《自然》（20220602出版）一周论文导读

编译 | 冯维维

Nature,2 June 2022,Volume 606 Issue 7912

《自然》2022年6月2日，第606卷，7912期

物理学Physics

Resolving the H I in damped Lyman α systems that power star formation

解析阻尼莱曼α系统中驱动恒星形成的物质

作者：Rongmon Bordoloi, John M. O’Meara, Keren Sharon, Jane R. Rigby, Jeff Cooke, Ahmed Shaban, Mateusz Matuszewski, Luca Rizzi, Greg Doppmann, D. Christopher Martin, Anna M. Moore, Patrick Morrissey & James D. Neill

链接：

https://www.nature.com/articles/s41586-022-04616-1

摘要：

致密原子气体（主要是氢）的储层包含约90%红移为3的中性气体，并贡献了宇宙中总重子的2%至3%。科学家研究这些“阻尼莱曼α系统”（名字源自它们吸收背景源内部和来自背景源的莱曼α光子）已有几十年，但只能通过背景类星体光谱和γ射线暴中的吸收线来研究。这样的光束不会限制系统的物理范围。

作者报告了一个明亮的，红移2.7的引力透镜星系的积分场光谱，有两个前景阻尼莱曼α系统。这些系统均值列密度是1020.46到1020.84平方厘米，总质量大于5.5 108 - 1.4 109倍太阳质量，表明它们包含下一代恒星形成的必要燃料，与红移大于2的质量相对较低的原始星系相一致。

Abstract：

Reservoirs of dense atomic gas (primarily hydrogen) contain approximately 90 per cent of the neutral gas at a redshift of 3, and contribute to between 2 and 3 per cent of the total baryons in the Universe. These ‘damped Lyman α systems’—so called because they absorb Lyman α photons within and from background sources—have been studied for decades, but only through absorption lines present in the spectra of background quasars and γ-ray bursts. Such pencil beams do not constrain the physical extent of the systems. Here we report integral-field spectroscopy of a bright, gravitationally lensed galaxy at a redshift of 2.7 with two foreground damped Lyman α systems. The mean column densities are between 1020.46 and 1020.84 centimetres squared and the total masses are greater than 5.5 108–1.4 109 times the mass of the Sun, showing that they contain the necessary fuel for the next generation of star formation, consistent with relatively massive, low-luminosity primeval galaxies at redshifts greater than 2.

Magneto-optical trapping and sub-Doppler cooling of a polyatomic molecule

多原子分子的磁光俘获和亚多普勒冷却

作者：Nathaniel B. Vilas, Christian Hallas, Loïc Anderegg, Paige Robichaud, Andrew Winnicki, Debayan Mitra & John M. Doyle

链接：

https://www.nature.com/articles/s41586-022-04620-5

摘要：

激光冷却和俘获，特别是磁光俘获方法，使科学取得了突破性进展，包括玻色-爱因斯坦凝聚，中性原子的量子计算和高精度光学时钟。最近，双原子分子的磁光阱（MOTs）已经被证明，为量子模拟研究和探索标准模型之外的物理提供了途径。

与双原子分子相比，多原子分子具有不同的旋转和振动自由度，从而提供了多种转变的可能性。然而，这些分子的复杂性到目前为止阻碍了对多原子物种的MOT的实现。

作者证明了磁光阱多原子分子，一氢氧化钙（CaOH）。捕获后，分子在蓝失谐光学糖蜜中被激光冷却到110μK的温度，低于多普勒冷却极限。

这里实现的温度和密度使CaOH成为各种量子科学应用的可行候选，包括量子模拟和使用光镊阵列计算。这项工作也表明，激光冷却和磁光阱的许多其他多原子物种将是可行的和实际的。

Abstract：

Laser cooling and trapping and magneto-optical trapping methods in particular, have enabled groundbreaking advances in science, including Bose–Einstein condensation, quantum computation with neutral atoms and high-precision optical clocks. Recently, magneto-optical traps (MOTs) of diatomic molecules have been demonstrated, providing access to research in quantum simulation and searches for physics beyond the standard model. Compared with diatomic molecules, polyatomic molecules have distinct rotational and vibrational degrees of freedom that promise a variety of transformational possibilities. However, the complexity of these molecules has so far precluded the realization of MOTs for polyatomic species. Here we demonstrate magneto-optical trapping of a polyatomic molecule, calcium monohydroxide (CaOH). After trapping, the molecules are laser cooled in a blue-detuned optical molasses to a temperature of 110μK, which is below the Doppler cooling limit. The temperatures and densities achieved here make CaOH a viable candidate for a wide variety of quantum science applications, including quantum simulation and computation using optical tweezer arrays. This work also suggests that laser cooling and magneto-optical trapping of many other polyatomic species will be both feasible and practical.

Quantum computational advantage with a programmable photonic processor

量子计算优势与可编程光子处理器

作者：Lars S. Madsen, Fabian Laudenbach, Mohsen Falamarzi. Askarani, Fabien Rortais, Trevor Vincent, Jacob F. F. Bulmer, Filippo M. Miatto, Leonhard Neuhaus, Lukas G. Helt, Matthew J. Collins, Adriana E. Lita, Thomas Gerrits, Sae Woo Nam, Varun D. Vaidya, Matteo Menotti, Ish Dhand, Zachary Vernon, Nicolás Quesada & Jonathan Lavoie

链接：

https://www.nature.com/articles/s41586-022-04725-x

摘要：

当量子计算机在定义明确的任务上运行着最知名的算法时，它的性能超过了最好的经典计算机，从而获得了计算优势。

在所有量子门之上提供可编程性的光子机器都没有展示出量子计算的优势：以前的机器在很大程度上局限于静态门序列。早期的光子演示也容易受到欺骗，在这种情况下，经典启发式产生的样本，没有直接模拟，比来自量子硬件的样本更接近理想分布。

作者报告了使用Borealis的量子计算优势，这是一种在所有实现的门上提供动态可编程的光子处理器。他们采用时间复用和光子数分辨的结构，对216个与三维连通性纠缠的压缩模进行了高斯玻色子采样。

平均而言，最好的算法和超级计算机使用精确的方法从编程分布中产生一个样本需要9000多年的时间，而Borealis只需要36 微秒（1微秒等于百万分之一秒）。

这种运行时优势是早期光子机报告的5000万倍以上。该实验构成了一个非常大的GBS实验，记录了多达219个光子的事件，平均光子数为125个。这项工作是通向实用量子计算机道路上的一个关键里程碑，验证了光子学作为实现这一目标的平台的关键技术特征。

Abstract：

A quantum computer attains computational advantage when outperforming the best classical computers running the best-known algorithms on well-defined tasks. No photonic machine offering programmability over all its quantum gates has demonstrated quantum computational advantage: previous machines were largely restricted to static gate sequences. Earlier photonic demonstrations were also vulnerable to spoofing, in which classical heuristics produce samples, without direct simulation, lying closer to the ideal distribution than do samples from the quantum hardware.

Here we report quantum computational advantage using Borealis, a photonic processor offering dynamic programmability on all gates implemented. We carry out Gaussian boson sampling4 (GBS) on 216 squeezed modes entangled with three-dimensional connectivity, using a time-multiplexed and photon-number-resolving architecture. On average, it would take more than 9,000years for the best available algorithms and supercomputers to produce, using exact methods, a single sample from the programmed distribution, whereas Borealis requires only 36μs. This runtime advantage is over 50 million times as extreme as that reported from earlier photonic machines. Ours constitutes a very large GBS experiment, registering events with up to 219 photons and a mean photon number of 125. This work is a critical milestone on the path to a practical quantum computer, validating key technological features of photonics as a platform for this goal.

Non-Hermitian chiral phononics through optomechanically induced squeezing

光机械诱导压缩的非厄米手性声子

作者：Javier del Pino, Jesse J. Slim & Ewold Verhagen

链接：

https://www.nature.com/articles/s41586-022-04609-0

摘要：

在物理系统上施加手性会产生非常规的能量流和响应，例如在对称破缺磁场中电子的阿哈罗诺夫-玻姆效应和拓扑量子霍尔相。最近，人们对将这一原理与破厄米特性相结合来探索新的拓扑相及其应用产生了极大的兴趣。

作者报告了具有独特对称性和动力学的声子态，这些声子态是在将时间反转对称性的受控破缺与非厄米动力学相结合时形成的。这两者都是通过时间调制辐射压力在小型纳米光力学网络中诱导的。

作者观察了机械谐振腔在合成维度下的手性能量流动和本征模的阿哈罗诺夫-玻姆调谐。引入粒子-非守恒的压缩相互作用，他们观察到环形网络中的非厄米阿哈罗诺夫-玻姆效应，其中力学准粒子经历参数增益。

得到的复模谱显示了压缩、异常点、不稳定性和单向声子放大的通量调谐。这种丰富的现象学指出了探索新的非厄米拓扑玻色子相的方法，以及利用时空对称性破缺在传感和传输中的应用。

Abstract：

Imposing chirality on a physical system engenders unconventional energy flow and responses, such as the Aharonov–Bohm effect1 and the topological quantum Hall phase for electrons in a symmetry-breaking magnetic field. Recently, great interest has arisen in combining that principle with broken Hermiticity to explore novel topological phases and applications. Here we report phononic states with unique symmetries and dynamics that are formed when combining the controlled breaking of time-reversal symmetry with non-Hermitian dynamics. Both of these are induced through time-modulated radiation pressure forces in small nano-optomechanical networks. We observe chiral energy flow among mechanical resonators in a synthetic dimension and Aharonov–Bohm tuning of their eigenmodes. Introducing particle-non-conserving squeezing interactions, we observe a non-Hermitian Aharonov–Bohm effect in ring-shaped networks in which mechanical quasiparticles experience parametric gain. The resulting complex mode spectra indicate flux-tuning of squeezing, exceptional points, instabilities and unidirectional phononic amplification. This rich phenomenology points the way to exploring new non-Hermitian topological bosonic phases and applications in sensing and transport that exploit spatiotemporal symmetry breaking.

化学chemistry

Epitaxial single-crystal hexagonal boron nitride multilayers on Ni (111)

Ni（111）表面外延单晶六方氮化硼多层膜

作者：Kyung Yeol Ma, Leining Zhang, Sunghwan Jin, Yan Wang, Seong In Yoon, Hyuntae Hwang, Juseung Oh, Da Sol Jeong, Meihui Wang, Shahana Chatterjee, Gwangwoo Kim, A-Rang Jang, Jieun Yang, Sunmin Ryu, Hu Young Jeong, Rodney S. Ruoff, Manish Chhowalla, Feng Ding & Hyeon Suk Shin

链接：

https://www.nature.com/articles/s41586-022-04745-7

摘要：

大面积单晶单层二维材料，如石墨烯，六方氮化硼（hBN）和过渡金属二卤族化合物已经生长。hBN被认为是基于二维材料的场效应晶体管（fet）的“理想”介电介质，提供了扩展摩尔定律的潜力。虽然比单层厚的hBN更适合作为二维半导体衬底，但高度均匀的单晶多层hBN生长还没有得到证实。
作者报告了用化学气相沉积（CVD）方法外延生长晶圆级单晶三层hBN。发现在单晶Ni（111）上早期生长出均匀排列的hBN岛，最终形成单晶薄膜。透射电镜结果表明，硼在Ni中的溶解使单晶hBN薄膜与Ni基体之间在冷却过程中形成了Ni23B6中间层。hBN与Ni23B6、Ni23B6与Ni之间存在外延关系。

hBN膜在氢催化演化过程中起到了完整的保护层作用，表明hBN是连续的单晶。在MoS2 fet中，转移到SiO2 （300纳米）/Si晶圆上的hBN作为介电层，减少了SiO2 衬底上的电子掺杂。研究结果证明了大面积高质量的单晶多层hBN，这将为使其成为二维半导体普遍存在的衬底开辟新的途径。

Abstract：

Large-area single-crystal monolayers of two-dimensional (2D) materials such as graphene, hexagonal boron nitride (hBN) and transition metal dichalcogenides have been grown. hBN is considered to be the ‘ideal’ dielectric for 2D-materials-based field-effect transistors (FETs), offering the potential for extending Moore’s law. Although hBN thicker than a monolayer is more desirable as substrate for 2D semiconductors, highly uniform and single-crystal multilayer hBN growth has yet to be demonstrated. Here we report the epitaxial growth of wafer-scale single-crystal trilayer hBN by a chemical vapour deposition (CVD) method. Uniformly aligned hBN islands are found to grow on single-crystal Ni (111) at early stage and finally to coalesce into a single-crystal film. Cross-sectional transmission electron microscopy (TEM) results show that a Ni23B6 interlayer is formed (during cooling) between the single-crystal hBN film and Ni substrate by boron dissolution in Ni. There are epitaxial relationships between hBN and Ni23B6 and between Ni23B6 and Ni. We also find that the hBN film acts as a protective layer that remains intact during catalytic evolution of hydrogen, suggesting continuous single-crystal hBN. This hBN transferred onto the SiO2 (300 nm)/Si wafer acts as a dielectric layer to reduce electron doping from the SiO2 substrate in MoS2 FETs. Our results demonstrate high-quality single-crystal multilayered hBN over large areas, which should open up new pathways for making it a ubiquitous substrate for 2D semiconductors.

[18F]Difluorocarbene for positron emission tomography

[18F]二氟苯用于正电子发射断层扫描

作者：Jeroen B. I. Sap, Claudio F. Meyer, Joseph Ford, Natan J. W. Straathof, Alexander B. Dürr, Mariah J. Lelos, Stephen J. Paisey, Tim A. Mollner, Sandrine M. Hell, Andrés A. Trabanco, Christophe Genicot, Christopher W. am Ende, Robert S. Paton, Matthew Tredwell & Véronique Gouverneur

链接：

https://www.nature.com/articles/s41586-022-04669-2

摘要：

全身正电子发射断层扫描（PET）的出现极大地拓宽了这种强大的分子成像技术的研究和临床应用范围。这种可能性加快了氟-18 （18F）放射化学的进展，有许多方法可用于18F标记（杂）芳烃和烷烃。

然而，获得高摩尔活性的18F -二氟甲基化分子大多是一个未解决的问题，尽管二氟甲基对药物的发现是不可或缺的。

作者报告了一种通用的解决方案，将卡本化学引入核成像领域，使用一种能够进行无数个18F-二氟甲基化过程的[18F]二氟苯试剂。

与几十种已知的二氟苯试剂相比，这种18F试剂是精心设计的，易于获得，具有高摩尔活性和通用性。摩尔活性的问题是通过检测二氟苯前体电子变化的同位素稀释可能性的方法解决的。

通过多种[18F]二氟苯反应，包括O-H、S-H和N-H插入，以及利用普遍官能团（如硫代苯酚、n -异质芳烃和易于安装的芳基硼酸）的反应性的交叉偶联，证明了其通用性。通过标记高度复杂和功能化的生物相关分子和放射性示踪剂来说明其影响。

Abstract：

The advent of total-body positron emission tomography (PET) has vastly broadened the range of research and clinical applications of this powerful molecular imaging technology1. Such possibilities have accelerated progress in fluorine-18 (18F) radiochemistry with numerous methods available to 18F-label (hetero)arenes and alkanes2. However, access to 18F-difluoromethylated molecules in high molar activity is mostly an unsolved problem, despite the indispensability of the difluoromethyl group for pharmaceutical drug discovery3. Here we report a general solution by introducing carbene chemistry to the field of nuclear imaging with a [18F]difluorocarbene reagent capable of a myriad of 18F-difluoromethylation processes. In contrast to the tens of known difluorocarbene reagents, this 18F-reagent is carefully designed for facile accessibility, high molar activity and versatility. The issue of molar activity is solved using an assay examining the likelihood of isotopic dilution on variation of the electronics of the difluorocarbene precursor. Versatility is demonstrated with multiple [18F]difluorocarbene-based reactions including O–H, S–H and N–H insertions, and cross-couplings that harness the reactivity of ubiquitous functional groups such as (thio)phenols, N-heteroarenes and aryl boronic acids that are easy to install. The impact is illustrated with the labelling of highly complex and functionalized biologically relevant molecules and radiotracers.