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发布日期：2024-09-16 作者：开云
编译|冯维维
Nature, Volume 631 Issue 8020, 11 July 2024
《天然》第631卷8020期，2024年7月11日
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物理学Physics
Observation of Bose–Einstein condensation of dipolar molecules
偶极份子玻色-爱因斯坦凝集的不雅察
▲ 作者：Niccolò Bigagli, Weijun Yuan, Siwei Zhang, Boris Bulatovic, Tijs Karman, Ian Stevenson Sebastian Will
▲链接：
https://www.nature.com/articles/s41586-024-07492-z
▲摘要：
受量子力学定律安排的粒子群表示出有趣的出现行动。量子材猜中的原子量子气体、液氦和电子因为它们的构成和彼此感化都表示出分歧的性质。超冷偶极份子的量子简并样品有望实现物资的新相，并为量子摹拟和量子计较供给新的路子。但即便经由过程碰撞屏障手艺削减了快速损掉，到今朝为止也阻碍了蒸发冷却到玻色-爱因斯坦凝集体（BEC）。
研究者报导了偶极份子的BEC的实现。经由过程加强碰撞屏障来按捺二体和三体损掉，他们蒸发冷却钠-铯份子到量子简并并逾越相变到BEC。当相空间密度跨越1时，BEC表示为双峰散布。生成了冷凝分数为60(10)%，温度为6(2)nK的BECs，并发现其不变寿命接近2秒。这项工作为摸索迄今为止没法进入的体系体例中的偶极量子物资打开了年夜门，有望在光学晶格中缔造奇特的偶极液滴，自组织晶体相和偶极自旋液体。
▲ Abstract：
Ensembles of particles governed by quantum mechanical laws exhibit intriguing emergent behaviour. Atomic quantum gases, liquid helium and electrons in quantum materials all exhibit distinct properties because of their composition and interactions. Quantum degenerate samples of ultracold dipolar molecules promise the realization of new phases of matter and new avenues for quantum simulation and quantum computation. However, rapid losses, even when reduced through collisional shielding techniques, have so far prevented evaporative cooling to a Bose–Einstein condensate (BEC). Here we report on the realization of a BEC of dipolar molecules. By strongly suppressing two- and three-body losses via enhanced collisional shielding, we evaporatively cool sodium–caesium molecules to quantum degeneracy and cross the phase transition to a BEC. The BEC reveals itself by a bimodal distribution when the phase-space density exceeds 1. BECs with a condensate fraction of 60(10)% and a temperature of 6(2) nK are created and found to be stable with a lifetime close to 2 s. This work opens the door to the exploration of dipolar quantum matter in regimes that have been inaccessible so far, promising the creation of exotic dipolar droplets, self-organized crystal phases and dipolar spin liquids in optical lattices.
Tunable entangled photon-pair generation in a liquid crystal
液晶中可调谐纠缠光子对的发生
▲ 作者：Vitaliy Sultanov, Alja? Kav?i?, Emmanouil Kokkinakis, Nerea Sebastián, Maria V. Chekhova Matja? Humar
▲链接：
https://www.nature.com/articles/s41586-024-07543-5
▲摘要：
液晶具有自组装、对电场的强响应和可集成到复杂系统中的能力，是光束把持的要害材料。比来发现的铁电向列液晶也具有相当年夜的二阶光学非线性，使其成为非线性光学的潜伏材料。它们作为量子光源的利用可以年夜年夜扩大光子量子手艺的鸿沟。但是，自觉参数下转换，纠缠光子的根基来历，预示的单光子和紧缩光，到今朝为止还没有在液晶或任何液体或有机材猜中不雅察到。
研究者在铁电向列液晶中实现了自觉参数下转换，并展现了电场可调谐的纠缠光子宽带发生，其效力可与最好非线性晶体相媲美。施加几伏电压或沿样品标的目的改变份子取向，光子对的发射速度和偏振态会产生显著转变。液晶源可以实现一种非凡类型的准相位匹配，这类匹配基在份子扭曲布局，是以可以按照光子对的所需光谱和偏振特征进行从头设置装备摆设。
这类光源有望在功能、亮度和所发生量子态的可调性方面优在尺度非线性光学材料。这一概念可以扩大到复杂的拓扑布局，宏不雅器件和多像素可调量子光源。
▲ Abstract：
Liquid crystals, with their ability to self-assemble, strong response to an electric field and integrability into complex systems, are key materials in light-beam manipulation1. The recently discovered ferroelectric nematic liquid crystals also have considerable second-order optical nonlinearity, making them a potential material for nonlinear optics. Their use as sources of quantum light could considerably extend the boundaries of photonic quantum technologies6. However, spontaneous parametric down-conversion, the basic source of entangled photons, heralded single photons and squeezed light, has so far not been observed in liquid crystals—or in any liquids or organic materials. Here we implement spontaneous parametric down-conversion in a ferroelectric nematic liquid crystal and demonstrate electric-field tunable broadband generation of entangled photons, with an efficiency comparable to that of the best nonlinear crystals. The emission rate and polarization state of photon pairs is markedly varied by applying a few volts or twisting the molecular orientation along the sample. A liquid-crystal source enables a special type of quasi-phase matching, which is based on the molecular twist structure and is therefore reconfigurable for the desired spectral and polarization properties of photon pairs. Such sources promise to outperform standard nonlinear optical materials in terms of functionality, brightness and the tunability of the generated quantum state. The concepts developed here can be extended to complex topological structures, macroscopic devices and multi-pixel tunable quantum light sources.
Fast-moving stars around an intermediate-mass black hole in ω Centauri
环绕半人马ω球状星团内一个中等质量黑洞的快速移动恒星
▲ 作者：Maximilian H?berle, Nadine Neumayer, Anil Seth, Andrea Bellini, Mattia Libralato, Holger Baumgardt, Matthew Whitaker, Antoine Dumont, Mayte Alfaro-Cuello, Jay Anderson, Callie Clontz, Nikolay Kacharov, Sebastian Kamann, Anja Feldmeier-Krause, Antonino Milone, Maria Selina Nitschai, Renuka Pechetti Glenn van de Ven
▲链接：
https://www.nature.com/articles/s41586-024-07511-z
▲摘要：
科学家在银河系半人马座欧米茄星团（半人马ω球状星团）内不雅测到的快速移动恒星为一个中等质量黑洞的存在供给了证据。该研究基在哈勃空间千里镜20多年的不雅测成果，或有助在此后研究人员搜刮这类难以发现的黑洞。
科学家已发现各类质量的黑洞，从5~150倍太阳质量（M⊙）的恒星质量黑洞到星系中心的超年夜质量黑洞（跨越10万倍太阳质量；105M⊙）。不外，今朝只发现了少数存在争议的候选中等质量黑洞，这类黑洞的质量在太阳质量的150倍到10万倍不等。
鉴在半人马ω球状星团高质量和复杂星族的特征，它是寻觅中等质量黑洞的一个很有但愿的方针，但之前对该区域发现了一个黑洞的报导一向面对争议。德国马普学会天文研究所的MaximilianHaberle和同事操纵哈勃空间千里镜20年的影象，监测了该星团中心四周恒星的活动。他们提出有7个恒星在中心区域快速移动，并认为这申明半人马ω球状星团的中心有一个中等质量黑洞。他们猜测该黑洞质量的下限为8200M⊙摆布。
“这些新发现的恒星是半人马ω球状星团中存在一个中等质量黑洞的最好证据。”加拿年夜麦吉尔年夜学的DarylHaggard和美国旧金山州立年夜学的AdrienneCool在一篇同期颁发的新闻不雅点文章中写道，研究成果或注解在其他球状星团中搜索中等质量黑洞是公道的。
欧空局哈勃拍摄的半人马座欧米茄星团新彩色图象。图片来自：ESA哈勃 NASA，M.Haberle ▲ Abstract：
Black holes have been found over a wide range of masses, from stellar remnants with masses of 5–150 solar masses (M☉), to those found at the centres of galaxies with M 105M☉. However, only a few debated candidate black holes exist between 150M☉ and 105M☉. Determining the population of these intermediate-mass black holes is an important step towards understanding supermassive black hole formation in the early universe. Several studies have claimed the detection of a central black hole in ω Centauri, the most massive globular cluster of the Milky Way. However, these studies have been questioned because of the possible mass contribution of stellar mass black holes, their sensitivity to the cluster centre and the lack of fast-moving stars above the escape velocity. Here we report the observations of seven fast-moving stars in the central 3 arcsec (0.08 pc) of ω Centauri. The velocities of the fast-moving stars are significantly higher than the expected central escape velocity of the star cluster, so their presence can be explained only by being bound to a massive black hole. From the velocities alone, we can infer a firm lower limit of the black hole mass of about 8,200M☉, making this a good case for an intermediate-mass black hole in the local universe.
Tunable superconductivity in electron- and hole-doped Bernal bilayer graphene
电子和空穴搀杂Bernal双层石墨烯的可调谐超导性
▲ 作者：Chushan Li, Fan Xu, Bohao Li, Jiayi Li, Guoan Li, Kenji Watanabe, Takashi Taniguchi, Bingbing Tong, Jie Shen, Li Lu, Jinfeng Jia, Fengcheng Wu, Xiaoxue Liu Tingxin Li
▲链接：
https://www.nature.com/articles/s41586-024-07584-w
▲摘要：
基在石墨烯的高质量二维电子系统已成为研究超导性的高度可调平台。具体来讲，在电子和空穴搀杂的扭曲石墨烯涡流系统中都不雅察到了超导性，而在晶体石墨烯系统中，迄今为止只在空穴搀杂的菱形三层石墨烯(RTG)和空穴搀杂的Bernal双层石墨烯(BBG)中不雅察到超导性。比来，因为接近单层WSe2, BBG中的超导性获得了加强。
研究者报导了经由过程静电搀杂在电子和空穴搀杂的BBG/WSe2器件中不雅察到的超导性和一系列风味对称性破缺相。不雅察到的超导性的强度可以经由过程施加垂直电场来调理。电子搀杂和空穴搀杂超导的最年夜berezinski - kosterlitz - Thouless改变温度别离约为210 mK和400 mK。只有当外加电场驱动BBG电子或空穴波函数向WSe2层移动时，超导性才会呈现，这强调了WSe2层在不雅察到的超导性中的主要性。空穴搀杂的超导背反了泡利顺磁极限，合适伊辛类超导体。比拟之下，电子搀杂的超导性遵从泡利极限，虽然在导带中临近引诱的伊辛自旋轨道耦合也很较着。该发现凸起了与BBG中传导带相干的丰硕物理特征，为进一步研究晶体石墨烯的超导机制和基在BBG的超导体器件的开辟摊平了道路。
▲ Abstract：
Graphene-based, high-quality, two-dimensional electronic systems have emerged as a highly tunable platform for studying superconductivity. Specifically, superconductivity has been observed in both electron- and hole-doped twisted graphene moiré systems, whereas in crystalline graphene systems, superconductivity has so far been observed only in hole-doped rhombohedral trilayer graphene (RTG) and hole-doped Bernal bilayer graphene (BBG). Recently, enhanced superconductivity has been demonstrated in BBG because of the proximity to a monolayer WSe2. Here we report the observation of superconductivity and a series of flavour-symmetry-breaking phases in electron- and hole-doped BBG/WSe2 devices by electrostatic doping. The strength of the observed superconductivity is tunable by applied vertical electric fields. The maximum Berezinskii–Kosterlitz Thouless transition temperature for the electron- and hole-doped superconductivity is about 210mK and 400mK, respectively. Superconductivities emerge only when the applied electric fields drive the BBG electron or hole wavefunctions towards the WSe2 layer, underscoring the importance of the WSe2 layer in the observed superconductivity. The hole-doped superconductivity violates the Pauli paramagnetic limit, consistent with an Ising-like superconductor. By contrast, the electron-doped superconductivity obeys the Pauli limit, although the proximity-induced Ising spin–orbit coupling is also notable in the conduction band. Our findings highlight the rich physics associated with the conduction band in BBG, paving the way for further studies into the superconducting mechanisms of crystalline graphene and the development of superconductor devices based on BBG.
化学Chemistry
Glassy gels toughened by solvent
用溶剂增韧的玻璃状凝胶
▲ 作者：Meixiang Wang, Xun Xiao, Salma Siddika, Mohammad Shamsi, Ethan Frey, Wen Qian, Wubin Bai, Brendan T. O’Connor Michael D. Dickey
▲链接：
https://www.nature.com/articles/s41586-024-07564-0
▲摘要：
玻璃状聚合物凡是坚固而坚忍，但延展性有限。经由过程溶胀，玻璃状聚合物可以酿成柔嫩而懦弱的凝胶，但具有加强的延展性。机能的显著转变是因为溶剂增添了链间的自由体积，同时削弱了聚合物与聚合物之间的彼此感化。研究者展现了极性聚合物与离子液体——离子凝胶，在恰当浓度下的溶剂化可以发生一种怪异的材料，称为玻璃凝胶，具有玻璃和凝胶的抱负机能。
离子液体增添了自由体积，是以，虽然缺少传统的溶剂(例如，水)，可扩大性。但在室温下，离子液体在聚合物链之间构成强而丰硕的非共价交联，构成坚固、坚韧、玻璃状和平均的收集(即没有相分手)。虽然液体含量跨越54wt %，但玻璃凝胶具有庞大的断裂强度(42 MPa)、韧性(110 MJ m?3)、屈就强度(73 MPa)和杨氏模量(1 GPa)。这些值与热塑性塑料(如聚乙烯)类似，但与热塑性塑料分歧的是，玻璃状凝胶可以变形到670%的应变，而且在加热时可以完全快速恢复。这些透明材料经由过程一步聚合构成，具有使人印象深入的粘合、自愈和外形记忆特征。
▲ Abstract：
Glassy polymers are generally stiff and strong yet have limited extensibility. By swelling with solvent, glassy polymers can become gels that are soft and weak yet have enhanced extensibility. The marked changes in properties arise from the solvent increasing free volume between chains while weakening polymer–polymer interactions. Here we show that solvating polar polymers with ionic liquids (that is, ionogels) at appropriate concentrations can produce a unique class of materials called glassy gels with desirable properties of both glasses and gels. The ionic liquid increases free volume and therefore extensibility despite the absence of conventional solvent (for example, water). Yet, the ionic liquid forms strong and abundant non-covalent crosslinks between polymer chains to render a stiff, tough, glassy, and homogeneous network (that is, no phase separation), at room temperature. Despite being more than 54wt% liquid, the glassy gels exhibit enormous fracture strength (42 MPa), toughness (110 MJ m?3), yield strength (73 MPa) and Young’s modulus (1 GPa). These values are similar to those of thermoplastics such as polyethylene, yet unlike thermoplastics, the glassy gels can be deformed up to 670% strain with full and rapid recovery on heating. These transparent materials form by a one-step polymerization and have impressive adhesive, self-healing and shape-memory properties.
Direct radical functionalization of native sugars
自然糖的直接自由基功能化
▲ 作者：Yi Jiang, Yi Wei, Qian-Yi Zhou, Guo-Quan Sun, Xia-Ping Fu, Nikita Levin, Yijun Zhang, Wen-Qiang Liu, NingXi Song, Shabaz Mohammed, Benjamin G. Davis Ming Joo Koh
▲链接：
https://www.nature.com/articles/s41586-024-07548-0
▲摘要：
自然存在的糖和碳水化合物含有很多具有类似反映活性的羟基。是以，化学家凡是依托吃力的、多步调的庇护基团策略，将这些可再生原料转化为制造聚糖的试剂(糖基供体)。
将自然糖直接转化为复合糖依然是一个显著的挑战。研究者描写了一种光引诱方式，经由过程均溶(单电子)化学绕过没必要要的羟基掩膜和把持，从普遍可用的自然糖构建块实现位点和立体选择性化学糖基化。这一进程令人联想到天然界在区域节制下发生瞬时糖基供体，在光激活下与亲电试剂进行基在自由基的交叉偶联。
经由过程选择性的单糖和寡糖的头聚糖功能化，这类无庇护基团的“帽和糖基酸”方式供给了一种直接的路子，可以取得年夜量代谢兴旺的糖基化合物。因为其生物相容性，该方式被扩大到卵白质的直接翻译后糖基化。
▲ Abstract：
Naturally occurring (native) sugars and carbohydrates contain numerous hydroxyl groups of similar reactivity. Chemists, therefore, rely typically on laborious, multi-step protecting-group strategies3 to convert these renewable feedstocks into reagents (glycosyl donors) to make glycans. The direct transformation of native sugars to complex saccharides remains a notable challenge. Here we describe a photoinduced approach to achie开云体育appve site- and stereoselective chemical glycosylation from widely available native sugar building blocks, which through homolytic (one-electron) chemistry bypasses unnecessary hydroxyl group masking and manipulation. This process is reminiscent of nature in its regiocontrolled generation of a transient glycosyl donor, followed by radical-based cross-coupling with electrophiles on activation with light. Through selective anomeric functionalization of mono- and oligosaccharides, this protecting-group-free ‘cap and glycosylate’ approach offers straightforward access to a wide array of metabolically robust glycosyl compounds. Owing to its biocompatibility, the method was extended to the direct post-translational glycosylation of proteins.
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