编译|冯维维
Science,17 Dec 2021,Volume 374 Issue 6574
《科学》2021年12月17日,第374卷,6574期
物理学Physics
Many-body–localized discrete time crystal with a programmable spin-based quantum simulator
多体局部化离散时间晶体
▲ 作者:J. RANDALL,C. E. BRADLEY,F. V. VAN DER GRONDENA. GALICIA,M. H. ABOBEIH,M. MARKHAM,D. J. TWITCHEN,XF. MACHADO ,N. Y. YAO ,T. H. TAMINIAU
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▲ 摘要
科学家提出一种新的物质相离散时间晶体(DTC)的形成,并将其用于一些周期性驱动条件下的多体量子系统。作者利用围绕金刚石氮空位中心的核自旋阵列作为多体量子系统。
将该系统置于一系列周期性驱动脉冲中,他们观察到自旋的顺序是驱动频率的两倍,他们声称这一特征建立了离散时间晶体的形成。这种动态控制有望用于操纵量子系统和实现量子信息协议。
▲ Abstract
Abstract: The formation of discrete time crystals,a novel phase of matter,has been proposed for some many-body quantum systems under periodic driving conditions. Randall et al. used an array of nuclear spins surrounding a nitrogen vacancy center in diamond as their many-body quantum system. Subjecting the system to a series of periodic driving pulses,they observed ordering of the spins occurring at twice the driving frequency,a signature that they claim establishes the formation of a discrete time crystal. Such dynamic control is expected to be useful for manipulating quantum systems and implementing quantum information protocols.
Information scrambling in quantum circuits
量子电路中的信息置乱
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▲ 摘要
在相互作用的量子系统中,信息的传播与从黑洞到奇怪的金属等广泛的环境相关。作者使用Sycamore量子处理器研究了这一过程。通过量子电路的合理设计,研究人员能够分离算子扩散和算子纠缠的贡献。通过测量特定相关系数的平均值和波动,可以量化这些不同的贡献。
▲ Abstract
Information spreading in interacting quantum systems is of relevance to a wide range of settings,from black holes to strange metals. Mi et al. used the Sycamore quantum processor to study this process. Through judicial design of quantum circuits,the researchers were able to separate the contributions of operator spreading and operator entanglement. Measuring the mean value and fluctuations of a specific correlator enabled quantifying these distinct contributions.
Atomic-scale visualization of topological spin textures in the chiral magnet MnGe
锗化锰中拓扑自旋织构的原子尺度可视化
▲ 作者:JACOB REPICKY,PO-KUAN WU,TAO LIUJOSEPH P. CORBETT,TIANCONG ZHU,SHUYU CHENGADAM S. AHMEDN. TAKEUCHIJ. GUERRERO-SANCHEZ,JAY A. GUPTA
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▲ 摘要
拓扑自旋织构有望成为可靠的信息载体,并已在具有特定晶体结构的块状材料中观察到。其中一种材料,锗化锰(MnGe),以块状形式表现出不同寻常的纹理。作者使用自旋极化扫描隧道显微镜研究了MnGe薄膜的表面磁性。
为了获得高空间分辨率,研究人员观察到与螺旋状态一致的条纹状特征。在薄膜因应变而略微弯曲的区域,畴壁的交集产生了可以用电流/电压脉冲控制的特征闭合模式。
▲ Abstract
Topological spin textures hold promise as robust carriers of information and have been observed in bulk materials with a specific crystal structure. One of these materials,manganese germanide (MnGe),exhibits unusual textures in bulk form. Repicky et al. used spin-polarized scanning tunneling microscopy to study surface magnetism in thin films of MnGe. Achieving high spatial resolution,the researchers observed stripe-like features consistent with a helical state. In regions where the film was slightly curved due to strain,the intersection of domain walls led to characteristic closed patterns that could be manipulated with current/voltage pulses.
自由基对中的量子振荡
▲ 作者:DAVID MIMS,JONATHAN HERPICHNIKITA N. LUKZEN,XULRICH E. STEINER,AND CHRISTOPH LAMBERT
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▲ 摘要
光诱导自由基对的自旋动力学,涉及自旋态与自旋态之间的相互转换,在自然界中起着重要作用,例如在鸟类的磁接收中。自旋转换是一个具有特征相干振荡(量子拍)的真正的量子过程,应该反映在反应动力学中。
然而,他们的实验观察仍然具有挑战性。作者开发了一种光学读出技术,可以直接监测单态-三重态相互转换量子拍,用于电子给体-受体二分体的光诱导、电荷分离状态。
▲ Abstract
The spin dynamics of photoinduced radical pairs,involving an interconversion between singlet and triplet spin states,plays an important role in nature,for example,in avian magnetoreception. The spin interconversion is a truly quantum process with characteristic coherent oscillations (quantum beats) that should be reflected in the reaction kinetics. However,their experimental observation has remained challenging. Mims et al. developed an optical readout technique that can directly monitor the singlet-triplet interconversion quantum beats,as demonstrated for a photoinduced,charge-separated state of an electron donor–acceptor dyad. The present work opens a new way to monitor the spin evolution in radical pairs,which will be important not only in biological physics but also in organic solar cells and other practical applications.
化学Chemistry
Scalable thermochromic smart windows with passive radiative cooling regulation
可伸缩的热变色智能窗户与被动辐射冷却调节
▲ 作者:SHANCHENG WANG,TENGYAO JIANG,YUN MENGRONGGUI YANG,GANG TAN,AND YI LONG
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▲ 摘要
被动辐射冷却技术利用红外大气窗,使外太空成为一个热量的冷吸收源。然而,这种效应只对温暖月份的节能有帮助。
因为这种转变简单地依赖于温度,所以这种效应也是被动地发生的。模型模拟表明,在美国的大部分气候区,这些材料会带来全年的能源节约。
▲ Abstract
生态学Ecology
Ecosystem fluxes during drought and recovery in an experimental forest
试验林干旱和恢复过程中的生态系统通量
▲ 作者:CHRISTIANE WERNER,LAURA K. MEREDITH,NEMIAH LADD,JOHANNES INGRISCH,ANGELIKA KÜBERT,JOOST VAN HAREN,MICHAEL BAHN,KINZIE BAILEY,INES BAMBERGER,JONATHAN WILLIAMS
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▲ 摘要
严重干旱危及全球生态系统的正常运行。通过在封闭的实验雨林中追踪CO2和深水H2O标记脉冲以及挥发性有机化合物(VOCs),作者研究了干旱如何影响碳和水通量以及土壤-植物-大气相互作用。不同植物功能类群对干旱的响应驱动了生态系统的动态变化。
对干旱敏感的冠层树种在总通量中占主导地位,但对表土干燥的响应最强。尽管所有形成树冠的树木都能进入深水区,但这些保护区直到干旱后期才得以幸免。
地下碳运输速度减缓,但新鲜碳对VOCs的分配仍然很高。大气VOC组成反映了胁迫响应的增加和土壤-植物-大气动态相互作用,可能影响大气化学和气候反馈。因此,这些相互作用和不同的功能群策略调节干旱影响和生态系统对气候变化的敏感性。
▲ Abstract