366 research outputs found
Mapping the local density of optical states of a photonic crystal with single quantum dots
We use single self-assembled InGaAs quantum dots as internal probes to map
the local density of optical states of photonic crystal membranes. The employed
technique separates contributions from non-radiative recombination and
spin-flip processes by properly accounting for the role of the exciton fine
structure. We observe inhibition factors as high as 55 and compare our results
to local density of optical states calculations available from the literature,
thereby establishing a quantitative understanding of photon emission in
photonic crystal membranes.Comment: 4 pages, 3 figure
Electro-optic routing of photons from single quantum dots in photonic integrated circuits
Recent breakthroughs in solid-state photonic quantum technologies enable
generating and detecting single photons with near-unity efficiency as required
for a range of photonic quantum technologies. The lack of methods to
simultaneously generate and control photons within the same chip, however, has
formed a main obstacle to achieving efficient multi-qubit gates and to harness
the advantages of chip-scale quantum photonics. Here we propose and demonstrate
an integrated voltage-controlled phase shifter based on the electro-optic
effect in suspended photonic waveguides with embedded quantum emitters. The
phase control allows building a compact Mach-Zehnder interferometer with two
orthogonal arms, taking advantage of the anisotropic electro-optic response in
gallium arsenide. Photons emitted by single self-assembled quantum dots can be
actively routed into the two outputs of the interferometer. These results,
together with the observed sub-microsecond response time, constitute a
significant step towards chip-scale single-photon-source de-multiplexing,
fiber-loop boson sampling, and linear optical quantum computing.Comment: 7 pages, 4 figues + supplementary informatio
The Apolipoprotein E Antagonistic Pleiotropy Hypothesis: Review and Recommendations
Research on apolipoprotein E (APOE) has consistently revealed a relationship between the gene's Δ4 allele and risk for development of Alzheimer's disease (AD). However, research with younger populations of Δ4 carriers has suggested that the APOE Δ4 allele may in fact be beneficial in earlier ages and may only confer risk of cognitive decline later in life. Accordingly, we and others have proposed that APOE may represent an example of antagonistic pleiotropy. Antagonistic pleiotropy is an evolutionary biology concept that proposes certain genes or alleles that may differentially impact fitness during different life stages. We critically review this hypothesis in light of new research of the impact of APOE on cognition and neural integrity across the lifespan. We provide recommendations for the revision of the antagonistic pleiotropy hypothesis of APOE and suggest important avenues for future research in this area
Single-photon nonlinear optics with a quantum dot in a waveguide
Strong nonlinear interactions between photons enable logic operations for
both classical and quantum-information technology. Unfortunately, nonlinear
interactions are usually feeble and therefore all-optical logic gates tend to
be inefficient. A quantum emitter deterministically coupled to a propagating
mode fundamentally changes the situation, since each photon inevitably
interacts with the emitter, and highly correlated many-photon states may be
created . Here we show that a single quantum dot in a photonic-crystal
waveguide can be utilized as a giant nonlinearity sensitive at the
single-photon level. The nonlinear response is revealed from the intensity and
quantum statistics of the scattered photons, and contains contributions from an
entangled photon-photon bound state. The quantum nonlinearity will find
immediate applications for deterministic Bell-state measurements and
single-photon transistors and paves the way to scalable waveguide-based
photonic quantum-computing architectures
Impact Ionization in ZnS
The impact ionization rate and its orientation dependence in k space is
calculated for ZnS. The numerical results indicate a strong correlation to the
band structure. The use of a q-dependent screening function for the Coulomb
interaction between conduction and valence electrons is found to be essential.
A simple fit formula is presented for easy calculation of the energy dependent
transition rate.Comment: 9 pages LaTeX file, 3 EPS-figures (use psfig.sty), accepted for
publication in PRB as brief Report (LaTeX source replaces raw-postscript
file
Sobre o conceito e a tarefa da ciĂȘncia psĂquica
"Sobre o conceito e a tarefa da ciĂȘncia psĂquica" é a tradução do texto "Ueber Begriff und Aufgabe der psychischen Wissenschaft" de autoria do filĂłsofo alemĂŁo Franz Brentano. Trata-se, de fato, da primeira parte do capĂtulo 1 da principal obra brentaniana: Psychologie vom empirischen Standpunkte, Frankfurt, Ontos Verlag, 2008. p. 19-42.
Cavity Quantum Electrodynamics with Anderson-localized Modes
A major challenge in quantum optics and quantum information technology is to
enhance the interaction between single photons and single quantum emitters.
Highly engineered optical cavities are generally implemented requiring
nanoscale fabrication precision. We demonstrate a fundamentally different
approach in which disorder is used as a resource rather than a nuisance. We
generate strongly confined Anderson-localized cavity modes by deliberately
adding disorder to photonic crystal waveguides. The emission rate of a
semiconductor quantum dot embedded in the waveguide is enhanced by a factor of
15 on resonance with the Anderson-localized mode and 94 % of the emitted
single-photons couple to the mode. Disordered photonic media thus provide an
efficient platform for quantum electrodynamics offering an approach to
inherently disorder-robust quantum information devices
Size-Dependence of the Wavefunction of Self-Assembled Quantum Dots
The radiative and non-radiative decay rates of InAs quantum dots are measured
by controlling the local density of optical states near an interface. From
time-resolved measurements we extract the oscillator strength and the quantum
efficiency and their dependence on emission energy. From our results and a
theoretical model we determine the striking dependence of the overlap of the
electron and hole wavefunctions on the quantum dot size. We conclude that the
optical quality is best for large quantum dots, which is important in order to
optimally tailor quantum dot emitters for, e.g., quantum electrodynamics
experiments.Comment: 5 pages, 3 figure
Nonlocal Electrodynamics of Rotating Systems
The nonlocal electrodynamics of uniformly rotating systems is presented and
its predictions are discussed. In this case, due to paucity of experimental
data, the nonlocal theory cannot be directly confronted with observation at
present. The approach adopted here is therefore based on the correspondence
principle: the nonrelativistic quantum physics of electrons in circular
"orbits" is studied. The helicity dependence of the photoeffect from the
circular states of atomic hydrogen is explored as well as the resonant
absorption of a photon by an electron in a circular "orbit" about a uniform
magnetic field. Qualitative agreement of the predictions of the classical
nonlocal electrodynamics with quantum-mechanical results is demonstrated in the
correspondence regime.Comment: 23 pages, no figures, submitted for publicatio
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