202 research outputs found
Fast build up of photorefractive spatial solitons in iron doped indium phosphide
Conférence OralInternational audiencePhotorefractive (PR) spatial soliton propagation hints that all optical routing can be achieved through soliton interactions. This requires, however, fast build up and sensitivity to telecommunication wavelengths. We have investigated the build up of infrared (1,06m) photorefractive solitons in iron doped indium phosphide (InP:Fe) and shown that PR self focusing occurs at input powers of hundreds of W and intensities in the range of W/cm2, showing a build up time down to the microsecond
Wave-mixing origin and optimization in single and compact aluminum nanoantennas
The outstanding optical properties for plasmon resonances in noble metal
nanoparticles enable the observation of non-linear optical processes such as
second-harmonic generation (SHG) at the nanoscale. Here, we investigate the SHG
process in single rectangular aluminum nanoantennas and demonstrate that i) a
doubly resonant regime can be achieved in very compact nanostructures, yielding
a 7.5 enhancement compared to singly resonant structures and ii) the
local surface and nonlocal bulk
contributions can be separated while imaging resonant nanostructures excited by
a tightly focused beam, provided the local
surface is assumed to be zero, as it is the case in all existing models for
metals. Thanks to the quantitative agreement between experimental and simulated
far-field SHG maps, taking into account the real experimental configuration
(focusing and substrate), we identify the physical origin of the SHG in
aluminum nanoantennas as arising mainly from local
surface sources
Genetic diversity in Tetrachaetum elegans, a mitosporic aquatic fungus.
Tetrachaetum elegans Ingold is a saprobic aquatic hyphomycete for which no sexual stage has yet been described. It occurs most commonly during the initial decay of tree leaves in temperate freshwater habitats and typically sporulates under water. Dispersal of the aquatic fungus takes place primarily in the water column and has a large passive component. Differences in substrate composition (e.g. quality of leaf litter) may also play a role in the distribution of different species or genotypes. The population genetic structure of T. elegans was studied using amplified fragment length polymorphism (AFLP) multilocus fingerprints. The populations were isolated from the leaf litter of three different tree genera, sampled in nine streams distributed throughout a mixed deciduous forest. Molecular markers were developed for 97 monosporic isolates using four selective primer pairs. A total of 247 fragments were scored, of which only 32 were polymorphic. Significant stream differentiation was detected for the isolates considered in this study. Analysis of molecular variance revealed that 20% of the genetic variation observed was the result of differences between streams. No correlation between genetic and geographical distances was found but a few multilocus genotypes were observed in different locations. Altogether these results suggest that environmental barriers play a role in the population structure of this aquatic fungus. No clear-cut effect of leaf litter composition on genetic variation could be demonstrated. Finally, tests of linkage disequilibrium between the 32 polymorphic AFLP loci as well as simulations did not provide a final answer regarding clonality in T. elegans. Indeed, it was possible to reject linkage equilibrium at different sampling levels and show that full linkage was unlikely
Theory of Acceleration of Decision Making by Correlated Time Sequences
Photonic accelerators have been intensively studied to provide enhanced
information processing capability to benefit from the unique attributes of
physical processes. Recently, it has been reported that chaotically oscillating
ultrafast time series from a laser, called laser chaos, provide the ability to
solve multi-armed bandit (MAB) problems or decision-making problems at GHz
order. Furthermore, it has been confirmed that the negatively correlated
time-domain structure of laser chaos contributes to the acceleration of
decision-making. However, the underlying mechanism of why decision-making is
accelerated by correlated time series is unknown. In this study, we demonstrate
a theoretical model to account for accelerating decision-making by correlated
time sequence. We first confirm the effectiveness of the negative
autocorrelation inherent in time series for solving two-armed bandit problems
using Fourier transform surrogate methods. We propose a theoretical model that
concerns the correlated time series subjected to the decision-making system and
the internal status of the system therein in a unified manner, inspired by
correlated random walks. We demonstrate that the performance derived
analytically by the theory agrees well with the numerical simulations, which
confirms the validity of the proposed model and leads to optimal system design.
The present study paves the way for improving the effectiveness of correlated
time series for decision-making, impacting artificial intelligence and other
applications
Entangled N-photon states for fair and optimal social decision making
Situations involving competition for resources among entities can be modeled
by the competitive multi-armed bandit (CMAB) problem, which relates to social
issues such as maximizing the total outcome and achieving the fairest resource
repartition among individuals. In these respects, the intrinsic randomness and
global properties of quantum states provide ideal tools for obtaining optimal
solutions to this problem. Based on the previous study of the CMAB problem in
the two-arm, two-player case, this paper presents the theoretical principles
necessary to find polarization-entangled N-photon states that can optimize the
total resource output while ensuring equality among players. These principles
were applied to two-, three-, four-, and five-player cases by using numerical
simulations to reproduce realistic configurations and find the best strategies
to overcome potential misalignment between the polarization measurement systems
of the players. Although a general formula for the N-player case is not
presented here, general derivation rules and a verification algorithm are
proposed. This report demonstrates the potential usability of quantum states in
collective decision making with limited, probabilistic resources, which could
serve as a first step toward quantum-based resource allocation systems.Comment: 22 pages and 7 figures, version 1.1 of July 27th 202
Entangled-photon decision maker
The competitive multi-armed bandit (CMAB) problem is related to social issues
such as maximizing total social benefits while preserving equality among
individuals by overcoming conflicts between individual decisions, which could
seriously decrease social benefits. The study described herein provides
experimental evidence that entangled photons physically resolve the CMAB in the
2-arms 2-players case, maximizing the social rewards while ensuring equality.
Moreover, we demonstrated that deception, or outperforming the other player by
receiving a greater reward, cannot be accomplished in a
polarization-entangled-photon-based system, while deception is achievable in
systems based on classical polarization-correlated photons with fixed
polarizations. Besides, random polarization-correlated photons have been
studied numerically and shown to ensure equality between players and deception
prevention as well, although the CMAB maximum performance is reduced as
compared with entangled photon experiments. Autonomous alignment schemes for
polarization bases were also experimentally demonstrated based only on decision
conflict information observed by an individual without communications between
players. This study paves a way for collective decision making in uncertain
dynamically changing environments based on entangled quantum states, a crucial
step toward utilizing quantum systems for intelligent functionalities
- …