《自然》（20200820出版）一周論文導讀

編譯 | 李言

nature, 20 August 2020，Volume 584 Issue 7821

《自然》2020年8月20日，第584卷，7821期

地球科學Geoscience

The causes of sea-level rise since 1900

自1900年以來，海平面上升的原因

▲ 作者：Thomas Frederikse, Felix Landerer, Lambert Caron, Surendra Adhikari, David Parkes, et al.

▲ 連結：

https://www.nature.com/articles/s41586-020-2591-3

▲ 摘要

自1900年以來，全球平均海平面上升的速度隨時間而變化，但造成海平面上升的因素仍不清楚。

在此，我們提出了一個利用獨立觀測及其固有不確定性重建1900年以來海平面的概率框架。海洋熱膨脹、冰體損失和陸地儲水變化對海平面變化的貢獻之和與全球尺度和流域尺度觀測海平面變化趨勢和多年代際變化是一致的。

自1900年以來，主要由冰川造成的冰川數量減少造成的海平面上升是熱膨脹的兩倍。冰川和格陵蘭冰原的大量流失解釋了20世紀40年代全球海平面上升的高速率，而人工水庫蓄水的急劇增加是20世紀70年代低於平均水平的主要原因。

自20世紀70年代以來，海平面上升的加速是由海洋熱膨脹和格陵蘭島增加的冰蓋損失共同造成的。我們的結果將1900年以來觀測到的全球平均海平面上升的幅度與基於潛在過程的估計相一致，這意味著不需要額外的過程來解釋1900年以來觀測到的海平面變化。

▲ Abstract

The rate of global-mean sea-level rise since 1900 has varied over time, but the contributing factors are still poorly understood. Here we present a probabilistic framework to reconstruct sea level since 1900 using independent observations and their inherent uncertainties. The sum of the contributions to sea-level change from thermal expansion of the ocean, ice-mass loss and changes in terrestrial water storage is consistent with the trends and multidecadal variability in observed sea level on both global and basin scales, which we reconstruct from tide-gauge records. Ice-mass loss—predominantly from glaciers—has caused twice as much sea-level rise since 1900 as has thermal expansion. Mass loss from glaciers and the Greenland Ice Sheet explains the high rates of global sea-level rise during the 1940s, while a sharp increase in water impoundment by artificial reservoirs is the main cause of the lower-than-average rates during the 1970s. The acceleration in sea-level rise since the 1970s is caused by the combination of thermal expansion of the ocean and increased ice-mass loss from Greenland. Our results reconcile the magnitude of observed global-mean sea-level rise since 1900 with estimates based on the underlying processes, implying that no additional processes are required to explain the observed changes in sea level since 1900.

天文學Astronomy

Cold gas in the Milky Way’s nuclear wind

來自銀河系星系核風的冷氣體

▲ 作者：Enrico M. Di Teodoro, N. M. McClure-Griffiths, Felix J. Lockman & Lucia Armillotta

▲ 連結：

https://www.nature.com/articles/s41586-020-2595-z

▲ 摘要

銀河系的中心擁有數個高能量過程，這些過程強烈影響了我們銀河系的內部區域。到目前為止，還沒有證據表明存在冷密分子相（10到100 kelvin）。

在此，我們報告從銀河系中心流出的分子氣體的觀測結果。這種冷物質與在核風中行進的氫原子云有關。分子氣體的形態和運動學（約一秒差距）表明，這些星雲正在與較暖的介質混合，並可能被破壞。

數據還表明，分子氣體流出的質量是不容忽視的，並可能影響星系中心區域的恆星形成率。這種寒冷、稠密、高速氣體的存在令人費解，因為無論是射手座A*目前的活動水平，還是星系內部的恆星形成，似乎都不是這種物質的來源。

▲ Abstract

The centre of the Milky Way hosts several high-energy processes that have strongly affected the inner regions of our Galaxy. So far there has been no evidence of the cold dense molecular phase (10 to 100 kelvin). Here we report observations of molecular gas outflowing from the centre of our Galaxy. This cold material is associated with atomic hydrogen clouds travelling in the nuclear wind. The morphology and the kinematics of the molecular gas, resolved on a scale of about one parsec, indicate that these clouds are mixing with the warmer medium and are possibly being disrupted. The data also suggest that the mass of the molecular gas outflow is not negligible and could affect the rate of star formation in the central regions of the Galaxy. The presence of this cold, dense and high-velocity gas is puzzling, because neither Sagittarius A* at its current level of activity nor star formation in the inner Galaxy seems to be a viable source for this material.

量子通信Quantum Communication

Quantum error correction of a qubit encoded in grid states of an oscillator

振蕩器網格態量子比特的量子糾錯

▲ 作者：P. Campagne-Ibarcq, A. Eickbusch, S. Touzard, E. Zalys-Geller, et al.

▲ 連結：

https://www.nature.com/articles/s41586-020-2603-3

▲ 摘要

為了超越經典計算機，量子計算機必須提高對量子位進行邏輯操作的準確性。在這裡，我們通過反饋協議實驗製備了方形和六邊形的GKP編碼狀態，該反饋協議包含了非破壞性測量，這些測量是由一個超導微波諧振腔作為振蕩器實現的。

我們證明了一個編碼量子位的QEC與抑制所有邏輯錯誤，在定量上與基於實驗測量缺陷的理論估計一致。我們的協議適用於其他連續變量系統，與之前的QEC實現相比，可以減輕各種噪聲過程產生的所有邏輯錯誤，並促進量子計算容錯。

▲ Abstract

The accuracy of logical operations on quantum bits (qubits) must be improved for quantum computers to outperform classical ones in useful tasks. Here we experimentally prepare square and hexagonal GKP code states through a feedback protocol that incorporates non-destructive measurements that are implemented with a superconducting microwave cavity having the role of the oscillator. We demonstrate QEC of an encoded qubit with suppression of all logical errors, in quantitative agreement with a theoretical estimate based on the measured imperfections of the experiment. Our protocol is applicable to other continuous-variable systems and, in contrast to previous implementations of QEC, can mitigate all logical errors generated by a wide variety of noise processes and facilitate fault-tolerant quantum computation.

材料科學Material Science

Observation of superconducting diode effect

超導二極體效應的觀測

▲ 作者：Fuyuki Ando, Yuta Miyasaka, Tian Li, Jun Ishizuka, Tomonori Arakawa, et al.

▲ 連結：

https://www.nature.com/articles/s41586-020-2590-4

▲ 摘要

非線性光學和電學效應與缺乏空間反演對稱有關，允許方向選擇性的傳播和傳輸量子粒子，如光子和電子。這種非互易現象最常見的例子是具有p-n結的半導體二極體，在一個方向上電阻低，在另一個方向上電阻高。

在此，我們展示了一個沒有反轉中心、在人工超晶格[Nb/V/Ta]n中的磁可控超導二極體。通過直流電法測量，可以清楚地觀察到超導向法向躍遷時電阻與電流的非倒數曲線，並認為臨界電流的差異與空間反轉和時間反轉對稱性的打破所引起的手性磁各向異性有關。

由於非倒數臨界電流的存在，[Nb/V/Ta]n 超晶格只在一個方向上表現出零電阻。

▲ Abstract

Nonlinear optical and electrical effects associated with a lack of spatial inversion symmetry allow direction-selective propagation and transport of quantum particles, such as photons and electrons. The most common example of such nonreciprocal phenomena is a semiconductor diode with a p–n junction, with a low resistance in one direction and a high resistance in the other. Here we demonstrate a magnetically controllable superconducting diode in an artificial superlattice [Nb/V/Ta]n without a centre of inversion. The nonreciprocal resistance versus current curve at the superconducting-to-normal transition was clearly observed by a direct-current measurement, and the difference of the critical current is considered to be related to the magnetochiral anisotropy caused by breaking of the spatial-inversion and time-reversal symmetries. Owing to the nonreciprocal critical current, the [Nb/V/Ta]n superlattice exhibits zero resistance in only one direction.

Additive manufacturing of silica aerogels

矽氣凝膠的增材製造

▲ 作者：Shanyu Zhao, Gilberto Siqueira, Sarka Drdova, David Norris, Christopher Ubert, et al

▲ 連結：

https://www.nature.com/articles/s41586-020-2594-0

▲ 摘要

矽氣凝膠因其超低導熱性和開孔結構，在絕熱、催化、物理、環境修復、光學器件和超高速粒子捕獲等領域得到了廣泛的應用。

在此，我們提出了一種墨水直寫技術，用於從稀釋的二氧化矽納米顆粒懸浮液（sol）中的二氧化矽氣凝膠粉漿中創建微型矽氣凝膠物體。由於高體積分數的凝膠顆粒，墨水錶現出剪切稀釋行為。

因此，在列印過程中，它們很容易通過噴嘴流動，但在列印後它們的粘度迅速增加，以確保被列印的物體保持其形狀。印刷後，矽溶膠在氨氣中形成凝膠，使後續處理成為氣凝膠。

列印的氣凝膠是純矽，並保持典型的矽氣凝膠的高比表面積（751平方米/克）和超低導熱性。此外，我們還演示了功能納米顆粒可以很容易地結合在一起。列印的矽氣凝膠對象可以用於熱管理，作為小型氣體泵和降解揮發性有機化合物。

▲ Abstract

Owing to their ultralow thermal conductivity and open pore structure, silica aerogels are widely used in thermal insulation, catalysis, physics, environmental remediation, optical devices and hypervelocity particle capture. Here we present a direct ink writing protocol to create miniaturized silica aerogel objects from a slurry of silica aerogel powder in a dilute silica nanoparticle suspension (sol). The inks exhibit shear-thinning behaviour, owing to the high volume fraction of gel particles. As a result, they flow easily through the nozzle during printing, but their viscosity increases rapidly after printing, ensuring that the printed objects retain their shape. After printing, the silica sol is gelled in an ammonia atmosphere to enable subsequent processing into aerogels. The printed aerogel objects are pure silica and retain the high specific surface area (751 square metres per gram) and ultralow thermal conductivity (15.9 milliwatts per metre per kelvin) typical of silica aerogels. Furthermore, we demonstrate the ease with which functional nanoparticles can be incorporated. The printed silica aerogel objects can be used for thermal management, as miniaturized gas pumps and to degrade volatile organic compounds, illustrating the potential of our protocol.

Piezoelectric and pyroelectric effects induced by interface polar symmetry

界面極性對稱引起的壓電和熱釋電效應

▲ 作者：Ming-Min Yang, Zheng-Dong Luo, Zhou Mi, Jinjin Zhao, Sharel Pei E & Marin Alexe

▲ 連結：

https://www.nature.com/articles/s41586-020-2602-4

▲ 摘要

幾十年來，由於大量的獨特現象——例如光生伏打效應、量子霍爾效應及高溫超導——以及它們在如今技術設備中的關鍵角色，異質結構中的界面一直是凝聚態物理研究的重點。

在此我們表明，一個來自於異質結構界面帶彎曲的內建電場在其中誘發了極性對稱，從而產生了包括壓電和熱釋電在內的自然功能，即使元件材料是中心對稱的。

我們研究了由貴金屬和中心對稱半導體形成的經典界面，即肖特基連接點，包括摻雜鈮的鍶鈦氧化物晶體、摻雜鈮的二氧化鈦晶體、摻雜鈮的鋇鍶鈦氧化物陶瓷和矽。

耗盡區內嵌的電場在半導體中誘發極性結構，產生大量的壓電和熱釋電效應。尤其是，界面的熱釋電係數和優點比傳統的塊狀極性材料高出一個數量級。

▲ Abstract

Interfaces in heterostructures have been a key point of interest in condensed-matter physics for decades owing to a plethora of distinctive phenomena—such as rectification, the photovoltaic effect, the quantum Hall effect and high-temperature superconductivity—and their critical roles in present-day technical devices. Here we show that a built-in electric field that originates from band bending at heterostructure interfaces induces polar symmetry therein that results in emergent functionalities, including piezoelectricity and pyroelectricity, even though the component materials are centrosymmetric. We study classic interfaces—namely, Schottky junctions—formed by noble metal and centrosymmetric semiconductors, including niobium-doped strontium titanium oxide crystals, niobium-doped titanium dioxide crystals, niobium-doped barium strontium titanium oxide ceramics, and silicon. The built-in electric field in the depletion region induces polar structures in the semiconductors and generates substantial piezoelectric and pyroelectric effects. In particular, the pyroelectric coefficient and figure of merit of the interface are over one order of magnitude larger than those of conventional bulk polar materials.

化學Chemstry

Liquid–liquid transition and critical point in sulfur

硫的液-液轉變和臨界點

▲ 作者：Laura Henry, Mohamed Mezouar, Gaston Garbarino, David Sifré, Gunnar Weck & Frédéric Datchi

▲ 連結：

https://www.nature.com/articles/s41586-020-2593-1

▲ 摘要

液-液轉變（LLT）是一個有趣的現象，其中單組分液體通過一級相變轉變為另一種液體，改變了我們對液體狀態的認識。

在某些情況下，人們已經預測在分離低密度和高密度液體的LLT線的末端有一個類似氣液臨界點的液-液臨界點（LLCP），但還沒有對任何材料進行實驗觀察。這個假定的液-液臨界點已被用來解釋水的熱力學異常。

在此，我們的報告結合原位密度、x射線衍射和拉曼散射測量，為硫中的一級液-液轉變和液-液臨界點提供了直接證據。這種LLT轉變表現為低密度液體和高密度液體之間的急劇密度跳躍，並且在對分布函數中具有明顯的特徵。

我們觀察到密度躍遷隨溫度的非單調變化：當遠離臨界點時，密度躍遷先增大後減小。這種行為與密度和熵在推動轉變過程中的競爭效應有關。硫中一階液-液轉變和臨界點的存在有望用於揭示水等重要液體的異常現象。

▲ Abstract

The liquid–liquid transition (LLT), in which a single-component liquid transforms into another one via a first-order phase transition, is an intriguing phenomenon that has changed our perception of the liquid state. A liquid–liquid critical point (LLCP), similar to the gas–liquid critical point, has been predicted at the end of the LLT line that separates the low- and high-density liquids in some cases, but has not yet been experimentally observed for any materials. This putative LLCP has been invoked to explain the thermodynamic anomalies of water. Here we report combined in situ density, X-ray diffraction and Raman scattering measurements that provide direct evidence for a first-order LLT and an LLCP in sulfur. The transformation manifests itself as a sharp density jump between the low- and high-density liquids and by distinct features in the pair distribution function. We observe a non-monotonic variation of the density jump with increasing temperature: it first increases and then decreases when moving away from the critical point. This behaviour is linked to the competing effects of density and entropy in driving the transition. The existence of a first-order LLT and a critical point in sulfur could provide insight into the anomalous behaviour of important liquids such as water.