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Semiconductor quantum dots in microcavities are an excellent platform for the efficient generation of indistinguishable single photons. However, their use in a wide range of quantum technologies requires their controlled fabrication and integration in compact closed-cycle cryocoolers, with a key challenge being the efficient and stable extraction of the single photons into a single-mode fiber. Here we report on a novel method for fiber-pigtailing of deterministically fabricated single-photon sources. Our technique allows for nanometer-scale alignment accuracy between the source and a fiber, alignment that persists all the way from room temperature to 2.4 K. We demonstrate high performance of the device under near-resonant optical excitation with g$^{(2)}$(0) = 1.3 %, a photon indistinguishability of 97.5 % and a fibered brightness of 20.8 %. We show that the indistinguishability and single-photon rate are stable for over ten hours of continuous operation in a single cooldown. We further confirm that the device performance is not degraded by nine successive cooldown-warmup cycles., Comment: 7 pages, 5 figures

An essential requirement for universal quantum control of the centre-of-mass motion of levitated objects is the development of a precise readout of all three translational degrees of freedom. Improving that precision presents one key challenge: collecting all the information on the object's position, encoded in the scattered light, equivalent to minimising the measurement imprecision. Here, we propose a new detection technique based on spatial mode decomposition, which addresses this problem using a simple integrated setup, where all of the light back-scattered from a levitated nanoparticle couples into a spatial mode sorter. We observe that each mode of the sorter pairs predominantly to the in-elastically scattered field generated by the object's motion along a particular spatial axis. This results in each translational degree of freedom being selectively encoded in the amplitude of orthogonal information channels. Using this approach, we report measurement efficiencies ($\eta_{\mathrm{tot}}^x$, $\eta_{\mathrm{tot}}^y$, $\eta_{\mathrm{tot}}^z$) = (0.17, 0.15, 0.30), implying that our technique is capable of reaching the 3D quantum ground state.

Here we report the detection of dust depletion in a misaligned inner disk around UX Tau A using JWST MIRI spectra. Mid-infrared (MIR) continuum "seesaw" variability was detected in this disk by Spitzer and attributed to variable shadows cast on the outer disk by the inner disk. The JWST MIRI spectrum of UX Tau A also shows seesaw variability, but with a significant decrease of emission shortwards of 10 micron to nearly photospheric levels. We argue that UX Tau A's MIR continuum variability is due to depletion of dust in a misaligned inner disk. We speculate that this dust depletion occurs because the inner disk is misaligned from the outer disk, which can disrupt the replenishment of the inner disk from the outer disk. Using contemporaneous measurements of the mass accretion rate of UX Tau A and estimating the amount of dust necessary to produce the MIR excess in the Spitzer observations, we estimate a minimum dust depletion timescale of ~0.1 yr. These observations show that we can indirectly detect the signatures of misaligned inner disks through MIR continuum variability and that in some cases the inner disk may be significantly depleted of dust and become optically thin., Comment: accepted to ApJL

We report on the realization and characterization of a novel magic-wavelength nanofiber-based two-color optical dipole trap that allows us to generate a periodic one-dimensional array of trapping sites with a spacing significantly smaller than half of the resonant wavelength of the cesium D2-line. To this end, we launch a blue-detuned partial standing wave and two red-detuned light fields through the nanofiber. We demonstrate the trapping of atoms in the array and characterize the resulting trap configuration by measuring the trap frequencies in three directions and observe good agreement with theoretical predictions. The implementation of this nanofiber-based optical interface with magic trapping wavelengths and sub-$\lambda/2$ spacing is an important step towards the exploration of novel collective radiative effects such as selective radiance in 1D atomic arrays., Comment: 5 pages, 4 figures

Efficiently exciting and controlling phonons in diamond nanoresonators represents a fundamental challenge for quantum applications. Here, we theoretically demonstrate the possibility to excite mechanical modes within a double-hybrid-cavity (DHC), formed by adjoining to a diamond cavity a second cavity, made of aluminum nitride. The latter is piezoelectric and serves as a microwave-to-phonon transducer, activating mechanical modes in the entire DHC. We show the process to match the cavities phononic properties, making them work coordinately in the DHC and obtaining a well confined mode. In the diamond part of the cavity, this mode replicates the fundamental mode of the individual diamond cavity, showing that the piezoelectric transducer doesn't alter the diamond individual fundamental mode. In the piezoelectric part, the strong confinement of stress and electric field results in a high piezoelectric coupling rate, demonstrating the effectiveness of a phononic cavity as a transducer. The study is contextualized in the framework of a quantum networking application, where the DHC serves as a spin qubit, exploiting the spin-mechanical coupling within diamond color centers., Comment: 10 pages, 6 figures

A renewed interest in upright therapy is currently driven by the availability of upright positioning and imaging systems. Aside from reduced cost, upright positioning possibly provides clinical advantages. The comparison between upright and supine particle therapy treatments can be biased through multiple variables, such as differences in the target contouring on the two CTs. We present a method for upright and supine CT registration and structures propagation, and the investigation of an AI-based contouring tool for upright images. Six paired 4DCTs from Proton Therapy Collaboration Group registry were available from the Northwestern Medicine Proton Centre. Deformable image registration (DIR) is challenged by the different patient anatomy between postures, causing artefacts in the warped images. To achieve high quality contour propagation, we propose the construction of a region of interest covering the ribcage volume to overcome this problem. As no target contour ground truth was available, the registration quality analysis (QA) was performed on lung structures, for which dice score coefficient (DSC) and average Hausdorff distance (AHD) is reported. The TotalSegmentator tool, trained on supine dataset, was applied on upright images, verified against lung structures and used as additional comparison for contour propagation. The TotalSegmentator QA results in a maximum AHD of 2mm and a minimum DSC of 0.94. An average AHD of 1.5mm and 1.6mm, and an average DSC of 0.95 and 0.94 were obtained comparing the propagated volumes to manually contoured and AI structures, respectively. All AHD values are smaller than the CT slice distances. The developed framework allows for target propagation between upright and supine images, defining the first step to compare upright and supine therapy of thoracic patients and enabling the application of image fusion techniques in the upright therapy field.

One of the most innovative possibilities offered by oxides is the use of heat currents for computational purposes. Towards this goal, phase-change oxides, including ferroelectrics, ferromagnets and related materials, could reproduce sources, logic units and memories used in current and future computing schemes.

Similarity estimation is essential for many game AI applications, from the procedural generation of distinct assets to automated exploration with game-playing agents. While similarity metrics often substitute human evaluation, their alignment with our judgement is unclear. Consequently, the result of their application can fail human expectations, leading to e.g. unappreciated content or unbelievable agent behaviour. We alleviate this gap through a multi-factorial study of two tile-based games in two representations, where participants (N=456) judged the similarity of level triplets. Based on this data, we construct domain-specific perceptual spaces, encoding similarity-relevant attributes. We compare 12 metrics to these spaces and evaluate their approximation quality through several quantitative lenses. Moreover, we conduct a qualitative labelling study to identify the features underlying the human similarity judgement in this popular genre. Our findings inform the selection of existing metrics and highlight requirements for the design of new similarity metrics benefiting game development and research., Comment: Proceedings of the CHI Conference on Human Factors in Computing Systems (CHI '24), 11-16 May 2024, Honolulu, HI, USA

In this study, we investigate excitonic properties of epitaxially grown WS2, which is of particular interest for various applications due to its potential for upscaling to wafer sized structures. Understanding the effect of the dielectric environment due to changing layer numbers and multi-material heterostructures on the optical properties is crucial for tailoring device properties. Monochromated electron energy loss spectroscopy in a scanning transmission electron microscope is employed to characterize the excitonic spectrum of WS2 on graphene grown by metal organic chemical vapor deposition. This technique provides the required spatial resolution at the nanometer scale in combination with high quality spectra. To complement the experimental results, theoretical investigations using density functional theory and applying the Bethe-Salpeter equations are conducted. We find that by transitioning from mono- to bi- to multilayers of WS2 the spectra show redshifts for both, the K-valley excitons at about 2.0 and 2.4 eV as well as excitonic features of higher energies. The latter features originate from so called band nesting of transitions between the Gamma- and K-point. In summary, this study provides valuable insights into the excitonic properties of WS2 in different layer configurations and environments, which are realistically needed for future device fabrication and property tuning. Finally, we can show that nanometer scale electron spectroscopy supported by careful theoretical modelling can successfully link atomic structure and optical properties, such as exciton shifts, in non-idealized complex material systems like multilayer 2D heterostructures., Comment: 8 pages, 5 figures

Two-dimensional (2D) materials have received a lot of interest over the past decade. Especially van der Waals (vdW) 2D materials, such as transition metal dichalcogenides (TMDCs), and their heterostructures exhibit semiconducting properties that make them highly suitable for novel device applications. Controllable mixing and matching of the 2D materials with different properties and a precise control of the in-plane twist angle in these heterostructures are essential to achieve superior properties and need to be established through large-scale device fabrication. To gain fundamental insight into the control of these twist angles, 2D heterostructures of tungsten disulfide (WS2) and graphene grown by bottom-up synthesis via metal-organic chemical vapor deposition (MOCVD) are investigated using a scanning transmission electron microscope (STEM). Specifically, the combination of conventional high-resolution imaging with scanning nano beam diffraction (SNBD) using advanced 4D STEM techniques is used to analyze moir\'e structures. The latter technique is used to reveal the epitaxial alignment within the WS2/Gr heterostructure, showing a direct influence of the underlying graphene layers on the moir\'e formation in the subsequent WS2 layers. In particular, the importance of grain boundaries within the underlying WS2 and Gr layers for the formation of moir\'e patterns with rotation angles below 2{\deg} is discussed., Comment: 21 pages including the main article and supporting information, 5 figures (main text), 14 figures (supporting), submitted to Advanced Materials - Wiley

Many popular piecewise regression models rely on minimizing a cost function on the model fit with a linear penalty on the number of segments. However, this penalty does not take into account varying complexities of the model functions on the segments potentially leading to overfitting when models with varying complexities, such as polynomials of different degrees, are used. In this work, we enhance on this approach by instead using a penalty on the sum of the degrees of freedom over all segments, called degrees-of-freedom penalized piecewise regression (DofPPR). We show that the solutions of the resulting minimization problem are unique for almost all input data in a least squares setting. We develop a fast algorithm which does not only compute a minimizer but also determines an optimal hyperparameter -- in the sense of rolling cross validation with the one standard error rule -- exactly. This eliminates manual hyperparameter selection. Our method supports optional user parameters for incorporating domain knowledge. We provide an open-source Python/Rust code for the piecewise polynomial least squares case which can be extended to further models. We demonstrate the practical utility through a simulation study and by applications to real data. A constrained variant of the proposed method gives state-of-the-art results in the Turing benchmark for unsupervised changepoint detection., Comment: 35 pages, 11 figures, submitted to "Information and Inference: a Journal of the IMA"

High spin Chern-number insulator (HSCI) emerges as a novel 2D topological phase of condensed matter that is beyond the classification scheme of topological quantum chemistry. In this work, we report the observation of a semimetallic Sb monolayer with the same band topology as HSCI. Our first-principles calculations further indicate a moderate lattice strain can make Sb monolayer an insulator while retaining the nontrivial topological order. A quantized spin Hall conductivity is found in the HSCI phase of Sb monolayer. The results suggest strained Sb monolayer as a promising platform for exploring intriguing physical properties of the exotic HSCI topological matter, Comment: 4 figures

Two grapes irradiated inside a microwave (MW) oven typically produce a series of sparks and can ignite a violent plasma. The underlying cause of the plasma has been attributed to the formation of morphological-dependent resonances (MDRs) in the aqueous dielectric dimers that lead to the generation of a strong evanescent MW hotspot between them. Previous experiments have focused on the electric-field component of the field as the driving force behind the plasma ignition. Here we couple an ensemble of nitrogen-vacancy (NV) spins in nanodiamonds (NDs) to the magnetic-field component of the dimer MW field. We demonstrate the efficient coupling of the NV spins to the MW magnetic-field hotspot formed between the grape dimers using Optically Detected Magnetic Resonance (ODMR). The ODMR measurements are performed by coupling NV spins in NDs to the evanescent MW fields of a copper wire. When placing a pair of grapes around the NDs and matching the ND position with the expected magnetic-field hotspot, we see an enhancement in the ODMR contrast by more than a factor of two compared to the measurements without grapes. Using finite-element modelling, we attribute our experimental observation of the field enhancement to the MW hotspot formation between the grape dimers. The present study not only validates previous work on understanding grape-dimer resonator geometries, but it also opens up a new avenue for exploring novel MW resonator designs for quantum technologies.

We report on a study exploring the design of nanoparticles that can enhance their laser refrigeration efficiency for applications in levitated optomechanics. In particular, we developed lanthanide-doped nanocrystals with an inert shell coating and compared their performance with bare nanocrystals. While optically levitated, we studied the refrigeration of both types of nanoparticles while varying the pressure. We found that the core-shell design shows an improvement in the minimum final temperature: a fourth of the core-shell nanoparticles showed a significant cooling compared to almost none of the bare nanoparticles. Furthermore, we measured a core-shell nanoparticle cooling down to a temperature of 147 K at 26 mbar in the underdamped regime. Our study is a first step towards engineering nanoparticles that are suitable for achieving absolute (centre-of-mass and internal temperature) cooling in levitation, opening new avenues for force sensing and the realization of macroscopic quantum superpositions., Comment: Any comments are welcome !

Ultrafast carrier and phonon dynamics at the buried heterointerface of GaP/Si(001) are investigated by means of two-color pump-probe reflectivity measurements. The carrier-induced reflectivity signal exhibits a resonant enhancement at pump-photon energies of 1.4 eV, which can be assigned to an optical transition between electronic interface states. The transient reflectivity is modulated by a coherent oscillation at 2 THz, whose amplitude also becomes maximum at 1.4 eV. The observed resonant behavior of the phonon mode in combination with a characteristic wavelength-dependence of, both, its frequency and initial phase, strongly indicate that the 2-THz mode is a difference-combination mode of a GaP-like and a Si-like phonon at the heterointerface and that this second-order scattering process can be enhanced by a double resonance involving the interfacial electronic states.