编译｜冯维维
Nature, 27 JANUARY 2022, Vol 601,Issue 7894
《自然》2022年1月27日，第601卷，7894期
物理Physics
A radio transient with unusually slow periodic emission
具有异常慢周期发射的无线电瞬变
▲ 作者：N. Hurley-Walker, X. Zhang, A. Bahramian, S. J. McSweeney, T. N. O’Doherty, P. J. Hancock, J. S. Morgan, G. E. Anderson, G. H. Heald & T. J. Galvin
▲ 链接：
http://www.nature.com/articles/s41586-021-04272-x
▲ 摘要
高频射电天空伴随着大量恒星爆炸和吸积事件产生的同步加速瞬变现象，而低频射电天空迄今为止在星系脉冲星群和活动星系核的长期闪烁之外一直是安静的。作者分析了档案中一个低频无线电数据，揭示了其具有周期性的低频无线电瞬变。
他们发现这个源每18.18分钟会发出一次脉冲，这是以前从未观测到的一个不寻常的周期。通过测量射电脉冲相对频率的色散，作者将其定位在银河系内，并指出它可能是一颗超长周期的磁星。
▲ Abstract
The high-frequency radio sky is bursting with synchrotron transients from massive stellar explosions and accretion events, but the low-frequency radio sky has, so far, been quiet beyond the Galactic pulsar population and the long-term scintillation of active galactic nuclei. Here we report an analysis of archival low-frequency radio data that reveals a periodic, low-frequency radio transient. We find that the source pulses every 18.18min, an unusual periodicity that has, to our knowledge, not been observed previously. These profiles evolve on timescales of hours. By measuring the dispersion of the radio pulses with respect to frequency, we have localized the source to within our own Galaxy and suggest that it could be an ultra-long-period magnetar.
Time-crystalline eigenstate order on a quantum processor
量子处理器的时间晶体本征态顺序
▲ 作者：
Xiao Mi, Matteo Ippoliti, Pedram Roushan Show authors
▲ 链接：
http://www.nature.com/articles/s41586-021-04257-w
▲ 摘要
量子多体系统在其低温平衡态下表现出丰富的相结构。然而，自然界的许多物质并不处于热平衡状态。
值得注意的是，最近有人预测，非平衡系统可表现出平衡热力学不能实现的新的动力学相，一个典型的例子是离散时间晶体（DTC）。具体地说，通过本征态阶的概念，可定义周期性驱动的多体局域（MBL）系统的动力学相。
作者在超导量子比特阵列上实现了可调可控相位（CPHASE）门，实验观察了MBL-DTC，并证明了其对一般初始态的时空响应特性。作者表示，这项研究采用了一种时间反转协议来量化外部脱散相干的影响，并利用量子典型化来规避密集采样本征态的指数代价。
此外，他们用实验的有限尺寸分析来定位出DTC的相变。这些结果建立了一个通过量子处理器研究非平衡阶段物质的可扩展的方法。
▲ Abstract
Quantum many-body systems display rich phase structure in their low-temperature equilibrium states. However, much of nature is not in thermal equilibrium. Remarkably, it was recently predicted that out-of-equilibrium systems can exhibit novel dynamical phases that may otherwise be forbidden by equilibrium thermodynamics, a paradigmatic example being the discrete time crystal (DTC). Concretely, dynamical phases can be defined in periodically driven many-body-localized (MBL) systems via the concept of eigenstate order. Here we implement tunable controlled-phase (CPHASE) gates on an array of superconducting qubits to experimentally observe an MBL-DTC and demonstrate its characteristic spatiotemporal response for generic initial states. Our work employs a time-reversal protocol to quantify the impact of external decoherence, and leverages quantum typicality to circumvent the exponential cost of densely sampling the eigenspectrum. Furthermore, we locate the phase transition out of the DTC with an experimental finite-size analysis. These results establish a scalable approach to studying non-equilibrium phases of matter on quantum processors.
Quantum register of fermion pairs
费米子对的量子寄存器
▲ 作者：Thomas Hartke, Botond Oreg, Ningyuan Jia & Martin Zwierlein
▲ 链接：
http://www.nature.com/articles/s41586-021-04205-8
▲ 摘要
在量子层面控制运动是现代原子钟和干涉仪的核心。它使协议能够处理和分发量子信息，并使得探测物质相关态的纠缠成为可能。然而，由于外部自由度与环境强烈耦合，单个粒子的运动一致性可能难以维持。
与此相对的是，自然界中具有强烈运动相干性的系统往往涉及到粒子对，例如从氦电子对到原子对、分子对和库珀对。
作者演示了在光学晶格阵列中费米原子对的长期运动相干性和纠缠。论文介绍的方法将有助于实现多费米子系统的相干可编程量子模拟器，基于原子对和分子的精确计量，并通过进一步推进，使用费米子对进行数字量子计算。
▲ Abstract
Quantum control of motion is central for modern atomic clocks and interferometers. It enables protocols to process and distribute quantum information, and allows the probing of entanglement in correlated states of matter. However, the motional coherence of individual particles can be fragile to maintain, as external degrees of freedom couple strongly to the environment. Systems in nature with robust motional coherence instead often involve pairs of particles, from the electrons in helium, to atom pairs, molecules and Cooper pairs. Here we demonstrate long-lived motional coherence and entanglement of pairs of fermionic atoms in an optical lattice array. The methods presented here will enable coherently programmable quantum simulators of many-fermion systems, precision metrology based on atom pairs and molecules and, by implementing further advances, digital quantum computation using fermion pairs.
Burning plasma achieved in inertial fusion
惯性聚变中实现等离子体燃烧
▲ 作者：A. B. Zylstra, O. A. Hurricane, G. B. Zimmerman, etc.
▲ 链接：
http://www.nature.com/articles/s41586-021-04281-w
▲ 摘要
美国加利福尼亚州劳伦斯利弗莫尔国家实验室的Alex Zylstra和合作者在一项新研究中报告了核聚变中的等离子态物质自热，这是使核聚变能量成为可行能源的一个里程碑。
核聚变是原子核结合以释放能量的反应，它有望提供可持续的能源。这是一个驱动恒星的物理过程，但在实验室中很难重现这一过程，且需要使用的能量多于它能产生的能量。
实现核聚变能量净发生器的关键步骤之一是燃烧的等离子体，其中的核聚变是热能主要来源，需维持燃料的等离子态，令其温度高到允许进一步的聚变反应。
作者报告了惯性约束聚变实验中的这一状态，其中聚变反应是由压缩和加热填充热核燃料的靶丸启动的。美国国家点火装置（NIF）的实验实现了使用192个激光束点燃等离子体，快速加热并使内含200微克氘-氚燃料的靶丸内爆，达到了足够高的温度和压力触发自加热聚变反应。
过去的尝试都受限于控制等离子形状的难题，从而无法避免扰乱激光束在等离子体内累积能量的方式，但作者改进了实验设计，使胶囊可以容纳更多燃料、并在包含等离子体时吸收更多能量。这些实验产生的效能（最高产生170千焦耳能量）三倍于过去实验的结果。
▲ Abstract
Obtaining a burning plasma is a critical step towards self-sustaining fusion energy. A burning plasma is one in which the fusion reactions themselves are the primary source of heating in the plasma, which is necessary to sustain and propagate the burn, enabling high energy gain. After decades of fusion research, here we achieve a burning-plasma state in the laboratory. These experiments were conducted at the US National Ignition Facility, a laser facility delivering up to megajoules of energy in pulses with peak powers up to 500terawatts. We use the lasers to generate X-rays in a radiation cavity to indirectly drive a fuel-containing capsule via the X-ray ablation pressure, which results in the implosion process compressing and heating the fuel via mechanical work. The burning-plasma state was created using a strategy to increase the spatial scale of the capsule through two different implosion concepts. These experiments show fusion self-heating in excess of the mechanical work injected into the implosions, satisfying several burning-plasma metrics. Additionally, we describe a subset of experiments that appear to have crossed the static self-heating boundary, where fusion heating surpasses the energy losses from radiation and conduction. These results provide an opportunity to study α-particle-dominated plasmas and burning-plasma physics in the laboratory.
Emergent interface vibrational structure of oxide superlattices
氧化物超晶格的界面振动结构
▲ 作者：Eric R. Hoglund, De-Liang Bao, Andrew O’Hara, Sara Makarem, Zachary T. Piontkowski, Joseph R. Matson, Ajay K. Yadav, Ryan C. Haislmaier, Roman Engel-Herbert, Jon F. Ihlefeld, Jayakanth Ravichandran, Ramamoorthy Ramesh, Joshua D. Caldwell, Thomas E. Beechem, John A. Tomko, Jordan A. Hachtel, Sokrates T. Pantelides, Patrick E. Hopkins & James M. Howe
▲ 链接：
http://www.nature.com/articles/s41586-021-04238-z
▲ 摘要
随着材料长度尺度的减小，与界面相关的非均质性变得几乎和周围材料一样重要。作者结合先进的扫描透射电子显微镜成像和光谱学、密度泛函理论计算和超快光谱学，研究了钛酸锶-钛酸钙超晶格中界面的局部振动响应。
他们观察到连接边界材料的结构上漫反射界面，这个局部结构创造了声子模式，一旦界面间距接近声子空间范围，就决定了超晶格的整体响应。
作者表示，该结果提供了局部原子结构和界面振动进程的直接可视化，因为它们决定了整个超晶格的振动响应。对这种局部原子和振动现象的直接观察表明，它们的空间范围需要量化才能理解宏观行为。裁剪界面，了解其局部振动响应，提供了一种利用红外和热响应追踪设计固体的方法。
▲ Abstract
As the length scales of materials decrease, the heterogeneities associated with interfaces become almost as important as the surrounding materials. Here we demonstrate the localized vibrational response of interfaces in strontium titanate–calcium titanate superlattices by combining advanced scanning transmission electron microscopy imaging and spectroscopy, density functional theory calculations and ultrafast optical spectroscopy. Structurally diffuse interfaces that bridge the bounding materials are observed and this local structure creates phonon modes that determine the global response of the superlattice once the spacing of the interfaces approaches the phonon spatial extent. Our results provide direct visualization of the progression of the local atomic structure and interface vibrations as they come to determine the vibrational response of an entire superlattice. Direct observation of such local atomic and vibrational phenomena demonstrates that their spatial extent needs to be quantified to understand macroscopic behaviour. Tailoring interfaces, and knowing their local vibrational response, provides a means of pursuing designer solids with emergent infrared and thermal responses.
Inhibiting the Leidenfrost effect above 1,000 °C for sustained thermal cooling
在1000℃以上抑制莱顿弗罗斯特效应，保持热冷却
▲ 作者：Mengnan Jiang, Yang Wang, Fayu Liu, Hanheng Du, Yuchao Li, Huanhuan Zhang, Suet To, Steven Wang, Chin Pan, Jihong Yu, David Quéré & Zuankai Wang
▲ 链接：
http://www.nature.com/articles/s41586-021-04307-3
▲ 摘要
莱顿弗罗斯特效应，即液滴在热固体上的悬浮，已知会在高温下恶化传热。莱顿弗罗斯特点可通过纹理材料来提高，以有利于固-液接触，并通过在表面设置通道来将湿润现象与蒸汽动力学解耦。然而，在大范围的温度范围内最大化莱顿弗罗斯特点和热冷却可能是相互排斥的。
作者报告了一种结构合理的热装甲设计，它可以抑制高达1150℃的莱顿弗罗斯特效应，这比以前达到的温度高出600℃，但仍保持了热传递。作者表示，该策略具有在超高固体温度下实现高效水冷却的潜力，这是一个此前未知的特性。
▲ Abstract
The Leidenfrost effect, namely the levitation of drops on hot solids, is known to deteriorate heat transfer at high temperature. The Leidenfrost point can be elevated by texturing materials to favour the solid–liquid contact and by arranging channels at the surface to decouple the wetting phenomena from the vapour dynamics. However, maximizing both the Leidenfrost point and thermal cooling across a wide range of temperatures can be mutually exclusive. Here we report a rational design of structured thermal armours that inhibit the Leidenfrost effect up to 1,150 °C, that is, 600 °C more than previously attained, yet preserving heat transfer. Our strategy holds the potential to enable the implementation of efficient water cooling at ultra-high solid temperatures, which is, to date, an uncharted property.
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