65 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
Unifying the low-temperature photoluminescence spectra of carbon nanotubes: the role of acoustic phonon confinement
At low temperature the photoluminescence of single-wall carbon nanotubes show
a large variety of spectral profiles ranging from ultra narrow lines in
suspended nanotubes to broad and asymmetrical line-shapes that puzzle the
current interpretation in terms of exciton-phonon coupling. Here, we present a
complete set of photoluminescence profiles in matrix embedded nanotubes
including unprecedented narrow emission lines. We demonstrate that the
diversity of the low-temperature luminescence profiles in nanotubes originates
in tiny modifications of their low-energy acoustic phonon modes. When low
energy modes are locally suppressed, a sharp photoluminescence line as narrow
as 0.7 meV is restored. Furthermore, multi-peak luminescence profiles with
specific temperature dependence show the presence of confined phonon modes
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
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
Intraband and intersubband many-body effects in the nonlinear optical response of single-wall carbon nanotubes
International audienceWe report on the nonlinear optical response of a mono-chiral sample of (6,5) single-wall carbon nanotubes by means of broad-band two-color pump-probe spectroscopy with selective excitation of the S11 excitons. By using a moment analysis of the transient spectra, we show that all the nonlinear features can be accurately accounted for by elementary deformations of the linear absorption spectrum. The photo-generation of S11 excitons induces a broadening and a blue shift of both the S11 and S22 excitonic transitions. In contrast, only the S11 transition shows a reduction of oscillator strength, ruling out population up-conversion. These nonlinear signatures result from many-body effects, including phase-space filling, wave-function renormalization and exciton collisions. This framework is sufficient to interpret the magnitude of the observed nonlinearities and stress the importance of intersubband exciton interactions. Remarkably, we show that these intersubband interactions have the same magnitude as the intraband ones and bring the major contribution to the photo-bleaching of the S22 excitonic transition upon S11 excitation through energy shift and broadening
An aqueous one-pot route to gold/quantum rod heterostructured nanoparticles functionalized with DNA
International audienc
The use of passive seismological imaging in speleogenetic studies: an example from Kanaan Cave, Lebanon
Among many parameters that control the evolution of caves stands the volume of unconsolidated clay sediments generally produced by the alteration of the calcareous rocks. Here we introduce the use of a passive seismological imaging technique to investigate the clay deposits and estimate its total volume in a cave. Applied for the first time for speleogenesis studies, the HVSR (Horizontal / Vertical Spectral Ration) is a geophysical technique that can help better interpret cave geomorphology. We apply seismological spectral techniques (H/V ratio) on ambient noise vibrations to derive the clay volume, as well as its shape. This technique applied on the clay volume reveals some internal details, such as fallen blocks prior to the deposit accumulation and helps to understand deposit evacuation dynamics. The study focuses on the Kanaan Cave, located in Metn District, Lebanon, and reveals new stages related to the cave speleogenesis. This technique could be applied on ‘paragenetic’ caves where clay volume is frequently present in order to constrain the clay volume and reconstruct the buried floor shape of the cave, underneath the clay deposit
Framework for in-service teacher education for sustainability: some principles and strategies
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Framework for education for sustainability: enhancing competences in education
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