《科學》（20201218出版）一周論文導讀

編譯 | 未玖

Science, 18 DECEMBER 2020, VOL 370, ISSUE 6523

《科學》2020年12月18日，第370卷，6523期

天文學Astronomy

Multimessenger constraints on the neutron-star equation of state and the Hubble constant

中子星狀態方程和哈勃常數的多信使約束

▲ 作者：Tim Dietrich, Michael W. Coughlin, Peter T. H. Pang, Mattia Bulla, Jack Heinzel, Lina Issa, et al.

▲ 連結：

https://science.sciencemag.org/content/370/6523/1450#aff-3

▲ 摘要

通過不同信使（包括引力波和電磁信號）觀測中子星合併，可用於研究比原子核密度更大的物質的行為，並測量由哈勃常數量化的宇宙膨脹率。

研究組對引力波事件GW170817與它的電磁波對應物AT2017gfo和GRB170817A以及引力波事件GW190425進行了聯合分析，這兩個引力波事件均來自中子星合併。

研究組將這些數據與此前使用X射線和射電觀測的脈衝星測量結果與使用手性有效場理論的核理論計算相結合，以約束中子星狀態方程。研究組發現，一個1.4太陽質量中子星的半徑在90％置信度下為11.75千米，哈勃常數在1σ不確定度下為66.2。

▲ Abstract

Observations of neutron-star mergers with distinct messengers, including gravitational waves and electromagnetic signals, can be used to study the behavior of matter denser than an atomic nucleus and to measure the expansion rate of the Universe as quantified by the Hubble constant. We performed a joint analysis of the gravitational-wave event GW170817 with its electromagnetic counterparts AT2017gfo and GRB170817A, and the gravitational-wave event GW190425, both originating from neutron-star mergers. We combined these with previous measurements of pulsars using x-ray and radio observations, and nuclear-theory computations using chiral effective field theory, to constrain the neutron-star equation of state. We found that the radius of a 1.4–solar mass neutron star is 11.75 km at 90% confidence and the Hubble constant is 66.2 at 1σ uncertainty.

物理學Physics

Relativistic kinematics of a magnetic soliton

磁孤子的相對論運動學

▲ 作者：Lucas Caretta, Se-Hyeok Oh, Takian Fakhrul, Dong-Kyu Lee, Byung Hun Lee, Se Kwon Kim, et al.

▲ 連結：

https://science.sciencemag.org/content/370/6523/1438

▲ 摘要

狹義相對論的一個原則是，沒有粒子可以超過光速。在某些磁性材料中，最大磁振子群速度可充當磁孤子速度的類似相對論極限。

研究組利用自旋霍爾效應產生的純自旋電流，在低耗散磁絕緣體中驅動疇壁達到這個極限。研究組達到了創紀錄的電流驅動速度，每秒超過4300米（在相對論極限的10％以內），還觀察到與洛倫茲收縮相關的相對論運動的關鍵特徵，這導致了速度飽和。

通過分析和原子建模可以很好地解釋實驗結果。這些觀察為磁孤子動力學基本極限提供了關鍵見解，並為研究相對論孤子物理學建立了一個易於理解的實驗框架。

▲ Abstract

A tenet of special relativity is that no particle can exceed the speed of light. In certain magnetic materials, the maximum magnon group velocity serves as an analogous relativistic limit for the speed of magnetic solitons. Here, we drive domain walls to this limit in a low-dissipation magnetic insulator using pure spin currents from the spin Hall effect. We achieve record current-driven velocities in excess of 4300 meters per second—within ~10% of the relativistic limit—and we observe key signatures of relativistic motion associated with Lorentz contraction, which leads to velocity saturation. The experimental results are well explained through analytical and atomistic modeling. These observations provide critical insight into the fundamental limits of the dynamics of magnetic solitons and establish a readily accessible experimental framework to study relativistic solitonic physics.

Direct observation of Klein tunneling in phononic crystals

聲子晶體中克萊因隧道的直接觀測

▲ 作者：Xue Jiang, Chengzhi Shi, Zhenglu Li, Siqi Wang, Yuan Wang, Sui Yang, et al.

▲ 連結：

https://science.sciencemag.org/content/370/6523/1447

▲ 摘要

隧道效應在物理學的許多分支中都起著至關重要的作用，並實現了一些重要的應用。從理論上講，當準粒子在法線入射情況下，通過勢壘時不受其高度和寬度的影響，從而不受阻礙地穿透時，就會發生克萊因隧道效應。

研究組通過將兩種具有不同狄拉克點能量的人造聲子晶體夾在中間來創建聲子異質結。統一傳輸的關鍵特徵證實了克萊因隧道效應的直接觀測。實驗表明，克萊因隧道效應發生在一個很寬的聲頻頻帶上。

直接觀測聲子晶體中的克萊因隧道，有助於發現其在信號處理、超準直光束和通信中的應用潛力。

▲ 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

利用光子的量子計算優勢

▲ 作者：Han-Sen Zhong, Hui Wang, Yu-Hao Deng, Ming-Cheng Chen, Li-Chao Peng, Yi-Han Luo, et al.

▲ 連結：

https://science.sciencemag.org/content/370/6523/1460

▲ 摘要

量子計算機有望執行某些傳統計算機難以完成的任務。玻色子採樣就是這樣一項任務，它被認為是證明量子計算優勢的強有力候選。

研究組將50路難以區分的單模壓縮態發送到一個具有全連通隨機矩陣的100模式超低損耗幹涉儀中（整個光學裝置是鎖相的），並使用100個高效單光子探測器對輸出進行採樣，從而進行高斯玻色採樣。利用熱態、可分辨光子和均勻分布，針對可能出現的假設，對獲得的樣品進行驗證。

光子量子計算機「九章」產生多達76個輸出光子點擊，輸出狀態空間維數為1030，採樣速率比使用最先進的仿真策略和超級計算機快約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.

化學Chemistry

Tailored quinones support high-turnover Pd catalysts for oxidative C–H arylation with O2

修飾醌類助力高效鈀催化氧化C-H芳基化反應

▲ 作者：Chase A. Salazar, Kaylin N. Flesch, Brandon E. Haines, Philip S. Zhou, Djamaladdin G. Musaev, Shannon S. Stahl

▲ 連結：

https://science.sciencemag.org/content/370/6523/1454

▲ 摘要

鈀（II）催化的碳-氫（C-H）氧化反應可以簡化藥物、農藥和其他複雜有機分子的合成。然而，現有方法通常表現出較差的催化劑性能，高鈀（Pd）負載（例如10摩爾％）和需要（超）化學計量的氧化劑，例如苯醌和銀（I）鹽。

該研究探討了具有代表性的Pd催化氧化C-H芳基化反應的機理，並闡明了破壞催化劑性能的機理，包括消耗底物的副反應和螯合催化劑成為非活性物質的反應。

醌輔助催化劑的系統調節克服了這些有害特性。使用2,5-二叔丁基對苯醌可以有效地利用分子氧作為氧化劑，提高反應收率，Pd催化劑可循環使用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.

生態學Ecology

Novel trophic interactions under climate change promote alpine plant coexistence

氣候變化下的新型營養互作促進了高山植物的共存

▲ 作者：Patrice Descombes, Camille Pitteloud, Gaëtan Glauser, Emmanuel Defossez, Alan Kergunteuil, Pierre-Marie Allard, et al.

▲ 連結：

https://science.sciencemag.org/content/370/6523/1469

▲ 摘要

草食性和植物防禦表現出沿海拔梯度的耦合下降。但是，當前的生態平衡在氣候變化下可能會被破壞，動物向上遷移的速度會比植物更快。

研究組通過將低海拔食草動物昆蟲遷移到高山草原上，通過實驗模擬了這種向上遷移的食草動物範圍變化。研究組報告稱，新型食草動物和更多食草動物的引入破壞了植物冠層的垂直功能組織。

通過優先進食具有與低海拔寄主植物功能性狀相匹配的高山植物，食草動物減少了高山優勢植物物種的生物量，並有利於侵蝕抗食草動物的小型植物，從而增加了物種的豐富度。除了溫度的直接影響外，新的生物相互作用代表了在氣候變化下生態系統改變的一個被忽略但主要的驅動力。

▲ Abstract

Herbivory and plant defenses exhibit a coupled decline along elevation gradients. However, the current ecological equilibrium could be disrupted under climate change, with a faster upward range shift of animals than plants. Here, we experimentally simulated this upward herbivore range shift by translocating low-elevation herbivore insects to alpine grasslands. We report that the introduction of novel herbivores and increased herbivory disrupted the vertical functional organization of the plant canopy. By feeding preferentially on alpine plants with functional traits matching their low-elevation host plants, herbivores reduced the biomass of dominant alpine plant species and favored encroachment of herbivore-resistant small-stature plant species, inflating species richness. Supplementing a direct effect of temperature, novel biotic interactions represent a neglected but major driver of ecosystem modifications under climate change.