177 research outputs found
Determination of the complex microwave photoconductance of a single quantum dot
A small quantum dot containing approximately 20 electrons is realized in a
two-dimensional electron system of an AlGaAs/GaAs heterostructure. Conventional
transport and microwave spectroscopy reveal the dot's electronic structure. By
applying a coherently coupled two-source technique, we are able to determine
the complex microwave induced tunnel current. The amplitude of this
photoconductance resolves photon-assisted tunneling (PAT) in the non-linear
regime through the ground state and an excited state as well. The out-of-phase
component (susceptance) allows to study charge relaxation within the quantum
dot on a time scale comparable to the microwave beat period.Comment: 5.5 pages, 6 figures, accepted by Phys. Rev. B (Jan. B15 2001
Deterministic nano-assembly of a coupled quantum emitter - photonic crystal cavity system
The interaction of a single quantum emitter with its environment is a central
theme in quantum optics. When placed in highly confined optical fields, such as
those created in optical cavities or plasmonic structures, the optical
properties of the emitter can change drastically. In particular, photonic
crystal (PC) cavities show high quality factors combined with an extremely
small mode volume. Efficiently coupling a single quantum emitter to a PC cavity
is challenging because of the required positioning accuracy. Here, we
demonstrate deterministic coupling of single Nitrogen-Vacancy (NV) centers to
high-quality gallium phosphide PC cavities, by deterministically positioning
their 50 nm-sized host nanocrystals into the cavity mode maximum with
few-nanometer accuracy. The coupling results in a 25-fold enhancement of NV
center emission at the cavity wavelength. With this technique, the NV center
photoluminescence spectrum can be reshaped allowing for efficient generation of
coherent photons, providing new opportunities for quantum science.Comment: 13 pages, 4 figure
Hybride tussenbelichting met LEDs bij komkommer : Productie, lichtonderschepping, fotosynthese en ontwikkeling vergeleken met conventionele SON-T topbelichting
Bij Wageningen Universiteit zijn de effecten van hybride tussenbelichting (SON-T boven, LED’s tussen het gewas) op de productie van komkommer onderzocht. De verwachting was een 20% hogere energie-efficientie. Er werden gelijktijdig uitgebreide metingen gedaan verklarende factoren, w.o. lichtonderschepping, bladfotosynthese, droge stof verdeling en ontwikkelingssnelheid van het gewas. Hybride tussenbelichting (60% boven, 40% tussen het gewas) werd vergeleken met conventionele topbelichting (100% boven het gewas)
Macro- and Microscopic Aspects of Fruit Water Relations Influencing Growth and Quality in Tomato
Kondo effect and anti-ferromagnetic correlation in transport through tunneling-coupled double quantum dots
We propose to study the transport through tunneling-coupled double quantum
dots (DQDs) connected in series to leads, using the finite- slave-boson mean
field approach developed initially by Kotliar and Ruckenstein [Phys. Rev. Lett.
{\bf 57}, 1362 (1986)]. This approach treats the dot-lead coupling and the
inter-dot tunnelling nonperturbatively at arbitrary Coulomb correlation
, thus allows the anti-ferromagnetic exchange coupling parameter
to appear naturally. We find that, with increasing the inter-dot hopping, the
DQDs manifest three distinct physical scenarios: the Kondo singlet state of
each dot with its adjacent lead, the spin singlet state consisting of local
spins on each dot and the doubly occupied bonding orbital of the coupled dots.
The three states exhibit remarkably distinct behavior in transmission spectrum,
linear and differential conductance and their magnetic-field dependence.
Theoretical predictions agree with numerical renormalization group and Lanczos
calculations, and some of them have been observed in recent experiments.Comment: 5 pages, 5 figures. Physics Review B (Rapid Communication) (in press
Superposition of photon- and phonon- assisted tunneling in coupled quantum dots
We report on electron transport through an artificial molecule formed by two
tunnel coupled quantum dots, which are laterally confined in a two-dimensional
electron system of an AlGaAs/GaAs heterostructure. Coherent
molecular states in the coupled dots are probed by photon-assisted tunneling
(PAT). Above 10 GHz, we observe clear PAT as a result of the resonance between
the microwave photons and the molecular states. Below 8 GHz, a pronounced
superposition of phonon- and photon-assisted tunneling is observed. Coherent
superposition of molecular states persists under excitation of acoustic
phonons.Comment: 5 pages, 4 figure
Engineered arrays of NV color centers in diamond based on implantation of CN- molecules through nanoapertures
We report a versatile method to engineer arrays of nitrogen-vacancy (NV)
color centers in dia- mond at the nanoscale. The defects were produced in
parallel by ion implantation through 80 nm diameter apertures patterned using
electron beam lithography in a PMMA layer deposited on a diamond surface. The
implantation was performed with CN- molecules which increased the NV defect
formation yield. This method could enable the realization of a solid-state
coupled-spin array and could be used for positioning an optically active NV
center on a photonic microstructure.Comment: 12 pages, 3 figure
Renormalization approach for quantum-dot structures under strong alternating fields
We develop a renormalization method for calculating the electronic structure
of single and double quantum dots under intense ac fields. The nanostructures
are emulated by lattice models with a clear continuum limit of the
effective-mass and single-particle approximations. The coupling to the ac field
is treated non-perturbatively by means of the Floquet Hamiltonian. The
renormalization approach allows the study of dressed states of the nanoscopic
system with realistic geometries as well arbitrary strong ac fields. We give
examples of a single quantum dot, emphasizing the analysis of the
effective-mass limit for lattice models, and double-dot structures, where we
discuss the limit of the well used two-level approximation.Comment: 6 pages, 7 figure
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