PRL导读-2019年122卷08期

2019 年 3 月 11 日 中科院物理所

序

言

本着服务于中国物理学者和物理专业研究生的宗旨，我们根据PRL摘要和引言对本期部分文章进行中文导读。由于水平有限，不免出现一些不准确的地方乃至错译的地方。公众号下方有留言功能，欢迎专家学者通过留言指出不准确或错译的地方，共同提高公众号的服务质量。留言经编辑确认后，会显示在文章下方，供后来浏览者参考。

普通物理：统计与量子物理

责编：郭文安

量子和经典系统中互文性的实验检验

互文性被认为是非经典性的内在特征，是实现量子信息处理独特优势的关键资源。然而，最近有一些关于经典场是否也可以表现出互文性的争论。Aonan Zhang等人设计了一个光学场的互文测试实验，采用测量事件的各种定义，并分析这些定义如何影响非经典关联的出现。被预言的单光子态（一个典型非经典光场）在他们的设置中显示了互文性；而经典相干场的互文性强烈的依赖测量事件的具体定义，这相当于过滤输入态的非经典分量。他们的结果强调了测量事件定义对证明互文性的重要性，并且将互文关联性与相空间中准概率定义的非经典性联系起来。（崔石峰）

Experimental Test of Contextuality in Quantum and Classical Systems

Aonan Zhang, et al

Phys. Rev. Lett. 122, 080401 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.080401

用算符排序灵敏性

测量玻色场量子态的非经典性

Stephan De Bievre等人提出了一种新的基于距离的测量方法，它用来研究玻色场态的非经典性，它在几个方面优于现有的测量方法。为此，他们定义了态的算符排序灵敏度，它反映对准概率Renyi熵的算符排序的灵敏度性，并测量在其Wigner函数中的振荡。通过对经典态的算符排序灵敏度的严格控制，得到其在密度矩阵空间中位置的精确几何图像，从而引进一种基于距离的非经典测量。作者分析了这种非经典测量和最近引入的量子宏观测量的联系，表明这两种概念如何区分。（崔石峰）

Measuring Nonclassicality of Bosonic Field Quantum States via Operator Ordering Sensitiv

Stephan De Bievre, et al

Phys. Rev. Lett. 122, 080402 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.080402

通往非阿贝尔几何门的

非绝热捷径的实验实现

在简并希尔伯特空间中，通过参数循环缓慢驱动一个量子系统，量子态会获得一个非阿贝尔几何相位。这个相位是稳定的，构成了完整量子计算（HQC）的基础。然而，在绝热极限下，环境的退相干成为了错误的主要来源。最近很多非绝热完整量子计算(NHQC)方案被提出，但是所有都以增加对控制误差的敏感性为代价。通过“绝热性捷径”（STA）技术加速HQC的理论与此不同，但由于该理论涉及同时对四个能级的复杂控制，目前在实验上尚无验证。本文提出并实验证实：在可扩展的体系结构中，利用超导量子比特，通过绝热性捷径，HQC可以仅用三个能级构建。这样，所有完整单量子比特运算可以通过非绝热态演化的单循环来实现。作者已经能在实验上对照NHQC的系统检测STA+HQC的稳定性。这一灵活简单的方案在其他体系中也能够实现，比如氮晶格空位中心、量子点和核磁共振中。此外，这个方案可以被扩展为构建两量子比特的完整纠缠门，从而可用于构建一个STAHQC门的通用装置。（侯迪莎）

Experimental Realization of Nonadiabatic Shortcut to Non-Abelian Geometric Gates

Tongxing Yan, et al.

Phys. Rev. Lett. 122, 080501 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.080501

超导量子比特的门控条件位移读数

作者实现了超导量子比特和读出腔之间的新的相互作用。以量子比特的状态为条件，它导致腔中的相干态的位移。当到达腔体跟随的相敏功放时，该条件状态与其测量的可观察量（即，相位正交）匹配。在几个量子比特耦合到同一读出谐振器的装置中，作者表明可以测量目标量子比特态，同时其他量子比特的失相(dephase)最小。作者的结果给出了更快读出超导量子比特，并实现玻色量子纠错编码的新方向。(朱文静)

Gated Conditional Displacement Read out of Superconducting Qubits

S. Touzard, A. Kou et al.

Phys. Rev. Lett. 122, 080502 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.080502

通过多通道驱动测量量子比特

We theoretically propose and experimentally implement a method of measuring a qubit by driving it close to the frequency of a dispersively coupled bosonic mode. The separation of the bosonic states corresponding to different qubit states begins essentially immediately at maximum rate, leading to a speedup in the measurement protocol. Also the bosonic mode can be simultaneously driven to optimize measurement speed and fidelity. We experimentally test this measurement protocol using a superconducting qubit coupled to a resonator mode. For a certain measurement time, we observe that the conventional dispersive readout yields close to 100% higher average measurement error than our protocol. Finally, we use an additional resonator drive to leave the resonator state to vacuum if the qubit is in the ground state during the measurement protocol. This suggests that the proposed measurement technique may become useful in unconditionally resetting the resonator to a vacuum state after the measurement pulse.

Qubit Measurement by Multichannel Driving

Joni Ikonen, et al.

Phys. Rev. Lett. 122, 080503 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.080503

IBM量子计算中的容错逻辑门

Quantum computers will require encoding of quantum information to protect them from noise. Fault-tolerant quantum computing architectures illustrate how this might be done but have not yet shown a conclusive practical advantage. Here we demonstrate that a small but useful error detecting code improves the fidelity of the fault-tolerant gates implemented in the code space as compared to the fidelity of physically equivalent gates implemented on physical qubits. By running a randomized benchmarking protocol in the logical code space of the [4,2,2] code, we observe an order of magnitude improvement in the infidelity of the gates, with the two-qubit infidelity dropping from 5.8(2)% to 0.60(3)%. Our results are consistent with fault-tolerance theory and conclusively demonstrate the benefit of carrying out computation in a code space that can detect errors. Although the fault-tolerant gates offer an impressive improvement in fidelity, the computation as a whole is not below the fault-tolerance threshold because of noise associated with state preparation and measurement on this device.

Fault-Tolerant Logical Gates in the IBM Quantum Experience

Robin Harper and S. Flammia

Phys. Rev. Lett. 122, 080504 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.080504

对不可编程定理的资源量化

The no-programing theorem prohibits the existence of a universal programmable quantum processor. This statement has several implications in relation to quantum computation but also to other tasks of quantum information processing, making this construction a central notion in this context. Nonetheless, it is well known that, even when the strict model is not implementable, it is possible to conceive of it in an approximate sense. Unfortunately, the minimal resources necessary for this aim are still not completely understood. Here, we investigate quantitative statements of the theorem, improving exponentially previous bounds on the resources required by such a hypothetical machine. The proofs exploit a new connection between quantum channels and embeddings between Banach spaces which allows us to use classical tools from geometric Banach space theory in a clean and simple way.

Resource Quantification for the No-Programing Theorem

Aleksander M. Kubicki, et al.

Phys. Rev. Lett. 122, 080505 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.080505

在经典立方二聚化模型中柱状有序

相变中涌现的SO（5）对称性

立方晶格上的经典二聚化模型在柱状晶体和二聚化液体之间经历了非常规的相变，该相变与自旋1/2的反铁磁退禁闭量子临界点处于相同的普适类，但有着非常不同的微观物理和微观对称性。通过蒙特卡洛模拟，G. J. Sreejith等人证明该相变具有涌现的SO（5）对称性，相关的物理量可以刻画这两个相。虽然低温相有常规的序参量，在高温侧库伦液体的性质是单体的退禁闭，所以SO(5) 把根本不同类型的物理量联系起来。研究的系统线性尺寸达L=96, 他们发现这种对称性有极高的精度，且随尺寸增大不断提高。值得注意的是，SO（5）出现在立方二聚化模型这样具有简单的离散自由度的基础系统。此前为非紧致CP1场论提出的SO(5)对称性具有一般性，作者的结果为此提供了有力证据。作者为这些结果给出了一个解释，该解释基于对重整化流结构的一个假设，它考虑到SO（5）对称性最终可能只是近似对称性而非严格的。（刘玉海）

Emergent SO(5) Symmetry at the Columnar Ordering Transition in the Classical Cubic Dimer Model

G. J. Sreejith et al

Phys. Rev. Lett. 122, 080601 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.080601

用变分自回归网络求解统计力学

[编辑推荐语]深度神经网络可以高效地从玻尔兹曼分布中采样，并计算变分自由能，以及其他物理量，优于现有的平局场方法。

Dian Wu等人提出了一个解决有限大小系统统计力学的通用框架。该方法使用自回归神经网络扩展了著名的变分平均场方法，它支持直接采样和精确计算位形的归一化概率，可以一次完成计算变分自由能，测量诸如熵、磁化强度、关联等物理量，并生成无关联的样本。对网络的训练采用强化学习中可以无偏差的估计参数梯度的政策梯度算法。作者将该方法应用于几个经典系统，包括2D Ising模型，Hopfield模型，Sherrington-Kirkpatrick模型和逆Ising模型，以展示其优于现有变分平均场方法的优势。他们的方法为使用现代深度生成神经网络解决统计物理问题带来曙光。（刘玉海）

Solving Statistical Mechanics Using Variational Autoregressive Networks

Dian Wu, Lei Wang, Pan Zhang

Phys. Rev. Lett. 122, 080602 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.080602

预热化的典型性

Prethermalization refers to the remarkable relaxation behavior which an integrable many-body system in the presence of a weak integrability-breaking perturbation may exhibit: After initial transients have died out, it stays for a long time close to some nonthermal steady state, but on even much larger time scales, it ultimately switches over to the proper thermal equilibrium behavior. By extending Deutsch’s conceptual framework from Phys. Rev. A 43, 2046 (1991), we analytically predict that prethermalization is a typical feature for a very general class of such weakly perturbed systems.

Typicality of Prethermalization

Peter Reimann and L. Dabelow

Phys. Rev. Lett. 122, 080603 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.080603

非均匀量子相变的普适动力学过程:

抑制缺陷的形成

Kibble-Zurek机制预测：在穿过量子相变的非绝热动力学过程中，拓扑缺陷的形成被抑制，遵从猝火时间的一个普适幂律。非均匀系统中，系统局部可以达到临界点，因果关系将缺陷形成的有效系统尺寸减小到临界锋速低于声速的区域，这有利于绝热动力学过程。激发态密度的降低对猝火速率的依赖性更大，可以用作者在量子Ising链中说明的一个普适幂律来描述。（孙生红）

Universal Dynamics of Inhomogeneous Quantum Phase Transitions: Suppressing Defect Formation

F. J. Gómez-Ruiz and A. del Campo

Phys. Rev. Lett. 122, 080604 (2019)

https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.122.080604

引力与天体物理

导读：郭敏勇；责编：高思杰

皮米-稳定六角光学试验台：

用于验证LISA相位提取的线性度和精度

激光干涉仪空间天线（LISA）及其计量链必须满足严格的性能要求，以便能够对引力波进行基于空间的探测。这意味着性能验证方法的必要性。特别地，需要针对线性度和相位噪声贡献来探测由相位计实现的干涉相位的提取。为此本文章报告了一个六角形准四面体光学平台，可以执行三信号测试。文中展示了其低至皮米级别的稳定特性，以及其在LISA条件下用于基准相位计性能测量的用途。这些结果使其成为LISA计量验证设备核心的候选者。

Picometer-Stable Hexagonal Optical Bench to Verify LISA Phase Extraction Linearity and Precision

Thomas S. Schwarze, et al.

Phys. Rev. Lett. 122, 081104 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.081104

我们能否用引力波探测

视界尺度上的普朗克修正？

未来的探测器可以作为引力显微镜，利用引力波来探测合并黑洞的视界结构。但是，这种显微镜可以探测量子机制吗？作者研究了这个有趣的问题，发现 (i)距离分辨率的误差对勒夫数的误差呈指数敏感，(ii) 量子引力的不确定原理带来基本的分辨率极限 (iii) 小距离时空结构的结论依赖于对所考虑的（未知）紧密物体的性质的假设。

Can We Probe Planckian Corrections at the Horizon Scale with Gravitational Waves?

Andrea Addazi, et al.

Phys. Rev. Lett. 122, 081301 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.081301

永恒暴胀和精制的洼地猜想

作者将最近提出的“洼地”猜想应用于单标量场理论中的永恒暴胀。永恒的暴胀是准德西特宇宙无限自我再生的一个阶段，它被认为是宇宙暴胀的一般结果。Matsui 和Takahashi 以及 Dimopoulos 最初提出的德西特洼地猜想，通常与永恒暴胀不相容。然而，最近提出的“精制”沼泽地猜想对暴胀中的标量场势能施加了略微较弱的标准，与快子不稳定性的存在一致。在文章中，作者表明永恒暴胀与精制的德西特洼地猜想勉强一致。因此，如果精制的猜想是正确的，弦理论中基于景观的“多元宇宙”的存在与自洽的紫外实现并不矛盾，对弦理论中的模型构建具有重要影响。

Eternal Inflation and the Refined Swampland Conjecture

William H. Kinney

Phys. Rev. Lett. 122, 081302 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.081302

来自轴子的光爆炸

The nature of dark matter is one of the longest-standing puzzles inscience. Axions or axionlike particles are a key possibility and arise in mechanisms to solve the strong CP problem, but also in low-energy limits of string theory. Extensive experimental and observational efforts are actively looking for “axionic” imprints. Independent of their nature, abundance, and contribution to the dark matter problem, axions form dense clouds around spinning black holes, grown by superradiant mechanisms. It was recently suggested that once couplings to photons are considered, an exponential (quantum) stimulated emission of photons ensues at large enough axion number. Here we solve numerically the classical problem in different setups. We show that laserlike emission from clouds exists at the classical level, and we provide the first quantitative description of the problem.

Blasts of Light from Axions

Taishi Ikeda, R. Brito, V. Cardoso

Phys. Rev. Lett. 122, 081101 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.081101

高级LIGO O1数据的引力波背景天空图

We integrate the publicly available O1 LIGO time-domain data to obtain maximum-likelihood constraints on the gravitational-wave background (GWB) arising from stochastic, persistent signals. Our method produces sky maps of the strain intensity I as a function of direction on the sky at a reference frequency f0. The data are integrated assuming a set of fixed power-law spectra for the signal. The maps provide upper limits on the amplitude of the GWB density ΩGW(f0) and any anisotropy around the background. We find 95% confidence upper limits of ΩGW<4.8×10−7 at f0=50 Hz with similar constraints on a dipole modulation for the inspiral-dominated stochastic background case.

Gravitational-Wave Background Sky Maps from Advanced LIGO O1 Data

Arianna I. Renzini and C. Contaldi

Phys. Rev. Lett. 122, 081102 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.081102

利用引力波探测费米大天区望远镜

十亿电子伏过剩

If the gamma-ray excess towards the inner Galaxy (GCE) detected in Fermi-LAT data is due to millisecond pulsars (MSPs), one expects an associated gravitational wave (GW) signal, whose intensity exceeds the disk MSP population emission by an order of magnitude. We compute the expected GW counterpart of the bulge MSP population based on fits of the GCE, and estimate the sensitivity reach of current and future terrestrial GW detectors. The bounds on the average population ellipticity ϵ are competitive with the existing ones derived by LIGO/Virgo towards known MSPs. With a 10-yr data taking in current LIGO/Virgo configuration, one would detect a signal at the level ϵ≃10−7, while ϵ≃10−8 would be attainable with a similar data taking period with a third generation GW detector. This sensitivity should be sufficient for crucial diagnostics on the GCE interpretation in terms of MSPs.

Probing the Fermi-LAT GeV Excess with Gravitational Waves

Francesca Calore, et al.

Phys. Rev. Lett. 122, 081103 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.081103

基本粒子与场论

责编：晁伟、刘晓辉

复杂度作为探测量子淬火的

新方法：全局缩放和纯化

作者将最近发展的场论的复杂度的概念用于通过1+1维相变点的量子淬火。作者通过研究一系列模型后证实了复杂度可以用来探测纠缠熵所不敏感的一些特征。作者发现亚区域的复杂度是次可加的，作者评论了结果对全息理论可能的暗示。

Complexity as a Novel Probe of Quantum Quenches: Universal Scalings and Purifications

Hugo A. Camargo et. al.

Phys. Rev. Lett. 122, 081601 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.081601

用新物理解释

MiniBooNE超出的严格限制

[编辑推荐语]用新粒子来解释MiniBooNE超出被现有的实验数据严格限制。

MiniBooNE实验最近报道了与在短距ν_μ束流中出现ν_e相融洽的类电子事例4.5σ的反常超出。由于没有观测到惰性中微子相关震荡中对应的ν_μ的减少，因此有很强的动机需要其他新机制去解释该反常。作者考虑了观测到的类电子信号可能是来自于MiniBooNE靶中产生的粒子，而非新的中微子源或者任何中微子震荡。作者发现在完整MiniBooNE数据中的类电子事例的能量和角动量分布，包括中微子、反中微子等等严格限制了并在某些情况排除了解释正反中微子超出的新物理模型。更确切地说，靶中产生的粒子或者衰变或者在探测器中发生弹性散射的情况与数据强烈不吻合的。作者基于一般动力学的讨论，将存在的MiniBooNE结果和解释延拓到限制之前未曾考虑过的新物理迹象，并强调了在MiniBooNE beam dump搜索对于进一步限制解释超出的模型的能力。

Severe Constraints on New Physics Explanations of the MiniBooNE Excess

Johnathon R. Jordan et. al.

Phys. Rev. Lett. 122, 081801 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.081801

观测到了D⁰ → K⁻ π⁺e⁺e⁻衰变

本文报道了BABAR探测器观测到了稀有粲夸克衰变D⁰ → K⁻ π⁺e⁺e⁻。实验发现该衰变在正负电子对的不变质量范围为0.675 < m(e⁺e⁻) < 0.875 GeV的分支比为B(D⁰ → K⁻ π⁺e⁺e⁻)=(4.0±0.5±0.2±0.1)×10⁻⁶,其中第一项为统计误差，第二项为系统误差而第三项为使用D⁰→K−π⁺π⁺π⁻作为归一化的误差。在一系列长程效应较小的m(e⁺e⁻)质量区间，实验在90%的置信区间确认该分支比的上限为B(D⁰ → K⁻ π⁺e⁺e⁻)<3.1×10⁻⁶。

Observation of the Decay D⁰ → K⁻ π⁺e⁺e⁻

J. P. Lees et al. (BaBar Collaboration)

Phys. Rev. Lett. 122, 081802 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.081802

普朗克尺度轻子数破坏产生的中微子质量

作者考虑了标注模型的右手中微子拓展并论证在可靠的假设下，0.1eV数量级的中微子质量很自然的能通过在普朗克能标破坏轻子数来产生。这种破坏有可能是通过引力效应，而无需引入新的质量标度。

Neutrino Masses from Planck-Scale Lepton Number Breaking

Alejandro Ibarra, et.al.

Phys. Rev. Lett. 122, 081803 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.081803

在√s = 13 TeV质子质子对撞

搜索窄Hγ共振

使用LHC的CMS探测器在质子质子对撞能量为13TeV中搜索了索窄Hγ共振。实验选用的事例含有一个光子和高速boost的希格斯粒子强子衰变后产生的大半径的喷注。实验通过分析光子与喷注的不变质量谱来搜索窄共振。实验结果与标准模一致,并在质量区间为720-3250GeV给出了迄今为止最严格的限制。

Search for Narrow H γ Resonances in Proton-Proton Collisions at √ s = 13 TeV

M. Sirunyan et al. (CMS Collaboration)

Phys. Rev. Lett. 122, 081804 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.081804

在Belle上首次测量⁰_c强子的绝对分支

本文第一次给出⁰_c衰变到⁻ π⁺ , Λ K⁻π⁺ , and p K⁻ K⁻ π⁺的绝对分支为B (⁰_c→ ⁻ π⁺ ) = ( 1.80 ± 0.50 ± 0.14 ) % , B (⁰_c → Λ K⁻π⁺ ) = ( 1.17 ± 0.37 ± 0.09 ) % , and B (⁰_c →p K⁻ K⁻ π⁺ ) = ( 0.58 ± 0.23 ± 0.05 ) % ,其中第一项都是统计误差，第二项皆为系统误差。B (⁰_c→ ⁻ π⁺ ) 可以与⁰_c相对⁰_c→ ⁻ π⁺分支结合给出⁰_c的绝对分支。

First Measurements of Absolute Branching Fractions of the ⁰_c Baryon at Belle

Y. B. Li et al. (Belle Collaboration)

Phys. Rev. Lett. 122, 082001 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.082001

QCD两圈平面五胶子散射振幅的解析形式

作者展示了外腿胶子的全部螺旋度独立的，QCD两圈平面五胶子散射振幅的解析表达式。这包括首个与计算强子对撞机上次次领头阶QCD修正相关的两圈5点振幅的解析结果。作者通过重构数值计算的结果来获得解析表达式。作者通过使用振幅的物理以及解析性质，采用了所谓的五边形函数作为最小基，来简化了计算的复杂度。

Analytic Form of Planar Two-Loop Five-Gluon Scattering Amplitudes in QCD

AS. Abreu et al.

Phys. Rev. Lett. 122, 082002 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.082002

第一次测量长寿的π⁺ π⁻原子的寿命

本文报道了第一次在CERN的PS加速器上的DIRAC实验首次观测到了长寿的类氢π⁺ π⁻原子，并测得其2p态的寿命为τ_{2 p} = ( 0.4 5 ^{+ 1.08}₋_0.30|_tot ) × 10⁻¹¹秒，比之前测得的基态寿命τ = ( 3.1 5 ^{+ 0.28}₋_0.26 |_tot ) × 1 0⁻¹⁵ s大了3个数量级。测得的寿命与QED 2p态的预言τ^QED_2p = 1.17 × 1 0⁻¹¹秒无矛盾。进一步研究该原子允许我们去测量p与s原子态之间的能极差，并来区分同位旋标量和同位旋张量的π π 散射长度以检验QCD 的预言。

First Measurement of a Long-Lived π⁺ π⁻ Atom Lifetime

B. Adeva et al.

Phys. Rev. Lett. 122, 082003 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.082003

原子核物理

责编：耿立升；导读：王亚坤

p介子价夸克的内禀横向运动

基于Bethe-Salpeter方程对p介子的描述，采用超越求解Dyson-Schwinger方程所经常采用的彩虹-阶梯截断近似的方法，Chao Shi等人确定了p介子l_z=0和|l_z|=1领头阶Fock态的光前波函数（LFWFs--y_lz(x, k_T²)。利用这些LFWFs，直接得到了领头阶-扭曲时间反演偶横向动量依赖的p介子部分子分布函数（TMD）。在典型的强子尺度上，由动力学手征对称性破缺驱动的LFWFs的一个关键特征是，它们是光锥动量分数x的函数。LFWFs具有非平凡的(x, k_T²)依赖性，并且通常不能分解成每个变量单独的函数。对于k_T²≲1GeV²，LFWFs的k_T²依赖性可以用高斯函数很好地描述。然而，对于k_T²≳10 GeV²，这些LFWFs表现为为y₀µ x(1-x)/ k_T²和y₁µ x(1-x)/ k_T⁴，因此展现出微扰QCD所预测的幂率行为。p介子的TMD自然地从LFWFs继承了很多特性。他们利用b^*和z方法研究了其结果的TMD演化，从而可以与Drell-Yan数据进行定量的比较。

Intrinsic Transverse Motion of the Pion’s Valence Quarks

Chao Shi and Ian C. loët,

Phys. Rev. Lett. 122, 082301 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.082301

原子、分子与光学

导读：宋新秀；责编：张文凯

单个超冷两体碰撞引起的密度振荡

[编辑推荐语]文中新的实验装置允许研究人员观察两个超冷原子之间的碰撞，同时还可以调整它们的撞击力。

单粒子动量的获得为研究几个相互作用粒子动力学提供了新方法。通过结合理论和实验方法进行研究，作者观察并分析了有限数量的超冷两体碰撞对相对粒子密度和单粒子密度的影响，其方法是将两个超冷原子用一个初始窄波包淬火到一个倒置纵横比的宽陷阱中。本文还通过无参数零范围理论再现了实验观测到的相对密度的空间振荡，并根据交叉维度通量对其进行解释。作者从理论上研究了长时间的动力学，发现系统没有达到其热力学极限。该实验设置可被视为一种高级粒子对撞机，它允许人们观察碰撞过程本身。

Density Oscillations Induced by Individual Ultracold Two-Body Collisions

Q. Guan, et al.

Phys. Rev. Lett. 122, 083401 (2019）

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.083401

互动量子系统中的通用霍尔响应

[编辑推荐语]文中扩展的量子相位区域得以确定，其中霍尔响应变得独立于相互作用强度和粒子统计，这一结果对于相互作用的玻色子和费米子都是正确的。

本文从理论上研究了相互作用的M-leg阶梯系统的霍尔效应，比较了弱磁场极限下零温霍尔响应的不同测量和性质。并关注于SU（M）对称相互作用玻色子和费米子，这与典型的合成尺寸量子气体实验相关，从而作者确定了一种广泛的体系，对于大量的量子相位，其中霍尔非平衡Δ_H是通用的并且对应于经典的霍尔电阻率R_H= -1 / n。从这个高对称点出发，作者观察到了相互作用驱动的现象，比如，霍尔响应的信号反转和发散。

Universal Hall Response in Interacting Quantum Systems

Sebastian Greschner, et al.

Phys. Rev. Lett. 122, 083402 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.083402

圆偏振光光解离臭氧产生的光致碎片

仅依赖电子振动相互作用即可实现对齐

We present a direct determination of photofragment alignment produced by circularly polarized light in photolysis of a planar polyatomic molecule. This alignment arises via a new mechanism involving coherent excitation of two mutually perpendicular in-plane transition dipolemoment components. The alignment is described by a new anisotropy parameterγ′2 that wasisolated by a unique laser polarization geometry. The determination of the parameterγ′ 2 was realized in ozone photolysis at 266 nm where dc slice images of O(¹D₂) atomic fragments were acquired. A model developed for interpretation of the photolysis mechanism shows that it can exist only in case of failure of the Born-Oppenheimer approximation when electronic and vibrational (vibronic) interactions have to be taken into account. This finding suggests that determination of the alignment parameterγ′ 2 can be used as a key for direct insight into vibronic interactions in photolysis of polyatomic molecules. The results obtained for ozone photolysis via the Hartley band showed significantγ′ 2 alignment but little recoil speed dependence, consistent with the notion that, as opposedto the situation for derivative coupling, under our experimental conditions, the vibronic contributions to the nonadiabatic dynamics are not dependent on recoil speed.

Photodissociation by Circularly Polarized Light Yields Photofragment Alignment in Ozone Arising Solely from Vibronic Interactions

Chaya Weeraratna, et al.

Phys. Rev. Lett. 122, 083403 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.083403

通过多空间模式压缩实现光束聚焦

并降低少量光子能级宽度的量子不确定性

本文首次证明了，在四波混频过程中可以在少量光子层面上实现激光束聚焦，同时减小能级宽度上的量子不确定性。量子不确定性的降低直接来自于对局部强度波动的有力抑制。这种同时实现聚焦和降低宽度不确定性的惊人效果，是通过多空间模式压缩实现的，并且不可能通过任何经典光学方法或单空间模式压缩来实现。本文研究结果为量子增强成像和计量学开辟了广阔的前景；例如，由于多空间模式压缩过程中光束聚焦和无噪声放大，使得在可行的实验参数范围内，对非常小的光束位移测量的限制得到了提高。

Beam Focusing and Reduction of Quantum Uncertainty in Width at the Few-Photon Level via Multi-Spatial-Mode Squeezing

Lida Zhang, et al.

Phys. Rev. Lett. 122, 083601 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.083601

双折射发射腔系统中的偏振振荡

We present the effects of resonator birefringenceon the cavity-enhanced interfacing of quantum states of light and matter, including the first observation of single photons with a time-dependent polarization state that evolves within their coherence time. A theoretical model is introduced and experimentally verified by the modified polarization of temporally long single photons emitted from a ⁸⁷Rb atom coupled to a high-finesse optical cavity by a vacuum-stimulated Raman adiabatic passageprocess. Further theoretical investigation shows how a change in cavity birefringence can both impact the atom-cavity coupling and engender starkly different polarization behavior in the emitted photons. With polarization a key resource for encoding quantum states of light and modern micron-scale cavities particularly prone to birefringence, the consideration of these effects is vital to the faithful realization of efficient and coherent emitter-photon interfaces for distributed quantum networking and communications.

Polarization Oscillations in Birefringent Emitter-Cavity Systems

Thomas D. Barrett, et al.

Phys. Rev. Lett. 122, 083602 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.083602

散粒噪声极限下的纳米机械检测

和电子束辐射压力的反作用力

Detecting nanomechanical motion has become animportant challenge in science and technology. Recently, electromechanical coupling to focused electron beams has emerged as a promising method adapted to ultralow scale systems. However the fundamental measurement processes associated with such complex interaction remain to be explored. Here we reporta highly sensitive detection of the Brownian motion of μm-long semiconductor nanowires (InAs). The measurement imprecision is found to be set by the shot noise of the secondary electrons generated along the electromechanical interaction. By carefully analyzing the nanoelectromechanical dynamics, we demonstrate the existence of a radial backaction process that we identify as originating from the momentum exchange between the electron beam and the nanomechanical device, which is also known asradiation pressure.

Shot-Noise-Limited Nanomechanical Detection and Radiation Pressure Backaction from an Electron Beam

S. Pairis, et al.

Phys. Rev. Lett. 122, 083603 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.083603

非线性动力学与流体力学

责编：兰岳恒

结构化表面光学压力增强的证明

电磁波与凝聚态物质之间的相互作用和由此得到的力是物理科学的基础。平面上的最大压力可理解成背景速度归一化入射波功率密度的两倍。Li-FanYang等人首次证明了这个压力可以通过构造表面而数倍超出。实验结果显示激光束照射氮化硅上纳米金膜结构的直接光力偏转明显超过平面上的实验结果。这种压力增强可以认为是与在膜中实现的不对称光学腔阵列相关联。可能的增强取决于材料特性和结构化材料的几何参数。用纳米结构材料控制和增加光学压力应该在物理科学上有重要应用。（胡婧）

Demonstration of Enhanced Optical Pressure on a Structured Surface

Li-Fan Yang, et al.

Phys. Rev. Lett. 122. 083901 (2019).

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.083901

二维拓扑极化子激光器

We provide proof-of-principle illustration of lasing in a two-dimensional polariton topological insulator. Topological edgestates may arise in a structured polariton microcavity under the combined action of spinorbit coupling and Zeeman splitting in the magnetic field. Their properties and lifetime are strongly affected by gain. Thus, gain concentrated along the edge of the insulator can counteract intrinsic losses in such aselective way that the topologically protected edge states become amplified, while bulk modes remain damped. When gain is compensated by nonlinear absorption the metastable nonlinear edge states are formed. Taking a triangular structure instead of an infinite edge we observed persistent topological currents accompanied by the time-periodic oscillations of the polariton density.

Two-Dimensional Topological Polariton Laser

Yaroslav V. Kartashov, D. Skryabin

Phys. Rev. Lett. 122.083902 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.083902

平衡态弛豫的动力学冻结

We provide evidence of an extremely slow thermalization occurring in the discrete nonlinear Schrödinger model. Atvariance with many similar processes encountered in statistical mechanics—typically ascribed to the presence of (free) energy barriers—here the slowness has a purely dynamical origin: it is due to the presence of an adiabatic invariant, which freezes the dynamics of a tall breather. Consequently, relaxation proceeds via rare events, where energy is suddenly released towards the background. We conjecture that this exponentially slow relaxation is a key ingredient contributing to the nonergodic behavior recently observed in the negative-temperature region of the discrete nonlinear Schrödinger equation.

Dynamical Freezing of Relaxation to Equilibrium

Stefano Iubini, et al.

Phys. Rev. Lett. 122. 084102 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.084102

声波携带的重力质量

Angelo Esposito等人表明，声波不传输质量这一普遍被接受的命题仅在线性近似下成立。使用有效场理论，作者确认了Nicolis和Penco [Phys. Rev. B 97,134516(2018)]对零温超流体的结果，并将其扩展到固体和普通液体。事实上，Angelo Esposito等人表明声波确实带有质量，就是重力质量。这意味着声波不仅受到重力的影响，而且还产生微小的引力场，这是迄今为止尚未被理解的方面。该研究结果也适用于非相对论介质，或具有趣实验意义。（胡婧）

Gravitational Mass Carried by Sound Waves

A. Esposito, R. Krichevsky, A. Nicolis

Phys. Rev. Lett. 122. 084501 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.084501

具有合成频率和轨道角动量维度的

单腔光子规范势

Yuan等人探索了一个支持合成二维空间的简并光学单腔，包括光的频率和轨道角动量（OAM）两个坐标轴。作者在这个合成空间内创建了有效规范势，并显示系统在频率维度的边界沿着OAM轴表现出拓扑保护的单向边缘态。在这个合成空间中，还展示了光子频率和OAM之间纠缠的鲁棒生成和操纵。这篇文章表明，在“零维”空间结构中可以实现涉及多个光自由度的高维合成空间，指向探索拓扑光子学的独特平台，并实现在光通信和量子信息处理方面的应用。（胡婧）

Photonic Gauge Potential in One Cavity with Synthetic Frequency and Orbital Angular Momentum Dimensions

Luqi Yuan, et al.

Phys. Rev. Lett. 122. 083903 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.083903

呼吸波分子

Gang Xu等人在一维非线性收聚Schrödinger方程的框架下，给出了一对共传播呼吸子之间非线性相互作用的理论描述和实验观察。作为一般情况，Gang Xu等人表明，所产生的呼吸子束缚状态表现出类分子行为的准周期振荡（即内部相干相互作用和脉动），而对于可公度条件，分子振荡表现出精确的周期性。Gang Xu等人的理论模型通过有形类分子呼吸模的实验观察得到证实，光波在几乎保守的光纤系统中传播。Gang Xu等人的工作揭示了局部波结构的存在以及超出多孤子复合体之外的复现动力学。（胡婧）

Breather Wave Molecules

Gang Xu, et al.

Phys. Rev. Lett. 122. 084101 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.084101

等离子体与束物理

责编：陈少永

激光加热毛细管放电波导中的

拍瓦激光引导与8GeV电子束加速

Gonsalves等人利用激光逆轫致辐射加热提高毛细管放电波导的聚焦强度，实现了在15个衍射长度上引导峰值功率为0.85PW的强激光脉冲。这使得电子束的准单能峰值可达到7.8 GeV，比之前的能量提高了一倍。该峰值为7.8 GeV时电荷为5pC，峰值为6 GeV时电荷为62pC，典型的束发散为0.2 mrad。（秦晨晨，牟茂淋）

Petawatt Laser Guiding and Electron Beam Acceleration to 8 GeV in a Laser-Heated Capillary Discharge Waveguide

A. J. Gonsalves, et al

Phys. Rev. Lett. 122, 084801 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.084801

最简单液态金属中费米简并的击穿

Zaghoo等人在最简单的元素（金属氘）中观察到电子简并的击穿和经典统计的出现。作者们研究了动态压缩液体氘在其费米温度T_F下的光学反射率、激波速度和温度。在绝缘体-金属过渡区上方，光学反射率显示出独特的与温度无关的电阻率饱和，这是由莫特最小金属极限（Mott’s minimum metallic limit）决定的，也与先前的实验结果一致。然而，在T>0.4T_F时，金属氘的反射率呈与温度相关的斜率开始上升，这与费米表面的击穿一致。实验推断的该区域的电子-离子碰撞时间表现出经典Landau-Spitzer等离子体预期的特征温度依赖性。作者关于电子简并态的观测，将简并态的研究扩展到新的费米子种类——电子费米系统，并在与稠密天体和点火物理相关的大的温度范围内为库仑系统的量子统计模型提供了一个宝贵的基准。（阳青程，牟茂淋）

Breakdown of Fermi Degeneracy in the Simplest Liquid Metal

M. Zaghoo, et al

Phys. Rev. Lett. 122, 085001 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.085001

凝聚态物理：结构

责编：马天星

禁闭条件下³He超流相空间调制的证据

[编辑推荐语]当氦-3超流体被禁闭在微米厚的单元中并暴露于磁场时，出现了令人惊奇的二维图像。

在禁闭于板型几何结构的超流体³He-B中，一般而言，不同序参量取向的区域之间的畴壁在能量上是稳定的。Levitin等人提出了空间调制的流体条纹相的形成。作者将³He限制在1.1 μm高的微流控腔，并在低压时冷却至B态，由此预测出条纹相。作者用NMR测量了表面诱导的序参量畸变，其与畴的形成关系敏感。该结果排除了条纹相的说法，但与2D调制的超流体序一致。（马驰）

Evidence for a Spatially Modulated Superfluid Phase of ³Heunder Confinement

Lev V. Levitin, et al

Phys. Rev. Lett. 122, 085301 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.085301

准脆性压缩破坏中

集体损伤增长控制缺陷方向

摩尔-库仑准则被广泛地用于地球科学和固体力学，以将破坏时的应力状态与所得缺陷的观察方向联系起来。这种关系基于假设：沿着库仑应力最大值的平面发生宏观破坏。本文通过在具有弹性损伤的材料上模拟受压试验来评估该假设，该材料遵循介观尺度下的摩尔-库仑准则。Dansereau等人发现摩尔-库仑准则没有给出宏观缺陷方向。相反，对于弱无序材料，它对应于最不稳定的损伤增长模式，作者通过对其均匀受损态的线性稳定性分析来确定这种模式。研究表明，压缩破坏是由材料中受损簇的聚结产生，并且通过在连续尺度上引入描述这些簇之间相互作用的弹性内核，适当地描述这个集体过程。（马驰）

Collective Damage Growth Controls Fault Orientation in Quasibrittle Compressive Failure

Véronique Dansereau, et al

Phys. Rev. Lett. 122, 085501 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.085501

凝聚态物理：电子性质

责编：袁喆，马锋杰，沈卡

近邻过渡金属二硫化合物中

可调节的自旋极化边缘电流

在基于过渡金属二硫化物的谷自旋电子学应用中，最基本的是要解除体系中谷的简并度。目前，一般都是通过施加外磁场来退简并。由于在该过程中需要的外磁场比较大，为技术上的实现增加了难度。近邻效应可以使得非磁材料诱导出可观的磁性，有望作为更实用的替代方法。基于此，本文中作者以沉积在铁磁性氧化铕(europium oxide, EuO)表面的锯齿状二碲化钼(molybdenum ditelluride,MoTe₂)带为例，研究了过渡金属二硫化物表面的近邻效应。结果显示，EuO在界面处诱导出可观的磁交换场和Rashba场。进一步分析表明，当费米能级处于带隙内时，纳米带中的电子模式可以沿边缘局域化，此时的纳米带可充当具有可调自旋极化电流的一维导电通道。该结果为进一步研究复杂一维系统中的近邻效应提供了一个平台。（刘钱）

Tunable Spin-Polarized Edge Currents in Proximitized Transition Metal Dichalcogenides.

Natalia Cortés et al.

Phys. Rev. Lett. 122, 086401 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.086401

转角同质双层过渡金属

二硫化物中的拓扑绝缘体

Wu等人发现转角同质双层结构中的波纹带(moiré bands)可以是拓扑非平庸的，并通过研究转角双层过渡金属二硫化物MoTe₂_，在±K谷处的价带态展示了这种趋势。由于单层MoTe₂的价带最高点存在很强的自旋轨道劈裂，转角双层MoTe₂在+K（-K）谷处的低能价态可以由含有波纹周期的层赝自旋磁场Δ(r)的双带模型来描述。作者发现Δ(r)在实空间有着拓扑非平庸斯格明子晶格结构，并且最顶部的波纹价带提供了一种实现Kane-Mele量子自旋霍尔模型——二维时间反演不变拓扑绝缘体 ——的平台。因为能带在小转角情况下变窄，当平均每个波纹单元有整数个电子时会出现一系列丰富的对称性破缺的绝缘态。（李松）

Topological Insulators in Twisted Transition Metal Dichalcogenide Homobilayers

Fengcheng Wu et al.

Phys. Rev. Lett. 122, 086402 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.086402

浓稠液态铁中的顺磁-抗磁转变

及其对电子输运性质的影响

使用Kubo-Greenwood形式，Korell等人使用基于自旋极化的密度泛函理论,在一个广泛的压力和温度范围内模拟计算了液态铁的电导率σ和热导率λ。他们的计算表明，常规压力下，液体铁中顺磁态直到高温下都是稳定的，并且对σ和λ的实验测量与自旋简并模拟间超过30％的差异在选取较小的由自旋极化模拟得到的数值后降低到10％以内。沿着3700 K等温线，他们探索了磁涨落相对于高密度的持久性，并且液体在超过20-50 GPa后变为反磁性，这表明存在连续的顺磁 - 抗磁转变。这种转变对液态铁的物理性质产生了重大影响，尤其是在σ和λ上，并且可能与水星和火星中的发电机过程高度相关。（方子明）

Paramagnetic-to-Diamagnetic Transition in Dense Liquid Iron and Its Influence on Electronic Transport Properties

Jean-Alexander Korell et al.

Phys. Rev. Lett. 122, 086601 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.086601

金表面芳香族硫醇化合物与脂肪族硫醇

化合物中选择性纳米力学的对比

S-Au纳米界面在科学、技术以及现代医学的许多领域中都起着关键作用。本文中，作者从计算上研究金表面脂肪族硫醇化合物的力学稳定性和热稳定性与芳香族硫醇化合物的对比。结果显示，脂肪族硫醇化合物具有较高的热解吸能和较低的机械断裂力。通过对沿着剥离路径的电子结构进行分析，表明不同的机械化学分离机制会影响纳米结中S-Au键的电子性质，进而影响体系的热学和力学性质。作者指出该类纳米接触会根据硫醇化合物的性质产生不同的局部纳米结构，对指导S-Au纳米触点的合理设计具有重要意义。（刘钱）

Selective Nanomechanics of Aromatic versus Aliphatic Thiolates on Gold Surfaces.

M. Michoff et al.

Phys. Rev. Lett. 122, 086801 (2019).

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.086801

在平行磁场内的碳纳米管中调节

电子波函数

[编辑推荐语]在碳纳米管量子点中的晶格结构、拓扑结构以及受限的共同作用下，使得磁场可以影响电子的波函数。

当一个带电粒子在有限的电磁势中运动时，它的波函数可得到一个相位，且该相位的大小由电子运动所围成的封闭区域的磁通量决定。由于该磁通量只依赖于垂直于该表面的磁场分量，所以该电磁势通常只在横向上引起电子波函数的变化。本文中，作者证明，在同时具有柱状拓扑结构和双向六角晶格的碳纳米管量子点中，沿纳米管轴向的磁场也会影响电子态的纵向特性。实验结果表明，当磁场增大到17T时，波函数可以从两端有节点的半波谐振腔形状调节到一端有反节点的四分之一波谐振腔形状。作者进一步指出，波函数的改变会导致该类体系中的电导对磁场有明显的依赖性。（刘钱）

Shaping Electron Wave Functions in a Carbon Nanotube with a Parallel Magnetic Field

M. Margańska et al.

Phys. Rev. Lett. 122, 086802 (2019).

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.086802

零磁场分数量子态

Since the discovery of the fractional quantum Halleffect in 1982 there has been considerable theoretical discussion on the possibility of fractional quantization of conductance in the absence of Landau levels formed by a quantizing magnetic field. Although various situations have been theoretically envisaged, particularly lattice models in which band flattening resembles Landau levels, the predicted fractions have never been observed. In this Letter, we show that odd and even denominator fractions can be observed, and manipulated, in the absence of a quantizing magnetic field, when a low-density electron system in a GaAs based one-dimensional quantum wireis allowed to relax in the second dimension. It is suggested that such a relaxation results in formation of a zigzag array of electrons with ring paths which establish a cyclic current and a resultant lowering of energy. The behavior has been observed for both symmetric and asymmetric confinement but increasing the asymmetry of the confinement potential, to result in a flattening of confinement, enhances the appearance of new fractional states. We find that an in-plane magnetic field induces new even denominator fractions possibly indicative of electron pairing. The new quantum states described here have implications both for the physics of low dimensional electron systems and also for quantum technologies. This work will enable further development of structures which are designed to electrostatically manipulate the electrons for the formation of particular configurations. In turn, this could result in a designer tailoring of fractional states to amplify particular properties of importance in future quantum computation.

Zero-Magnetic Field Fractional Quantum States

S. Kumar et al.

Phys. Rev. Lett. 122, 086803 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.086803

四极相中的螺旋拓扑边缘态

拓扑电四极是最近提出的概念，其将晶体的电极化理论扩展到更高阶。这种四极相位允许局域在边缘和拐角上的拓扑状态。在这项工作中，Liu等人表明，通过利用与点群对称性相关的赝自旋度, 拓扑螺旋边缘态和赝自旋极化角态在蜂窝晶格的四极相中出现。此外，他们认为在（赝）自旋四极相中出现螺旋边缘状态的一般条件是存在镜像或时间反演对称性。他们的结果提供了一种在没有自旋-轨道耦合的情况下产生拓扑螺旋边缘态的方法。（方子明）

Helical Topological Edge States in a Quadrupole Phase

Feng Liu et al.

Phys. Rev. Lett. 122, 086804 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.086804

拓扑超导体中量子磁杂质的近藤特征

Wang等人使用数值重整化群方法研究了二维拓扑超导体（TSCs）中量子磁杂质的近藤物理，其或者是本征的或者是在体拓扑绝缘体表面上诱导出的。他们表明，尽管都有p + ip配对对称性，本征和非本征拓扑超导体具有不同的物理过程，表现出不同的近藤特征。非本征拓扑超导体具有一种不寻常的屏蔽机制，涉及电子和轨道自由度，从而产生丰富而显著的近藤现象，特别是超导能隙中非常有趣的赝自旋近藤单态以及空间各向异性自旋关联。与之完全不同的是，本征拓扑超导体中能够存在稳定的杂质自旋双重基态和各向同性自旋关联。这些发现推进了对拓扑超导体中新奇近藤现象的基础研究，并给出了实验检测和区分的建议途径。（方子明）

Kondo Signatures of a Quantum Magnetic Impurity in Topological Superconductors

Rui Wang et al.

Phys. Rev. Lett. 122, 087001 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.087001

半导体KFe_0.8Ag_1.2Te₂中

相互交错的磁性和向列相序

Superconductivity in the iron pnictides emerges from metallic parent compounds exhibiting intertwined stripe-type magnetic order and nematic order, with itinerant electrons suggested to be essential for both. Here we use x-ray and neutron scattering to show that a similar intertwined state is realized in semiconducting KFe_0.8Ag_1.2Te₂(K₅Fe₄Ag₆Te₁₀) without itinerant electrons. We find that Fe atoms in KFe_0.8Ag_1.2Te₂form isolated 2×2 blocks, separated by nonmagnetic Ag atoms. Long-rangemagnetic order sets in below TN≈35K, with magnetic moments within the 2×2 Fe blocksordering into the stripe-type configuration. A nematic order accompanies the magnetic transition, manifest as a structural distortion that breaks the fourfold rotational symmetry of the lattice. The nematic orders in KFe_0.8Ag_1.2Te₂and iron pnictide parent compounds are similar in magnitude and in how they relate to the magnetic order, indicating a common origin. Since KFe_0.8Ag_1.2Te₂is a semiconductor without itinerant electrons, this indicates that local-moment magnetic interactions are integral to its magnetic and nematic orders, and such interactions may play a key role in iron-based superconductivity.

Intertwined Magnetic and Nematic Orders in Semiconducting KFe_0.8Ag_1.2Te₂.

Y. Song et al.

Phys. Rev. Lett. 122, 087201 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.087201

纳米腔和p壳层激子间

超越偶极近似的增强相互作用

激子和光子间的耦合强度对实现量子光子网络意义重大。但目前对微腔和量子点间相互作用的研究都集中于s壳层激子，耦合强度较弱。本文中Qian等人证明，通过原位波函数操控可以极大地增强微腔和p壳层激子间的相互作用。相比于s壳层激子，p壳层激子波函数的范围更广，且具有超越偶极近似的非局域相互作用。随着波函数压缩，相互作用从非局域状态过渡到局域状态，耦合强度就会增强。作者采用这种方式获得了高达210 μeV的耦合强度。这说明p壳层激子在相干信息交换中可能具有可观的应用前景。此外，作者还提出了一个理论模型来定量解释耦合强度的变化，阐明了激子和光子之间偶极近似之上的相互纠缠。（李松）

Enhanced Strong Interaction between Nanocavities and p-shell Excitons Beyond the Dipole Approximation

Chenjiang Qian et al.

Phys. Rev. Lett. 122, 087401 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.087401

软物质与交叉科学

责编：徐留芳

二维泡沫中的聚并：

依赖于薄膜面积的纯粹统计过程

虽然聚并最终是泡沫中最剧烈的失稳过程，但其基本过程仍不清楚。为了更好地理解它们，Forel等人在受控的毛细压力下跟踪二维泡沫中的各个聚并事件。他们得到的统计信息揭示了不同参数的影响，这些参数以前曾被用来解释聚并。他们的主要结论是，聚并概率与分离两个气泡的薄膜面积成正比，说明聚并主要是随机的。（王赫）

Coalescence in Two-Dimensional Foams: A Purely Statistical Process Dependent on Film Area

Emilie Forel, et al.

Phys. Rev. Lett. 122, 088002 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.088002

通过沉淀形成超稳玻璃的建模研究

Douglass等人使用研究非晶态材料溶解动力学的晶格模型，来模拟玻璃态形成时溶质从溶液中析出沉淀的过程。该模型主要研究了玻璃态物质与塑化剂接触时在玻璃表面上的动力学增强行为。他们证明了沉淀法生产的玻璃比长时间退火产生的大块玻璃要稳定得多，并且这些超稳非晶态沉淀物的能量主要是由残留溶剂而不是由玻璃内部涨落造成的高能构型决定。（何寒梅）

Ian Douglass, et al.

Phys. Rev. Lett. 122, 088003 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.088003

极性液晶中剪切诱导的一级相变

极性液晶的流体力学理论被广泛应用于描述生物活性流体和惰性分子材料。在惰性或弱活性的极性流体中，根据剪切取向参数的不同，有外部剪切作用时，极性序参量p要么倾向于以固定的(Leslie)角流动，要么是连续旋转。Markovich等人研究了一个附加的“剪切伸长参数”的作用，这个参数在最近的文献中被忽略并导致序参量|p|在流动下发生变化。他们的结果表明，这种效应能引起剪切诱导的从各向同性到极性的一级相变，并能显著改变活性和惰性的极性流体的流变特性。（王赫）

Tomer Markovich, et al.

Phys. Rev. Lett. 122, 088004 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.088004

细胞内钙峰电位的确定性极限

在非兴奋性细胞中，细胞内整体Ca^{2 +}浓度峰值的出现来自通过扩散耦合的Ca^{2 +}通道簇的集体动力学。目前的建模方法已将这些系统的随机描述与确定性模型对立起来，但目前所存在的矛盾是两者均与实验数据相吻合。结合完全随机模拟和平均场分析，Voorsluijs等人证明了这两种方法是一致的。他们的完全随机模型生成的尖峰序列，可以看作是由确定源所引起的噪声微扰振荡，这显示出了与实验数据一致的统计特性。这些潜在的确定性振荡源于现象学的尖峰成核机制。（何寒梅）

Deterministic Limit of Intracellular Calcium Spikes

V. Voorsluijs, et al.

Phys. Rev. Lett. 122, 088101 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.088101

纳米颗粒与病毒吞噬过程的随机动力学

纳米颗粒或病毒的细胞摄取要求附着能的增加量大于质膜弯曲消耗的能量。众所周知，这会导致最小的颗粒吞噬粒径。通过使用简单的确定性理论对该过程进行分析，Felix等人发现，在法向和切向上圆柱形颗粒应比具有相同半径和体积的球形颗粒具有更快的吞噬过程。随后他们讨论了加上随机效应的吞噬过程，由于系统尺寸较小，这些随机效应应该是相关的，结果表明，因为平均首次通过时间受益于由球形几何引起的乘性噪声，球形颗粒可以更快地被吞噬。他们得出结论，随机效应具有强烈的几何依赖性，并且在粘附力驱动下球形颗粒的更易于被吞噬。（何寒梅）

Stochastic Dynamics of Nanoparticle and Virus Uptake

Felix Frey, et al.

Phys. Rev. Lett. 122, 088102 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.088102

肌肉力学中无序现象的功能性

Asalient feature of skeletal muscles is their ability to take up an applied slack in a microsecond timescale. Behind this fast adaptation is a collective folding in a bundle of elastically interacting bistable elements. Since this interaction has a long-range character, the behavior of the system in force and length controlled ensembles is different; in particular, it can have two distinct order-disorder–type critical points. We show that the account of the disregistry between myosin and actin filaments places the elementary force-producing units of skeletal muscles close to both such critical points. The ensuing “double criticality” contributes to the system’s ability to perform robustly and suggests that the disregistry is functional.

Functionality of Disorder in Muscle Mechanics

H. da Rocha and L. Truskinovsky

Phys. Rev. Lett. 122, 088103 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.088103

组织蔓延中的活性指进失稳

During the spreading of epithelial tissues, the advancing tissue front often develops fingerlike protrusions. Their resemblance to traditional viscous fingering patterns in driven fluids suggests that epithelial fingers could arise from an interfacial instability. However, the existence and physical mechanism of such a putative instability remain unclear. Here, based on an active polar fluid model for epithelial spreading, we analytically predict a generic instability of the tissue front. On the one hand, active cellular traction forces impose avelocity gradient that leads to an accelerated front, which is, thus, unstable to long-wavelength perturbations. On the other hand, contractile intercellular stresses typically dominate over surface tension in stabilizing short-wavelength perturbations. Finally, the finite range of hydrodynamic interactions in the tissue selects a wavelength for the fingering pattern, which is, thus, given by the smallest between the tissue size and the hydrodynamic screening length. Overall, we show that spreading epithelia experience an active fingering instability based on a simple kinematic mechanism. Moreover, our results underscore the crucial role of long-range hydrodynamic interactions in the dynamics of tissue morphology.

Active Fingering Instability in Tissue Spreading

Ricard Alert, etal.

Phys. Rev. Lett. 122, 088104 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.088104

超越亚浓区的柔性聚合物

溶液的普适状态方程

We reconsider the isothermal equation of state (EOS) for linear homopolymers in good solvents, p = p (c, T), which relates the osmotic pressure p of polymers with the bulk concentration c and the temperature T. The classical scaling theory predictsthe EOS in dilute and semidilute regimes. We suggest a generalized EOS that extends the universal behavior of polymer solutions up to the highly concentrated state and confirm it by molecular dynamics simulations and available experimental data. Our conjecture implies that properties of polymer chains dominate the EOS in the presence of many-body interactions. Our theoretical approachis based on a viral expansion in terms of concentration blobs leading to a superposition of two power laws in the regime of concentrated solutions.

Universal Equation of State for Flexible Polymers Beyond the Semidilute Regime

Jarosław Paturej, et al.

Phys. Rev. Lett. 122, 087801 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.087801

缠结聚合物中管扩张的直接评估

A key ingredient within theories focusing on the rheology of entangled polymers is the way how the topological constraints of an entangled chain are lifted by unconstrained segments, i.e., how the constraining tube is dilated. This important question has been addressed by directly measuring the tube diameter d at the scale of the tube by neutron spin echo spectroscopy. The tube diameter d and plateau modulus of highly entangled polyethylene oxide (PEO) chains of volume fraction c that are diluted by low molecular PEO show a concentration dependence d ∝ c^a/2 and ∝ c^1+a with an exponent a close to 4/3. This result allows the clear discrimination between different theoretical models that predict 4/3 or other values between 1 and 2 and provides an important ingredient to tube model theories.