136 research outputs found
From Strong to Weak Coupling Regime in a Single GaN Microwire up to Room Temperature
Large bandgap semiconductor microwires constitute a very advantageous
alternative to planar microcavities in the context of room temperature strong
coupling regime between exciton and light. In this work we demonstrate that in
a GaN microwire, the strong coupling regime is achieved up to room temperature
with a large Rabi splitting of 125 meV never achieved before in a Nitride-based
photonic nanostructure. The demonstration relies on a method which doesn't
require any knowledge \'a priori on the photonic eigenmodes energy in the
microwire, i.e. the details of the microwire cross-section shape. Moreover,
using a heavily doped segment within the same microwire, we confirm
experimentally that free excitons provide the oscillator strength for this
strong coupling regime. The measured Rabi splitting to linewidth ratio of 15
matches state of the art planar Nitride-based microcavities, in spite of a much
simpler design and a less demanding fabrication process. These results show
that GaN microwires constitute a simpler and promising system to achieve
electrically pumped lasing in the strong coupling regime.Comment: 14 pages, 4 figure
Controlling the charge environment of single quantum dots in a photonic-crystal cavity
We demonstrate that the presence of charge around a semiconductor quantum dot
(QD) strongly affects its optical properties and produces non-resonant coupling
to the modes of a microcavity. We first show that, besides (multi)exciton
lines, a QD generates a spectrally broad emission which efficiently couples to
cavity modes. Its temporal dynamics shows that it is related to the Coulomb
interaction between the QD (multi)excitons and carriers in the adjacent wetting
layer. This mechanism can be suppressed by the application of an electric
field, making the QD closer to an ideal two-level system.Comment: 12 pages, 4 figure
Single photonics at telecom wavelengths using nanowire superconducting detectors
Single photonic applications - such as quantum key distribution - rely on the
transmission of single photons, and require the ultimate sensitivity that an
optical detector can achieve. Single-photon detectors must convert the energy
of an optical pulse containing a single photon into a measurable electrical
signal. We report on fiber-coupled superconducting single-photon detectors
(SSPDs) with specifications that exceed those of avalanche photodiodes (APDs),
operating at telecommunication wavelength, in sensitivity, temporal resolution
and repetition frequency. The improved performance is demonstrated by measuring
the intensity correlation function g(2)(t) of single-photon states at 1300nm
produced by single semiconductor quantum dots (QDs).Comment: 7 pages, 5 figures - submitted 12 OCT 200
Quantum magnetism and counterflow supersolidity of up-down bosonic dipoles
We study a gas of dipolar Bosons confined in a two-dimensional optical
lattice. Dipoles are considered to point freely in both up and down directions
perpendicular to the lattice plane. This results in a nearest neighbor
repulsive (attractive) interaction for aligned (anti-aligned) dipoles. We find
regions of parameters where the ground state of the system exhibits insulating
phases with ferromagnetic or anti-ferromagnetic ordering, as well as with
rational values of the average magnetization. Evidence for the existence of a
novel counterflow supersolid quantum phase is also presented.Comment: 8 pages, 6 figure
Enhanced spontaneous emission in a photonic crystal light-emitting diode
We report direct evidence of enhanced spontaneous emission in a photonic
crystal (PhC) light-emitting diode. The device consists of p-i-n heterojunction
embedded in a suspended membrane, comprising a layer of self-assembled quantum
dots. Current is injected laterally from the periphery to the center of the
PhC. A well-isolated emission peak at 1300nm from the PhC cavity mode is
observed, and the enhancement of the spontaneous emission rate is clearly
evidenced by time-resolved electroluminescence measurements, showing that our
diode switches off in a time shorter than the bulk radiative and nonradiative
lifetimesComment: 10 page
Growth-interruption-induced low-density InAs quantum dots on GaAs
We investigate the use of growth interruption to obtain low-density InAs quantum dots (QDs) on GaAs. The process was realized by Ostwald-type ripening of a thin InAs layer. It was found that the optical properties of the QDs as a function of growth interruption strongly depend on InAs growth rate. By using this approach, a low density of QDs (4 dots/ ”m2) with uniform size distribution was achieved. As compared to QDs grown without growth interruption, a larger energy separation between the QD confined levels was observed, suggesting a situation closer to the ideal zero-dimensional system. Combining with an InGaAs capping layer such as In-rich QDs enable 1.3 ”m emission at 4 K
Growth-interruption-induced low-density InAs quantum dots on GaAs
We investigate the use of growth interruption to obtain low-density InAs quantum dots (QDs) on GaAs. The process was realized by Ostwald-type ripening of a thin InAs layer. It was found that the optical properties of the QDs as a function of growth interruption strongly depend on InAs growth rate. By using this approach, a low density of QDs (4 dots/mu m(2)) with uniform size distribution was achieved. As compared to QDs grown without growth interruption, a larger energy separation between the QD confined levels was observed, suggesting a situation closer to the ideal zero-dimensional system. Combining with an InGaAs capping layer such as In-rich QDs enable 1.3 mu m emission at 4 K. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.3000483
Enhanced spontaneous emission rate from single InAs quantum dots in a photonic crystal nanocavity at telecom wavelengths
The authors demonstrate coupling at 1.3 micro m between single InAs quantum dots (QDs) and a mode of a two dimensional photonic crystal (PhC) defect cavity with a quality factor of 15 000. By spectrally tuning the cavity mode, they induce coupling with excitonic lines. They perform a time integrated and time-resolved photoluminescence and measure an eightfold increase in the spontaneous emission rate inducing a coupling efficiency of 96%. These measurements indicate the potential of single QDs in PhC cavities as efficient single-photon emitters for fiber-based quantum information processing applications. [on SciFinder (R)
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