forming期刊最新论文

编译 | 未玖

Nature , 14 April 2022, VOL 604, ISSUE 7905

《自然》 2022年4月14日，第604卷，7905期

天文学 Astronomy

A dusty compact object bridging galaxies and quasars at cosmic dawn

在宇宙黎明时分，星系由尘埃致密体过渡到类星体

作者：S. Fujimoto, G. B. Brammer, D. Watson, G. E. Magdis, V. Kokorev, T. R. Greve, et al.

链接：

摘要：

自从发现发光类星体在宇宙大爆炸后仅存在7亿年以来，了解超大质量黑洞在早期宇宙中如何形成和生长已成为一个重大难题。

理论模拟显示了一种进化序列，尘埃红移的类星体从严重尘埃遮蔽的星暴星系中出现，然后通过释放气体和尘埃过渡到无遮蔽的发光类星体。尽管最后一个阶段的红移已被确定为，但由于它们在光学和近红外波长上的微弱性，目前尚未发现具有类似红移的过渡类星体。

研究组报道了一个紫外致密天体GNz7q的观测结果，它与一个红移为   、尘埃掩蔽的星暴有关。

在该时期，宿主星系的尘埃辐射比任何其他已知物体都要明亮，在480秒差距的中心半径范围内，每年形成1600个太阳质量的恒星。在深部、高分辨率成像和无狭缝光谱中，可识别出一个远紫外的红点源。

GNz7q在X射线中非常微弱，这表明在尘埃星暴核心出现了一个独特的紫外致密恒星形成区或一个康普顿厚、超过爱丁顿极限的黑洞吸积盘。在后一种情况下，观测到的性质与宇宙学模拟的预测一致，并表明GNz7q是晚期无遮蔽发光类星体的祖先。

Abstract：

Understanding how super-massive black holes form and grow in the early Universe has become a major challenge since it was discovered that luminous quasars existed only 700 million years after the Big Bang. Simulations indicate an evolutionary sequence of dust-reddened quasars emerging from heavily dust-obscured starbursts that then transition to unobscured luminous quasars by expelling gas and dust. Although the last phase has been identified out to a redshift of , a transitioning quasar has not been found at similar redshifts owing to their faintness at optical and near-infrared wavelengths. Here we report observations of an ultraviolet compact object, GNz7q, associated with a dust-enshrouded starburst at a redshift of    . The host galaxy is more luminous in dust emission than any other known object at this epoch, forming 1,600 solar masses of stars per year within a central radius of 480 parsec. A red point source in the far-ultraviolet is identified in deep, high-resolution imaging and slitless spectroscopy. GNz7q is extremely faint in X-rays, which indicates the emergence of a uniquely ultraviolet compact star-forming region or a Compton-thick super-Eddington black-hole accretion disk at the dusty starburst core. In the latter case, the observed properties are consistent with predictions from cosmological simulations and suggest that GNz7q is an antecedent to unobscured luminous quasars at later epochs.

物理学 Physics

Intelligent infrared sensing enabled by tunable moiré quantum geometry

可调谐莫尔量子几何实现智能红外传感

作者：Chao Ma, Shaofan Yuan, Patrick Cheung, Kenji Watanabe, Takashi Taniguchi, Fan Zhang, et al.

链接：

摘要：

众所周知，固体中布洛赫波函数的量子几何性质，即贝里曲率和量子度量，显著影响着电子的基态和激发态行为。

体光伏效应（BPVE）是一种依赖于激发光偏振的非线性现象，在很大程度上取决于光学跃迁中的量子几何特性。红外BPVE尚未在石墨烯或莫尔体系等新兴平台中观察到，尽管这些平台已报道过与量子几何有关的激发强关联现象。

研究组报道了在扭曲双双层石墨烯（TDBG）中观察到5 µm和 µm处可调谐中红外BPVE，由莫尔诱导的强对称性破缺和量子几何贡献产生。光响应在很大程度上取决于激发光的偏振态，且可通过外部电场进行高度调谐。

这种量子几何特性的广泛可调性使研究组能够使用卷积神经网络同时实现全斯托克斯偏振测量和波长检测，仅使用一个亚波长足迹仅为3  3  µm2的TDBG器件 。

该研究工作不仅揭示了莫尔工程量子几何在可调谐非线性光-物质相互作用中的独特作用，还以极其紧凑的芯片方式为未来智能传感技术开辟了新途径。

Abstract：

Quantum geometric properties of Bloch wave functions in solids, that is, Berry curvature and the quantum metric, are known to significantly influence the ground- and excited-state behaviour of electrons. The bulk photovoltaic effect (BPVE), a nonlinear phenomenon depending on the polarization of excitation light, is largely governed by the quantum geometric properties in optical transitions. Infrared BPVE has yet to be observed in graphene or moiré systems, although exciting strongly correlated phenomena related to quantum geometry have been reported in this emergent platform. Here we report the observation of tunable mid-infrared BPVE at 5 µm and  µm in twisted double bilayer graphene (TDBG), arising from the moiré-induced strong symmetry breaking and quantum geometric contribution. The photoresponse depends substantially on the polarization state of the excitation light and is highly tunable by external electric fields. This wide tunability in quantum geometric properties enables us to use a convolutional neural network to achieve full-Stokes polarimetry together with wavelength detection simultaneously, using only one single TDBG device with a subwavelength footprint of merely 3   3 µm2. Our work not only reveals the unique role of moiré engineered quantum geometry in tunable nonlinear light–matter interactions but also identifies a pathway for future intelligent sensing technologies in an extremely compact, on-chip manner.

材料科学 Materials Science

Uniting tensile ductility with ultrahigh strength via composition undulation

通过成分起伏同时实现拉伸塑性与超高强度

作者：Heng Li, Hongxiang Zong, Suzhi Li, Shenbao Jin, Yan Chen, Matthew J. Cabral, et al.

链接：

摘要：

具有纳米晶粒的金属有接近2 GPa的超高强度。然而，这种极端的晶界强化导致几乎所有拉伸塑性的丧失，即使当金属具有面心立方结构（所有晶体结构中塑性最强的结构）时亦如此。

研究组证明了纳米晶镍-钴固溶体虽仍是面心立方单相，但其拉伸强度约为  GPa，塑性断裂伸长率约为16 %。

这种不寻常的拉伸强度和塑性的结合是通过高浓度固溶体中的成分起伏实现的。这种起伏使得层错能和晶格应变在1-10纳米的尺度范围内发生空间变化，从而显著影响了位错运动。

尽管纳米晶粒内部空间非常有限，但位错运动变得缓慢，促进了它们的交互作用、联锁和增殖。因此，流动应力增加，同时位错储存增加，从而提升了应变硬化能力，提高了塑性。

同时，沿位错线的分段脱捕需要较小的激活体积，因此应变速率敏感性增加，这也稳定了拉伸流动。因此，抗位错传播的起伏结构提供了一种强化机制，可在高流动应力下保持拉伸塑性。

Abstract：

Metals with nanocrystalline grains have ultrahigh strengths approaching two gigapascals. However, such extreme grain-boundary strengthening results in the loss of almost all tensile ductility, even when the metal has a face-centred-cubic structure—the most ductile of all crystal structures. Here we demonstrate that nanocrystalline nickel–cobalt solid solutions, although still a face-centred-cubic single phase, show tensile strengths of about  gigapascals with a respectable ductility of about 16 per cent elongation to failure. This unusual combination of tensile strength and ductility is achieved by compositional undulation in a highly concentrated solid solution. The undulation renders the stacking fault energy and the lattice strains spatially varying over length scales in the range of one to ten nanometres, such that the motion of dislocations is thus significantly affected. The motion of dislocations becomes sluggish, promoting their interaction, interlocking and accumulation, despite the severely limited space inside the nanocrystalline grains. As a result, the flow stress is increased, and the dislocation storage is promoted at the same time, which increases the strain hardening and hence the ductility. Meanwhile, the segment detrapping along the dislocation line entails a small activation volume and hence an increased strain-rate sensitivity, which also stabilizes the tensile flow. As such, an undulating landscape resisting dislocation propagation provides a strengthening mechanism that preserves tensile ductility at high flow stresses.

Perovskite–organic tandem solar cells with indium oxide interconnect

钙钛矿-氧化铟互连有机串联太阳能电池

作者：K. O. Brinkmann, T. Becker, F. Zimmermann, C. Kreusel, T. Gahlmann, M. Theisen, et al.

链接：

摘要：

多结太阳能电池可以克服单结器件的基本效率限制。金属卤化物钙钛矿型太阳能电池的带隙可调性使其在多结结构中具有吸引力。硅和铜铟硒化镓（CIGS）以及全钙钛矿串联电池的组合已有报道。与此同时，窄间隙非富勒烯受体为有机太阳能电池带来了快速提升的效率。

有机和钙钛矿半导体是一种很有吸引力的组合，具有相似的加工技术。目前，钙钛矿-有机串联电池的效率低于标准，并且受到宽间隙钙钛矿电池的低开路电压（Voc）和子电池之间互连引入损耗的限制。

研究组展示了钙钛矿-有机串联电池的效率为（认证为），Voc高达 伏特。优化的电荷提取层使钙钛矿子电池具有高Voc和填充因子的出色组合。

该串联电池的有机子电池在近红外下提供了高外部量子效率，与对非富勒烯电池有限光稳定性的典型担忧相反，如果激子主要在非富勒烯受体上产生，则表现出出色的操作稳定性。子电池由一层超薄（约纳米）类金属氧化铟层连接，具有前所未有的低光/电损耗。

这项工作为钙钛矿-有机串联电池竖了一座里程碑，它优于最好的p–i–n钙钛矿单结，并与钙钛矿-CIGS和所有钙钛矿多结相媲美。

Abstract：

Multijunction solar cells can overcome the fundamental efficiency limits of single-junction devices. The bandgap tunability of metal halide perovskite solar cells renders them attractive for multijunction architectures. Combinations with silicon and copper indium gallium selenide (CIGS), as well as all-perovskite tandem cells, have been reported. Meanwhile, narrow-gap non-fullerene acceptors have unlocked skyrocketing efficiencies for organic solar cells. Organic and perovskite semiconductors are an attractive combination, sharing similar processing technologies. Currently, perovskite–organic tandems show subpar efficiencies and are limited by the low open-circuit voltage (Voc) of wide-gap perovskite cells and losses introduced by the interconnect between the subcells. Here we demonstrate perovskite–organic tandem cells with an efficiency of per cent (certified per cent) and a high Voc of  volts. Optimized charge extraction layers afford perovskite subcells with an outstanding combination of high Voc and fill factor. The organic subcells provide a high external quantum efficiency in the near-infrared and, in contrast to paradigmatic concerns about limited photostability of non-fullerene cells, show an outstanding operational stability if excitons are predominantly generated on the non-fullerene acceptor, which is the case in our tandems. The subcells are connected by an ultrathin (approximately  nanometres) metal-like indium oxide layer with unprecedented low optical/electrical losses. This work sets a milestone for perovskite–organic tandems, which outperform the best p–i–n perovskite single junctions and are on a par with perovskite–CIGS and all-perovskite multijunctions.

机械工程 Mechanical Engineering

Thermophotovoltaic efficiency of 40%

科学家实现40%的热光伏效率

作者：Alina LaPotin, Kevin L. Schulte, Myles A. Steiner, Kyle Buznitsky, Colin C. Kelsall, Daniel J. Friedman, et al.

链接：

摘要：

热光伏（TPV）主要通过光伏效应将红外波长的光转换为电能，可使用比目前普遍存在于电力生产中的涡轮机更高温度的热源进行能量存储和转换。

自从在2000 下使用集成背表面反射器和钨发射极首次展示29%的高效TPV以来，TPV的制造和性能得到了改善。然而，尽管预测TPV的效率可能超过50%，但在温度低于1300 下，实际效率仍仅为32%。

研究组报道了效率超过40%的TPV电池的制造和测量，并通过实验证明了高带隙串联TPV电池的效率。TPV电池是由带隙在 eV的III–V材料组成的双结器件，针对1900-2400 的发射极温度进行了优化。

电池利用带边光谱滤波的概念来获得高效率，使用高反射背表面反射器来拒绝不可用的子带隙辐射返回发射极。在功率密度为 W cm –2 ，发射极温度为2400 的条件下， eV器件的最大效率为（   1）%。在功率密度为 W cm–2，发射极温度为2127 的条件下， eV器件的最大效率为（   1）%。

这些电池可以集成到一个TPV系统中，用于热能电网存储，以实现可调度的可再生能源。这为热能电网存储创造了一条途径，以达到足够高的效率和足够低的成本，从而实现电网脱碳。

Abstract：

Thermophotovoltaics (TPVs) convert predominantly infrared wavelength light to electricity via the photovoltaic effect, and can enable approaches to energy storage and conversion that use higher temperature heat sources than the turbines that are ubiquitous in electricity production today. Since the first demonstration of 29% efficient TPVs using an integrated back surface reflector and a tungsten emitter at 2,000  C, TPV fabrication and performance have improved. However, despite predictions that TPV efficiencies can exceed 50%, the demonstrated efficiencies are still only as high as 32%, albeit at much lower temperatures below 1,300  C. Here we report the fabrication and measurement of TPV cells with efficiencies of more than 40% and experimentally demonstrate the efficiency of high-bandgap tandem TPV cells. The TPV cells are two-junction devices comprising III–V materials with bandgaps between and eV that are optimized for emitter temperatures of 1,900–2,400  C. The cells exploit the concept of band-edge spectral filtering to obtain high efficiency, using highly reflective back surface reflectors to reject unusable sub-bandgap radiation back to the emitter. A eV device reached a maximum efficiency of (   1)% operating at a power density of  W cm–2 and an emitter temperature of 2,400  C. A eV device reached a maximum efficiency of (   1)% operating at a power density of  W cm –2 and an emitter temperature of 2,127  C. These cells can be integrated into a TPV system for thermal energy grid storage to enable dispatchable renewable energy. This creates a pathway for thermal energy grid storage to reach sufficiently high efficiency and sufficiently low cost to enable decarbonization of the electricity grid.

地球科学 Earth Science

Realization of Paris Agreement pledges may limit warming just below 2

实现《巴黎协定》的承诺有望将全球变暖控制在2 以下

作者：Malte Meinshausen, Jared Lewis, Christophe McGlade, Johannes Gütschow, Zebedee Nicholls, Rebecca Burdon, et al.

链接：

摘要：

在《格拉斯哥气候公约》签署前的过去五年中，154个缔约方在其国家自主贡献中提交了新的或更新的2030年减缓目标，76个缔约方提出了长期承诺。对2021联合国气候变化大会（COP26）之前承诺的量化表明，将升温控制在2 以下的可能性低于50 %。

研究组证明，如果所有有条件和无条件的承诺都得到充分和及时的执行，全球变暖可以控制在2  以下。根据政府间气候变化专门委员会（IPCC）第六次评估报告中第一工作组对地球系统不确定性进行的概率表征，在全面执行的情况下，峰值升温可被限制在  之间。

研究组回顾性地预测了21世纪的气候变暖，以显示2015-2021年雄心勃勃的总体目标水平如何变化。研究结果依赖于对2030年或2050年之后的限时目标外推、IPCC 特别报告（）情景数据库的特征和承诺的全面实施情况。

对这些因素更悲观的假设将导致更高的升温预测。另一个独立的排放模型框架预测，全球升温峰值为 ，这支持了该研究发现，即各国兑现承诺可能会将全球变暖限制在略低于2 的范围内。

若不仅要将升温控制在“略低于”，还要控制在“远低于”2  或 ，则迫切需要制定政策和采取行动，以在本世纪中叶实现全球C O2 净零排放。

Abstract：

Over the last five years prior to the Glasgow Climate Pact, 154 Parties have submitted new or updated 2030 mitigation goals in their nationally determined contributions and 76 have put forward longer-term pledges. Quantifications of the pledges before the 2021 United Nations Climate Change Conference (COP26) suggested a less than 50 per cent chance of keeping warming below 2 degrees Celsius. Here we show that warming can be kept just below 2 degrees Celsius if all conditional and unconditional pledges are implemented in full and on time. Peak warming could be limited to – degrees Celsius in the full implementation case—building on a probabilistic characterization of Earth system uncertainties in line with the Working Group I contribution to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). We retrospectively project twenty-first-century warming to show how the aggregate level of ambition changed from 2015 to 2021. Our results rely on the extrapolation of time-limited targets beyond 2030 or 2050, characteristics of the IPCC   C Special Report () scenario database and the full implementation of pledges. More pessimistic assumptions on these factors would lead to higher temperature projections. A second, independent emissions modelling framework projected peak warming of  degrees Celsius, supporting the finding that realized pledges could limit warming to just below 2 degrees Celsius. Limiting warming not only to ‘just below’ but to ‘well below’ 2 degrees Celsius or  degrees Celsius urgently requires policies and actions to bring about steep emission reductions this decade, aligned with mid-century global net-zero C O2 emissions

编译 | 未玖

Nature , 20 January 2022, VOL 601, ISSUE 7893

《自然》 2022年1月20日，第601卷，7893期

天文学 Astronomy

Star formation near the Sun is driven by expansion of the Local Bubble

局部气泡的扩张驱动太阳附近恒星形成

作者：Catherine Zucker, Alyssa A. Goodman, João Alves, Shmuel Bialy, Michael Foley, Joshua S. Speagle, et al.

链接：

摘要

几十年来，我们已知道太阳位于一个局部气泡内，即一个由低密度、高温等离子体构成的空腔，周围环绕着一层寒冷的中性气体和尘埃。然而，由于局部星际介质的低分辨率模型，这个外壳的精确形状和范围、形成的动力和时间尺度以及它与附近恒星形成的关联仍不确定。

研究组利用新的空间和动力学约束，对太阳200 pc范围内致密气体和年轻恒星的三维位置、形状和运动进行了分析。他们发现，太阳附近几乎所有的恒星形成复合体都位于局部气泡的表面，它们的年轻恒星主要垂直于气泡表面向外扩张。

对这些年轻恒星轨迹的追踪支持了这样一种说法，即局部气泡起源于大约1400万年前发生在气泡中心附近的恒星诞生和死亡（超新星）的爆发。超新星产生的局部气泡膨胀将周围的星际介质卷起，形成一个扩张的外壳，该外壳现已碎裂并坍缩成附近最明显的分子云，从而为超新星驱动恒星形成理论提供了强有力的观测支持。

Abstract

For decades we have known that the Sun lies within the Local Bubble, a cavity of low-density, high-temperature plasma surrounded by a shell of cold, neutral gas and dust. However, the precise shape and extent of this shell, the impetus and timescale for its formation, and its relationship to nearby star formation have remained uncertain, largely due to low-resolution models of the local interstellar medium. Here we report an analysis of the three-dimensional positions, shapes and motions of dense gas and young stars within 200 pc of the Sun, using new spatial and dynamical constraints. We find that nearly all of the star-forming complexes in the solar vicinity lie on the surface of the Local Bubble and that their young stars show outward expansion mainly perpendicular to the bubble’s surface. Tracebacks of these young stars’ motions support a picture in which the origin of the Local Bubble was a burst of stellar birth and then death (supernovae) taking place near the bubble’s centre beginning approximately 14 Myr ago. The expansion of the Local Bubble created by the supernovae swept up the ambient interstellar medium into an extended shell that has now fragmented and collapsed into the most prominent nearby molecular clouds, in turn providing robust observational support for the theory of supernova-driven star formation.

Black-hole-triggered star formation in the dwarf galaxy Henize 2-10

矮星系Henize 2-10中黑洞触发恒星形成

作者：Zachary Schutte & Amy E. Reines

链接：

摘要

在一些有活动星系核的矮星系中，人们已观察到黑洞驱动的外流，它们可能在加热和喷出气体（从而抑制恒星形成）方面发挥作用，就像它们在较大的星系中所做的那样。黑洞外流能在多大程度上触发矮星系中的恒星形成尚不清楚，因为这一领域的工作以前主要集中在大质量星系上，观测证据很少。

Henize 2-10是一个矮星暴星系，此前有报道称其中心有一个大质量黑洞，但由于某些观测证据与超新星残骸一致，这种解释一直存在争议。在大约9 Mpc距离处有一个机会可了解中心区域，并确定是否有证据表明黑洞流出影响恒星形成。

研究组报道了Henize 2-10的光学观测结果，其线性分辨率为几秒差距。他们发现了一条约150 pc长的电离丝状物，将黑洞区域与一个最新恒星形成区域连接起来。光谱学揭示了一种类似正弦波的位置-速度结构，通过一个简单的进动双极流出进行描述。研究组得出结论，黑洞流出触发了恒星的形成。

Abstract

Black-hole-driven outflows have been observed in some dwarf galaxies with active galactic nuclei, and probably play a role in heating and expelling gas (thereby suppressing star formation), as they do in larger galaxies. The extent to which black-hole outflows can trigger star formation in dwarf galaxies is unclear, because work in this area has previously focused on massive galaxies and the observational evidence is scarce. Henize 2-10 is a dwarf starburst galaxy previously reported to have a central massive black hole, although that interpretation has been disputed because some aspects of the observational evidence are also consistent with a supernova remnant. At a distance of approximately 9 Mpc, it presents an opportunity to resolve the central region and to determine if there is evidence for a black-hole outflow influencing star formation. Here we report optical observations of Henize 2-10 with a linear resolution of a few parsecs. We find an approximately 150-pc-long ionized filament connecting the region of the black hole with a site of recent star formation. Spectroscopy reveals a sinusoid-like position–velocity structure that is well described by a simple precessing bipolar outflow. We conclude that this black-hole outflow triggered the star formation.

物理学 Physics

Topological triple phase transition in non-Hermitian Floquet quasicrystals

非厄米-弗洛凯准晶体的拓扑三重相变

作者：Sebastian Weidemann, Mark Kremer, Stefano Longhi & Alexander Szameit

链接：

摘要

相变连接着物质的不同状态，通常伴随着对称性的自发破坏。一个重要的相变类型是迁移率转变，其中著名的安德森局域化增加随机性会导致金属-绝缘体跃迁。凝聚态物理学中拓扑学的引入导致了拓扑相变和拓扑绝缘体材料的发现。

非厄米系统对称性的相变描述了向平均守恒能量和新拓扑相的转变。体电导率、拓扑学和非厄米对称破缺似乎源于不同的物理学，因此可能以分离的现象出现。然而，在非厄米准晶体中，这种转变可通过形成一个三重相变而相互关联。

研究组报道了一个三重相变的实验观察，其中改变单个参数的同时会引起局域化（金属-绝缘体）、拓扑和奇偶-时间对称破缺（能量）相变。物理学表现为时间驱动（弗洛凯）耗散准晶体。

研究组通过耦合光纤环路中的光子量子行走来实现他们的想法，并强调了非厄米准晶体合成物质中拓扑、对称破缺和迁移率相变的相互关联。该研究结果有望应用于相变器件，在其中可预测和控制体-边输运以及与环境的能量或粒子交换。

Abstract

Phase transitions connect different states of matter and are often concomitant with the spontaneous breaking of symmetries. An important category of phase transitions is mobility transitions, among which is the well known Anderson localization, where increasing the randomness induces a metal–insulator transition. The introduction of topology in condensed-matter physics lead to the discovery of topological phase transitions and materials as topological insulators. Phase transitions in the symmetry of non-Hermitian systems describe the transition to on-average conserved energy and new topological phases. Bulk conductivity, topology and non-Hermitian symmetry breaking seemingly emerge from different physics and, thus, may appear as separable phenomena. However, in non-Hermitian quasicrystals, such transitions can be mutually interlinked by forming a triple phase transition. Here we report the experimental observation of a triple phase transition, where changing a single parameter simultaneously gives rise to a localization (metal–insulator), a topological and parity–time symmetry-breaking (energy) phase transition. The physics is manifested in a temporally driven (Floquet) dissipative quasicrystal. We implement our ideas via photonic quantum walks in coupled optical fibre loops. Our study highlights the intertwinement of topology, symmetry breaking and mobility phase transitions in non-Hermitian quasicrystalline synthetic matter. Our results may be applied in phase-change devices, in which the bulk and edge transport and the energy or particle exchange with the environment can be predicted and controlled.

Quantum logic with spin qubits crossing the surface code threshold

超越表面码阈值的自旋比特量子逻辑

作者：Xiao Xue, Maximilian Russ, Nodar Samkharadze, Brennan Undseth, Amir Sammak, Giordano Scappucci, et al.

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摘要

量子比特的高保真控制对于量子算法的可靠执行和实现容错（纠正错误的速度快于错误发生的速度）至关重要。容错的核心要求用错误阈值表示。然而实际阈值取决于许多细节，一个常见目标是约1%误差阈值的表面码。

两比特门保真度超过99%一直是半导体自旋量子比特的主要目标。由于可以利用先进的半导体技术，这些量子比特有望扩展。

研究组报道了一种基于自旋的硅量子处理器，其单比特门和两比特门保真度都高于，通过门集断层扫描进行验证。当包含相邻量子比特的串扰和空转误差时，平均单比特门保真度仍保持在99%以上。

通过这个高保真门集，研究组使用变分量子本征求解器算法完成了计算分子基态能量的艰巨任务。半导体量子比特超越了两比特门保真度99%的阈值，身处高噪声的中等规模量子器件时代，在容错和可能的应用方面已争取到一席之地。

Abstract

High-fidelity control of quantum bits is paramount for the reliable execution of quantum algorithms and for achieving fault tolerance—the ability to correct errors faster than they occur. The central requirement for fault tolerance is expressed in terms of an error threshold. Whereas the actual threshold depends on many details, a common target is the approximately 1% error threshold of the well-known surface code. Reaching two-qubit gate fidelities above 99% has been a long-standing major goal for semiconductor spin qubits. These qubits are promising for scaling, as they can leverage advanced semiconductor technology. Here we report a spin-based quantum processor in silicon with single-qubit and two-qubit gate fidelities, all of which are above , extracted from gate-set tomography. The average single-qubit gate fidelities remain above 99% when including crosstalk and idling errors on the neighbouring qubit. Using this high-fidelity gate set, we execute the demanding task of calculating molecular ground-state energies using a variational quantum eigensolver algorithm. Having surpassed the 99% barrier for the two-qubit gate fidelity, semiconductor qubits are well positioned on the path to fault tolerance and to possible applications in the era of noisy intermediate-scale quantum devices.

Fast universal quantum gate above the fault-tolerance threshold in silicon

硅中超越容错阈值的快速通用量子门

作者：Akito Noiri, Kenta Takeda, Takashi Nakajima, Takashi Kobayashi, Amir Sammak, Giordano Scappucci, et al.

链接：

摘要

能够解决难题的容错量子计算机依赖于量子纠错。表面码是最有前途的纠错码之一，它要求通用门保真度超过99%的纠错阈值。

在众多量子位平台中，只有超导电路、捕获离子和金刚石中的氮空位中心能满足这一要求。硅中的电子自旋量子位因其纳米制造能力而颇有潜力应用于大规模量子计算机，但由于运行缓慢，两比特门保真度被限制在98%。

研究组通过使用微磁感应梯度场和可调谐双量子位耦合的快速电子控制，在硅自旋量子位中实现了的两比特门保真度和的单比特门保真度。他们确定了量子位的旋转速度和耦合强度，稳健地实现了高保真门。

使用该通用门集，研究组成功实现了Deutsch-Jozsa和Grover搜索算法。研究结果表明，通用门保真度超越了容错阈值，并有望实现可扩展硅量子计算机。

Abstract

Fault-tolerant quantum computers that can solve hard problems rely on quantum error correction. One of the most promising error correction codes is the surface code, which requires universal gate fidelities exceeding an error correction threshold of 99 per cent. Among the many qubit platforms, only superconducting circuits, trapped ions and nitrogen-vacancy centres in diamond have delivered this requirement. Electron spin qubits in silicon are particularly promising for a large-scale quantum computer owing to their nanofabrication capability, but the two-qubit gate fidelity has been limited to 98 per cent owing to the slow operation. Here we demonstrate a two-qubit gate fidelity of per cent, along with single-qubit gate fidelities of per cent, in silicon spin qubits by fast electrical control using a micromagnet-induced gradient field and a tunable two-qubit coupling. We identify the qubit rotation speed and coupling strength where we robustly achieve high-fidelity gates. We realize Deutsch–Jozsa and Grover search algorithms with high success rates using our universal gate set. Our results demonstrate universal gate fidelity beyond the fault-tolerance threshold and may enable scalable silicon quantum computers.

地球科学 Earth Science

Historical glacier change on Svalbard predicts doubling of mass loss by 2100

2100年斯瓦尔巴群岛的冰川质量损失将翻倍

作者：Emily C. Geyman, Ward J. J. van Pelt, Adam C. Maloof, Harald Faste Aas & Jack Kohler

链接：

摘要

冰川和冰盖的融化约占目前海平面上升的三分之一，超过了体积更大的格陵兰岛或南极冰原所造成的损失。北极斯瓦尔巴群岛的空间气候梯度比下个世纪预测的现世气候变化要大，它是一个自然实验室，用于限制冰川的气候敏感性并预测其对未来变暖的反应。

研究组将 历史 冰川和现代冰川的观测联系起来，预测21世纪冰川变薄的速度将是1936-2010年的两倍多。利用1936和1938年的 历史 航拍图像存档，他们通过运动结构摄影测量法重建了斯瓦尔巴群岛上1594条冰川的三维几何形状。

研究组将这些重建数据与现代冰川海拔数据进行比较，得出了70多年时间跨度内质量平衡的空间模式，使人们能够通过年际和年代际变化的噪声，来量化诸如温度和降水等变量如何控制冰川的损失。

研究组发现融化速率对温度有很强的依赖性，即平均夏季温度每升高1 ，面积归一化质量平衡每年减少 m的水当量。最后，研究组设计了一个时空替代方案，将他们的 历史 冰川观测与气候预测相结合，并对斯瓦尔巴群岛的21世纪冰川变化做出一级预测。

Abstract

The melting of glaciers and ice caps accounts for about one-third of current sea-level rise, exceeding the mass loss from the more voluminous Greenland or Antarctic Ice Sheets. The Arctic archipelago of Svalbard, which hosts spatial climate gradients that are larger than the expected temporal climate shifts over the next century, is a natural laboratory to constrain the climate sensitivity of glaciers and predict their response to future warming. Here we link historical and modern glacier observations to predict that twenty-first century glacier thinning rates will more than double those from 1936 to 2010. Making use of an archive of historical aerial imagery from 1936 and 1938, we use structure-from-motion photogrammetry to reconstruct the three-dimensional geometry of 1,594 glaciers across Svalbard. We compare these reconstructions to modern ice elevation data to derive the spatial pattern of mass balance over a more than 70-year timespan, enabling us to see through the noise of annual and decadal variability to quantify how variables such as temperature and precipitation control ice loss. We find a robust temperature dependence of melt rates, whereby a 1  C rise in mean summer temperature corresponds to a decrease in area-normalized mass balance of m yr 1 of water equivalent. Finally, we design a space-for-time substitution to combine our historical glacier observations with climate projections and make first-order predictions of twenty-first century glacier change across Svalbard.