81 research outputs found
The rebellious girl who wants the perfect man: role assignments in folktales of the bulsa in Northern Ghana
Girls are social misfits in patrilineal and virilocal societies. (Or: Are patrilineal
societies not fit to meet the emotional needs of nubile girls?) They cause problems for their parents as well as for their husbands because their place in
patrilineal societies shifts between their ‘family of orientation’ and their ‘family of procreation.
Boys, in contrast to girls, have their place fixed in their patrilineage as well as in their father’s house and local clan section from birth until death,
and even thereafter as ancestors2
Energiedissipation von Eigenschwingungen im rechteckigen Tank bei laminarer Grenzschicht
Messungen der Energiedissipation stehender Wellen mit laminarer Bewegung wurden im Tank durchgeführt und mit theoretischen Werten verglichen, die sich aus Ableitungen der linearisierten Bewegungsgleichung von NAVIER-STOKES ergeben. Dabei wurde die Dämpfung der Oberflächenauslenkung sowie die von den stehenden Wellen auf den Tankboden ausgeübte Schubspannung gemessen. Es ergab sich eine etwas größere Energiedämpfung als die theoretisch vorhergesagte. Die Schubspannung stimmte innerhalb der Fehlerbreite mit der Theorie überein
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
Nanomechanical single-photon routing
The merger between integrated photonics and quantum optics promises new
opportunities within photonic quantum technology with the very significant
progress on excellent photon-emitter interfaces and advanced optical circuits.
A key missing functionality is rapid circuitry reconfigurability that
ultimately does not introduce loss or emitter decoherence, and operating at a
speed matching the photon generation and quantum memory storage time of the
on-chip quantum emitter. This ambitious goal requires entirely new active
quantum-photonic devices by extending the traditional approaches to
reconfigurability. Here, by merging nano-optomechanics and deterministic
photon-emitter interfaces we demonstrate on-chip single-photon routing with low
loss, small device footprint, and an intrinsic time response approaching the
spin coherence time of solid-state quantum emitters. The device is an essential
building block for constructing advanced quantum photonic architectures
on-chip, towards, e.g., coherent multi-photon sources, deterministic
photon-photon quantum gates, quantum repeater nodes, or scalable quantum
networks.Comment: 7 pages, 3 figures, supplementary informatio
Deterministic positioning of nanophotonic waveguides around single self-assembled quantum dots
The capability to embed self-assembled quantum dots (QDs) at predefined
positions in nanophotonic structures is key to the development of complex
quantum photonic architectures. Here, we demonstrate that QDs can be
deterministically positioned in nanophotonic waveguides by pre-locating QDs
relative to a global reference frame using micro-photoluminescence (PL)
spectroscopy. After nanofabrication, PL images reveal misalignments
between the central axis of the waveguide and the embedded QD of only
) nm and ) nm, for QDs embedded in undoped and doped
membranes, respectively. A priori knowledge of the QD positions allows us to
study the spectral changes introduced by nanofabrication. We record average
spectral shifts ranging from 0.1 to 1.1 nm, indicating that the
fabrication-induced shifts can generally be compensated by electrical or
thermal tuning of the QDs. Finally, we quantify the effects of the
nanofabrication on the polarizability, the permanent dipole moment and the
emission frequency at vanishing electric field of different QD charge states,
finding that these changes are constant down to QD-surface separations of only
70 nm. Consequently, our approach deterministically integrates QDs into
nanophotonic waveguides whose light-fields contain nanoscale structure and
whose group index varies at the nanometer level.Comment: 26 pages, 9 figures. Updated version of the manuscript, with new
appendices and new figure
Quantum optics with near lifetime-limited quantum-dot transitions in a nanophotonic waveguide
Establishing a highly efficient photon-emitter interface where the intrinsic
linewidth broadening is limited solely by spontaneous emission is a key step in
quantum optics. It opens a pathway to coherent light-matter interaction for,
e.g., the generation of highly indistinguishable photons, few-photon optical
nonlinearities, and photon-emitter quantum gates. However, residual broadening
mechanisms are ubiquitous and need to be combated. For solid-state emitters
charge and nuclear spin noise is of importance and the influence of photonic
nanostructures on the broadening has not been clarified. We present near
lifetime-limited linewidths for quantum dots embedded in nanophotonic
waveguides through a resonant transmission experiment. It is found that the
scattering of single photons from the quantum dot can be obtained with an
extinction of , which is limited by the coupling of the quantum
dot to the nanostructure rather than the linewidth broadening. This is obtained
by embedding the quantum dot in an electrically-contacted nanophotonic
membrane. A clear pathway to obtaining even larger single-photon extinction is
laid out, i.e., the approach enables a fully deterministic and coherent
photon-emitter interface in the solid state that is operated at optical
frequencies.Comment: 27 pages, 7 figure
Suspended Spot-Size Converters for Scalable Single-Photon Devices
We report on the realization of a highly efficient optical spot-size
converter for the end-face coupling of single photons from GaAs-based
nanophotonic waveguides with embedded quantum dots. The converter is realized
using an inverted taper and an epoxy polymer overlay providing a 1.3~m
output mode field diameter. We demonstrate the collection of single photons
from a quantum dot into a lensed fiber with a rate of 5.84~MHz and
estimate a chip-to-fiber coupling efficiency of ~\%. The stability and
compatibility with cryogenic temperatures make the epoxy waveguides a promising
material to realize efficient and scalable interconnects between heterogeneous
quantum photonic integrated circuits.Comment: 16 pages, 5 figures, 1 tabl
Photon bound state dynamics from a single artificial atom
The interaction between photons and a single two-level atom constitutes a fundamental paradigm in quantum physics. The nonlinearity provided by the atom leads to a strong dependence of the light–matter interface on the number of photons interacting with the two-level system within its emission lifetime. This nonlinearity unveils strongly correlated quasiparticles known as photon bound states, giving rise to key physical processes such as stimulated emission and soliton propagation. Although signatures consistent with the existence of photon bound states have been measured in strongly interacting Rydberg gases, their hallmark excitation-number-dependent dispersion and propagation velocity have not yet been observed. Here we report the direct observation of a photon-number-dependent time delay in the scattering off a single artificial atom—a semiconductor quantum dot coupled to an optical cavity. By scattering a weak coherent pulse off the cavity–quantum electrodynamics system and measuring the time-dependent output power and correlation functions, we show that single photons and two- and three-photon bound states incur different time delays, becoming shorter for higher photon numbers. This reduced time delay is a fingerprint of stimulated emission, where the arrival of two photons within the lifetime of an emitter causes one photon to stimulate the emission of another
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