Observation of topology transition in Floquet non-Hermitian skin effects in silicon photonics

Non-Hermitian physics has greatly enriched our understanding of nonequilibrium phenomena and uncovered novel effects such as the non-Hermitian skin effect (NHSE) that has profoundly revolutionized the field. NHSE is typically predicted in systems with nonreciprocal couplings which, however, are difficult to realize in experiments. Without nonreciprocal couplings, the NHSE can also emerge in systems with coexisting gauge fields and loss or gain (e.g., in Floquet non-Hermitian systems). However, such Floquet NHSE remains largely unexplored in experiments. Here, we realize the Floquet NHSEs in periodically modulated optical waveguides integrated on a silicon photonics platform. By engineering the artificial gauge fields induced by the periodical modulation, we observe various Floquet NHSEs and unveil their rich topological transitions. Remarkably, we discover the transitions between the normal unipolar NHSEs and an unconventional bipolar NHSE which is accompanied by the directional reversal of the NHSEs. The underlying physics is revealed by the band winding in complex quasienergy space which undergoes a topology change from isolated loops with the same winding to linked loops with opposite windings. Our work unfolds a new route toward Floquet NHSEs originating from the interplay between gauge fields and dissipation effects and offers fundamentally new ways for steering light and other waves.Comment: 12 pages, 3 figure

T Cell Receptor Signaling That Regulates the Development of Intrathymic Natural Regulatory T Cells

T cell receptor (TCR) signaling plays a critical role in T cell development, survival and differentiation. In the thymus, quantitative and/or qualitative differences in TCR signaling determine the fate of developing thymocytes and lead to positive and negative selection. Recently, it has been suggested that self-reactive T cells, escape from negative selection, should be suppressed in the periphery by regulatory T cells (Tregs) expressing Foxp3 transcription factor. Foxp3 is a master factor that is critical for not only development and survival but also suppressive activity of Treg. However, signals that determine Treg fate are not completely understood. The availability of mutant mice which harbor mutations in TCR signaling mediators will certainly allow to delineate signaling events that control intrathymic (natural) Treg (nTreg) development. Thus, we summarize the recent progress on the role of TCR signaling cascade components in nTreg development from the studies with murine model

<i>Bacillus-</i> and <i>Lactobacillus</i>-Based Dietary Synbiotics Are Associated with Shifts in the Oropharyngeal, Proximal Colonic, and Vaginal Microbiomes of Korean Native Black Pigs

In this study, we evaluated the modulatory effect of synbiotics (probiotics + prebiotics) on the oropharyngeal, proximal colonic, and vaginal microbiomes of Korean native pigs using 16S rRNA gene sequencing. We found increased abundances of an unclassified deltaproteobacterial genus in oropharyngeal communities of pigs supplemented with a Lactobacillus-based synbiotic. These pigs also had increased abundances of unclassified genera of Tremblayales and Lactobacillales in their proximal colons. In another group, pigs supplemented with a Bacillus-based synbiotic had increased Megasphaera and reduced Campylobacter within their oropharyngeal microbiota. In addition, their vaginal microbiota had increased Clostridium and Halalkalibacillus, as well as reduced Filifactor and Veillonella. We then explored changes in the predicted microbial functionality, associated with the synbiotics. Our analysis showed a reduction in the abundance of a fatty acid and lipid biosynthesis pathway among proximal colonic microbiomes of the Lactobacillus-fed pigs. In pigs supplemented with a Bacillus-based synbiotic, the analysis showed reduced pathway abundances for the biosynthesis of carbohydrates, as well as vitamins, cofactors, and carrier molecules within their oropharyngeal microbiomes. Meanwhile, their vaginal microbiomes had higher pathway abundances for aromatic compound degradation and secondary metabolite biosynthesis, but lower abundances for amino acid degradation. The results confirmed our hypothesis that dietary synbiotics modulate the microbiome, not only in the proximal colon, but also the oropharyngeal cavity and vaginal tract of these pigs

Gauge-induced Floquet topological states in photonic waveguides

Tremendous efforts have been devoted to the search for exotic topological states, which usually exist at an interface between lattices with differing topological invariants according to the bulk-edge correspondence. Here, we show a new finding of topological states localized at the interface between two gauge-shifted Floquet photonic lattices, despite the same topological order across the entire structure. The quasienergy band structures reveal that these new interface modes belong to the Floquet {\pi} modes, which are further found to enable a robust one-way propagation thanks to the flexible control of the Floquet gauge. The intriguing propagations of these {\pi}-interface modes are experimentally verified in a silicon waveguides platform at near-infrared wavelengths, which show both broad working bandwidth and high tolerance to the structural fluctuations. Our approach provides a new route for light manipulations with robust behaviours in Floquet engineering and beyond.Comment: 4 figure

Neural network assisted high-spatial-resolution polarimetry with non-interleaved chiral metasurfaces

Abstract Polarimetry plays an indispensable role in modern optics. Nevertheless, the current strategies generally suffer from bulky system volume or spatial multiplexing scheme, resulting in limited performances when dealing with inhomogeneous polarizations. Here, we propose a non-interleaved, interferometric method to analyze the polarizations based on a tri-channel chiral metasurface. A deep convolutional neural network is also incorporated to enable fast, robust and accurate polarimetry. Spatially uniform and nonuniform polarizations are both measured through the metasurface experimentally. Distinction between two semblable glasses is also demonstrated. Our strategy features the merits of compactness and high spatial resolution, and would inspire more intriguing design for detecting and sensing

Supplementary document for Bifacial metasurface enabled pancake metalens by polarized space folding - 6121320.pdf

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Bound-extended mode transition in type-II synthetic photonic Weyl heterostructures

Photonic structures with Weyl points (WPs), including type-I and type-II, promise nontrivial surface modes and intriguing light manipulations for their three-dimensional topological bands. While previous studies mainly focus on exploring WPs in a uniform Weyl structure, here we establish Weyl heterostructures (i.e., a nonuniform Weyl lattice) with different rotational orientations in the synthetic dimension by nanostructured photonic waveguides. In this work, we unveil a transition between bound and extended modes on the interface of type-II Weyl heterostructures by tuning their rotational phases, despite the reversed topological order across the interface. This mode transition is also manifested from the total transmission to total reflection at the interface. All of these unconventional effects are attributed to the tilted dispersion of type-II Weyl band structure that can lead to mismatched bands and gaps across the interface. As a comparison, the type-I Weyl heterostructures lack the phase transition due to the untilted band structure. This work establishes a flexible scheme of artificial Weyl heterostructures that opens a new avenue towards high-dimensional topological effects and significantly enhances our capabilities in on-chip light manipulations