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Entangled photon pairs are an important resource for many types of quantum protocols. Semiconductor Bragg-reflection waveguides are a promising photon-pair source due to mature fabrication, integrability, large transparency window in the telecom wavelength range, integration capabilities for electro-optical devices as well as a high second-order nonlinear coefficient. To increase performance, we improved the fabrication of Bragg-reflection waveguides by employing fixed-beam-moving-stage optical lithography, low-pressure, and low chlorine concentration etching, and resist reflow. The reduction in sidewall roughness yields a low optical loss coefficient for telecom wavelength light of alpha reflow = 0.08 (6) mm-1. Owing to the decreased losses, we achieved a photon-pair production rate of 8800 (300) (mW center dot s center dot mm)-1, which is 15-fold higher than in previous samples. Published by Optica Publishing Group under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI., Optical Materials Express, 13 (5), ISSN:2159-3930

In the field of topological materials, the interaction between band topology and magnetism remains a current frontier for the advancement of new topological states and spintronic functionalities. D...

We fabricate low-loss AlGaAs Bragg-reflection waveguides for the creation of telecom wavelength photon pairs via parametric down-conversion. These photon pairs are used in a hybrid on-chip time-bin entanglement scheme.

Structural moir\'e superstructures arising from two competing lattices may lead to unexpected electronic behavior, such as superconductivity or Mottness. Most investigated moir\'e heterostructures are based on van der Waals (vdW) materials, as strong interface interactions typically lead to the formation of strained films or regular surface reconstructions. Here we successfully synthesize ultrathin Sb films, that are predicted to show thickness-dependent topological properties, on semi-insulating InSb(111)A. Despite the covalent nature of the substrate surface, we prove by scanning transmission electron microscopy (STEM) that already the first layer of Sb atoms grows completely unstrained, while azimuthally aligned. Rather than compensating the lattice mismatch of -6.4% by structural modifications, the Sb films form a pronounced moir\'e pattern as we evidence by scanning tunneling microscopy (STM) topography up to film thicknesses of several bilayers. Our model calculations based on density functional theory (DFT) assign the moir\'e pattern to a periodic surface corrugation. In agreement with DFT predictions, irrespective of the moir\'e modulation, the topological surface state known on thick Sb film is experimentally confirmed to persist down to low film thicknesses, and the Dirac point shifts towards lower binding energies with decreasing Sb thickness., Comment: 34 pages in total, 4 figures, 1 table and 1 TOC in the main text

Disordered heterostructures stand as a general description for compounds that are part of homologous series such as bismuth chalcogenides. In device engineering, van der Waals epitaxy of these compounds is very promising for applications in spintronic and quantum computing. Structural analysis methods are essential to control and improve their synthesis in the form of thin films. Recently, X-rays tools have been proposed for structural modeling of disordered heterostructures [arXiv:2107.12280]. Here, we further evaluate the use of these tools to study the compound Mn$_x$Bi$_2$Te$_{3+x}$ in the grazing incidence region of the reflectivity curves, as well as the effect of thickness fluctuation in the wide angle region., 10 pages, 3 figures, and 1 table

The authors study, as a promising candidate for photovoltaic applications, the Mott insulator LaVO${}_{3}$, epitaxially grown as a thin film on SrTiO${}_{3}$. They elucidate the electronic properties by electrical transport and photoemission measurements. The origin of the conducting interface is identified to be electronic reconstruction due to the polar discontinuity between film and substrate. The authors find a potential gradient in the film and a downward band bending in the substrate, with the electrons residing in interfacial Ti states.

In this work, monolithic mode-locked GaSb-based lasers at 1.7 µm emission wavelength with heterodyne measurement of the frequency comb are presented. Mode-locking operation was confirmed by measuring the optical beatnote at the round-trip frequency of 9.56 GHz and analysing the frequency comb. Mode-locking operation occurred from 0.1 to 3.3 V reverse bias voltages at the absorber section and driving currents from 160 to 400 mA at the laser section with a minimum beatnote width of 6.6 kHz. The frequency comb spans over 13 nm with a mode spacing of 0.10 nm, measured by heterodyne-detection with a distributed feedback laser.

In this letter, we present evanescently coupled semiconductor laser arrays designed with a distributed Bragg reflector section for spectrally narrow emission and a combined waveguide section for high optical output powers. These devices were designed and fabricated in the AlGaAs material system with an InGaAsP quantum well providing emission in the 760–770 nm wavelength range. Measurements of the light-current characteristics reveal high optical output powers of 600 mW at 20 °C and 700 mW at 5 °C limited by thermal rollover without any signs of a catastrophic optical mirror damage or rapid power degradation. Spectrally narrow emission of 0.2 nm at −3 dB and a high wavelength stability with a small current tuning coefficient of 0.7 pm/mA were found. Far-field investigations reveal pre-dominant coupling of lowest order in-phase supermode emission without any sections for adjusting the phase of the electrical field vector for adjacent elements. Postprint

Single-molecule localization microscopy (SMLM) aims for maximized precision and a high signal-to-noise ratio1. Both features can be provided by placing the emitter in front of a metal-dielectric nanocoating that acts as a tuned mirror2–4. Here, we demonstrate that a higher photon yield at a lower background on biocompatible metal-dielectric nanocoatings substantially improves SMLM performance and increases the localization precision by up to a factor of two. The resolution improvement relies solely on easy-to-fabricate nanocoatings on standard glass coverslips and is spectrally and spatially tunable by the layer design and wavelength, as experimentally demonstrated for dual-color SMLM in cells.

We demonstrate a deterministic Purcell-enhanced single photon source realized by integrating an atomically thin WSe

Following the ultrafast optical excitation of an inhomogeneously broadened ensemble, the macroscopic optical polarization decays rapidly due to dephasing. This destructive interference is, however, reversible in photon echo experiments. Here, we propose a concept in which a control pulse slows down either the dephasing or the rephasing of the exciton ensemble during its presence. We analyze and visualize this optical freezing process by showing and discussing results for different single and multiple sequences of control pulses using a simple model of inhomogeneously broadened two-level systems. This idea has been realized in experiments performed on self-assembled (In,Ga)As quantum dots where it was possible to retard or advance the photon echo emission time by several picoseconds. The measurements are in very good agreement with numerical simulations for a more realistic model which, in particular, takes the spatial shape of the laser pulses into account.

We demonstrate a deterministic Purcell-enhanced single-photon source realized by integrating an atomically thin WSe$_{2}$ layer with a circular Bragg grating cavity. The cavity significantly enhances the photoluminescence from the atomically thin layer, and supports single-photon generation with $g^{(2)}(0), 11 pages, 3 figures in the main text, 6 figures in the supplementary material

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ DATA DESCRIPTION FOR "Difference-frequency generation in an AlGaAs Bragg-reflection waveguide using an on-chip electrically-pumped quantum dot laser" Alexander Schlager ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ also available as readme.txt 2021-06-16 Table of Contents ───────────────── 1) Figure 2 - Lasing Threshold 2) Figure 3 - Difference Frequency Generation 3) Table 1 - Conversion Efficiency 4) Figure A3 - Temperature Dependency 5) Table A3 - Further Conversion Efficiencies Each filename pre-pended with the figure/table number of the main and supplementary text that it contributes to. All files relevant to each figure/table are included. All numeric data is presented in tab separated variable (in a '*.txt' file) which can be opened with standard spreadsheet or text editing programs. Aside from the JSI ('FIG3c-JSI.txt') and the temperature dependency of the internal laser spectrum ('FIGA3a-laser-temp.txt') all the plots are directly generated with a Latex package called `pgfplots'. For the two exceptions a high resolution image ('*.png') has been generated with Wolfram Mathematica and imported via 'pgfplots'. The code used to process this data and calculate e.g. the conversion efficiencies is not contained in this repository, but can be requested from the authors if required. 1) Figure 2 - Lasing Threshold ══════════════════════════════ 'FIG2-threshold-data.txt' contains the raw data of the lasing threshold measurement. Column 1 and 2 contain the current and its standard deviation in Ampere and column 3 and 4 the optical power and its standard deviation in micro Watt after a measurement time of 30 seconds. 'FIG2-inset-540mA.txt' and 'FIG2-inset-700mA.txt' contain the data representing the spectra of the internal laser below and above lasing threshold. Column 1 is the wavelength in nanometers and column 2 the signal strength in kCounts/s and MCounts/s for a current of 540mA and 700mA, respectively. 2) Figure 3 - Difference Frequency Generation ═════════════════════════════════════════════ 'FIG3b-example-data.txt' contains a background subtracted dataset utilizing the internal laser and a seed wavelength of 1614nm. Column 1 is the wavelength in nanometers and column 2 the signal strength in Counts per second (Hz). This data has been averaged for an acquisition time of 300 seconds. 'FIG3c-JSI.txt' contains processed data for the joint spectral intensity. The DFG peaks collected in the measurements (such as in 'FIG3b-example-data.txt') have been fitted with a Gaussian function and these functions have been utilized to generate the data in this file. This allows us to properly show the Full-Width-Half-Maximum of the measured spectrum and get rid of residual background light from e.g. the telecom seed laser near the degeneracy. This data has been corrected for the bandpass filters utilized in the experiment and the detection efficiency of our detector at different wavelengths. It has then be renormalized to ease the creation of the plot. The raw data for the individual wavelength settings are not included in this repository, but can be requested from the authors if required. The data for Fig. 3d) is included 3) Table 1 - Conversion Efficiency (next section). 3) Table 1 - Conversion Efficiency ══════════════════════════════════ 'TAB1-DFG-power-int-1626nm.txt', 'TAB1-DFG-power-ext-1619nm.txt' and 'TAB1-DFG-power-pas-1510nm.txt' include the data to get the slope for the conversion efficiency for the internal laser, the external laser and the passive sample, respectively. Column 1 and 2 describe the optical power and its standard deviation of the seed laser within the waveguide in milli Watt (for correction, see supplementary materials) for a measurement time of 30 seconds. Column 3 and 4 contain the signal strength of the DFG light in counts/s (Hz) and its poissonian standard error of mean for an acquisition time of 300 seconds (internal), 10 seconds (external) and 2 seconds (passive). To extract the signal strength, we simple take sum of the maximum of the corresponding peak in the raw data (such as in 'FIG3b-example-data.txt') and its nearest neighbors, as this corresponds to the peak width of about 1-2 nm. The raw data are not included in this repository, but can be requested from the authors if required. 4) Figure A3 - Temperature Dependency ═════════════════════════════════════ 'FIGA3a-laser-temp.txt' contains the spectra of the internal laser for different temperature settings as shown in the supplementary materials. Column 1 is the temperature in °C, column 2 the wavelength in nanometers and column 3 the normalized signal strength. Note, that the picture used in Fig. A3a) is only a small cutout of the spectra, but contains all the important information, as there is only background below 788nm and above 794nm. 'FIGA3b-shg-type0.txt', 'FIGA3b-shg-type1.txt' and 'FIGA3b-shg-type2.txt' contain the spectral information of the type-0, type-1 and type-2 second harmonic generation process, respectively. This data has been processed already, as it contains the peak maximum position (column 3) and half-width-half-maximum (column 4) in nanometers extracted from Gaussian fits for the individual SHG spectra at different temperatures in °C (column 1) with an accuracy of 0.05°C (column 2). The maximum peak position is used to create the thick line and the half-width-half-maximum is used to create the slightly transparent bands in Fig. A3b). The raw data are not included in this repository, but can be requested from the authors if required. 'FIGA3c-spectrum-693mA.txt' and 'FIGA3c-spectrum-700mA.txt' include the raw internal laser spectrum at a temperature of 3.5°C and 693mA and 700mA of current, respectively. Column 1 is the wavelength in nanometers and column 2 the normalized laser power. 'FIGA3d-shg-spectrum.txt' shows the second harmonic generation spectrum of the type-2 process in our waveguide at a temperature of 3.5°C. Column 1 is the wavelength in nanometers and column 2 the normalized SHG power. This data has been generated by measuring the maximum of the SHG spectrum for different pump laser wavelengths. This way, we can extract the SHG spectrum at a much higher resolution by slowly varying the laser wavelength in steps of 0.01nm. The raw data are not included in this repository, but can be requested from the authors if required. 5) Table A3 - Further Conversion Efficiencies ══════════════════════════════════════════════ All files starting with 'TABA3-DFG-power-*.txt' include the data to get the slope for the conversion efficiency for the internal laser, the external laser and the passive sample shown in the supplementary materials, respectively. Aside from additional wavelength settings for the telecom seed laser, the description is exactly the same as in 3) Table 1 - Conversion efficiency.

Adolescents with ADHD are at increased risk of having a co-existing medical disorder. Research shows that having co-existing ADHD and a medical disorder interferes with the adolescents' daily life, creating a dual task that cannot be managed as two independent disorders. Interventions to support adolescents in managing the dual task of living with co-existing ADHD and medical disorder are needed. The Guided-Self-Determination intervention might be suitable for this population, as it is an empowerment-based intervention facilitating patient involvement and self-management of a disease. The purpose of this study was to evaluate how the Guided Self-Determination intervention impacted 10 adolescents with ADHD and a co-existing medical disorder. The study used a convergent mixed methods design. Quantitative data measuring support from nurses, support from parents, and self-management were collected though self-reported questionnaires at baseline, 3 months, and 6 months and were analyzed with descriptive statistics. Qualitative data capturing the adolescents' experiences of the intervention and the intervention's impact on support from nurses, parents, and self-management were collected through semi-structured interviews and analyzed thematically. Results of the quantitative and qualitative analyses were integrated in a mixed methods analysis. The integrated results suggest that this intervention may improve adolescents' management of the difficulties of living with co-existing ADHD and a medical disorder, and that self-insight and nurse support are prerequisites for developing self-management strategies. However, the results showed that the intervention did not impact parental support. Further research is needed to evaluate the impact of the intervention on a larger scale.

The phase distributions of Anderson localized modes are measured in 2D disordered photonic crystals, using single-shot interferograms. The distribution closely follows the theoretical prediction.

We report the growth of CuMnSb thin films by molecular beam epitaxy on InAs (001) substrates. The CuMnSb layers are compressively strained (0.6 %) due to lattice mismatch. The thin films have a $\ensuremath{\omega}$ full width at half-maximum of 7.7 arcsec according to high resolution x-ray diffraction, and a root-mean-square roughness of 0.14 nm as determined by atomic force microscopy. Magnetic and electrical properties are found to be consistent with reported values from bulk samples. We find a N\'eel temperature of 62 K, a Curie-Weiss temperature of \ensuremath{-}65 K, and an effective moment of $5.9\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{B}/\mathrm{f}.\mathrm{u}.$ Transport measurements confirm the antiferromagnetic transition and show a residual resistivity at 4 K of $35\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}$\textohm{} cm.

D.W. acknowledges financial support by the Polish National Agency for Academic Exchange (NAWA) within the ULAM program (No. PPN/ULM/2019/1/00064). The Würzburg team acknowledges the support by the State of Bavaria and the Deutsche Forschungsgemeinschaft (DFG) within Project No. SCHN1376 5.1 / PR1749 1.1. The Jaynes-Cummings (JC) model represents one of the simplest ways in which single qubits can interact with single photon modes, leading to profound quantum phenomena like superpositions of light and matter states. One system, that can be described with the JC model, is a single quantum dot embedded in a micropillar cavity. In this joint experimental and theoretical study we investigate such a system using four-wave mixing (FWM) micro-spectroscopy. Special emphasis is laid on the dependence of the FWM signals on the number of photons injected into the microcavity. By comparing simulation and experiment, which are in excellent agreement with each other, we infer that up to ∼20 photons take part in the observed FWM dynamics. Thus we verify the validity of the JC model for the system under consideration in this non-trivial regime. We find that the inevitable coupling between the quantum dot exciton and longitudinal acoustic phonons of the host lattice influences the real time FWM dynamics and has to be taken into account for a sufficient description of the quantum dot-microcavity system. Performing additional simulations in an idealized dissipation-less regime, we observe that the FWM signal exhibits quasi-periodic dynamics, analog to the collapse and revival phenomenon of the JC model. In these simulations we also see that the FWM spectrum has a triplet structure, if a large number of photons is injected into the cavity. Postprint

In this paper, we describe an interactive implementation of a Virtual Reality prototype for creating rock art. The aim was to explore the possibilities of emerging technologies to safeguard the intangible cultural heritage of the San people in Namibia. The VR implementation combines an oral San tale narrative with the display of rock art paintings in a virtual cave. The user becomes a co-illustrator of the narrative being requested to paint or engrave the missing rock art in the cave. A user experience evaluation was conducted by eight San people from the Kalahari Desert. A logging system has been implemented to record detailed movements and interactions of the user throughout the system use. The interpretation of the logging data serves to understand user experiences and guide further system improvements.

There is a great desire to extend ultrasonic techniques to the imaging and characterization of nanoobjects. This can be achieved by picosecond ultrasonics, where by using ultrafast lasers it is possible to generate and detect acoustic waves with frequencies up to terahertz and wavelengths down to nanometers. In our work we present a picosecond ultrasonics setup based on miniaturized mode-locked semiconductor lasers, whose performance allows us to obtain the necessary power, pulse duration and repetition rate. Using such a laser, we measure the ultrasonic echo signal with picosecond resolution in a Al film deposited on a semiconductor substrate. We show that the obtained signal is as good as the signal obtained with a standard bulky mode-locked Ti-Sa laser. The experiments pave the way for designing integrated portable picosecond ultrasonic setups on the basis of miniaturized semiconductor lasers., 9 pages, 4 figures

When an electron-hole pair is optically excited in a semiconductor quantum dot the host crystal lattice needs to adapt to the presence of the generated charge distribution. Therefore the coupled exciton-phonon system has to establish a new equilibrium, which is reached in the form of a quasiparticle called polaron. Especially, when the exciton is abruptly generated on a timescale faster than the typical lattice dynamics, the lattice displacement cannot follow adiabatically. Consequently, a rich dynamics on the picosecond timescale of the coupled system is expected. In this study we combine simulations and measurements of the ultrafast, coherent, nonlinear optical response, obtained by four-wave mixing spectroscopy, to resolve the formation of this polaron. By detecting and investigating the phonon sidebands in the four-wave mixing spectra for varying pulse delays and different temperatures we have access to the influence of phonon emission and absorption processes which finally result in the emission of an acoustic wave packet out from the quantum dot., Comment: accepted in Optics Letters

A non-intuitive combination of near-Wigner Dyson spacing statistics and lognormal conductance distribution is measured in a two-dimensional finite-sized Anderson localizing system. Theoretical analysis uncovers a novel nonlinear connection between repulsion exponent and localization length.