编译 | 未玖
Nature,26 May 2022, VOL 605, ISSUE 7911
《自然》2022年5月26日，第605卷，7911期
天文学Astronomy
In situ recording of Mars soundscape
火星声景的现场录音
▲ 作者：S. Maurice, B. Chide, N. Murdoch, R. D. Lorenz, D. Mimoun, R. C. Wiens, et al.
▲ 链接：
https://www.nature.com/articles/s41586-022-04679-0
▲ 摘要：
在“毅力号”探测器着陆之前，火星的声学环境是未知的。模型预测：（1）在分子粘度将动能转化为热量时，大气湍流以厘米或更小的尺度变化；（2）表面声速随频率变化；（3）高频波在CO2中随距离增加而强烈衰减。然而，由于缺乏低压实验数据以及难以表征封闭环境中的湍流或衰减，理论模型存在不确定性。
研究组利用“毅力号”麦克风现场录音，首次描述了火星上的声学环境，以及可听范围内外（20 Hz至50kHz）的压力波动。他们发现，大气声音将压力变化的测量范围扩展到比以往任何测量小1000倍的尺度，显示出一种能量扩展超过五个数量级的耗散状态。
使用点声源（精巧旋翼机、激光诱导火花），研究组突出显示了240Hz以下和以上两个不同声速值相差约10ms-1，这是CO2主导低压大气的独特特征。
研究组还提供了2kHz以上的声波衰减，从而解释CO2振动弛豫在可听范围内的巨大贡献。该研究结果为声学过程建模奠定了基础，这对研究火星和金星等大气至关重要。
▲ Abstract：
Before the Perseverance rover landing, the acoustic environment of Mars was unknown. Models predicted that: (1) atmospheric turbulence changes at centimetre scales or smaller at the point where molecular viscosity converts kinetic energy into heat, (2) the speed of sound varies at the surface with frequency and (3) high-frequency waves are strongly attenuated with distance in CO2. However, theoretical models were uncertain because of a lack of experimental data at low pressure and the difficulty to characterize turbulence or attenuation in a closed environment. Here, using Perseverance microphone recordings, we present the first characterization of the acoustic environment on Mars and pressure fluctuations in the audible range and beyond, from 20 Hz to 50 kHz. We find that atmospheric sounds extend measurements of pressure variations down to 1,000 times smaller scales than ever observed before, showing a dissipative regime extending over five orders of magnitude in energy. Using point sources of sound (Ingenuity rotorcraft, laser-induced sparks), we highlight two distinct values for the speed of sound that are about 10 m s−1 apart below and above 240 Hz, a unique characteristic of low-pressure CO2-dominated atmosphere. We also provide the acoustic attenuation with distance above 2 kHz, allowing us to explain the large contribution of the CO2 vibrational relaxation in the audible range. These results establish a ground truth for the modelling of acoustic processes, which is critical for studies in atmospheres such as those of Mars and Venus.
物理学Physics
Free-electron lasing with compact beam-driven plasma wakefield accelerator
紧凑型束流驱动等离子体尾场加速器的自由电子激光
▲ 作者：R. Pompili, D. Alesini, M. P. Anania, S. Arjmand, M. Behtouei, M. Bellaveglia, et al.
▲ 链接：
https://www.nature.com/articles/s41586-022-04589-1
▲ 摘要：
等离子体技术可在短距离内将电子束加速到超相对论速度，这有望为粒子加速器领域带来一场革命。
基于等离子体加速器的紧凑特性有望实现能够驱动自由电子激光器（FEL）的台式机器，这是一种强大的工具，通过产生亚埃米波长和亚飞秒持续时间的相干光脉冲，来研究亚原子水平的物质。
但迄今为止，操作FEL所需的高能电子束必须通过使用传统的大型射频（RF）加速器来获得，由于加速场有限，其占地面积相当大。
研究组报道了一个紧凑型（3cm）粒子束驱动等离子体加速器产生FEL的实验证据。加速光束在六维相空间中可完全表征，质量高，可与最先进的加速器媲美。这使得人们能够在红外范围内观察到窄带放大辐射，其强度在六个连续波荡器上呈典型的指数增长。
该原理验证实验代表了等离子体加速器使用的一个里程碑，有助于开发面向用户的下一代紧凑型设备。
▲ Abstract：
The possibility to accelerate electron beams to ultra-relativistic velocities over short distances by using plasma-based technology holds the potential for a revolution in the field of particle accelerators. The compact nature of plasma-based accelerators would allow the realization of table-top machines capable of driving a free-electron laser (FEL), a formidable tool to investigate matter at the sub-atomic level by generating coherent light pulses with sub-ångström wavelengths and sub-femtosecond durations. So far, however, the high-energy electron beams required to operate FELs had to be obtained through the use of conventional large-size radio-frequency (RF) accelerators, bound to a sizeable footprint as a result of their limited accelerating fields. Here we report the experimental evidence of FEL lasing by a compact (3-cm) particle-beam-driven plasma accelerator. The accelerated beams are completely characterized in the six-dimensional phase space and have high quality, comparable with state-of-the-art accelerators. This allowed the observation of narrow-band amplified radiation in the infrared range with typical exponential growth of its intensity over six consecutive undulators. This proof-of-principle experiment represents a fundamental milestone in the use of plasma-based accelerators, contributing to the development of next-generation compact facilities for user-oriented applications.
信息科学Information Science
Realizing repeated quantum error correction in a distance-three surface code
在距离为3的表面码中实现重复量子纠错
▲ 作者：Sebastian Krinner, Nathan Lacroix, Ants Remm, Agustin Di Paolo, Elie Genois, Catherine Leroux, et al.
▲ 链接：
https://www.nature.com/articles/s41586-022-04566-8
▲ 摘要：
量子计算机有望解决用传统方法难以解决的计算问题。对于容错操作，量子计算机必须纠正由于不可避免的退相干和有限控制精度而发生的错误。
研究组演示了使用表面码的量子纠错，表面码以其极高的容错性而闻名。在超导电路中使用17个物理量子位，以最近的距离为2误差检测实验为基础，在距离为3的逻辑量子位中对量子信息进行编码。
在仅需1.1 μs的纠错周期中，研究组证明了逻辑量子位的四种基态保持。重复执行周期，使用无错误模型方法中的最小权重完美匹配算法，来测量和解码位翻转和相位翻转错误伴随式，并在后处理中进行校正。
研究组发现，当拒绝已泄漏实验运行时，每个周期的逻辑错误概率低至3%。该装置的测量特性与数值模型吻合良好。该研究对重复、快速和高性能量子纠错周期的演示，以及离子阱的最新进展，证明了容错量子计算实现在即。
▲ Abstract：
Quantum computers hold the promise of solving computational problems that are intractable using conventional methods. For fault-tolerant operation, quantum computers must correct errors occurring owing to unavoidable decoherence and limited control accuracy. Here we demonstrate quantum error correction using the surface code, which is known for its exceptionally high tolerance to errors. Using 17 physical qubits in a superconducting circuit, we encode quantum information in a distance-three logical qubit, building on recent distance-two error-detection experiments. In an error-correction cycle taking only 1.1 μs, we demonstrate the preservation of four cardinal states of the logical qubit. Repeatedly executing the cycle, we measure and decode both bit-flip and phase-flip error syndromes using a minimum-weight perfect-matching algorithm in an error-model-free approach and apply corrections in post-processing. We find a low logical error probability of 3% per cycle when rejecting experimental runs in which leakage is detected. The measured characteristics of our device agree well with a numerical model. Our demonstration of repeated, fast and high-performance quantum error-correction cycles, together with recent advances in ion traps, support our understanding that fault-tolerant quantum computation will be practically realizable
Demonstration of fault-tolerant universal quantum gate operations
容错通用量子门操作演示
▲ 作者：Lukas Postler, Sascha Heuβen, Ivan Pogorelov, Manuel Rispler, Thomas Feldker, Michael Meth, et al.
▲ 链接：
https://www.nature.com/articles/s41586-022-04721-1
▲ 摘要：
通过使用纠错码将逻辑量子信息冗余编码成多个量子位，可以保护量子计算机免受噪声的影响。在操纵逻辑量子态时，必须确保由不完美操作引起的错误不会通过量子寄存器不可控传播。这就要求量子寄存器上的所有操作都遵循容错电路设计，通常会增加实现的复杂性。
研究组演示了一个离子阱量子计算机中两个逻辑量子位上的容错通用门集，特别利用了最近引入的标志容错范式，通过使用辅助标志量子位来预示危险错误的存在与否。
研究组在两个7量子位色码实例之间执行逻辑双量子位受控非门，并容错地制备逻辑“魔法态”。然后通过从一个逻辑量子位隐形传态至另一个逻辑量子位注入“魔法态”来实现容错逻辑T门。
研究组观察到与非容错实现相比，容错的标志性特征具有更优越的性能。结合最近证明的重复量子纠错周期，该结果将助力实现纠错通用量子计算。
▲ Abstract：
Quantum computers can be protected from noise by encoding the logical quantum information redundantly into multiple qubits using error-correcting codes. When manipulating the logical quantum states, it is imperative that errors caused by imperfect operations do not spread uncontrollably through the quantum register. This requires that all operations on the quantum register obey a fault-tolerant circuit design, which, in general, increases the complexity of the implementation. Here we demonstrate a fault-tolerant universal set of gates on two logical qubits in a trapped-ion quantum computer. In particular, we make use of the recently introduced paradigm of flag fault tolerance, where the absence or presence of dangerous errors is heralded by the use of auxiliary flag qubits. We perform a logical two-qubit controlled-NOT gate between two instances of the seven-qubit colour code, and fault-tolerantly prepare a logical magic state. We then realize a fault-tolerant logical T gate by injecting the magic state by teleportation from one logical qubit onto the other. We observe the hallmark feature of fault tolerance—a superior performance compared with a non-fault-tolerant implementation. In combination with recently demonstrated repeated quantum error-correction cycles, these results provide a route towards error-corrected universal quantum computation.
材料科学Materials Science
Cilia metasurfaces for electronically programmable microfluidic manipulation
电子可编程微流控操作的纤毛超表面
▲ 作者：Wei Wang, Qingkun Liu, Ivan Tanasijevic, Michael F. Reynolds, Alejandro J. Cortese, Marc Z. Miskin, et al.
▲ 链接：
https://www.nature.com/articles/s41586-022-04645-w
▲ 摘要：
纤毛泵送是生物有机体在微尺度上控制和操纵流体的一种强有力策略。然而，尽管最近在光、磁和电驱动致动方面取得了许多进展，但开发具有应用潜力的人工纤毛平台仍然很难实现。
研究组报道了电子驱动人工纤毛的主动超表面，它可以在表面附近的液体中创建任意流动模式。首先创建了电压驱动的纤毛，在1V的驱动电压下产生非互易运动，以每秒数十微米的速度驱动表面流动。
然后展示了纤毛晶胞可以局部创建一系列基本流动几何形状。通过组合这些晶胞，研究组创建了一个主动纤毛超表面，可以产生和切换任何所需的表面流动模式。
最后将纤毛与光驱动互补金属氧化物半导体（CMOS）时钟电路集成，以演示无线操作。作为概念证明，研究组使用该电路输出不同相位延迟的电压脉冲，以证明利用异时波提高了泵浦效率。
实验和理论计算证实了这些强有力的结果，该研究开辟了一条精细尺度微流控操作的新途径，其应用范围从微流控泵到微机器人运动。
▲ Abstract：
Cilial pumping is a powerful strategy used by biological organisms to control and manipulate fluids at the microscale. However, despite numerous recent advances in optically, magnetically and electrically driven actuation, development of an engineered cilial platform with the potential for applications has remained difficult to realize. Here we report on active metasurfaces of electronically actuated artificial cilia that can create arbitrary flow patterns in liquids near a surface. We first create voltage-actuated cilia that generate non-reciprocal motions to drive surface flows at tens of microns per second at actuation voltages of 1 volt. We then show that a cilia unit cell can locally create a range of elemental flow geometries. By combining these unit cells, we create an active cilia metasurface that can generate and switch between any desired surface flow pattern. Finally, we integrate the cilia with a light-powered complementary metal–oxide–semiconductor (CMOS) clock circuit to demonstrate wireless operation. As a proof of concept, we use this circuit to output voltage pulses with various phase delays to demonstrate improved pumping efficiency using metachronal waves. These powerful results, demonstrated experimentally and confirmed using theoretical computations, illustrate a pathway towards fine-scale microfluidic manipulation, with applications from microfluidic pumping to microrobotic locomotion.
地球科学Earth Science
Enhanced silica export in a future ocean triggers global diatom decline
未来海洋二氧化硅析出增加引发全球硅藻减少
▲ 作者：Jan Taucher, Lennart T. Bach, A. E. Friederike Prowe, Tim Boxhammer, Karin Kvale & Ulf Riebesell
▲ 链接：
https://www.nature.com/articles/s41586-022-04687-0
▲ 摘要：
硅藻占海洋初级生产力的40%，需要硅酸来生长和建造蛋白石壳。在生理和生态层面上，硅藻被认为能够抵抗海洋酸化，甚至从中受益。然而，未来海洋生物地球化学循环的全球范围响应和影响在很大程度上仍然未知。
研究组对不同生物群系的自然浮游生物群落进行了5次原位围隔实验研究，发现到2100年，在pCO2条件下，海洋酸化将使下沉生源物质中硅（Si）与氮（N）的元素比增加17 ± 6%。Si:N的这种变化似乎是因海水pH值降低时二氧化硅的化学溶解速度变慢所致。
研究组用全球沉积物捕集数据验证了这一发现，这些数据证实了pH值对海洋水柱中Si:N的广泛影响。地球系统模型模拟表明，未来pH值驱动的下沉物质二氧化硅溶解减少会降低表层海洋中硅酸的利用率，导致2200年由于海洋酸化将造成全球硅藻数量减少13-26%。
该结果与以往实验研究的结论形成了鲜明对比，表明人们目前对海洋变化生物影响的认识如何通过地球系统中意想不到的反馈机制在全球范围内发生重大变化。
▲ Abstract：
Diatoms account for up to 40% of marine primary production and require silicic acid to grow and build their opal shell. On the physiological and ecological level, diatoms are thought to be resistant to, or even benefit from, ocean acidification. Yet, global-scale responses and implications for biogeochemical cycles in the future ocean remain largely unknown. Here we conducted five in situ mesocosm experiments with natural plankton communities in different biomes and find that ocean acidification increases the elemental ratio of silicon (Si) to nitrogen (N) of sinking biogenic matter by 17 ± 6 per cent under pCO2 conditions projected for the year 2100. This shift in Si:N seems to be caused by slower chemical dissolution of silica at decreasing seawater pH. We test this finding with global sediment trap data, which confirm a widespread influence of pH on Si:N in the oceanic water column. Earth system model simulations show that a future pH-driven decrease in silica dissolution of sinking material reduces the availability of silicic acid in the surface ocean, triggering a global decline of diatoms by 13–26 per cent due to ocean acidification by the year 2200. This outcome contrasts sharply with the conclusions of previous experimental studies, thereby illustrating how our current understanding of biological impacts of ocean change can be considerably altered at the global scale through unexpected feedback mechanisms in the Earth system.