Bose condensation of upper-branch exciton-polaritons in a transferrable microcavity

Exciton-polaritons are composite bosonic quasiparticles arising from the strong coupling of excitonic transitions and optical modes. Exciton-polaritons have triggered wide exploration in the past decades not only due to their rich quantum phenomena such as superfluidity, superconductivity and quantized vortices but also due to their potential applications for unconventional coherent light sources and all-optical control elements. Here, we report the observation of Bose-Einstein condensation of the upper polariton branch in a transferrable WS$_2$ monolayer microcavity. Near the condensation threshold, we observe a nonlinear increase in upper polariton intensity. This sharp increase in intensity is accompanied by a decrease of the linewidth and an increase of the upper polariton temporal coherence, all of which are hallmarks of Bose-Einstein condensation. By simulating the quantum Boltzmann equation, we show that the upper polariton condensation only occurs for a particular range of particle density. We can attribute the creation of Bose condensation of the upper polariton to the following requirements: 1) the upper polariton is more excitonic than the lower one; 2) there is relatively more pumping in the upper branch; and 3) the conversion time from the upper to the lower polariton branch is long compared to the lifetime of the upper polaritons

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Bilayer-favored intercalation induced efficient and selective liquid phase production of bilayer graphene

Bilayer graphene (BLG) is gaining increasing attention as one of the most promising candidate materials for post-silicon nanoelectronics. It is still a tremendous challenge to selectively and efficiently produce BLG at low cost and under mild conditions. Herein, a novel strategy of bilayer-favored intercalation (BFI) induced liquid phase exfoliation of BLG under mild conditions was developed. This simple approach can effectively exfoliate graphite to give BLG with a high yield of 52.3%, and selectivity as high as 86.5%. The obtained twisted BLG not only maintains the structural integrity and low surface oxidation of graphene, but also demonstrates great electron mobility. With careful experimental design and use of DFT calculations, such efficient production of BLG is proved to originate from the formation of a stage-two graphite intercalation compound via the bilayer-favored intercalation of chromyl chloride (CrO2Cl2) into graphite flakes driven by the electrostatic interactions between CrO2Cl2 and graphene sheets. The BFI-induced liquid phase exfoliation strategy shows great potential for the industrial scale production of high-quality BLG

Bilayer-favored intercalation induced efficient and selective liquid phase production of bilayer graphene

Bilayer graphene (BLG) is gaining increasing attention as one of the most promising candidate materials for post-silicon nanoelectronics. It is still a tremendous challenge to selectively and efficiently produce BLG at low cost and under mild conditions. Herein, a novel strategy of bilayer-favored intercalation (BFI) induced liquid phase exfoliation of BLG under mild conditions was developed. This simple approach can effectively exfoliate graphite to give BLG with a high yield of 52.3%, and selectivity as high as 86.5%. The obtained twisted BLG not only maintains the structural integrity and low surface oxidation of graphene, but also demonstrates great electron mobility. With careful experimental design and use of DFT calculations, such efficient production of BLG is proved to originate from the formation of a stage-two graphite intercalation compound via the bilayer-favored intercalation of chromyl chloride (CrO2Cl2) into graphite flakes driven by the electrostatic interactions between CrO2Cl2 and graphene sheets. The BFI-induced liquid phase exfoliation strategy shows great potential for the industrial scale production of high-quality BLG

Bose Condensation of Upper-Branch Exciton-Polaritons in a Transferable Microcavity

Exciton-polaritons are composite quasiparticles that result from the coupling of excitonic transitions and optical modes. They have been extensively studied because of their quantum phenomena and potential applications in unconventional coherent light sources and all-optical control elements. In this work, we report the observation of Bose–Einstein condensation of the upper polariton branch in a transferable WS2 monolayer microcavity. Near the condensation threshold, we observe a nonlinear increase in upper polariton intensity accompanied by a decrease in line width and an increase in temporal coherence, all of which are hallmarks of Bose–Einstein condensation. Simulations show that this condensation occurs within a specific particle density range, depending on the excitonic properties and pumping conditions. The manifestation of upper polariton condensation unlocks new possibilities for studying the condensate competition while linking it to practical realizations in polaritonic lasers. Our findings contribute to the understanding of bosonic systems and offer potential for the development of polaritonic devices

The evolutionary origin and domestication history of goldfish (Carassius auratus)

Goldfish have been subjected to over 1,000 y of intensive domestication and selective breeding. In this report, we describe a high-quality goldfish genome (2n = 100), anchoring 95.75% of contigs into 50 pseudochromosomes. Comparative genomics enabled us to disentangle the two subgenomes that resulted from an ancient hybridization event. Resequencing 185 representative goldfish variants and 16 wild crucian carp revealed the origin of goldfish and identified genomic regions that have been shaped by selective sweeps linked to its domestication. Our comprehensive collection of goldfish varieties enabled us to associate genetic variations with a number of well-known anatomical features, including features that distinguish traditional goldfish clades. Additionally, we identified a tyrosine-protein kinase receptor as a candidate causal gene for the first well-known case of Mendelian inheritance in goldfish-the transparent mutant. The goldfish genome and diversity data offer unique resources to make goldfish a promising model for functional genomics, as well as domestication