科学要读的讲义（科学20220916出版一周论文导读）

编译 | 未玖

Science,16 SEPTEMBER 2022, VOL 377, ISSUE 6612

《科学》2022年9月16日，第377卷，6612期

天文学Astronomy

Loss of a satellite could explain Saturn’s obliquity and young rings

前卫星毁灭或可解释土星的倾角和年轻行星环

▲ 作者：JACK WISDOM, ROLA DBOUK, BURKHARD MILITZER, WILLIAM B. HUBBARD, FRANCIS NIMMO, BRYNNA G. DOWNEY, ET AL.

▲ 链接：

https://www.science.org/doi/10.1126/science.abn1234

▲ 摘要：

土星约26.7°的倾角和大约1亿年前土星环的起源仍未知。人们观测到土星最大卫星土卫六快速向外迁移，可能通过与海王星的自旋轨道进动共振增加了土星的倾角。

研究组使用卡西尼号的数据来精确估计土星的转动惯量，发现它刚好超出了共振所需的范围。他们认为土星之前曾另有一个卫星，并将其命名为“蛹”，这导致土星的倾角通过海王星共振增加。

大约1亿年前“蛹”轨道的不稳定可以解释该系统接近共振，以及通过与土星的潮汐撕裂形成土星环。

▲ Abstract：

The origin of Saturn’s ~26.7° obliquity and ~100-million-year-old rings is unknown. The observed rapid outward migration of Saturn’s largest satellite, Titan, could have raised Saturn’s obliquity through a spin-orbit precession resonance with Neptune. We use Cassini data to refine estimates of Saturn’s moment of inertia, finding that it is just outside the range required for the resonance. We propose that Saturn previously had an additional satellite, which we name Chrysalis, that caused Saturn’s obliquity to increase through the Neptune resonance. Destabilization of Chrysalis’s orbit ~100 million years ago can then explain the proximity of the system to the resonance and the formation of the rings through a grazing encounter with Saturn.

物理学Physics

Few-cycle vacuum squeezing in nanophotonics

纳米光子学中少周期真空压缩

▲ 作者：RAJVEER NEHRA, RYOTO SEKINE, LUIS LEDEZMA, QIUSHI GUO, ROBERT M. GRAY, ARKADEV ROY, ET AL.

▲ 链接：

https://www.science.org/doi/10.1126/science.abo6213

▲ 摘要：

光最基本的量子态之一是压缩真空，其中一个正交噪声小于标准量子噪声极限。在纳米光子学中，要产生、操纵和测量这种具有广泛可扩展量子信息系统所需性能的量子态，仍颇具挑战性。

研究组报道了基于铌酸锂的纳米光子平台开发，以演示在同一芯片上压缩态的产生和全光学测量。产生的压缩态跨越超过25太赫兹的带宽，仅支持几个光周期。测量到的4.9分贝压缩超过了广泛量子信息系统的要求，展示了一条可扩展超快量子纳米光子学的实用路径。

▲ Abstract：

One of the most fundamental quantum states of light is the squeezed vacuum, in which noise in one of the quadratures is less than the standard quantum noise limit. In nanophotonics, it remains challenging to generate, manipulate, and measure such a quantum state with the performance required for a wide range of scalable quantum information systems. Here, we report the development of a lithium niobate–based nanophotonic platform to demonstrate the generation and all-optical measurement of squeezed states on the same chip. The generated squeezed states span more than 25 terahertz of bandwidth supporting just a few optical cycles. The measured 4.9 decibels of squeezing surpass the requirements for a wide range of quantum information systems, demonstrating a practical path toward scalable ultrafast quantum nanophotonics.

Direct geometric probe of singularities in band structure

能带结构中奇点的直接几何探测

▲ 作者：CHARLES D. BROWN, SHAO-WEN CHANG, MALTE N. SCHWARZ, TSZ-HIM LEUNG, VLADYSLAV KOZII, ALEXANDER AVDOSHKIN, ET AL.

▲ 链接：

https://www.science.org/doi/10.1126/science.abm6442

▲ 摘要：

一个量子系统的能量景观可能有多个能量面简并的点，并表现出波函数流形的奇异几何结构，这对系统的性质产生重大影响。光学晶格中的超冷原子可间接表征能带结构中的这些点。

研究组测量了通过奇点直接传输所产生的非阿贝尔变换。他们沿着一个准动量轨迹加速原子，该原子进入、转向，然后离开蜂巢晶格的线性和二次能带接触点处的奇点。传输后的测量确定了这些奇点的拓扑绕组数分别为1和2。

该工作介绍了一种探测奇点的独特方法，有助于研究超冷原子量子模拟器中的非狄拉克奇点。

▲ Abstract：

A quantum system’s energy landscape may have points where multiple energy surfaces are degenerate and that exhibit singular geometry of the wave function manifold, with major consequences for the system’s properties. Ultracold atoms in optical lattices have been used to indirectly characterize such points in the band structure. We measured the non-Abelian transformation produced by transport directly through the singularities. We accelerated atoms along a quasi-momentum trajectory that enters, turns, and then exits the singularities at linear and quadratic band-touching points of a honeycomb lattice. Measurements after transport identified the topological winding numbers of these singularities to be 1 and 2, respectively. Our work introduces a distinct method for probing singularities that enables the study of non-Dirac singularities in ultracold-atom quantum simulators.

化学Chemistry

Halogen-atom and group transfer reactivity enabled by hydrogen tunneling

氢隧穿引发的卤素原子和基团转移反应性

▲ 作者：TIMOTHÉE CONSTANTIN, BARTOSZ GÓRSKI, MICHAEL J. TILBY, SALOUA CHELLI, FABIO JULIÁ, JOSEP LLAVERIA, ET AL.

▲ 链接：

https://www.science.org/doi/10.1126/science.abq8663

▲ 摘要：

通过卤素原子和基团转移反应生成碳自由基通常使用锡和硅试剂来实现，最大限度地发挥焓（热力学）和极性（动力学）效应的相互作用。

在这项工作中，研究组展示了在温和光化学条件下，利用环己二烯衍生物γ-萜品烯作为萃取剂的量子力学隧穿的独特反应模式。该方案活化烷基和芳基卤化物以及几种醇和硫醇衍生物。

实验和计算研究揭示了一个非典型途径，即环己二烯基自由基通过有效H原子的反应性进行协同芳构化和卤原子或基团萃取化。这种激活机制似乎在热力学和动力学上都很难实现，但通过量子隧穿却是可行的。

▲ Abstract：

The generation of carbon radicals by halogen-atom and group transfer reactions is generally achieved using tin and silicon reagents that maximize the interplay of enthalpic (thermodynamic) and polar (kinetic) effects. In this work, we demonstrate a distinct reactivity mode enabled by quantum mechanical tunneling that uses the cyclohexadiene derivative γ-terpinene as the abstractor under mild photochemical conditions. This protocol activates alkyl and aryl halides as well as several alcohol and thiol derivatives. Experimental and computational studies unveiled a noncanonical pathway whereby a cyclohexadienyl radical undergoes concerted aromatization and halogen-atom or group abstraction through the reactivity of an effective H atom. This activation mechanism is seemingly thermodynamically and kinetically unfavorable but is rendered feasible through quantum tunneling.

地球科学Earth Science

The Bengal Water Machine: Quantified freshwater capture in Bangladesh

孟加拉水机：孟加拉国定量淡水收集

▲ 作者：MOHAMMAD SHAMSUDDUHA, RICHARD G. TAYLOR, MD IZAZUL HAQ, SARA NOWREEN, ANWAR ZAHID AND KAZI MATIN UDDIN AHMED.

▲ 链接：

https://www.science.org/doi/10.1126/science.abm4730

▲ 摘要：

全球粮食安全取决于灌溉农业的可持续性。亚洲热带地区季节性潮湿的冲积平原地下水抽取不断增加，使旱季亦能种植水稻。这种地下水抽运增加了可用地下储水量，因为在有利条件下，之后的季风期会增加地下水补充。

研究组对这种基于自然的季节性淡水储存收集解决方案进行了经验量化，称之为“孟加拉水机”，揭示了它的潜力和局限性。

根据来自465口监测井的100万次压测观测，研究组表明，1988至2018年孟加拉国孟加拉盆地约1600万小农集体作业造成的累计淡水收集量（75至90立方千米）相当于三峡大坝水库容量的两倍。

▲ Abstract：

Global food security depends on the sustainability of irrigated agriculture. Rising groundwater withdrawals from seasonally humid, alluvial plains across tropical Asia have enabled dry-season rice cultivation. This groundwater pumpage increases available subsurface storage that under favorable conditions amplifies groundwater replenishment during the subsequent monsoon. We empirically quantified this nature-based solution to seasonal freshwater storage capture described as the “Bengal Water Machine,” revealing its potential and limitations. On the basis of a million piezometric observations from 465 monitoring wells, we show that the collective operation of ~16 million smallholder farmers in the Bengal Basin of Bangladesh from 1988 to 2018 has induced cumulative freshwater capture that volumetrically (75 to 90 cubic kilometers) is equivalent to twice the reservoir capacity of the Three Gorges Dam.

社会学Sociology

A causal test of the strength of weak ties

薄弱联系强度的因果检验

▲ 作者：KARTHIK RAJKUMAR, GUILLAUME SAINT-JACQUES, IAVOR BOJINOV, ERIK BRYNJOLFSSON AND SINAN ARA.

▲ 链接：

https://www.science.org/doi/10.1126/science.abl4476

▲ 摘要：

研究组分析了LinkedIn“你可能认识的人”算法（该算法向LinkedIn成员推荐新的联系人）的多个大规模随机实验数据，以测试在世界上最大的职业社交网络中，薄弱联系在多大程度上增加了工作流动性。

在5年的时间里，实验随机改变了2000多万人网络中薄弱联系的普遍程度，在此期间创造了20亿条新联系和60万个新工作。研究结果提供了支持薄弱联系强度的实验因果证据，并建议对理论进行三次修正。

首先，薄弱联系的强度是非线性的。统计分析发现，联系强度和工作传递之间呈倒U型关系，较弱的联系增加了工作传递，但仅在一定程度上，之后薄弱联系的边际收益递减。

其次，以互动强度和相互联系数量衡量的薄弱联系表现出不同的效应。中等弱联系（通过相互联系来衡量）和最弱联系（通过互动强度来衡量）创造了最多的工作流动性。

第三，薄弱联系的强度因行业而异。弱联系增加了高科技行业的工作流动性，而强联系则增加了低技术行业的工作流动性。

▲ Abstract：

The authors analyzed data from multiple large-scale randomized experiments on LinkedIn’s People You May Know algorithm, which recommends new connections to LinkedIn members, to test the extent to which weak ties increased job mobility in the world’s largest professional social network. The experiments randomly varied the prevalence of weak ties in the networks of over 20 million people over a 5-year period, during which 2 billion new ties and 600,000 new jobs were created. The results provided experimental causal evidence supporting the strength of weak ties and suggested three revisions to the theory. First, the strength of weak ties was nonlinear. Statistical analysis found an inverted U-shaped relationship between tie strength and job transmission such that weaker ties increased job transmission but only to a point, after which there were diminishing marginal returns to tie weakness. Second, weak ties measured by interaction intensity and the number of mutual connections displayed varying effects. Moderately weak ties (measured by mutual connections) and the weakest ties (measured by interaction intensity) created the most job mobility. Third, the strength of weak ties varied by industry. Whereas weak ties increased job mobility in more digital industries, strong ties increased job mobility in less digital industries.　

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