易坊好文馆

  1. 首页 > 生活百科 >

出版 《科学》（20201218出版）一周论文导读( 二 )


▲ Abstract
Tunneling plays an essential role in many branches of physics and has found important applications. It is theoretically proposed that Klein tunneling occurs when, under normal incidence, quasiparticles exhibit unimpeded penetration through potential barriers independent of their height and width. We created a phononic heterojunction by sandwiching two types of artificial phononic crystals with different Dirac point energies. The direct observation of Klein tunneling as shown by the key feature of unity transmission is demonstrated. Our experiment reveals that Klein tunneling occurs over a broad band of acoustic frequency. The direct observation of Klein tunneling in phononic crystals could find applications in signal processing, supercollimated beams, and communications.
Quantum computational advantage using photons
利用光子的量子计算优势
▲ 作者：Han-Sen Zhong, Hui Wang, Yu-Hao Deng, Ming-Cheng Chen, Li-Chao Peng, Yi-Han Luo, et al.
▲ 链接：
https://science.sciencemag.org/content/370/6523/1460
▲ 摘要
量子计算机有望执行某些传统计算机难以完成的任务。玻色子采样就是这样一项任务，它被认为是证明量子计算优势的强有力候选。
研究组将50路难以区分的单模压缩态发送到一个具有全连通随机矩阵的100模式超低损耗干涉仪中（整个光学装置是锁相的），并使用100个高效单光子探测器对输出进行采样，从而进行高斯玻色采样。利用热态、可分辨光子和均匀分布，针对可能出现的假设，对获得的样品进行验证。
光子量子计算机“九章”产生多达76个输出光子点击，输出状态空间维数为1030，采样速率比使用最先进的仿真策略和超级计算机快约1014倍。
▲ Abstract
Quantum computers promise to perform certain tasks that are believed to be intractable to classical computers. Boson sampling is such a task and is considered a strong candidate to demonstrate the quantum computational advantage. We performed Gaussian boson sampling by sending 50 indistinguishable single-mode squeezed states into a 100-mode ultralow-loss interferometer with full connectivity and random matrix—the whole optical setup is phase-locked—and sampling the output using 100 high-efficiency single-photon detectors. The obtained samples were validated against plausible hypotheses exploiting thermal states, distinguishable photons, and uniform distribution. The photonic quantum computer, Jiuzhang, generates up to 76 output photon clicks, which yields an output state-space dimension of 1030 and a sampling rate that is faster than using the state-of-the-art simulation strategy and supercomputers by a factor of ~1014.
化学Chemistry
Tailored quinones support high-turnover Pd catalysts for oxidative C–H arylation with O2
修饰醌类助力高效钯催化氧化C-H芳基化反应
▲ 作者：Chase A. Salazar, Kaylin N. Flesch, Brandon E. Haines, Philip S. Zhou, Djamaladdin G. Musaev, Shannon S. Stahl
▲ 链接：
https://science.sciencemag.org/content/370/6523/1454
▲ 摘要
钯（II）催化的碳-氢（C-H）氧化反应可以简化药物、农药和其他复杂有机分子的合成。然而，现有方法通常表现出较差的催化剂性能，高钯（Pd）负载（例如10摩尔％）和需要（超）化学计量的氧化剂，例如苯醌和银（I）盐。
该研究探讨了具有代表性的Pd催化氧化C-H芳基化反应的机理，并阐明了破坏催化剂性能的机理，包括消耗底物的副反应和螯合催化剂成为非活性物质的反应。
醌辅助催化剂的系统调节克服了这些有害特性。使用2,5-二叔丁基对苯醌可以有效地利用分子氧作为氧化剂，提高反应收率，Pd催化剂可循环使用1900次以上。
▲ Abstract
Palladium (II)-catalyzed carbon-hydrogen (C–H) oxidation reactions could streamline the synthesis of pharmaceuticals, agrochemicals, and other complex organic molecules. Existing methods, however, commonly exhibit poor catalyst performance with high palladium (Pd) loading (e.g., 10 mole %) and a need for (super) stoichiometric quantities of undesirable oxidants, such as benzoquinone and silver (I) salts. The present study probes the mechanism of a representative Pd-catalyzed oxidative C–H arylation reaction and elucidates mechanistic features that undermine catalyst performance, including substrate-consuming side reactions and sequestration of the catalyst as an inactive species. Systematic tuning of the quinone cocatalyst overcomes these deleterious features. Use of 2,5-di-tert-butyl-p-benzoquinone enables efficient use of molecular oxygen as the oxidant, high reaction yields, and >1900 turnovers by the Pd catalyst.
生态学Ecology
Novel trophic interactions under climate change promote alpine plant coexistence
【 出版|《科学》（20201218出版）一周论文导读】气候变化下的新型营养互作促进了高山植物的共存

推荐阅读


上一篇：暴力 新运载火箭试射，五个巨型助推器彰显暴力美学，白宫感叹优势不在

下一篇：前世 神舟十号的前世今生