科研
科研
Science, 21 JUN 2024, VOL 384, ISSUE 6702
《科学》2024年6月21日，第384卷，6702期
物理学Physics
Topological Hong-Ou-Mandel interference
拓扑Hong-Ou-Mandel干涉
▲ 作者：MAX EHRHARDT, CHRISTOPH DITTEL, MATTHIAS HEINRICH AND ALEXANDER SZAMEIT
▲ 链接：
https://www.science.org/doi/10.1126/science.ado8192
▲ 摘要：
拓扑学和光学的相互作用为追求稳健的光子器件提供了一条途径，其在光子量子计算中的应用尚处于起步阶段。然而，通过光子的量子干涉，利用线性光学拓扑结构处理量子信息的可能性在很大程度上仍然未知。
研究组提出了一种拓扑起源的Hong-Ou-Mandel干涉效应。结果表明，光子对的这种从相长到相消的干涉完全由合成磁通量决定，使其在基本水平上对误差具有弹性。
该策略建立了一个量子化通量，仅促进相消量子干涉。该发现为受拓扑稳健量子门保护的下一代光子量子电路和可扩展量子计算的发展铺平了道路。
▲ Abstract：
The interplay of topology and optics provides a route to pursue robust photonic devices, with the application to photonic quantum computation in its infancy. However, the possibilities of harnessing topological structures to process quantum information with linear optics, through the quantum interference of photons, remain largely uncharted. Here, we present a Hong-Ou-Mandel interference effect of topological origin. We show that this interference of photon pairs—ranging from constructive to destructive—is solely determined by a synthetic magnetic flux, rendering it resilient to errors on a fundamental level. Our implementation establishes a quantized flux that facilitates exclusively destructive quantum interference. Our findings pave the way toward the development of next-generation photonic quantum circuitry and scalable quantum computing protected by virtue of topologically robust quantum gates.
材料科学Materials Science
Carbon nanotube fibers with dynamic strength up to 14 GPa
动态强度高达14 GPa的碳纳米管纤维
▲ 作者：XINSHI ZHANG, XUDONG LEI, XIANGZHENG JIA, TONGZHAO SUN, JIAJUN LUO, SHICHEN XU, ET AL.
▲ 链接：
https://www.science.org/doi/10.1126/science.adj1082
▲ 摘要：
高动态强度对于在高应变率环境中使用的纤维材料至关重要。碳纳米管纤维是最有前景的候选纤维之一。
采用优化分层结构的策略，研究组制备出动态强度为14 GPa且能量吸收性能优异的碳纳米管纤维。纤维的动态性能归因于高应变率加载过程中单个纳米管的同时断裂和冲击能量的离域；这些行为则归因于界面相互作用、纳米管排列和致密化的改善。
这项工作提出了一种在宏观尺度上利用单个碳纳米管强度的有效策略，并提供了新的机制见解。
▲ Abstract：
High dynamic strength is of fundamental importance for fibrous materials that are used in high–strain rate environments. Carbon nanotube fibers are one of the most promising candidates. Using a strategy to optimize hierarchical structures, we fabricated carbon nanotube fibers with a dynamic strength of 14 gigapascals (GPa) and excellent energy absorption. The dynamic performance of the fibers is attributed to the simultaneous breakage of individual nanotubes and delocalization of impact energy that occurs during the high–strain rate loading process; these behaviors are due to improvements in interfacial interactions, nanotube alignment, and densification therein. This work presents an effective strategy to utilize the strength of individual carbon nanotubes at the macroscale and provides fresh mechanism insights.
Spin torque–driven electron paramagnetic resonance of a single spin in a pentacene molecule
并五苯分子中单个自旋的自旋力矩驱动的电子顺磁共振
▲ 作者：STEPAN KOVARIK, RICHARD SCHLITZ, AISHWARYA VISHWAKARMA, DOMINIC RUCKERT, PIETRO GAMBARDELLA AND SEBASTIAN STEPANOW
▲ 链接：
https://www.science.org/doi/10.1126/science.adh4753
▲ 摘要：
对量子系统的调控通常由与时间相关的电场或磁场来实现。另外，电子自旋可通过自旋极化电流来控制。
研究组演示了从扫描隧道显微镜尖端注入射频自旋极化电流至有机分子中的单个自旋相干驱动。在电子顺磁共振激发下，利用局域电流通过自旋力矩建立了单个自旋的动态控制。
此外，该工作强调了自旋转移力矩的耗散作用，这与基于受控退相干操纵单个自旋的磁场非耗散作用迥然不同。
▲ Abstract：
Control over quantum systems is typically achieved by time-dependent electric or magnetic fields. Alternatively, electronic spins can be controlled by spin-polarized currents. Here, we demonstrate coherent driving of a single spin by a radiofrequency spin-polarized current injected from the tip of a scanning tunneling microscope into an organic molecule. With the excitation of electron paramagnetic resonance, we established dynamic control of single spins by spin torque using a local electric current. In addition, our work highlights the dissipative action of the spin-transfer torque, in contrast to the nondissipative action of the magnetic field, which allows for the manipulation of individual spins based on controlled decoherence.
化学Chemistry
Water-hydroxide trapping in cobalt tungstate for proton exchange membrane water electrolysis
钨酸钴中水-氢氧化物网络捕获助力质子交换膜水电解
▲ 作者：RANIT RAM, LU XIA, HIND BENZIDI, ANKU GUHA, VIKTORIA GOLOVANOVA, ALBA GARZóN MANJóN, ET AL.
▲ 链接：
https://www.science.org/doi/10.1126/science.adk9849
▲ 摘要：
析氧反应是高能效水基电解生产氢气和其他太阳能燃料的瓶颈。在质子交换膜水电解（PEMWE）中，贵金属通常是稳定催化该反应所必需的。
在这项工作中，研究组报道了钨酸钴的分层通过稳定酸中晶格缺陷的氧化物和水—氢氧化物网络，实现了高活性和耐久性。所得到的催化剂具有较低的过电位，2 V下的电流密度为1.8 A/cm2，1.77 V的工业条件下（80℃）在PEMWE系统中稳定运行时可高达1 A/cm2；活性提高了三倍；在1 A/cm2的电流密度下可稳定运行600小时。
▲ Abstract：
The oxygen evolution reaction is the bottleneck to energy-efficient water-based electrolysis for the production of hydrogen and other solar fuels. In proton exchange membrane water electrolysis (PEMWE), precious metals have generally been necessary for the stable catalysis of this reaction. In this work, we report that delamination of cobalt tungstate enables high activity and durability through the stabilization of oxide and water-hydroxide networks of the lattice defects in acid. The resulting catalysts achieve lower overpotentials, a current density of 1.8 amperes per square centimeter at 2 volts, and stable operation up to 1 ampere per square centimeter in a PEMWE system at industrial conditions (80°C) at 1.77 volts; a threefold improvement in activity; and stable operation at 1 ampere per square centimeter over the course of 600 hours.
地球科学Earth Science
Temperature-dependent emissions dominate aerosol and ozone formation in Los Angeles
温度依赖的排放主导着洛杉矶气溶胶和臭氧形成
▲ 作者：EVA Y. PFANNERSTILL, CALEB ARATA, QINDAN ZHU, BENJAMIN C. SCHULZE, RYAN WARD, ROY WOODS, ET AL.
▲ 链接：
https://www.science.org/doi/10.1126/science.adg8204
▲ 摘要：
尽管交通排放量有所下降，但北美和欧洲城市仍面临着不健康的空气污染水平。这挑战了对其挥发性有机化合物（VOC）前体来源的传统理解。
使用空气通量测量来绘制大范围VOC的排放图，研究组表明，生物萜类排放约占夏季洛杉矶排放的VOC OH反应活性、臭氧和二次有机气溶胶形成潜力的60%，并且该影响随着温度的升高而强烈增加。这意味着控制氮氧化物是减少洛杉矶臭氧形成的关键。
研究组还表明，一些人为VOC排放量随着温度升高而增加，这是当前减排清单中未体现的变数。缓解空气污染的努力必须考虑到气候变暖将强烈改变排放量和排放成分。
▲ Abstract：
Despite declines in transportation emissions, urban North America and Europe still face unhealthy air pollution levels. This has challenged conventional understanding of the sources of their volatile organic compound (VOC) precursors. Using airborne flux measurements to map emissions of a wide range of VOCs, we demonstrate that biogenic terpenoid emissions contribute ~60% of emitted VOC OH reactivity, ozone, and secondary organic aerosol formation potential in summertime Los Angeles and that this contribution strongly increases with temperature. This implies that control of nitrogen oxides is key to reducing ozone formation in Los Angeles. We also show some anthropogenic VOC emissions increase with temperature, which is an effect not represented in current inventories. Air pollution mitigation efforts must consider that climate warming will strongly change emission amounts and composition.
Bomb radiocarbon evidence for strong global carbon uptake and turnover in terrestrial vegetation
全球陆地植被强大碳吸收和周转量的核弹放射性碳证据
▲ 作者：HEATHER D. GRAVEN, HAMISH WARREN, HOLLY K. GIBBS, SAMAR KHATIWALA, CHARLES KOVEN, JOANNA LESTER, ET AL.
▲ 链接：
https://www.science.org/doi/10.1126/science.adl4443
▲ 摘要：
由于生产力和周转量产生的大量总碳交换存在约束很差的微小不平衡，植被和土壤吸收了大约30%的人为二氧化碳排放。
研究组将20世纪60年代核弹试验产生的放射性碳的新预算与模型模拟相结合，以评估陆地植被的碳循环。结果发现，在耦合模式比对项目中使用的大多数最先进的植被模型都低估了植被生物量中的放射性碳积累。
该发现结合对植被碳储量和生产力趋势的约束，表明目前净初级生产力可能至少为每年800亿吨碳，而当前模型预测的是每年430至760亿吨碳。人为碳在陆地植被中的储存可能比此前预测的更为短暂和脆弱。
▲ Abstract：
Vegetation and soils are taking up approximately 30% of anthropogenic carbon dioxide emissions because of small imbalances in large gross carbon exchanges from productivity and turnover that are poorly constrained. We combined a new budget of radiocarbon produced by nuclear bomb testing in the 1960s with model simulations to evaluate carbon cycling in terrestrial vegetation. We found that most state-of-the-art vegetation models used in the Coupled Model Intercomparison Project underestimated the radiocarbon accumulation in vegetation biomass. Our findings, combined with constraints on vegetation carbon stocks and productivity trends, imply that net primary productivity is likely at least 80 petagrams of carbon per year presently, compared with the 43 to 76 petagrams per year predicted by current models. Storage of anthropogenic carbon in terrestrial vegetation is likely more short-lived and vulnerable than previously predicted.
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