280,371 research outputs found
Solid-state quantum optics with quantum dots in photonic nanostructures
Quantum nanophotonics has become a new research frontier where quantum optics
is combined with nanophotonics in order to enhance and control the interaction
between strongly confined light and quantum emitters. Such progress provides a
promising pathway towards quantum-information processing on an all-solid-state
platform. Here we review recent progress on experiments with single quantum
dots in nanophotonic structures. Embedding the quantum dots in photonic
band-gap structures offers a way of controlling spontaneous emission of single
photons to a degree that is determined by the local light-matter coupling
strength. Introducing defects in photonic crystals implies new functionalities.
For instance, efficient and strongly confined cavities can be constructed
enabling cavity-quantum-electrodynamics experiments. Furthermore, the speed of
light can be tailored in a photonic-crystal waveguide forming the basis for
highly efficient single-photon sources where the photons are channeled into the
slowly propagating mode of the waveguide. Finally, we will discuss some of the
surprises that arise in solid-state implementations of quantum-optics
experiments in comparison to their atomic counterparts. In particular, it will
be shown that the celebrated point-dipole description of light-matter
interaction can break down when quantum dots are coupled to plasmon
nanostructures.Comment: Review. 15 pages, 9 figure
Anomalous lack of decoherence of the Macroscopic Quantum Superpositions based on phase-covariant Quantum Cloning
We show that all Macroscopic Quantum Superpositions (MQS) based on
phase-covariant quantum cloning are characterized by an anomalous high
resilence to the de-coherence processes. The analysis supports the results of
recent MQS experiments and leads to conceive a useful conjecture regarding the
realization of complex decoherence - free structures for quantum information,
such as the quantum computer.Comment: 4 pages, 3 figure
Polariton Dispersion Law in Periodic Bragg and Near-Bragg Multiple Quantum Well Structures
The structure of polariton spectrum is analyzed for periodic multiple quantum
well structures with periods at or close to Bragg resonance condition at the
wavelength of the exciton resonance. The results obtained used to discuss
recent reflection and luminescent experiments by M. H\"{u}bner et al [Phys.
Rev. Lett. {\bf 83}, 2841 (1999)] carried out with long multiple quantum well
structures. It is argued that the discussion of quantum well structures with
large number of wells is more appropriate in terms of normal modes of infinite
periodic structures rather then in terms of super- and sub- radiant modes.Comment: replaced with a new version, an error in one of the equations is
correcte
Quantum Structure in Cognition, Origins, Developments, Successes and Expectations
We provide an overview of the results we have attained in the last decade on
the identification of quantum structures in cognition and, more specifically,
in the formalization and representation of natural concepts. We firstly discuss
the quantum foundational reasons that led us to investigate the mechanisms of
formation and combination of concepts in human reasoning, starting from the
empirically observed deviations from classical logical and probabilistic
structures. We then develop our quantum-theoretic perspective in Fock space
which allows successful modeling of various sets of cognitive experiments
collected by different scientists, including ourselves. In addition, we
formulate a unified explanatory hypothesis for the presence of quantum
structures in cognitive processes, and discuss our recent discovery of further
quantum aspects in concept combinations, namely, 'entanglement' and
'indistinguishability'. We finally illustrate perspectives for future research.Comment: 25 pages. arXiv admin note: text overlap with arXiv:1412.870
Spin and orbital mechanisms of the magneto-gyrotropic photogalvanic effects in GaAs/AlGaAs quantum well structures
We report on the study of the linear and circular magneto-gyrotropic
photogalvanic effect (MPGE) in GaAs/AlGaAs quantum well structures. Using the
fact that in such structures the Land\'e-factor g* depends on the quantum well
(QW) width and has different signs for narrow and wide QWs, we succeeded to
separate spin and orbital contributions to both MPGEs. Our experiments show
that, for most quantum well widths, the PGEs are mainly driven by spin-related
mechanisms, which results in a photocurrent proportional to the g* factor. In
structures with a vanishingly small g* factor, however, linear and circular
MPGE are also detected, proving the existence of orbital mechanisms.Comment: 10 pages, 10 figure
Optical Properties and Modal Gain of InGaN Quantum Dot Stacks
We present investigations of the optical properties of stacked InGaN quantum
dot layers and demonstrate their advantage over single quantum dot layer
structures. Measurements were performed on structures containing a single layer
with quantum dots or threefold stacked quantum dot layers, respectively. A
superlinear increase of the quantum dot related photoluminescence is detected
with increasing number of quantum dot layers while other relevant GaN related
spectral features are much less intensive when compared to the
photoluminescence of a single quantum dot layer. The quantum dot character of
the active material is verified by microphotoluminescence experiments at
different temperatures. For the possible integration within optical devices in
the future the threshold power density was investigated as well as the modal
gain by using the variable stripe length method.Comment: 9 Pages, 4 Figure
Subband Engineering Even-Denominator Quantum Hall States
Proposed even-denominator fractional quantum Hall effect (FQHE) states
suggest the possibility of excitations with non-Abelian braid statistics.
Recent experiments on wide square quantum wells observe even-denominator FQHE
even under electrostatic tilt. We theoretically analyze these structures and
develop a procedure to accurately test proposed quantum Hall wavefunctions. We
find that tilted wells favor partial subband polarization to yield Abelian
even-denominator states. Our results show that tilting quantum wells
effectively engineers different interaction potentials allowing exploration of
a wide variety of even-denominator states
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