Microwave-to-Optical Quantum Transduction Utilizing the Topological Faraday Effect of Topological Insulator Heterostructures

The quantum transduction between microwave and optical photons is essential for realizing scalable quantum computers with superconducting qubits. Due to the large frequency difference between microwave and optical ranges, the transduction needs to be done via intermediate bosonic modes or nonlinear processes. So far, the transduction efficiency $\eta$ via the magneto-optic Faraday effect (i.e., the light-magnon interaction) in the ferromagnet YIG has been demonstrated to be small as $\eta\sim 10^{-8} \mathrm{-} 10^{-15}$ due to the sample size limitation inside the cavity. Here, we take advantage of the fact that three-dimensional topological insulator thin films exhibit a topological Faraday effect that is independent of the sample thickness. This leads to a large Faraday rotation angle and therefore enhanced light-magnon interaction in the thin film limit. We show theoretically that the transduction efficiency can be greatly improved to $\eta\sim10^{-4}$ by utilizing the heterostructures consisting of topological insulator thin films such as Bi$_2$Se$_3$ and ferromagnetic insulator thin films such as YIG.Comment: 6 pages, 5 figures + Supplemental Materia

Emergent One-Dimensional Helical Channel in Higher-Order Topological Insulators with Step Edges

We study theoretically the electronic structure of three-dimensional (3D) higher-order topological insulators in the presence of step edges. We numerically find that a 1D conducting state with a helical spin structure, which also has a linear dispersion near the zero energy, emerges at a step edge and on the opposite surface of the step edge. Such a 1D helical conducting state can exist when the Fermi level is in the bulk bandgap, as well as the ordinary 1D topological hinge states. We also find that the 1D helical conducting state on the opposite surface of a step edge emerges when the electron hopping strength in the direction perpendicular to the step is weak. In other words, the existence of the emergent 1D helical conducting state on the opposite surface of a step edge can be understood by considering an addition of different-sized independent blocks of 3D higher-order topological insulators. Our finding paves the way for on-demand creation of 1D helical conducting states from 3D higher-order topological insulators employing experimental processes commonly used in thin-film devices, which could lead to, e.g., a realization of high-density Majorana qubits.Comment: 11 pages, 10 figure

Human matrix metalloproteinases: An ubiquitarian class of enzymes involved in several pathological processes

Human matrix metalloproteinases (MMPs) belong to the M10 family of the MA clan of endopeptidases. They are ubiquitarian enzymes, structurally characterized by an active site where a Zn(2+) atom, coordinated by three histidines, plays the catalytic role, assisted by a glutamic acid as a general base. Various MMPs display different domain composition, which is very important for macromolecular substrates recognition. Substrate specificity is very different among MMPs, being often associated to their cellular compartmentalization and/or cellular type where they are expressed. An extensive review of the different MMPs structural and functional features is integrated with their pathological role in several types of diseases, spanning from cancer to cardiovascular diseases and to neurodegeneration. It emerges a very complex and crucial role played by these enzymes in many physiological and pathological processes

Quantum Spin Hall States in 2D Monolayer WTe₂/MoTe₂ Lateral Heterojunctions for Topological Quantum Computation

The quantum spin Hall (QSH) states in two-dimensional topological insulators (2DTIs) are expected to be applied to future topological quantum computation. We investigate the two-dimensional (2D) lateral heterojunctions of the monolayer 1T′–WTe2 as a 2DTI and the monolayer 2H–MoTe2 as a topologically trivial insulator using density functional theory. This 2D material is expected to have QSH states at each periodically arranged junction as well as properties distinct from the individual properties of each constituent material. At heterojunctions perpendicular to the dimer chains of W atoms in 1T′–WTe2 (in the y direction), two pairs of helical (QSH) states, one at each junction, connect the valence and conduction bands. The strain induced by the large lattice mismatch of the two materials in the y direction widens the bandgap of the 1T′–WTe2 monolayer as a QSH insulator. In the case of the heterojunctions in the x direction, the difference in atomic structure between the two junctions due to low symmetry creates an energy difference between two helical states and a potential gradient in the wide-bandgap 2H–MoTe2 region, resulting in various junction-localized bands. The widening bandgap of the heterojunctions in the y direction is essential for electronic applications of the QSH states, suggesting that this 2D material, namely, 2D WTe2/MoTe2 heterojunctions, can be a promising candidate for integrating Majorana qubits for future topological quantum computation

Electronic properties of the steps in bilayer Td-WTe2

Monolayer WTe2 stripes are quantum spin Hall (QSH) insulators. Density functional theory was used for investigating the electronic properties of the stripes and steps in bilayer Td-WTe2. For the stripes oriented along the dimer chains of W atoms (x direction), the hybridization between the two layers suppresses the QSH states. However, the QSH nature can be recovered by forming a step, depending on the atomic structure of the step. Conversely, the stripes and steps along the y direction maintain the QSH states. These findings can expand the application range of the QSH states in WTe2

STAP-2 positively regulates Fc epsilon RI-mediated basophil activation and basophil-dependent allergic inflammatory reactions

Basophils are an important cell type in the regulation of T(h)2 immune responses. Recently, we revealed that signal-transducing adaptor protein-2 (STAP-2) negatively regulates mast cell activation via Fc epsilon RI. However, the role of STAP-2 in basophil maturation and activation remained unclear. In this study, we demonstrated the normal development of basophils in STAP-2-deficient (STAP-2(-/-)) mice. We also demonstrated in vitro normal basophil differentiation and FceRI expression in STAP2(-/-) mice, suggesting that STAP-2 is dispensable for basophil maturation. Using bone marrow-derived cultured basophils (BMBs), we showed that degranulation and cytokine production of STAP-2(-/-) BMBs were lower than those of wild-type (WT) BMBs upon stimulation with IgE/Ag. In accordance with the reduction of degranulation and cytokine production, phosphorylation of several signal molecules such as Lyn, PLC-gamma 2 and Erk was reduced in STAP-2(-/-) BMBs after stimulation via Fc epsilon RI. Finally, it was observed that IgE-dependent chronic allergic inflammation of STAP-2(-/-) mice was significantly inhibited compared with WT mice. Taken together, we conclude that STAP-2 is an adaptor molecule that positively regulates FceRI-mediated basophil activation and basophil-dependent allergic inflammatory reactions