More Like this

1. Laser cooling of antihydrogen atoms

   https://doi.org/10.1038/s41586-021-03289-6  

   Baker, C. J. ; Bertsche, W. ; Capra, A. ; Carruth, C. ; Cesar, C. L. ; Charlton, M. ; Christensen, A. ; Collister, R. ; Mathad, A. Cridland ; Eriksson, S. ; et al ( April 2021 , Nature)

   Abstract The photon—the quantum excitation of the electromagnetic field—is massless but carries momentum. A photon can therefore exert a force on an object upon collision 1 . Slowing the translational motion of atoms and ions by application of such a force 2,3 , known as laser cooling, was first demonstrated 40 years ago 4,5 . It revolutionized atomic physics over the following decades 6–8 , and it is now a workhorse in many fields, including studies on quantum degenerate gases, quantum information, atomic clocks and tests of fundamental physics. However, this technique has not yet been applied to antimatter. Heremore »we demonstrate laser cooling of antihydrogen 9 , the antimatter atom consisting of an antiproton and a positron. By exciting the 1S–2P transition in antihydrogen with pulsed, narrow-linewidth, Lyman-α laser radiation 10,11 , we Doppler-cool a sample of magnetically trapped antihydrogen. Although we apply laser cooling in only one dimension, the trap couples the longitudinal and transverse motions of the anti-atoms, leading to cooling in all three dimensions. We observe a reduction in the median transverse energy by more than an order of magnitude—with a substantial fraction of the anti-atoms attaining submicroelectronvolt transverse kinetic energies. We also report the observation of the laser-driven 1S–2S transition in samples of laser-cooled antihydrogen atoms. The observed spectral line is approximately four times narrower than that obtained without laser cooling. The demonstration of laser cooling and its immediate application has far-reaching implications for antimatter studies. A more localized, denser and colder sample of antihydrogen will drastically improve spectroscopic 11–13 and gravitational 14 studies of antihydrogen in ongoing experiments. Furthermore, the demonstrated ability to manipulate the motion of antimatter atoms by laser light will potentially provide ground-breaking opportunities for future experiments, such as anti-atomic fountains, anti-atom interferometry and the creation of antimatter molecules.« less
2. Lorentz breaking and SU(2)L × U(1)Y gauge invariance for neutrinos

   https://doi.org/10.1142/S0218301319500721  

   Jentschura, U. D. ; Nándori, I. ; Somogyi, G. ( September 2019 , International Journal of Modern Physics E)

   Conceivable Lorentz-violating effects in the neutrino sector remain a research area of great general interest, as they touch upon the very foundations on which the Standard Model and our general understanding of fundamental interactions are laid. Here, we investigate the relation of Lorentz violation in the neutrino sector in light of the fact that neutrinos and the corresponding left-handed charged leptons form [Formula: see text] doublets under the electroweak gauge group. Lorentz-violating effects thus cannot be fully separated from questions related to gauge invariance. The model dependence of the effective interaction Lagrangians used in various recent investigations is explored withmore »a special emphasis on neutrino splitting, otherwise known as the neutrino-pair Cerenkov radiation and vacuum-pair emission (electron–positron-pair Cerenkov radiation). We highlight two scenarios in which Lorentz-violating effects do not necessarily also break electroweak gauge invariance. The first of these involves a restricted set of gauge transformations, a subgroup of [Formula: see text], while in the second where differential Lorentz violation is exclusively introduced by the mixing of the neutrino flavor and mass eigenstates. Our study culminates in a model which fully preserves [Formula: see text] gauge invariance, involves flavor-dependent Lorentz-breaking parameters, and still allows for Cerenkov-type decays to proceed.« less
3. Organic solvates in the Cambridge Structural Database

   https://doi.org/10.1039/D0CE01749C  

   Werner, Jen E. ; Swift, Jennifer A. ( February 2021 , CrystEngComm)

   Data informatics approaches were applied to the Cambridge Structural Database (CSD) in an effort to discern fundamental trends related to the preparation, occurrence, and general properties of organic solvates. Foremost, the 50 most abundant solvate classes in the CSD were identified through SMILES string matching implemented through CSD Python API, and their relative occurrence rates were compared against data reported 20 years prior. These two sets of data suggest that solvate preparation methods have become less diverse over that time period with an increasing fraction derived from a smaller subset of solvents, though the relative abundance of hetero-solvates containing moremore »than one type of solvent molecule simultaneously increased. A subsequent SMILES string matching facilitated the identification of ∼2700 pairs of solvate and solvent-free structures from the top 10 solvate classes. Data from the two related groups showed statistical differences in both the lattice symmetries and packing fractions. Solvates exhibited an inherent bias favoring triclinic lattice symmetry, which is likely related to the larger number of unique molecular components in the asymmetric unit. More surprising was the fact that solvates that do not exhibit disorder statistically had lower packing fractions than their solvent-free analogues. While solvate formation may in fact be a means to achieve phases with higher packing efficiency for some organic molecules, the data indicate this is not a general trend.« less
4. PICO: Procedural Iterative Constrained Optimizer for Geometric Modeling

   https://doi.org/10.1109/TVCG.2020.2995556  

   Krs, Vojtech ; Mech, Radomir ; Gaillard, Mathieu ; Carr, Nathan ; Benes, Bedrich ( May 2020 , IEEE Transactions on Visualization and Computer Graphics)

   Procedural modeling has produced amazing results, yet fundamental issues such as controllability and limited user guidance persist. We introduce a novel procedural system called PICO (Procedural Iterative Constrained Optimizer) using PICO-Graph, a procedural model designed with optimization in mind. PICO enables the exploration of generative designs by combining user and environmental constraints into a single framework and using optimization without the need to write procedural rules. The PICO-Graph is a data-flow procedural model consisting of a set of geometry-generating operation nodes. The forward generation is initiated by sending geometric objects from initial nodes. These objects travel through the graph, triggeringmore »generation of more objects along the way. We combine the PICO-Graph with evolutionary optimization that allows for exploration of the generated models and the generation of variants. The user defines the geometry-generating operations and the set of constraints; e.g, whether an existing object should be supported by the generated model, whether symmetries exist, etc. PICO then generates geometric models that fulfill the constraints through optimization, allowing interactive user control of constraints. We show PICO on a variety of examples, including generation of procedural chairs, generation of support structures for 3D printing, or generation of procedural terrains matching a given input.« less
5. Ferroicity-driven nonlinear photocurrent switching in time-reversal invariant ferroic materials

   https://doi.org/10.1126/sciadv.aav9743  

   Wang, Hua ; Qian, Xiaofeng ( August 2019 , Science Advances)

   Nonlinear optical responses to external electromagnetic field, characterized by second- and higher-order susceptibilities, play crucial roles in nonlinear optics and optoelectronics. Here, we demonstrate the possibility to achieve ferroicity-driven nonlinear photocurrent switching in time-reversal invariant multiferroics. It is enabled by the second-order current response to electromagnetic field whose direction can be controlled by both internal ferroic orders and external light polarization. Second-order direct photocurrent consists of shift current and circular photocurrent under linearly and circularly polarized light irradiation, respectively. We elucidate the microscopic mechanism in a representative class of two-dimensional multiferroic materials using group theoretical analyses and first-principles theory. Themore »complex interplay of symmetries, shift vector, and Berry curvature governs the fundamental properties and switching behavior of shift current and circular photocurrent. Ferroicity-driven nonlinear photocurrent switching will open avenues for realizing nonlinear optoelectronics, nonlinear multiferroics, etc., using the coupled ferroic orders and nonlinear responses of ferroic materials under external field.« less