53 research outputs found
Fabrication and tuning of plasmonic optical nanoantennas around droplet epitaxy quantum dots by cathodoluminescence
We use cathodoluminescence to locate droplet epitaxy quantum dots with a
precision nm before fabricating nanoantennas in their vicinity by
electron-beam lithography. Cathodoluminescence is further used to evidence the
effect of the antennas as a function of their length on the light emitted by
the dot. Experimental results are in good agreement with numerical simulations
of the structures
Plasmonic interferometry: probing launching dipoles in scanning-probe plasmonics
We develop a semi-analytical method for analyzing surface plasmon
interferometry using near-field scanning optical sources. We compare our
approach to Young double hole interferometry experiments using scanning
tunneling microscope (STM) discussed in the literature and realize experiments
with an aperture near-field scanning optical microscope (NSOM) source
positioned near a ring like aperture slit milled in a thick gold film. In both
cases the agreement between experiments and model is very good. We emphasize
the role of dipole orientations and discuss the role of magnetic versus
electric dipole contributions to the imaging process as well as the
directionality of the effective dipoles associated with the various optical and
plasmonic sources.Comment: To appear in Journal of Applied Physics (2014
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
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
Elements for a Theory of Financial Risks
Estimating and controlling large risks has become one of the main concern of
financial institutions. This requires the development of adequate statistical
models and theoretical tools (which go beyond the traditionnal theories based
on Gaussian statistics), and their practical implementation. Here we describe
three interrelated aspects of this program: we first give a brief survey of the
peculiar statistical properties of the empirical price fluctuations. We then
review how an option pricing theory consistent with these statistical features
can be constructed, and compared with real market prices for options. We
finally argue that a true `microscopic' theory of price fluctuations (rather
than a statistical model) would be most valuable for risk assessment. A simple
Langevin-like equation is proposed, as a possible step in this direction.Comment: 22 pages, to appear in `Order, Chance and Risk', Les Houches (March
1998), to be published by Springer/EDP Science
Propriétés optiques de nano-structures métalliques et semi-conductrices
The Raman spectroscopy, involving phonons with nanometric wavelengths, is a powerful technique for investigating nanostructures. It evidences the localisation or mixing effects associated with the electronic states. On the other hand, the spatial coherence of the vibrational modes, at the origin of Raman interferences, allows to probe both electronic and acoustic properties. The approach developed in this manuscript lies in the comparison between measurements and scattering cross section calculations. It gives a quantitative understanding of both frequencies and intensities of observed Raman features. This approach allowed to identify a new coupling mechanism between plasmons and phonons which indeed dominates the low-frequency Raman scattering in metal nano-particules.La spectrométrie Raman, mettant en jeu des phonons de longueur d'onde nanométrique, est une technique de choix pour l'étude des nanostructures. Elle met en évidence les effets de localisation ou de mélange des états électroniques. La cohérence spatiale des modes de vibration, à l'origine du phénomène d'interférence Raman, permet quant à elle de sonder de la structuration spatiale de la matière, tant d'un point de vue électronique qu'acoustique, ouvrant ainsi la voie vers des dispositifs de caractérisation intégrés. La spécificité de l'approche développée dans ce manuscrit réside dans la comparaison entre mesures et calculs de la section efficace de diffusion Raman. Elle apporte une compréhension quantitative des fréquences mais aussi des intensités des pics mesurés. Ainsi, cette démarche a permis d'identifier un nouveau mécanisme de couplage phonon-plasmon qui s'est avéré être le mécanisme dominant la diffusion Raman basses fréquences dans les nano-particules métalliques
Propriétés optiques de nano-structures métalliques et semi-conductrices
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