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

偶极份子博色-爱因斯坦凝结的不雅察

▲ 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

▲择要：

受量子力学定律支配的粒子群体现出有趣的涌现举动。量子质料中的原子量子气体、液氦以及电子因为它们的构成以及彼此作用都体现出差别的性子。超冷偶极份子的量子简并样品无望实现物资的新相，并为量子模仿以及量子计较提供新的路子。但纵然经由过程碰撞屏蔽技能削减了倏地丧失，到今朝为止也拦阻了蒸发冷却到博色-爱因斯坦凝结体（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蔽来按捺二体以及三体丧失，他们蒸发冷却钠-铯份子到量子简并并超过相变到BEC。当相空间密度跨越1时，BEC体现为双峰漫衍。天生了冷凝分数为60(10)%，温度为6(2)nK的BECs，并发明其不变寿命靠近2秒。这项事情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，无望于光学晶格中创举奇特的偶极液滴，自构造晶体相以及偶极自旋液体。

▲ 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于的孕育发生

▲ 作者：Vitaliy Sultanov, Alja? Kav?i?, E妹妹anouil Kokkinakis, Nerea Sebastián, Maria V. Chekhova Matja? Humar

▲链接：

https://www.nature.com/articles/s41586-024-07543-5

▲择要：

液晶具备自拆卸、对于电场的强相应以及可集成到繁杂体系中的威力，是光束把持的要害质料。近来发明的铁电向列液晶也具备相称年夜的二阶光学非线性，使其成为非线性光学的潜于质料。它们作为量子光源的使用可以年夜年夜扩大光子量子技能的界限。然而，自觉参数下转换，纠缠光子的基原来源，预示的单光子以及压缩光，到今朝为止尚未于液晶或者任何液体或者无机质料中不雅察到。

研究者于铁电向列液晶中实现了自觉参数下转换，并展示了电场可调谐的纠缠光子宽带孕育发生，其效率可与最好非线性晶体相媲美。施加几伏电压或者沿样品标的目的旋转份子取向，光子对于的发射速度以及偏振态会发生显著变迁。液晶源可以实现一种非凡类型的准相位婚配，这类婚配基在份子扭曲布局，是以可以按照光子对于的所需光谱以及偏振特征举行从头配置。

这类光源无望于功效、亮度以及所孕育发生量子态的可调性方面优在尺度非线性光学质料。这一律念可以扩大到繁杂的拓扑布局，宏不雅器件以及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

缭绕半人马ω球状星团内一个中等品质黑洞的倏地挪动恒星

▲ 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

▲择要：

科学家于星河系半人马座欧米茄星团（半人马ω球状星团）内不雅测到的倏地挪动恒星为一个中等品质黑洞的存于提供了证据。该研究基在哈勃空间千里镜20多年的不雅测成果，或者有助在此后研究职员搜刮这种难以发明的黑洞。

科学家已经发明各类品质的黑洞，从5~150倍太阳品质（M⊙）的恒星品质黑洞到星系中心的超年夜品质黑洞（跨越10万倍太阳品质；105M⊙）。不外，今朝只发明了少数存于争议的候选中等品质黑洞，这种黑洞的品质于太阳品质的150倍到10万倍不等。

鉴在半人马ω球状星团高品质以及繁杂星族的特征，它是寻觅中等品质黑洞的一个颇有但愿的方针，但以前对于该区域发明了一个黑洞的报导始终面对争议。德国马普学会天文研究所的MaximilianHaberle以及同事哄骗哈勃空间千里镜20年的影像，监测了该星团中心四周恒星的运动。他们提出有7个恒星于中心区域倏地挪动，并以为这申明半人马ω球状星团的中心有一个中等品质黑洞。他们猜度该黑洞品质的下限为8200M⊙摆布。

“这些新发明的恒星是半人马ω球状星团中存于一个中等品质黑洞的最好证据。”加拿年夜麦吉尔年夜学的DarylHaggard以及美国旧金山州立年夜学的AdrienneCool于一篇同期揭晓的新闻不雅点文章中写道，研究成果或者注解于其他球状星团中征采中等品质黑洞是合理的。

▲ 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

电子以及空穴掺杂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

▲择要：

基在石墨烯的高品质二维电子体系已经经成为研究超导性的高度可调平台。详细来讲，于电子以及空穴掺杂的扭曲石墨烯涡流系统中都不雅察到了超导性，而于晶体石墨烯系统中，迄今为止只于空穴掺杂的菱形三层石墨烯(RTG)以及空穴掺杂的Bernal双层石墨烯(BBG)中不雅察到超导性。近来，因为靠近单层WSe2, BBG中的超导性获得了加强。

研究者报导了经由过程静电掺杂于电子以及空穴掺杂的BBG/WSe2器件中不雅察到的超导性以及一系列风韵对于称性破缺相。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治。电子掺杂以及空穴掺杂超导的最年夜berezinski - kosterlitz - Thouless改变温度别离约为210 mK以及400 mK。只要当外加电场驱动BBG电子或者空穴波函数向WSe2层挪动时，超导性才会呈现，这夸大了WSe2层于不雅察到的超导性中的主要性。空穴掺杂的超导违背了泡利顺磁极限，切合伊辛类超导体。比拟之下，电子掺杂的超导性听从泡利极限，只管于导带中相近引诱的伊辛自旋轨道耦合也很较着。该发明凸起了与BBG中传导带相干的富厚物理特征，为进一步研究晶体石墨烯的超导机制以及基在BBG的超导体器件的开发摊平了门路。

▲ 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-sy妹妹etry-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

用溶剂增韧的博璃状凝胶

▲ 作者：Meixiang Wang, Xun Xiao, Salma Siddika, Moha妹妹ad 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

▲择要：

博璃状聚合物凡是坚硬而结实，但延展性有限。经由过程溶胀，博璃状聚合物可以酿成柔软而懦弱的凝胶，但具备加强的延展性。机能的显著变迁是因为溶剂增长了链间的自由体积，同时削弱了聚合物与聚合物之间的彼此作用。研究者展示了极性聚合物与离子液体——离子凝胶，于适量浓度下的溶剂化可以孕育发生一种怪异的质料，称为博璃凝胶，具备博璃以及凝胶的抱负机能。

离子液体增长了自由体积，是以，只管缺少传统的溶剂(例如，水)，可扩大性。但于室温下，离子液体于聚合物链之间造成强而富厚的非共价交联，造成坚硬、坚韧、博璃状以及匀称的收集(即没有相分散)。只管液体含量跨越54wt %，但博璃凝胶具备伟大的断裂强度(42 MPa)、韧性(110 MJ m?3)、屈就强度(73 MPa)以及杨氏模量(1 GPa)。这些值与热塑性塑料(如聚乙烯)相似，但与热塑性塑料差别的是，博璃状凝胶可以变形到670%的应变，而且于加热时可以彻底倏地恢复。这些通明质料经由过程一步聚合造成，具备使人印象深刻的粘合、自愈以及外形影象特征。

▲ 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

自然糖的间接自由基功效化

▲ 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 Moha妹妹ed, Benjamin G. Davis Ming Joo Koh

▲链接：

https://www.nature.com/articles/s41586-024-07548-0

▲择要：

自然存于的糖以及碳水化合物含有很多具备相似反映活性的羟基。是以，化学家凡是依赖吃力的、多步调的掩护基团计谋，将这些可再生原料转化为打造聚糖的试剂(糖基供体)。

将自然糖间接转化为复合糖仍旧是一个显著的应战。研究者描写了一种光引诱要领，经由过程均溶(单电子)化学绕过没必要要的羟基掩膜以及把持，从广泛可用的自然糖构建块实现位点以及立体选择性化学糖基化。这一历程令人遐想到天然界于区域节制下孕育发生瞬时糖基供体，于光激活下与亲电试剂举行基在自由基的交织偶联。

经由过程选择性的单糖以及寡糖的头聚糖功效化，这类无掩护基团的“帽以及糖基酸”要领提供了一种间接的路子，可以得到年夜量代谢旺盛的糖基化合物。因为其生物相容性，该要领被扩大到卵白质的间接翻译后糖基化。

▲ 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 achieve 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.