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Optical trapping is having ever-increasing impact in science $-$ particularly biophysics, photonics and most recently in quantum optomechanics $-$ owing to its superior capability for manipulating nanoscale structures and materials. However, essentially all experimental optical trapping studies in the optical dipole regime have, to date, been dominated by the interaction between a material's electric polarizability, $\alpha_{e}$, and the electric part of the incident electromagnetic field, and therefore described by electric field intensity gradient forces. Optical trapping based on optical magnetic light-matter interactions has not been experimentally addressed despite it's immediate extension of the boundaries of optical trapping research and applications. This paper addresses this long-standing deficiency through the realization of optical magnetic trapping of large index of refraction (i.e., Si) nanoparticles and also presents a formalism for quantitative understanding of the experimental findings. Our experimental optical trapping results require including optical magnetic polarizability, $\alpha_{m}$, and electric-magnetic scattering forces associated with the Photonic Hall effect that are qualitatively and quantitatively validated by Maxwell stress tensor calculations. Our findings bring new opportunities for nanoparticle manipulation, potentially relax the limitations Ashkin claimed based on the optical Earnshaw's theorem, motivate optical matter formation by optical magnetic interactions, and suggest new N-body effects and symmetry breaking to drive dynamics of optical matter systems.

Statistical physics courses typically employ abstract language that describes objects too small to be seen, making the topic challenging for students to understand. In this work, we introduce a simple experiment that allows conceptualizing some of the underlying ideas of stochastic processes through direct experimentation. Students analyze stochastic trajectories of beads in a bouncing bed of smaller beads subjected to an external periodic drive. The analysis of the trajectories involves the application of a vast tool kit of statistical estimators that are useful in many fields of physics., Comment: 28 pages, 7 figures, 2 supplementary materials, accepted in American Journal of Physics

Photonic spectrographs offer a highly miniaturized, flexible, and stable on-chip solution for astronomical spectroscopy and can be used for various science cases such as determining the atmospheric composition of exoplanets to understand their habitability, formation, and evolution. Arrayed Waveguide Gratings (AWGs) have shown the best promise to be used as an astrophotonic spectrograph. We developed a publically-available tool to conduct a preliminary examination of the capability of the AWGs in spectrally resolving exoplanet atmospheres. We derived the Line-Spread-Function (LSF) as a function of wavelength and the Full-Width-at-Half-Maximum (FWHM) of the LSF as a function of spectral line width to evaluate the response of a discretely- and continuously-sampled low-resolution AWG (R $\sim$ 1000). We observed that the LSF has minimal wavelength dependence ($\sim$5\%), irrespective of the offset with respect to the center-wavelengths of the AWG channels, contrary to the previous assumptions. We further confirmed that the observed FWHM scales linearly with the emission line width. Finally, we present simulated extraction of a sample molecular absorption spectrum with the discretely- and continuously-sampled low-resolution AWGs. From this, we show that while the discrete AWG matches its expected resolving power, the continuous AWG spectrograph can, in principle, achieve an effective resolution significantly greater ($\sim$ 2x) than the discrete AWG. This detailed examination of the AWGs will be foundational for future deployment of AWG spectrographs for astronomical science cases such as exoplanet atmospheres., Comment: 13 pages, 6 figures, Presented at and published in the proceedings of SPIE Photonics West 2022

Being capable of estimating the pose of uncooperative objects in space has been proposed as a key asset for enabling safe close-proximity operations such as space rendezvous, in-orbit servicing and active debris removal. Usual approaches for pose estimation involve classical computer vision-based solutions or the application of Deep Learning (DL) techniques. This work explores a novel DL-based methodology, using Convolutional Neural Networks (CNNs), for estimating the pose of uncooperative spacecrafts. Contrary to other approaches, the proposed CNN directly regresses poses without needing any prior 3D information. Moreover, bounding boxes of the spacecraft in the image are predicted in a simple, yet efficient manner. The performed experiments show how this work competes with the state-of-the-art in uncooperative spacecraft pose estimation, including works which require 3D information as well as works which predict bounding boxes through sophisticated CNNs., Comment: 9 pages, 5 figures, published at AI4Space 2021 IEEE/CVF Conference on Computer Vision and Pattern Recognition Workshops (CVPRW)

This paper proposes the SPARK dataset as a new unique space object multi-modal image dataset. Image-based object recognition is an important component of Space Situational Awareness, especially for applications such as on-orbit servicing, active debris removal, and satellite formation. However, the lack of sufficient annotated space data has limited research efforts in developing data-driven spacecraft recognition approaches. The SPARK dataset has been generated under a realistic space simulation environment, with a large diversity in sensing conditions for different orbital scenarios. It provides about 150k images per modality, RGB and depth, and 11 classes for spacecrafts and debris. This dataset offers an opportunity to benchmark and further develop object recognition, classification and detection algorithms, as well as multi-modal RGB-Depth approaches under space sensing conditions. Preliminary experimental evaluation validates the relevance of the data, and highlights interesting challenging scenarios specific to the space environment., Comment: 5 pages, 7 figures

We present universal features of the topological invariant of p-wave superconducting wires after the inclusion of spatial inhomogeneities. Three classes of distributed potentials are studied, a single- impurity, a commensurate and an incommensurate model using periodic site modulations. An analytical polynomial description is achieved by splitting the topological invariant into two parts, one dependent on the chemical potential and the other not. For the homogeneous case, an elliptical region is found where the topological invariant oscillates. The zeros of these oscillations occur at points where the fermion parity switches for finite wires. The increase of these oscillations with the inhomogeneity strength leads to new non-topological phases. We characterize these new phases according to each class of spatial distributions. Such phases could also be observed in the XY model.

Under stable atmospheric conditions, the zenithal brightness of the urban sky varies throughout the night following the time course of the anthropogenic emissions of light. Different types of artificial light sources (e.g. streetlights, residential, and vehicle lights) present specific time signatures, and this feature makes it possible to estimate the amount of sky brightness contributed by each one of them. Our approach is based on transforming the time representation of the zenithal sky brightness into a modal coefficients one, in terms of the time course signatures of the sources. The modal coefficients, and hence the absolute and relative contributions of each type of source, can be estimated from the measured brightness by means of linear least squares fits. A method for determining the time signatures is described, based on wide-field time-lapse photometry of the urban nightscape. Our preliminary results suggest that artificial light leaking out of the windows of residential buildings may account for a significant share of the time-varying part of the zenithal sky brightness, whilst the contribution of the vehicle lights seems to be significantly smaller., Comment: ArXiv identifier added; acknowledgments updated