編譯 | 李言
Nature , 17 March 2022, Volume 603 Issue 7901
《自然》 2022年3月17日，第603卷，7901期
化學 Chemistry
High-resolution laser resonances of antiprotonic helium in superfluid 4He
超流體4He中反質子氦的高分辨率激光***振
作者：Anna Sótér, Hossein Aghai-Khozani et al.
鏈接：
/articles/s41586-022-04440-7
摘要
在此，我們展示了當壹個具有反質子成分的奇異氦原子被嵌入到超流氦中時，它的可見波長譜線保持了亞千兆赫的線寬。當原子周圍的液體轉變為超流相時，反質子激光***振線寬突然減小。
這就解決了電子和反質子之間自旋-自旋相互作用所產生的超精細結構，相對光譜分辨率為106的兩部分，盡管反質子氦位於正常物質原子的密集矩陣中。在激光激發期間，反質子原子的電子殼層保持壹個大約40皮米的小半徑。
這意味著，其他含有反核的氦原子以及帶負電荷的介子和超子，包括在超流氦中形成的奇異誇克，可以通過具有高光譜分辨率的激光光譜學來研究，從而能夠確定粒子的質量。清晰的光譜線可以探測到宇宙射線的反質子，也可以搜索到滯留在液氦目標中的反氘核。
Abstract
Here we show that when an exotic helium atom with a constituent antiproton is embedded into superfluid helium, its visible-wavelength spectral line retains a sub-gigahertz linewidth. An abrupt reduction in the linewidth of the antiprotonic laser resonance was observed when the liquid surrounding the atom transitioned into the superfluid phase. This resolved the hyperfine structure arising from the spin–spin interaction between the electron and antiproton with a relative spectral resolution of two parts in 106, even though the antiprotonic helium resided in a dense matrix of normal matter atoms. The electron shell of the antiprotonic atom retains a small radius of approximately 40 picometres during the laser excitation. This implies that other helium atoms containing antinuclei, as well as negatively charged mesons and hyperons that include strange quarks formed in superfluid helium, may be studied by laser spectroscopy with a high spectral resolution, enabling the determination of the particle masses. The sharp spectral lines may enable the detection of cosmic-ray antiprotons or searches for antideuterons that come to rest in liquid helium targets.
Flat-surface-assisted and self-regulated oxidation resistance of Cu(111)
平坦表面和自調節抗氧化性能的銅薄膜材料Cu(111)
作者：Su Jae Kim, Yong In Kim, Bipin Lamichhane et al.
鏈接：
/articles/s41586-021-04375-5#Sec9
摘要
氧化會降低銅的性能，而銅的性能對其使用至關重要，尤其是在半導體工業和電光應用中。在此，我們展示半永久抗氧化的銅薄膜制備，因為它們由平坦的表面組成，只有偶發單原子臺階。第壹性原理計算證實，單原子臺階邊緣與平坦表面壹樣不受氧的影響，並且壹旦達到50%氧面心立方FCC表面位置覆蓋率，氧原子表面吸附就被抑制。這些綜合效應解釋了超平攤銅表面特殊的抗氧化性。
Abstract
Oxidation can deteriorate the properties of copper that are critical for its use, particularly in the semiconductor industry and electro-optics applications. Here we report the fabrication of copper thin films that are semi-permanently oxidation resistant because they consist of flat surfaces with only occasional mono-atomic steps. First-principles calculations confirm that mono-atomic step edges are as impervious to oxygen as flat surfaces and that surface adsorption of O atoms is suppressed once an oxygen face-centred cubic (fcc) surface site coverage of 50% has been reached. These combined effects explain the exceptional oxidation resistance of ultraflat Cu surfaces.
物理學 Physics
Unbiasing fermionic quantum Monte Carlo with a quantum computer
無偏的費米子量子蒙特卡羅與量子計算機
作者：William J. Huggins, Bryan A. O’Gorman, Nicholas C. Rubin, David R. Reichman, Ryan Babbush & Joonho Lee
鏈接：
/articles/s41586-021-04351-z
摘要
用約束來控制費米符號問題保證了量子蒙特卡羅計算（QMC）的效率，但代價是由於經典計算的靈活性有限而可能存在顯著的偏差。
在此，我們提出了壹種將QMC與量子計算相結合的方法來減少這種偏差。我們的方案在實驗中實現了，我們使用了多達16個量子位來進行無偏約束QMC計算，這些計算是在多達120個軌道的化學系統上進行的。
這些實驗代表了在量子計算機的幫助下進行的最大的化學模擬，同時實現了與最先進的經典方法競爭的精度，而不需要負擔的錯誤緩解。
與流行的變分量子本征求解器相比，我們的量子-經典混合計算模型為電子結構問題提供了另壹種實現實際量子優勢的途徑，而不需要非常精確的基態波函數的制備和測量。
Abstract
Controlling the fermionic sign problem with constraints ensures the efficiency of QMC at the expense of potentially significant biases owing to the limited flexibility of classical computation. Here we propose an approach that combines constrained QMC with quantum computation to reduce such biases. We implement our scheme experimentally using up to 16 qubits to unbias constrained QMC calculations performed on chemical systems with as many as 120 orbitals. These experiments represent the largest chemistry simulations performed with the help of quantum computers, while achieving accuracy that is competitive with state-of-the-art classical methods without burdensome error mitigation. Compared with the popular variational quantum eigensolver, our hybrid quantum-classical computational model offers an alternative path towards achieving a practical quantum advantage for the electronic structure problem without demanding exceedingly accurate preparation and measurement of the ground-state wavefunction.
HighlWind dispersal of battery-free wireless devices
風擴散的無電池無線設備
作者：Vikram Iyer, Hans Gaensbauer, Thomas L. Daniel & Shyamnath Gollakota
鏈接：
/articles/s41586-021-04363-9
摘要
植物覆蓋了地球陸地的很大壹部分，盡管大多數物種都不能運動。為了運輸繁殖後代，許多植物進化出了利用風傳播種子的機制。
例如，蒲公英的種子有壹種剛毛狀的絲狀結構，可以降低其末端速度，並在種子飄向地面時幫助其定位。受此啟發，我們在此展示無電池無線的風擴散傳感設備。我們的毫米級設備重量為30毫克，基於壹個靈活的基板上，使用可編程的、現成的部件，為各種傳感和計算應用提供可擴展性和靈活性。
該系統使用輕型太陽能電池和能量收集電路供電，電路對低光照和可變光照條件非常穩定，並有壹個反向散射通信鏈路，可以實現數據傳輸。
為了實現太陽能收集所必需的大面積分散和垂直降落，我們開發了蒲公英啟發的薄膜多孔結構，其終端速度為0.87 0.02米/秒，空氣動力學穩定性，垂直降落的概率超過95%。戶外環境實驗的結果表明，這些設備可以在輕柔到正常的微風中移動50-100米。
最後，在自然系統中，個別種子形態的差異導致壹些種子落得更近，而另壹些則傳播得更遠。我們采用了類似的方法，並展示了我們如何調節結構的孔隙度和直徑，以實現設備間的分散變化。
Abstract
Plants cover a large fraction of the Earth’s land mass despite most species having limited to no mobility. To transport their propagules, many plants have evolved mechanisms to disperse their seeds using the wind. A dandelion seed, for example, has a bristly filament structure that decreases its terminal velocity and helps orient the seed as it wafts to the ground. Inspired by this, we demonstrate wind dispersal of battery-free wireless sensing devices. Our millimetre-scale devices weigh 30?milligrams and are designed on a flexible substrate using programmable, off-the-shelf parts to enable scalability and flexibility for various sensing and computing applications. The system is powered using lightweight solar cells and an energy harvesting circuit that is robust to low and variable light conditions, and has a backscatter communication link that enables data transmission. To achieve the wide-area dispersal and upright landing that is necessary for solar power harvesting, we developed dandelion-inspired, thin-film porous structures that achieve a terminal velocity of 0.87? 0.02?metres?per second and aerodynamic stability with a probability of upright landing of over 95%. Our results in outdoor environments demonstrate that these devices can travel 50–100?metres in gentle to moderate breeze. Finally, in natural systems, variance in inpidual seed morphology causes some seeds to fall closer and others to travel farther. We adopt a similar approach and show how we can modulate the porosity and diameter of the structures to achieve dispersal variation across devices.
地球科學 Geoscience
Limited increases in savanna carbon stocks over decades of fire suppression
幾十年沒有火災的稀樹草原碳儲量的增長有限
作者：Yong Zhou, Jenia Singh, John R. Butnor, Corli Coetsee, Peter B. Boucher, Madelon F. Case, Evan G. Hockridge, Andrew B. Davies & A. Carla Staver
鏈接：
/articles/s41586-022-04438-1
摘要
在此，我們提供了壹個首次直接評估壹個60年沒有火災的非洲濕地大草原整個生態系統碳響應
我們發現滅火增加整個生態系統碳儲存只有35.4 12%（平均值 標準錯誤），即使樹木覆蓋增加了78.9 29.3%，相應的總收益為23.0 6.1 Mg?C?ha 1 平均約為0.35 0.09 Mg?C?ha 1 year 1 ，低於之前的設想。
經常被燒毀的稀樹草原地下有大量的碳，特別是在生物量和深層土壤中。這些地下水庫在造林或滅火計劃中沒有得到充分考慮，但這可能意味著熱帶稀樹草原的十年封存潛力是微不足道的，特別是與隨之而來的生物多樣性和功能損失相比。
Abstract
Here we provide one of the first direct estimates of whole-ecosystem carbon response to more than 60?years of fire exclusion in a mesic African savanna. We found that fire suppression increased whole-ecosystem carbon storage by only 35.4 12% (mean standard error), even though tree cover increased by 78.9 29.3%, corresponding to total gains of 23.0 6.1?Mg?C?ha 1 at an average of about 0.35 0.09?Mg?C?ha 1 ?year 1 , more than an order of magnitude lower than previously assumed. Frequently burned savannas had substantial belowground carbon, especially in biomass and deep soils. These belowground reservoirs are not fully considered in afforestation or fire-suppression schemes but may mean that the decadal sequestration potential of savannas is negligible, especially weighed against concomitant losses of biopersity and function.
化學 Chemistry
New land-use-change emissions indicate a declining CO2 airborne fraction
新的土地利用變化排放表明空氣中二氧化碳的比例在下降
作者：Margreet J. E. van Marle, Dave van Wees, Richard A. Houghton, Robert D. Field, Jan Verbesselt & Guido. R. van der Werf
鏈接：
/articles/s41586-021-04376-4
摘要
在此，我們使用可見性數據在關鍵的森林砍伐區構建了壹個土地利用與土地覆蓋變化（LULCC）排放數據集。這些可見性觀測與火災排放相關，而火災排放又與LULCC相關。雖然這是間接的，但它提供了壹個長期壹致的LULCC排放數據集，表明自1958年開始CO2濃度測量以來，熱帶森林砍伐排放大幅增加。
到目前為止，這些排放被認為是相對穩定的，導致空氣中的比例不斷增加。然而，我們的結果表明，自1959年以來，大氣中CO2含量下降了0.014 0.010 decade 1。這表明，陸地-海洋聯合匯的增長速度至少與人為排放的增長速度壹樣快。
Abstract
Here we construct a LULCC emissions dataset using visibility data in key deforestation zones. These visibility observations are a proxy for fire emissions, which are — in turn — related to LULCC. Although indirect, this provides a long-term consistent dataset of LULCC emissions, showing that tropical deforestation emissions increased substantially (0.16?Pg?C?decade 1) since the start of CO2 concentration measurements in 1958. So far, these emissions were thought to be relatively stable, leading to an increasing airborne fraction. Our results, however, indicate that the CO2 airborne fraction has decreased by 0.014 0.010?decade 1 since 1959. This suggests that the combined land–ocean sink has been able to grow at least as fast as anthropogenic emissions.