FAULTTOLERANCE的简单介绍

《自然》（20220120出版）一周论文导读

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, Jo?o 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.

链接：

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99.5%，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 99.5%, 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99.5%的两比特门保真度和99.8%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 99.5 per cent, along with single-qubit gate fidelities of 99.8 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0.28 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 0.28 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.

错误的英文fault

fault，英语单词，名词、及物动词、不及物动词，作名词时意为“故障；[地质] 断层；错误；缺点；毛病；（网球等）发球失误”，作及物动词时意为“（通常用于疑问句或否定句）挑剔”，作不及物动词时意为“弄错；产生断层”。

短语搭配

active fault 活断层 ; 活动断裂 ; [地质] 活动断层

Page fault 页缺失 ; 页面失效 ; 页错误 ; 页面错误

Fault Tolerance 容错 ; 容错性 ; 故障包容 ; 容错能力

Double fault 双发失误 ; 两次失误 ; 发球双错误 ; 两次发球失误

Fault management 故障管理 ; 错误管理 ; 障碍管理 ; 进行故障管理

fault detection [计] 故障检测 ; 探伤 ; 故障监测 ; 故障探测

fault plane [地质] 断层面 ; 断面 ; 断层面上 ; 断层带

fault liability 过失责任 ; 过错责任 ; 过失赔偿责任 ; 过失责任险

拜占庭共识算法RBFT：Redundant Byzantine Fault Tolerance

最近在研究拜占庭共识，做个记录吧，有些可能也没理解透。

RBFT : Redundant Byzantine Fault Tolerance

论文地址：

提出其他已有的BFT算法（prime、Aardvark、Spinning）其实并不能真正的进行拜占庭容错，主要是由于存在一个“primary”用来排序的。如果primary作恶，整个系统的性能会显著下降而且不会被发现。而RBFT则提出了新的模式：采用多核机机器并行执行多个PBFT的协议实例，只有master实例的结果会被真正执行，每个协议实例都会被监控其性能并与master实例比较，如果master的性能不行，则会认为此master的primary节点为坏节点并发起替换流程。据测算RBFT在存在BFT攻击时的性能下降最大为3%，而其他的协议为：Prime(78%)、Aardvark(87%)、Spinning(99%)。

综述：

N= 3f+1个nodes(f为拜占庭节点最大数)，每个node里并行跑f+1个(why?:如果f个实例的primary都是坏节点，那么系统将无法识别拜占庭错误。当f+1个的时候就能保证，见下面的定理或者引理)BFT实例（PBFT协议），只有一个为master,其他的实例为backup。每个实例都有自己的replica，f+1个实例的primary必须满足：每个node最多只是一个实例的primary。每个实例都会对请求排序，但是只有master才会真正的执行,backup只排序与master性能作比较。每个node会运行一个监控程序，监控所有f+1个实例的吞吐量。如果2f+1个node发现master和最佳的backup实例性能差达到一定阈值则此master的primary节点会被认为是恶意节点，将会选出新的primary,还可以选择将表现最好的backup升级为master不过这样需要一个机制在切换master的时候保证各个实例状态的同步（机制参考文献11）。RBFT正确的工作需要f+1个实例接收到的是同样的客户端请求。不过当一个node收到req的时候并不会直接给他自己的f+1个实例运行，而是先转发给所有的其他节点。当他收到2f+1（why?:一定会收到2f+1个，不过应该只需要f+1就可以确定好节点一定都收到了这个请求）个客户端请求copy时（包括自己的）此节点会每一个好节点最终都会接收到请求（因为请求至少发送给了一个好节点）然后再将请求发给f+1个实例去执行。与Aardvark不同的是，RBFT的view change是又监控策略控制并且应用到所有f+1个实例里，而Aardvark由协议发起。

具体步骤：

1、客户端吧请求发送到所有节点

请求格式如下：o:请求操作，rid：请求标识符，c:client

RBFT提供一个监控机制来发现master实例是否坏掉了。

每个节点为每个实例维护一个计数器（一共f+1个），用来记录此实例已经排序的请求数（也就是说收到2f+1个COMMIT消息的请求数）。节点会使用这些计数器周期性的计算每个实例的吞吐量并更新计数器。以下一些情况master会认为坏掉了触发协议实例变更：

1、master的吞吐量比backup的平均吞吐量低达到一定阈值。阈值是根据无拜占庭错误和有拜占庭错误的吞吐量差异设定的。

2、监控程序还监控排序时间，此机制为了保证master对于所有的client处理都是公平的。设定了每个请求的最大处理时间和client在不同实例里处理的时间差值。如果请求超过最大处理时间或者某个client在不同的实例里处理的时间差异过大也会触发协议变更

变更坏掉的primary。由于每个节点最多是一个实例的primary所以要动就是要所有primary全动。

每个节点维护一个计数器来记录每个实例的变更信息。如果节点发现需要变更primary则会发送INSTANCE CHANGE消息给所有的节点，MAC认证。节点接收到传来的INSTANCE CHANGE消息后验证MAC，然后跟自身的计数器比对，如果自身的更大，则忽略，如果传来的更大则查看自己是否也需要传播INSTANCE CHANGE消息（也是比较master和backup的性能），如果收到2f+1个有效的INSTANCE CHANGE消息则计数器加1然后启动view change流程（就是改primary，PBFT也是）。此后每个实例的primary都得到了更新，当然也包括master 的。（更新策略如果又换到了坏的呢？那会触发再次更新。。 前面提到的直接换最好的backup为master可能会更好点）

f个node是坏的，所以运行在此node里的所有实例都是坏的，所有的client都是坏的。

master实例运行的primary的node是好的:

此时：坏节点的目标是尽可能降低master实例的性能而不触发协议变更（why要不触发协议变更？: 论文里有证明，当primay of master为好节点时不会触发，主要是master的吞吐量比backup的平均吞吐量低达到一定阈值的这个阈值是不是随意定的是根据理论算出来的）。

方式：

master实例运行的primary的node是坏的:

此时：坏节点的目标是尽可能的降低backup实例的性能，这样就可以留给坏的primary富裕的空间来降低master的性能而不被发现（怎么定义发现？）。

方式：