Exceptional dynamics at exceptional points

Exceptional points(EPs),singularities of non-Hermitian systems,often exhibit exotic behaviors by engineering the balance between the system gain and loss.Now,EPs have been demonstrated to enable unidirectional perfect absorption/reflection at the visible light spectrum.

Beyond biogeographic patterns:Processes shaping the microbial landscape in soils and sediments along the Yangtze River

Deciphering biogeographic patterns of microorganisms is important for evaluating the maintenance of microbial diversity with respect to the ecosystem functions they drives.However,ecological processes shaping distribution patterns of microorganisms across large spatial‐scale watersheds remain largely unknown.Using Illumina sequencing and multiple statistical methods,we characterized distribution patterns and maintenance diversity of microorganisms(i.e.,archaea,bacteria,and fungi)in soils and sediments along the Yangtze River.Distinct microbial distribution patterns were found between soils and sediments,and microbial community similarity significantly decreased with increasing geographical distance.Physicochemical properties showed a larger effect on microbial community composition than geospatial and climatic factors.Archaea and fungi displayed stronger species replacements and weaker environmental constraints in soils than that in sediments,but opposite for bacteria.Archaea,bacteria,and fungi in soils showed broader environmental breadths and stronger phylogenetic signals compared to those in sediments,suggesting stronger environmental adaptation.Stochasticity dominated community assemblies of archaea and fungi in soils and sediments,whereas determinism dominated bacterial community assembly.Our results have therefore highlighted distinct microbial distribution patterns and diversity maintenance mechanisms between soils and sediments,and emphasized important roles of species replacement,environmental adaptability,and ecological assembly processes on microbial landscape.Our findings are helpful in predicting loss of microbial diversity in the Yangtze River Basin,and might assist the establishment of environmental policies for protecting fragile watersheds.

Far-field super-resolution imaging by nonlinearly excited evanescent waves

Abbe’s resolution limit,one of the best-known physical limitations,poses a great challenge for any wave system in imaging,wave transport,and dynamics.Originally formulated in linear optics,the Abbe limit can be broken using nonlinear optical interactions.We extend the Abbe theory into a nonlinear regime and experimentally demonstrate a far-field,label-free,and scan-free super-resolution imaging technique based on nonlinear four-wave mixing to retrieve near-field scattered evanescent waves,achieving a sub-wavelength resolution ofλ∕5.6.This method paves the way for numerous new applications in biomedical imaging,semiconductor metrology,and photolithography.

Optically induced transparency in a micro-cavity

Electromagnetically induced transparency has the unique ability to optically control transparency windows with low light in atomic systems.However,its practical applications in quantum physics and information science are limited due to rigid experimental requirements.Here we demonstrate a new mechanism of optically induced transparency in a micro-cavity by introducing a four-wave mixing gain to nonlinearly couple two separated resonances of the micro-cavity in an ambient environment.A signature Fano-like resonance was observed owing to the nonlinear interference of the two coupled resonances.Moreover,we show that the unidirectional gain of the four-wave mixing can lead to the remarkable effect of non-reciprocal transmission at the transparency windows.Optically induced transparency may offer a unique platform for a compact,integrated solution to all-optical and quantum information.

Nonlinear thermal emission and visible thermometry

The control of thermal emission is of great importance for emerging applications in energy conversion and thermometric sensing.Usually,thermal emission at ambient temperature is limited to the midto far-infrared,according to the linear theory of Planck’s law.We experimentally demonstrate a broadband nonlinear thermal emission in the visible-NIR spectrum within a quadradic nonlinear medium,which emits visible thermal radiation through a pump-driven nonlinear upconversion from its mid-IR components even at room temperature,unlike its linear counterpart which requires ultrahigh temperature.The broadband emission is enabled by the crucial random quasi-phase-matching condition in our nonlinear nanocrystal powders.Moreover,nonlinear thermal emission also permits visible thermometry using traditional optical cameras instead of thermal ones.This scheme paves the way to understand thermal radiation dynamics with nonlinearity in many fields,such as nonlinear heat transfer and nonlinear thermodynamics.