source is theoretically characterized by means of the
second-order correlation function at zero time delay as the main figure of
merit, where major sources of loss and decoherence are taken into account
within a standard master equation treatment. These results could stimulate the
realization of integrated quantum photonic devices based on non-resonant
material media, fully integrable with current semiconductor technology and
matching the relevant telecom band operational wavelengths, as an alternative
to single-photon nonlinear devices based on cavity-QED with artificial atoms or
single atomic-like emitters.Comment: to appear in New J. Physic
An all-silicon single-photon source by unconventional photon blockade
The lack of suitable quantum emitters in silicon and silicon-based materials
has prevented the realization of room temperature, compact, stable, and
integrated sources of single photons in a scalable on-chip architecture, so
far. Current approaches rely on exploiting the enhanced optical nonlinearity of
silicon through light confinement or slow-light propagation, and are based on
parametric processes that typically require substantial input energy and
spatial footprint to reach a reasonable output yield. Here we propose an
alternative all-silicon device that employs a different paradigm, namely the
interplay between quantum interference and the third-order intrinsic
nonlinearity in a system of two coupled optical cavities. This unconventional
photon blockade allows to produce antibunched radiation at extremely low input
powers. We demonstrate a reliable protocol to operate this mechanism under
pulsed optical excitation, as required for device applications, thus
implementing a true single-photon source. We finally propose a state-of-art
implementation in a standard silicon-based photonic crystal integrated circuit
that outperforms existing parametric devices either in input power or footprint
area.Comment: 5 pages, 3 figures + Supplementary information (3 pages, 2 figures
Signatures of the super fluid-insulator phase transition in laser driven dissipative nonlinear cavity arrays
We analyze the non-equilibrium dynamics of a gas of interacting photons in an
array of coupled dissipative nonlinear cavities driven by a pulsed external
coherent field. Using a mean-field approach, we show that the system exhibits a
phase transition from a Mott-insulator-like to a superfluid regime. For a given
single-photon nonlinearity, the critical value of the photon tunneling rate at
which the phase transition occurs increases with the increasing photon loss
rate. We checked the robustness of the transition by showing its insensitivity
to the initial state prepared by the the pulsed excitation. We find that the
second-order coherence of cavity emission can be used to determine the phase
diagram of an optical many-body system without the need for thermalization.Comment: 4 pages, 4 figure
Acetaldehyde and parkinsonism: role of CYP450 2E1.
The present review update the relationship between acetaldehyde (ACE) and parkinsonism with a specific focus on the role of P450 system and CYP 2E1 isozyme particularly. We have indicated that ACE is able to enhance the parkinsonism induced in mice by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, a neurotoxin able to damage the nigrostriatal dopaminergic pathway. Similarly diethyldithiocarbamate, the main metabolite of disulfiram, a drug widely used to control alcoholism, diallylsulfide (DAS) and phenylisothiocyanate also markedly enhance the toxin-related parkinsonism. All these compounds are substrate/inhibitors of CYP450 2E1 isozyme. The presence of CYP 2E1 has been detected in the dopamine (DA) neurons of rodent Substantia Nigra (SN), but a precise function of the enzyme has not been elucidated yet. By treating CYP 2E1 knockout (KO) mice with the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, the SN induced lesion was significantly reduced when compared with the lesion observed in wild-type animals. Several in vivo and in vitro studies led to the conclusion that CYP 2E1 may enhance the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine toxicity in mice by increasing free radical production inside the dopaminergic neurons. ACE is a good substrate for CYP 2E1 enzyme as the other substrate-inhibitors and by this way may facilitate the susceptibility of dopaminergic neurons to toxic events. The literature suggests that ethanol and/or disulfiram may be responsible for toxic parkinsonism in human and it indicates that basal ganglia are the major targets of disulfiram toxicity. A very recent study reports that there are a decreased methylation of the CYP 2E1 gene and increased expression of CYP 2E1 mRNA in Parkinson's disease (PD) patient brains. This study suggests that epigenetic variants of this cytochrome contribute to the susceptibility, thus confirming multiples lines of evidence which indicate a link between environmental toxins and P
Effects of state dependent correlations on nucleon density and momentum distributions
The proton momentum and density distributions of closed shell nuclei are
calculated within a model treating short--range correlations up to first order
in the cluster expansion. The validity of the model is verified by comparing
the results obtained with purely scalar correlations with those produced by
finite nuclei Fermi Hypernetted Chain calculations. State dependent
correlations are used to calculate momentum and density distributions of 12C,
16O, 40Ca, and 48Ca, and the effects of their tensor components are studied.Comment: 16 pages, latex, 8 figures, accepted for publication in Phys. Rev.
Fabrication of Nanostructured GaAs/AlGaAs Waveguide for Low-Density Polariton Condensation from a Bound State in the Continuum
Exciton-polaritons are hybrid light-matter states that arise from strong
coupling between an exciton resonance and a photonic cavity mode. As bosonic
excitations, they can undergo a phase transition to a condensed state that can
emit coherent light without a population inversion. This aspect makes them good
candidates for thresholdless lasers, yet short exciton-polariton lifetime has
made it difficult to achieve condensation at very low power densities. In this
sense, long-lived symmetry-protected states are excellent candidates to
overcome the limitations that arise from the finite mirror reflectivity of
monolithic microcavities. In this work we use a photonic symmetry protected
bound state in the continuum coupled to an excitonic resonance to achieve
state-of-the-art polariton condensation threshold in GaAs/AlGaAs waveguide.
Most important, we show the influence of fabrication control and how surface
passivation via atomic layer deposition provides a way to reduce exciton
quenching at the grating sidewalls
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