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Broadband frequency comb generation through cascaded quadratic nonlinearity remains experimentally untapped in free-space cavities with bulk χ⁽²⁾materials mainly due to the high threshold power and restricted ability of dispersion engineering. Thin-film lithium niobate (LN) is a good platform for nonlinear optics due to the tight mode confinement in a nano-dimensional waveguide, the ease of dispersion engineering, large quadratic nonlinearities, and flexible phase matching via periodic poling. Here we demonstrate broadband frequency comb generation through dispersion engineering in a thin-film LN microresonator. Bandwidths of 150 nm (80 nm) and 25 nm (12 nm) for center wavelengths at 1560 and 780 nm are achieved, respectively, in a cavity-enhanced second-harmonic generation (doubly resonant optical parametric oscillator). Our demonstration paves the way for pure quadratic soliton generation, which is a great complement to dissipative Kerr soliton frequency combs for extended interesting nonlinear applications. 

Abstract Calcium ion transporting systems control cytosol Ca2+ levels ([Ca2+]cyt) and generate transient calcium (Ca2+) signatures that are key to environmental responses. Here, we report an impact of resting [Ca2+]cyt on plants from the functional study of calmodulin-regulated Ca2+ pumps or Ca2+-ATPases in Arabidopsis (Arabidopsis thaliana). The plasma membrane-localized pumps ACA8 (autoinhibited Ca2+-ATPase) and ACA10, as well as the vacuole-localized pumps ACA4 and ACA11, were critical in maintaining low resting [Ca2+]cyt and essential for plant survival under chilling and heat-stress conditions. Their loss-of-function mutants aca8 aca10 and aca4 aca11 had autoimmunity at normal temperatures, and this deregulated immune activation was enhanced by low temperature, leading to chilling lethality. Furthermore, these mutants showed an elevated resting [Ca2+]cyt, and a reduction of external Ca2+ lowered [Ca2+]cyt and repressed their autoimmunity and cold susceptibility. The aca8 aca10 and the aca4 aca11 mutants were also susceptible to heat, likely resulting from more closed stomata and higher leaf surface temperature than the wild type. These observations support a model in which the regulation of resting [Ca2+]cyt is critical to how plants regulate biotic and abiotic responses. 

Wavelength transduction of single-photon signals is indispensable to networked quantum applications, particularly those incorporating quantum memories. Lithium niobate nanophotonic devices have demonstrated favorable linear, nonlinear, and electro-optical properties to deliver this crucial function while offering superior efficiency, integrability, and scalability. Yet, their quantum noise level—a crucial metric for any single-photon-based application—has yet to be investigated. In this work, we report the first, to the best of our knowledge, study with the focus on telecom to near-visible conversion driven by a small detuned telecom pump for practical considerations in distributed quantum processing over fiber networks. Our results find the noise level to be on the order of ${10}^{-<\#comment/>4}$photons per time-frequency mode for high conversion, allowing faithful pulsed operations. Through carefully analyzing the origins of such noise and each’s dependence on the pump power and wavelength detuning, we have also identified a formula for noise suppression to ${10}^{-<\#comment/>5}$photons per mode. Our results assert a viable, low-cost, and modular approach to networked quantum processing and beyond using lithium niobate nanophotonics. 

Lode gold deposits, which are currently the world’s major gold supply, have been shown to be generated mostly by phase separation of metamorphic fluids and/or interaction between these fluids and wall rocks. Here we use garnet oxygen isotopes by secondary ion mass spectrometry to document the crucial role of magmatic hydrothermal fluids and their mixing with meteoric water in the formation of the world-class Dongping gold deposit in the North China Craton. Garnet grains from quartz veins of various paragenetic stages and the mineralized alteration envelope at Dongping have dynamic δ 18 O variations of 3.8 to −11.0‰, with large intragrain fluctuations up to 5.3‰. These values correspond to calculated δ 18 O values of 6.1 to −9.1‰ for the hydrothermal fluids from which the garnet formed. The isotope data, notably the cyclic alternation in δ 18 O within individual garnet grains, are best interpreted to reflect multiple pulses of magmatically derived fluids and subsequent mixing of each pulse with variable amounts of meteoric water. The results presented here allow us to quantify the significant interplay between magmatic hydrothermal fluids and meteoric water that spanned the entire mineralization history and triggered gold deposition of a lode gold deposit. This study highlights the potential use of in situ oxygen isotope analysis of garnet in tracing the origin and evolution of hydrothermal fluids in the Earth’s crust that may have formed other giant ore deposits. 

Thin-film lithium-niobate-on-insulator (LNOI) has emerged as a superior integrated-photonics platform for linear, nonlinear, and electro-optics. Here we combine quasi-phase-matching, dispersion engineering, and tight mode confinement to realize nonlinear parametric processes with both high efficiency and wide wavelength tunability. On a millimeter-long, Z-cut LNOI waveguide, we demonstrate efficient ( $1900\pm <\#comment/>500\mathrm{\%<\#comment/>}{\mathrm{W}}^{-<\#comment/>1}{\mathrm{c}\mathrm{m}}^{-<\#comment/>2}$) and highly tunable ( $-<\#comment/>1.71\mathrm{n}\mathrm{m}/\mathrm{K}$) second-harmonic generation from 1530 to 1583 nm by type-0 quasi-phase-matching. Our technique is applicable to optical harmonic generation, quantum light sources, frequency conversion, and many other photonic information processes across visible to mid-IR spectral bands.