PRL導讀-2019年122卷12期

序

言

本著服務於中國物理學者和物理專業研究生的宗旨，我們根據PRL摘要和引言對本期部分文章進行中文導讀。由於水平有限，不免出現一些不準確的地方乃至錯譯的地方。公眾號下方有留言功能，歡迎專家學者通過留言指出不準確或錯譯的地方，共同提高公眾號的服務質量。留言經編輯確認後，會顯示在文章下方，供後來瀏覽者參考。

普通物理：統計與量子物理

一維熱玻色氣體中的全計數統計與大偏差

本文作者通過全計數統計，得到了一維相互作用玻色子在某一區間內原子數量的分佈。文中結果適用於弱相互作用條件下，處於較大參數範圍內（溫度與區間長度）的所有系統。我們得到的分佈顯著地偏離準凝聚狀態的高斯分佈。而在足夠小的區間內，大數目漲落的概率劇烈地增大。

Full Counting Statistics and Large Deviations in a Thermal 1D Bose Gas

M. Arzamasovs and D. Gangardt

Phys. Rev. Lett. 122, 120401 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.120401

自發對稱破缺穩定光子貓態陣列

量子模擬與量子計算的關鍵是糾纏的受控產生與保護。在單模式層次上，基於光子貓態的方案給人們提供了巨大的希望。它能提供前所未有的長時間相干性，並且可能與強有力的誤差糾正方案結合起來。本文作者證明，在具有成對跳躍的Bose-Hubbard模型中基於自發U(1)對稱性破缺機制，可以產生穩健的“多體光子貓態”系綜。作者給出了基態為重度簡併流形，且包含局域貓態的參數區域。其中，貓態可在整個晶格上分解，它每個獨立的守恆宇稱量可用來實現一個量子比特的寄存器。只要保證長程序的建立，上述現象可產生於具有任意尺寸與幾何的系統之中，並可以被推廣到驅動-耗散的情形。在熱力學極限下，這與從Mott絕緣體到成對超流相的轉變相聯繫。

Stabilizing Arrays of Photonic Cat States via Spontaneous Symmetry Breaking

José Lebreuilly, et al.

Phys. Rev. Lett. 122, 120402 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.120402

功率限制下通過電子自旋進行的核自旋

量子控制與傳感

目前針對核自旋頻域測量或頻域處理的量子傳感實驗要求人們以目標頻率驅動探測系統。此外，在強磁場下進行上述實驗具有巨大的優勢。但此時被測量的自旋的拉莫頻率會很高。因此一個自然現存的巨大挑戰在於：當探測系統不能被設置為與目標頻率共振時，如何操縱一個非常高頻的目標系統。本文作者提出了一系列方案。即便在探測系統和目標系統之間存在較大頻率不匹配時，由此也可克服實驗上的挑戰。這在核極化以及量子傳感中都適用。

Quantum Control and Sensing of Nuclear Spins by Electron Spins under Power Limitations

Nati Aharon, et al.

Phys. Rev. Lett. 122, 120403 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.120403

基於實際測量裝置的

普適N體d

Entanglement witnesses are operators that are crucial for confirming the generation of specific quantum systems, such as multipartite and high-dimensional states. For this reason, many witnesses have been theoretically derived which commonly focus on establishing tight bounds and exhibit mathematical compactness as well as symmetry properties similar to that of the quantum state. However, for increasingly complex quantum systems, established witnesses have lacked experimental achievability, as it has become progressively more challenging to design the corresponding experiments. Here, we present a universal approach to derive entanglement witnesses that are capable of detecting the presence of any targeted complex pure quantum systemand that can be customized towards experimental restrictions or accessible measurementsettings. Using this technique, we derive experimentally optimized witnesses that are able to detect multipartite d-level cluster states, and that requireonly two measurement settings. We present explicit examples for customizing the witness operators given different realistic experimental restrictions,including witnesses for high-dimensional entanglement that use only two-dimensional projection measurements. Our work enables us to confirm the presence of probed quantum states using methods that are compatible with practical experimental realizations in different quantum platforms.

Universal N-Partite d-Level Pure-State Entanglement Witness Based on Realistic Measurement Settings

Stefania Sciara, et al.

Phys. Rev. Lett. 122, 120501 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.120501

陳絕緣體的標度不變性連續糾纏重整化

多標度糾纏重整化擬設（MERA）假設存在量子迴路，可進行實空間中不同標度糾纏的重整化。然而對陳絕緣體來說，這樣標度不變的有限維離散MERA迴路並不存在。本文中作者證明，適用於場論的連續MERA版本，cMERA，可得到陳數非零的不動點波函數。另外眾所周知，逆向的MERA迴路可被用來有效地製備量子態，其所用的時間隨系統尺寸僅以對數形式增長。然而以MERA方式進行的態製備通常需要藉助成熟的量子計算機。本文中作者說明，cMERA可以通過現有的模擬量子計算機得以實現，例如光晶格中，具有光致自旋軌道耦合的超冷原子費米氣體。

Scale-Invariant Continuous Entanglement Renormalization of a Chern Insulator

Su-Kuan Chu, et al.

Phys. Rev. Lett. 122, 120502 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.120502

具有唯一多體最大糾纏態的糾纏資源理論

Entanglement theory is formulated as a quantum resource theory in which the free operations are local operations and classical communication (LOCC). This defines a partial order among bipartite pure states that makes it possible to identify a maximally entangled state, which turns out to be the most relevant state in applications. However, the situation changes drastically in the multipartite regime. Not only do there exist in equivalent forms of entanglement forbidding the existence of a unique maximally entangled state, but recentresults have shown that LOCC induces a trivial ordering: almost all pure entangled multipartite states are incomparable (i.e., LOCC transformations among them are almost never possible). In order to cope with this problem weconsider alternative resource theories in which we relax the class of LOCC to operations that do not create entanglement. We consider two possible theories depending on whether resources correspond to multipartite entangled or genuinely multipartite entangled (GME) states and we show that they are both nontrivial: no inequivalent forms of entanglement exist in them and they inducea meaningful partial order (i.e., every pure state is transformable to more weakly entangled pure states). Moreover, we prove that the resource theory of GME that we formulate here has a unique maximally entangled state, the generalized GHZ state, which can be transformed to any other state by the allowed free operations.

Resource Theory of Entanglement with a Unique Multipartite Maximally Entangled State

Patricia Contreras-Tejada, et al.

Phys. Rev. Lett. 122, 120503 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.120503

實驗上具量子通信複雜性

指數型優勢的量子開關

在量子信息領域的研究中，對量子和經典信息任務間指數型差別的探尋成果豐碩。人們相信指數型差別在量子計算中存在，而對應的性質已經在量子通信複雜度中得到了嚴格證明。近期，一種被稱為量子開關的量子資源已在理論上得到。其中，量子開關通過量子因果律可以產生因果順序上不同事件的相干疊加。這是新的一種提供指數型差別的方案。作者通過實現兩方分佈計算中的通信方向疊加，在實驗上展示了此指數型優勢。文中的光子設備使用了d狀態（d可達2¹³

Experimental Quantum Switching for Exponentially Superior Quantum Communication Complexity

Kejin Wei, et al.

Phys. Rev. Lett. 122, 120504 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.120504

以隨機關聯矩表徵多體糾纏

對多體糾纏的實驗探測需要恰當地選擇一系列關於先前共有參考系校準過的局域量子測量。但對例如基於衛星的光子量子通信等過程來說，這樣的前提是十分苛刻的。因而發展一種替代性的手段十分需要。其中一種可能是：通過在一致隨機分佈的多個裝置中進行局域測量，排除經典參考系帶來的影響。本文作者以這種方式，證明通過結合各階統計矩，可以改進對多體糾纏的探測與表徵。作者使用了偽隨機數過程，由此將上述方法與傳統方法進行了比較。他們先將二比特系統作為例子，說明了本文方法的優越性，接下來進一步將示例延伸到了更為複雜的多體糾纏中。

Characterizing Multipartite Entanglement with Moments of Random Correlations

Andreas Ketterer, et al.

Phys. Rev. Lett. 122, 120505 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.120505

統計推斷的最大熵原理：

非香農熵的情形

作者證明，統計估計理論中最大熵原理的Shore-Johnson公理可以涵蓋說明遠超先前所理解的一大類熵泛函。除了證明並給出公理允許的一類單參數熵函數，作者還進一步通過分析弱關聯的影響支撐了自己的觀點。他們還討論了兩個相關的例子：二比特量子系統，以及高能質子-質子碰撞中強子的橫向動量行為。

Maximum Entropy Principle in Statistical Inference: Case for Non-Shannonian Entropies

Petr Jizba and Jan Korbel

Phys. Rev. Lett. 122, 120601 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.120601

引力與天體物理

正電子和511 keV

可作為近期雙中子星的合併的標記物

從中子星-中子星（NS-NS）和中子星-黑洞（NS-BH）合併中噴出的富含中子的物質被核過程加熱到幾百keV的溫度，導致產生很多電子-正電子對。一些正電子從噴射物的外層逃逸。作者表明，銀河系中由NS-NS和NS-BH合併產生的低能正電子群可以解釋觀測到的來自銀河系中心（GC）的511-keV線。此外，他們提出如何將正電子和相關的511-keV輻射作為近期合併的標記物。最近發現來自超微小矮星系Reticulum II的511-keV輻射，與罕見的NS-NS合併事件一致，為他們的提議提供了確鑿的證據。

Positrons and 511 keV Radiation as Tracers of Recent Binary Neutron Star Mergers

George M. Fuller, et al.

Phys. Rev. Lett. 122, 121101 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.121101

原始能譜中暴脹替代物的獨特指紋

原初宇宙中的有質量場作為標準時鍾和密度擾動中的特徵時鐘信號，可以直接記錄原初宇宙尺度因子隨時間的變化a(t)。對這些信號的測量會以模型無關的方式識別原初宇宙的特定情形。在這篇文章中，作者介紹了一種新的機制，通過這種機制，有質量場的量子漲落可作為標準時鍾。在替代暴脹方案的功率譜中，時鐘信號表現為尺度依賴的振盪信號。

Unique Fingerprints of Alternatives to Inflation in the Primordial Power Spectrum

Xingang Chen, et al.

Phys. Rev. Lett. 122, 121301 (2019)

https://journals.aps.org/prl/c/10.1103/PhysRevLett.122.121301

基本粒子與場論

4維簡單超共形場論的地形

作者探索了有著一個共軛和一對基本表示的螺旋多重態的N=1 超對稱SU(2)規範理論的重整化群流的空間 。考慮了所有可能的相關形變，作者發現在這個簡單的理論框架下，有34個固定點。作者發現這類理論有著許多新奇的現象：有湧現對稱性，算符解耦和較窄的中心荷a/c的分佈。這樣的理論配置包含了兩個N=2的最小Argyres-Douglas理論和他們的質量變化版本的理論。此外，作者發現了36個候選固定點理論，這些理論有非物理的費米算符，包括一個比任何已知的超共形理論都小的中心荷(a,c)~(0.2,0.2)，值得進一步的研究。

Landscape of Simple Superconformal Field Theories in 4D

Kazunobu Maruyoshi et al.

Phys. Rev. Lett. 122, 121601 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.121601

作者計算了N=4超楊-米爾斯理論中的完整色結構的兩圈、5粒子振幅的符號，包括了所有的非平面次領頭色的貢獻。該振幅能寫成Parke-Taylor樹圖振幅和維數正規化參數的純函數的組合，這與之前的猜測相一致。得到的結果有正確的共線極限和紅外因子化性質，因此能讓我們定義一個有限的剩餘函數。作者還研究了非平面項的多-Regge極限，分析了它的次領頭指數修正，並給出了領頭對數項的解析結果。

Analytic Result for a Two-Loop Five-Particle Amplitude

D. Chicherin et al.

Phys. Rev. Lett. 122, 121602 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.121602

N=4超楊-米爾斯理論的兩圈5

作者計算了N=4超楊-米爾斯理論中的兩圈5點振幅的符號，包括了完整的色貢獻。作者給出了所有所需的符號，包含了兩圈5點非平面無質量主積分 。

Two-Loop Five-Point Amplitudein N = 4 Super-Yang-Mills Theory

Samuel Abreu et. al.

Phys. Rev. Lett. 122, 121603 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.121603

測量D⁺s → η' e⁺ν_e衰變的動力學

實驗測量了分支比B_{D+s→ηe+νe}=(2.323±0.063stat±0.063syst)%和 B_D+s→η

Measurement of the Dynamics of the Decays D⁺s → η' e⁺ν_e

M. Ablikim et al.

(BESIII Collaboration)

Phys. Rev. Lett. 122, 121801 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.121801

ABRACADABRA-10釐米實驗的

首個結果：搜尋亞-μeV軸子暗物質

ABRACADABRA-10釐米發佈了1個月的搜索軸子暗物質結果。實驗沒有發現暗物質，並在95%置信度對質量區域為3.1 × 10⁻

First Results from ABRACADABRA-10cm: A Search for Sub- μ eV Axion Dark Matter

Jonathan L. Ouellet, et al.

Phys. Rev. Lett. 122, 121802 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.121802

在√ s= 13 TeV質子質子對撞中

綜合搜索希格斯粒子對的產生

文章報道了在質子質子對撞中，通過各個衰變道，對希格斯粒子對的產生進行搜索，並對希格斯對產生截面設置了上限。

Combination of Searches for Higgs Boson Pair Production in Proton-Proton Collisions at √ s = 13 TeV

A. M. Sirunyan et al.

(CMS Collaboration)

Phys. Rev. Lett. 122, 121803 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.121803

如果超出標準模型的物理在電弱能標進入我們的實現，他的低能效應由標準模型有效場論來描述。在6維，許多包含了反對稱夸克張量的算符很難被實驗、Ward恆等式或者低能定理來限制。然而，從格點QCD確定的歸一化，解析性和么正性常常允許我們在較大的動力學範圍內預言動量依賴。從最近的介子區域的結果開始，作者把這些結果拓展到了核子，從而提供了一系列綜合的夸克張量的核子形狀因子的結果。

Nucleon Matrix Elements of the Antisymmetric Quark Tensor

Martin Hoferichter et al.

Phys. Rev. Lett. 122, 122001 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.122001

原子核物理

夸克-膠子等離子體中的

預定標和遠離平衡態流體動力學

預定標是一種遠離平衡的現象，它描述了一種普適定標分佈形式的確定遠先於其定標指數達到普適數值的情況。Aleksas Mazeliauskas和 Jürgen Berges 研究了在能量足夠高的重離子碰撞中產生的夸克-膠子等離子體系統的時空演變，通過求解同時包含彈性和非彈散射過程的QCD 動力學理論，展示了膠子和夸克分佈非常快速地採取了一種自相似的定標形式，該形式與初始條件細節以及系統參數無關。隨後，預定標機制的動力學效應被完全編碼在少數幾個時間依賴的定標指數中，它們的緩慢演化導致了遠離平衡態的流體動力學行為。（肖楊）

Prescaling and Far-from-Equilibrium Hydrodynamics in the Quark-Gluon Plasma

A. Mazeliauskas and J. Berges

Phys. Rev. Lett. 122, 122301 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.122301

用QCD動力學理論匹配重離子

碰撞的非平衡初始階段和流體動力學

高能核碰撞會產生一種非平衡的夸克-膠子離子體，該夸克-膠子等離子體會熱化並表現出流體動力學流的性質。目前還沒有實用的框架能夠將經典場模擬中的早期粒子的產生與隨後的流體動力學演化聯繫起來。利用在QCD 動力學理論中計算的非平衡態格林函數，Kurkela等人建立了一個將初始能量-動量張量傳播到流體動力學態的理論框架。他們證明這種方法可以很容易地結合到現有的流體動力學模擬中，從而導致對早期能量密度和QCD介質的傳輸特性的更強約束。基於格林函數的（共形）定標特性，他們進一步獲得了流體動力學在核碰撞中的適用性的實用界限。（肖楊）

Matching the Nonequilibrium Initial Stage of Heavy Ion Collisions to Hydrodynamics with QCD Kinetic Theory

Aleksi Kurkela et al.

Phys. Rev. Lett. 122, 122302 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.122302

暈核¹¹Li的鏡像核——

非束縛¹¹O的首次觀測

T. B. Webb等人實現了對雙中子暈核¹¹₃Li₈的鏡像核，極豐質子核¹¹₈O₃結構的首次實驗研究。他們利用¹³O束流的雙中子敲出反應產生了

First Observation of Unbound ¹¹O, the Mirror of the Halo Nucleus¹¹Li

T. B. Webb et al.

Phys. Rev. Lett. 122, 122501 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.122501

類夸克偶素物質與中子星

Larry McLerran 和Sanjay Reddy指出類夸克偶素 (quarkyonic) 物質能自然地解釋中子星的各種觀測性質。他們認為這種物質可能存在於接近核物質飽和密度處，並且在形成階段，其中的壓力和聲速迅速增加。在夸克顏色數目N_c很大的極限下，該轉變（從核物質到類夸克偶素物質）表現為壓力隨著重子數密度改變的不連續變化。通過構建一個類夸克偶素的簡單模型，他們指出聲速一般是密度的非單調函數-它在相對較低的密度下達到最大值，接著減小，然後再次增加到其漸近值（1/√3）。（肖楊）

Quarkyonic Matter and Neutron Stars

Larry McLerran and Sanjay Reddy

Phys. Rev. Lett. 122, 122701 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.122701

原子、分子與光學

利用相干散射對懸浮納米粒子

進行腔基三維冷卻

[編輯推薦]研究人員對懸浮納米粒子進行了三維腔體冷卻，利用光在粒子上的散射達到了創紀錄的低溫。

本文在實驗上實現了空腔冷卻真空中懸浮納米粒子的所有三個平動自由度。粒子被與腔無關的光鑷所捕獲，並將光相干地散射到藍色失諧腔模式中。對於大約10^-5mbar的真空壓力，作者觀察到了毫開爾文的腔軸的極低溫度。同時，沿其他兩個空間方向的質心運動也被冷卻到幾百毫開爾文的極低溫度。隨著壓力的變化來測量溫度和阻尼率，作者發現冷卻效率取決於腔內駐波內的粒子位置。作為腔失諧和光鑷功率的函數的質心溫度的數據和狀態與實驗的理論分析相一致。本文進一步概述了該方法的實驗限制和各種可能性。

Cavity-Based 3D Cooling of a Levitated Nanoparticle via Coherent Scattering

Dominik Windey, et al.

Phys. Rev. Lett. 122, 123601 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.123601

利用相干散射法研究

懸浮納米粒子的腔體冷卻

[編輯推薦]研究人員對懸浮納米粒子進行了三維腔體冷卻，利用光在粒子上的散射達到了創紀錄的低溫。

本文主要研究光學腔內的懸浮納米粒子的三維（3D）冷卻。該冷卻機制是利用光鑷的腔增強相干散射。所觀察到的3D動力學和冷卻速率可在理論上由粒子運動和腔場之間的相互作用的線性和二次項而推導出來。通過對顆粒位置實現納米級控制，作者優化了位置相關的耦合，並在6×10-2mbar的背景壓力下演示了兩個數量級的軸向冷卻。本文還估計了對激光相位噪聲加熱的顯著壓制（> 40dB），這是相干散射方案的一個特殊特性。實驗觀察到的性能表明，在低於1×10-7mbar的背景壓力下，可以實現懸浮納米粒子的量子基態腔冷卻。

Cavity Cooling of a Levitated Nanosphere by Coherent Scattering

Uroš Delić, et al.

Phys. Rev. Lett. 122, 123602 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.123602

具有徑向週期勢的二維自旋軌道耦合

玻色-愛因斯坦凝聚體中的

穩定多環和旋轉孤子

We consider two-dimension alspin-orbit-coupled atomic Bose-Einstein condensate in a radially periodic potential. The system supports different types of stable self-sustained states including radially symmetric vorticity-carrying modes with different topological charges in two spinor components that may have multiring profilesand at the same time remain remarkably stable for repulsive interactions. Solitons of the second type show persistent rotation with constant angular frequency. They can be stable for both repulsive and attractive interatomic interactions. Because of the inequivalence between clockwise and counterclockwise rotation directions introduced by spin-orbit coupling, the properties of such solitons strongly differ for positive and negative rotation frequencies. The collision of solitons located in the same or different ringsis accompanied by a change of the rotation frequency that depends on the phase difference between colliding solitons.

Stable Multiring and Rotating Solitons in Two-Dimensional Spin-Orbit-Coupled Bose-Einstein Condensates with a Radially Periodic Potential

Y. Kartashov and D. Zezyulin

Phys. Rev. Lett. 122, 123201（2019）

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.123201

利用單光束在極阱中

連續加載超冷基態⁸⁵Rb₂分子

We have developed an approach to continuously load ultracold ⁸⁵Rb₂vibrational ground-state molecules into a crossed optical dipole trap from a magneto-optical trap. The technique relies on a single high-power light beam with a broad spectrum superimposed onto a narrow peak at an energy of about 9400 cm⁻¹. This single laser source performs all the required steps: the short-range photoassociation creating ground-state molecules after radiative emission, the cooling of the molecular vibrational population down to the lowest vibrational level ν_X=0, and the optical trapping of these molecules. Furthermore, we probe by depletion spectroscopy and determine that 75% of the ν_X=0 ground-state molecules are in the three lowest rotational levels J_X=0, 1, 2. The lifetime of the ultracold molecules in the optical dipole trap is limited to about 70 ms by off-resonant light scattering. The proposed technique opens perspectives for the formation of new molecular species in the ultracold domain, which are not yet accessible by well-established approaches.

Continuous Loading of Ultracold Ground-State ⁸⁵Rb₂ Molecules in a Dipole Trap Using a Single Light Beam

Henry Fernandes Passagem, et al.

Phys. Rev. Lett. 122, 123401 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.123401

基於弱值形式的亞波長結構的

多參數同步測量

在光學聚焦矢量束散射測量實驗的背景下，本文提出了從弱值形式到多參數同步測量的數學擴展。該示例利用空間變化極化的控制來實現預選和後選，並通過定製來優化其對參數變化的靈敏度。雙參數情況的初步實驗表明，該方法可用於測量其分辨率至少比光照波長小1000倍的物理參數。

Simultaneous Measurement of Multiple Parameters of a Subwavelength Structure Based on the Weak Value Formalism

Anthony Vella, et al.

Phys. Rev. Lett. 122, 123603 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.123603

多光子Jaynes-Cummings模型：

Fock空間和量子濾波器中的任意旋轉

The multiphoton Jaynes-Cummings model is investigated and applications in quantum information science are explored. Considering the strong atom-field coupling regime and an N-photon interaction, a nonlinear driving field can perform an arbitrary rotation in the Fock space of a bosonic mode involving the vacuum and an M-Fock state, with M

Multiphoton Jaynes-Cummings Model: Arbitrary Rotations in Fock Space and Quantum Filters

C. Villas-Boas and D. Rossatto

Phys. Rev. Lett. 122, 123604 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.123604

對確定性糾纏態製備中

局部洛倫茲不變性的改進檢驗

The high degree of control available over individual atoms enables precision tests of fundamental physical concepts. In this Letter, we experimentally study how precision measurements can be improvedby preparing entangled states immune to the dominant source of decoherence. Using ⁴⁰Ca⁺ions, we explicitly demonstrate the advantage from entanglement on a precision test of local Lorentz invariance for the electron. Reaching the quantum projection noise limit set by quantum mechanics, we observe, for bipartite entangled states, the expected gain of a factor of two in the precision. Under specific conditions, multipartite entangled states may yield substantial further improvements. Our measurements improve theprevious best limit for local Lorentz invariance of the electron using

Improved Test of Local Lorentz Invariance from a Deterministic Preparation of Entangled States

Eli Megidish, et al.

Phys. Rev. Lett. 122, 123605 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.123605

利用光譜定製的紫外線

頻梳對9Be+離子進行多功能控制

We demonstrate quantum control of ⁹Be⁺ions directly implemented by an optical frequency comb. Based on numerical simulations of the relevant processes in⁹Be⁺ for different magnetic field regimes, we demonstrate a wide applicability when controlling the comb’s spectral properties. We introduce a novel technique for the selective and efficient generation of a spectrally tailored narrow-bandwidth optical frequency comb near 313 nm. We experimentally demonstrate internal state control and internal-motional state coupling of⁹Be⁺ions implemented by stimulated-Raman manipulation using a spectrally optimized optical frequency comb. Our pulsed laser approach is a key enabling step for the implementation of quantum logic and quantum information experiments in Penning traps.

Versatile Control of ⁹Be

A.-G. Paschke, et al.

Phys. Rev. Lett. 122, 123606 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.123606

窄帶超糾纏光子的直接生成

在量子通信和光子量子信息處理中，對量子中繼器和量子存儲器的要求往往對糾纏光子施加了嚴格的帶寬先決條件。同時，對於光子對也有更多糾纏度的要求（即，超糾纏）。本文報告了冷原子中窄帶軌道角動量和極化超糾纏光子的直接生成。除了在冷原子集合中的自發四波混頻過程中由於自旋和軌道角動量守恆條件引起的時間-頻率自由度之外，窄帶光子對還自然地糾纏於極化和軌道角動量中。本文報道的窄帶超糾纏光子對光源有望在基於量子存儲器的長距離量子通信中發揮重要的作用。

Direct Generation of Narrow-band Hyperentangled Photons

Tian-Ming Zhao, et al.

Phys. Rev. Lett. 122, 123607 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.123607

薄膜腔的X

通過在X射線腔中嵌入一層鉭薄膜，作者觀察到了金屬內層電子躍遷的光譜特性的變化。腔模真空和L_III邊躍遷之間的相互作用得到了增強，這就容許了對集體蘭姆位移、超輻射和類Fano腔共振干涉效應的觀測。本文實驗證明了，在X射線範圍內具有電子共振的腔量子電動力學的可行性，並將其應用於在X射線腔中利用高分辨率X射線光譜學來操縱和探測凝聚態物質的電子結構。

Spectral Control of an X-Ray L-Edge Transition via a Thin-Film Cavity

Johann Haber, et al.

Phys. Rev. Lett. 122, 123608 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.123608

非線性動力學和流體力學

結構泵浦量子模式識別

Qiu等人報導了一種新的鬼影成像方法，用具有空間結構的泵在自發參數下轉換傅里葉域中基於量子相關進行模式識別。作者利用拉蓋爾 - 高斯模式傅里葉變換的數學特徵來描述鬼影圖像的泵調製形成。特別令人感興趣的是Vander Lugt濾波器量子等效的實驗證明，基於該實驗，作者成功用非局部螺旋相位對比，實現了渦旋映射和基於量子相關的人臉識別。用於探測測試對象，掃描數據庫和產生關聯信號的光子可以歸為三種不同的光束，表明這項技術可以在一些需要低光照明和保密操作的安全應用中起到作用。(鄭皓天)

Structured-Pump-Enabled Quantum Pattern Recognition

Xiaodong Qiu, et al

Phys. Rev. Lett. 122, 123901 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.123901

多模光纖中無序介導的波凝結劇烈加速

Classical nonlinear waves exhibit a phenomenon of condensation that results from the natural irreversible process of thermalization, in analogy with the quantum Bose-Einstein condensation. Wave condensation originates in the divergence of the thermodynamic equilibrium Rayleigh-Jeans distribution, whichis responsible for the macroscopic population of the fundamental mode of the system. However, achieving complete thermalization and condensation of incoherent waves through nonlinear optical propagation is known to require prohibitive large interaction lengths. Here, we derive a discrete kinetic equation describing the nonequilibrium evolution of the random wave in the presence of a structural disorder of the medium. Our theory reveals that a weak disorder accelerates the rate of thermalization and condensation by several order of magnitudes. Such a counterintuitive dramatic acceleration of condensation can provide a natural explanation for the recently discovered phenomenon of optical beam selfcleaning. Our experiments in multimode optical fibers report the observation of the transition from an incoherent thermal distribution to wave condensation, with a condensate fraction of up to 60% in the fundamental mode of the waveguide trapping potential. (鄭皓天)

Dramatic Acceleration of Wave Condensation Mediated by Disorder in Multimode Fibers

Adrien Fusaro, et al

Phys. Rev. Lett. 122, 123902 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.123902

用於選擇性濾波彈性超材料剛性的

時域週期調製：理論與實驗

具有時間調製剛性的彈性波導擁有頻域週期色散譜，其中不同分支在調製頻率半整數倍處合併，跨越一個有限波數範圍。在此範圍內，頻率變成複數，其實部保持不變。與這些平帶相關聯群速度的消失導致在非調製和時間調製介質界面處頻率的選擇性反射，將寬帶輸入轉換為以調製頻率一半為中心的窄帶輸出。這種行為表現在橫向運動的彈性波導中，其通過由開關電路控制的負電容分流壓電貼片陣列實現調製。切換時間規定了調製頻率並允許選擇性輸出頻率。該發現適用於研究時空調製彈性超材料的許多性質，例如非互易性和單向傳播，並且有助於在壓電基板上操作的聲波器件新功能的實現。(鄭皓天)

Time-Periodic Stiffness Modulation in Elastic Metamaterials for Selective Wave Filtering: Theory and Experiment

Giuseppe Trainiti, et al

Phys. Rev. Lett. 122, 124301 (2019）

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.124301

線性勢中波包的幅度和相位

We theoretically study and successfully observe the evolution of Gaussian and Airy surface gravity water wave packets propagating in an effective linear potential. This potential results from a homogeneous and time-dependent flow created by a computer-controlled water pump. For both wave packets we measure the amplitudes and the cubic phases appearing due to the linear potential. Furthermore, we demonstrate that the self-acceleration of the Airy surface gravity water wave packets can be completely canceled by a linear potential. (鄭皓天)

Amplitude and Phase of Wave Packets in a Linear Potential

Georgi Gary Rozenman, et al

Phys. Rev. Lett. 122, 124302 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.124302

粘彈性電解質中的電對流

具有聚合物添加劑液體電解質的直接數值模擬表明，粘彈性促進從穩定到不穩定電對流更早轉變。粘彈性還使對流產生的過限電流減少達40％。這兩種效應都會降低離子流空間變化的時間平均，表明聚合物流體可能抑制枝晶生長。表面附近的聚合物弛豫使流動結構不穩定並且減少了高通量流動的持續時間。這種聚合物誘導的流量減少機制廣泛適用於具有質量，熱量或動量傳遞的壁面限制流動。(鄭皓天)

Electroconvection in a Viscoelastic Electrolyte

Gaojin Li, et al

Phys. Rev. Lett. 122, 124501（2019）

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.124501

零雷諾數近似對於纖毛流是否有效？

Stokes方程通常用於模擬微米級纖毛周圍的流體動力行為。利用高時空分辨率的光學鑷子，準確測量週期流的速度，可以實驗研究零雷諾數近似的有效性。Da Wei等人發現擺動纖毛產生的流動與Stokes方程預測的斯托克斯場完全不同。特別地，流速在空間上衰減的速度更快，並且隨著遠離纖毛相位延遲增大。這表明擬穩態近似和用於不穩定纖毛流的Stokes方程並不總是合理的，並且渦度擴散的有限時間尺度不容忽視。Da Wei等人的結果在微觀遊動體的同步和集體動力學研究中具有重要意義。（張毓）

Is the Zero Reynolds Number Approximation Valid for Ciliary Flows?

Da Wei, et al.

Phys. Rev. Lett. 122, 124502 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.124502

慣性彈性湍流中的臨界層結構和機制

Simulations of elastoinertial turbulence (EIT) of a polymer solution at low Reynolds number are shown to display localized polymer stretch fluctuations. These are very similar to structures arising from linear stability (Tollmien-Schlichting modes) and resolvent analyses, i.e., critical-layer structures localized where the mean fluid velocity equals the wave speed. Computations of self-sustained nonlinear Tollmien-Schlichting waves reveal that the critical layer exhibits stagnation points that generate sheets of large polymer stretch. These kinematics may be the genesis of similar structures in EIT.（張毓）

Critical-Layer Structures and Mechanisms in Elastoinertial Turbulence

Ashwin Shekar, et al.

Phys. Rev. Lett. 122, 124503 (2019)

https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.122.124503

湍流中的功率波動

為了產生或維持湍流，需要引入動能。這種能量注入必然會波動，而功率波動作用於所有活躍的湍流長度尺度。如果注入功率用的是與速度成正比的力（例如，剪切流中常見的力）或僅用在最大尺度上起作用的力，那麼這些波動頻譜具有與能譜成正比的慣性區間。（張毓）

Power fluctuations in turbulence

Wouter J. T. Bos and R. Zamansky

Phys. Rev. Lett. 122, 124504 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.124504

超短脈衝攜帶軌道角動量的上界

Photons in a ring-shaped vortex light beam can have an arbitrarily high orbital angular momentum (OAM) lℏ, inaddition to the spin angular momentum ℏ. For a pulsed vortex beam, there is, however, an upper bound to the integer units l of OAM, or topological charge of the vortex, and a lower bound to the pulse duration to carry OAM. These limits have implications in experiments with ultrashort vortices, e.g., in the generation of twisted attosecond bursts in the extreme ultraviolet, in the temporal resolution in ultrafast spectroscopy, or in the performance of OAM-basedoptical communications or cryptographic systems, as well as in other areas of physics as acoustics or electron waves.（張毓）

Upper Bound to the Orbital Angular Momentum Carried by an Ultrashort Pulse

Miguel A. Porras

Phys. Rev. Lett. 122, 123904（2019）

https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.122.123904

通過光子高頻帶激發的

谷渦旋態和簡併提升

Daohong Song等人展示了光子石墨烯中谷渦旋的生成。兩個谷的激發導致在第三個等價谷處布拉格反射時光學渦旋的形成，而不破壞反轉對稱性，其手徵性由谷自由度決定。Daohong Song等人觀察到並通過數值模擬證實，渦-反渦對具有與谷相關的拓撲電荷翻轉。此外，Daohong Song等人開發了一個三波段有效哈密頓模型來描述耦合谷的動力學，並發現常用的雙波段模型不足以解釋觀察到的渦旋簡併提升。這種谷極化渦流態來自無合成場引發帶隙口的高頻帶激發。Daohong Song等人在光子裝置上得到的結果可以為在其他系統中研究谷比對和貝瑞相介導的拓撲現象提供思路。（張毓）

Valley Vortex States and Degeneracy Lifting via Photonic Higher-Band Excitation

Daohong Song, et al.

Phys. Rev. Lett. 122, 123903 (2019)

https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.1212.123903

凝聚態物理：結構

[編輯推薦]當夾在無序擴散板之間時，波導中的不透明勢壘傳輸更多。

Chéron等人發現，當把一個不透明勢壘放在對稱的擴散無序板之間，會產生顯著的、寬頻帶透射增強。透射增強伴隨著一個透射本徵值的雙峰分佈，並且對於給定的勢壘透射率，作者發現了無序板的最佳特定長度值。作者通過一個簡單的模型，進行了量化參數之間的無量綱換算，這些參數表明勢壘越強，最大可能增強越強。作者還探討了對稱缺陷的敏感性，這顯示出波基傳感的巨大潛力。（黃通昀）

Broadband-Enhanced Transmission through Symmetric Diffusive Slabs

É. Chéron, S. Félix, V. Pagneux

Phys. Rev. Lett. 122, 125501 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.125501

硅的高壓相圖中的非諧因素

和不規則晶相演化趨勢研究

本文使用密度泛函理論、演化算法和晶格動力學的多層面第一性原理方法，得到了高達4 TPa高壓和26000 K高溫下的硅相圖。通過計算分析發現：（i）在壓力分別為2.87和3.89 TPa時，沿著冷態有效性曲線，會出現從一系列不規則的面心立方晶體到體心立方晶體，再到簡單立方晶體的結晶相變過程；（ii）當只考慮吉布斯自由能的非諧波貢獻時，Imma和Cmce-16斜方晶相才會出現在相圖中；（iii）當考慮立方金剛石相的非諧自由能影響時，可以在相圖中觀察到Hugoniot曲線斜率明顯的變化。（張陸峰）

Anharmonic and Anomalous Trends in the High-Pressure Phase Diagram of Silicon

R. Paul, S. X. Hu, V. Karasiev

Phys. Rev. Lett. 122, 125701 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.125701

機械載荷下金屬材料中

晶界遷移的尺寸依賴性

傳統金屬材料變形過程中，晶界一般認為是位錯運動的“靜態”幾何障礙，材料的強度隨著晶粒尺寸減小而增加，符合Hall-Petch關係；但金屬材料晶粒尺寸減小至納米尺度時，機械變形過程中其晶界遷移性顯著增強，並伴隨著晶粒長大，如拉伸、壓縮、壓痕等過程中均可觀察到明顯的晶粒粗化現象，所以納米晶材料強度與晶粒尺寸的關係也逐漸偏離Hall-Petch關係。儘管機械驅動晶界遷移的內在機制存在爭議，但大量研究認為晶界遷移通過晶界原子短程運動或晶界位錯運動的方式進行，這說明該過程與晶界結構或成分等密切相關。Zhou等人對劇烈塑性變形制備的不同平均晶粒尺寸梯度分佈的納米晶Ag、Cu、Ni進行準靜態拉伸變形，通過對變形前後晶粒尺寸變化分析發現晶界遷移行為具有明顯的晶粒尺寸效應。從超細晶到納米晶，隨著晶粒尺寸減小，晶界遷移先逐漸增強，但當晶粒尺寸小於臨界值時，晶界遷移逐漸變弱。Ag、Cu、Ni中晶界遷移效應峰值對應平均晶粒尺寸分別約為80、75、38nm。此外，通過合適的後序熱處理，發現部分臨界尺寸附近納米晶晶界遷移效應也明顯減弱。分析發現納米晶晶界遷移受到抑制的主要原因是變形或熱處理誘導其晶界馳豫效應，晶界能量較低，穩定性提高。馳豫態的納米晶在變形過程中主導塑性變形機制從晶界遷移轉變為不全位錯運動形成變形孿晶或層錯。研究結果說明晶界馳豫與晶界偏聚效應類似，可通過調整晶界結構提高晶界穩定性，這為提高納米晶機械穩定性提供新的途徑。（王婧瑤）

Size Dependence of Grain Boundary Migration in Metals under Mechanical Loading

Xin Zhou, Xiuyan Li, and K. Lu

Phys. Rev. Lett. 122, 126101 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.126101

線性特徵：位錯中亞穩相的形成和共存

Turlo等人利用原子模擬方法，在體心立方鐵鎳合金的刃位錯附近發現了亞穩態B2−FeNi與穩態L10−FeNi、L12−FeNi3的三相共存。在較大範圍的組成和溫度下，觀察到了沿著位錯線受壓側形成的穩定的納米級沉澱陣列，並將其定義為線性特徵。作者通過分析穩態、亞穩態相變相關的熱力學解釋了亞穩相的形成和共存，並在此過程中定義了理論和實驗研究的新途徑。（馬馳）

Linear Complexions: Metastable Phase Formation and Coexistence at Dislocations

Vladyslav Turlo and T. Rupert

Phys. Rev. Lett. 122, 126102 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.126102

磁場控制晶界

在微結構工程中，利用外磁場影響多晶材料中微結構的能力具有巨大應用潛力。為了探索這種潛力並理解電磁場與固態物質輸運之間的複雜相互作用，Backofen等人研究了晶體相場模型。利用高效、可擴展的數值算法，這種模型可用來分析外磁場對缺陷構造與晶界的演變、擴散時間尺度所起的作用。作者以平面和圓形晶界為例，解釋了基本的原子過程，並採用二維大尺度模擬獲得了外場影響下晶粒生長的統計數據。（黃通昀）

Controlling Grain Boundaries by Magnetic Fields

R. Backofen, K. R. Elder, A. Voigt

Phys. Rev. Lett. 122, 126103 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.126103

凝聚態物理：電子性質

空穴摻雜LuFe₂O_4+δ中的

電荷-晶格耦合：二階調製的起源

理解有序結構中的奇異性，例如晶格調製中的位錯和電荷序中的孤子，為解開電子自由度和晶格之間的相互作用提供了很好的機會。具體地，調製結構傳統上以離散傅里葉級數的形式表示，每個分量具有恆定的相位和幅度。在這裡，Deng等人報導了空穴摻雜LuFe₂O_{4 +δ}中一種新調製波的原子尺度觀察和分析，需要對有序結構的傳統建模進行顯著修改。只有在相位和幅度參數空間中引入明確定義的第二調製矢量，才能準確地描述這種具有不尋常準週期奇異性的新調製。結合密度泛函理論（DFT）計算，他們的結果表明，這些奇異性源於系統中間隙氧原子引起的晶格錯位的不連續性。他們的工作方法適用於各種有序系統，提高了人們對奇異性和調製性質的理解。（方子明）

Charge-Lattice Coupling in Hole-Doped LuFe₂O_4+δ: The Origin of Second-Order Modulation

Shiqing Deng et al.

Phys. Rev. Lett. 122, 126401 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.126401

在π-結Rashba層中的二階拓撲超導性

We consider a Josephson junction bilayer consisting of two tunnel-coupled two-dimensional electron gas layers with Rashba spin-orbit interaction, proximitized by a topand bottom s-wave superconductor with phase difference ϕ close to π. We show that, in the presence of a finite weak in-plane Zeeman field, the bilayer canbe driven into a second order topological superconducting phase, hosting two Majorana corner states (MCSs). If ϕ = π, in a rectangular geometry, these zero-energy bound states are located at two opposite corners determined by the direction of the Zeeman field. If the phase difference ϕ deviates from π by acritical value, one of the two MCSs gets relocated to an adjacent corner. As the phase difference ϕ increases further, the system becomes trivially gapped. The obtained MCSs are robust against static and magnetic disorder. We propose two setups that could realize such a model: one is based on controlling ϕ by magnetic flux, the other involves an additional layer of randomly oriented magnetic impurities responsible for the phase shift of π in the proximity-induced superconducting pairing.

Second-Order Topological Superconductivity in π-Junction Rashba Layers

Y. Volpez et al.

Phys. Rev. Lett. 122, 126402 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.126402

兩種不同對稱自旋劈裂的共存

表面或界面的對稱性在確定二維能帶的自旋劈裂和紋理中起重要作用。Yaji等人通過自旋和角度分辨光電子能譜儀研究了SiC（0001）襯底上由Sn組成的三角晶格原子層（TLAL）的自旋極化帶。令人驚訝的是，Zeeman和Rashba型自旋分裂帶在沒有和具有自旋簡併性的情況下都共存於Sn TLAL的K點。根據SiC週期性的晶體結構，K點具有三重對稱性而沒有反演對稱性，這意味著Zeeman型與晶格的對稱性一致，而Rashba型不一致。他們的密度泛函理論計算表明，Rashba型（Zeeman型）能帶的電荷密度分佈在K點存在（無）反演對稱性。因此，電荷密度分佈的對稱性與兩種類型的自旋劈裂一致。（方子明）

Coexistence of Two Types of Spin Splitting Originating from Different Symmetries

Koichiro Yaji et al.

Phys. Rev. Lett. 122, 126403 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.126403

溫度誘導的無帶隙拓撲絕緣體

瞭解無序、相互作用和溫度對物質拓撲性的影響對於預測物質在真實環境中的拓撲特性及其穩定性至關重要。Haldane-Falicov-Kimball模型是一個集合了拓撲性、相互作用以及有限溫度下自發無序的模型。本文中，作者研究了Haldane-Falicov-Kimball模型的相圖。首先，作者藉助於數值方法，繪製出了相互作用-溫度平面上的相圖。在已知相的基礎上，作者揭示了具有無帶隙激發的絕緣電荷有序態以及溫度驅動的無帶隙拓撲絕緣相。這種意外的行為可以通過內稟（溫度產生）的無序來解釋。該研究結果為兩種費米子組成的質量不平衡系統中，溫度可驅動有帶隙和無帶隙拓撲絕緣相的產生提供了直接的證據。（劉錢）

Temperature-Driven Gapless Topological Insulator

M. Gonçalves et al.

Phys. Rev. Lett. 122, 126601 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.126601

Majorana束縛態是一維（1D）拓撲超導體末端的零能模式。引入無序通常會增加Majorana局域長度，直到最終導致拓撲相變為平凡相。在這篇快訊中，Haim等人表明，在某些情況下，弱無序會導致Majorana局域長度減少，使拓撲相更加穩健。進一步增加無序最終可導致趨勢變化並且相變到平庸相。有趣的是，轉變發生在ξ₀>>l，其中l是無序平均自由程，ξ₀是純淨極限中的局域長度。他們的結果與平面約瑟夫森結中形成的一維拓撲超導體尤其相關。（方子明）

Benefits of Weak Disorder in One-Dimensional Topological Superconductors

Arbel Haim and Ady Stern

Phys. Rev. Lett. 122, 126801 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.126801

隧穿至與噪聲電容電極耦合的

有限Luttinger液體

Tunneling spectroscopy of one-dimensional interacting wires can be profoundly sensitive to the boundary conditions of the wire. Here, we analyze the tunneling spectroscopy of a wire coupled to capacitive metallic leads. Strikingly, with increasing many-body interactions in the wire, the impact of the boundary noise becomes more prominent. This interplay allows for a smooth crossover from standard 1D tunneling signatures into a regime where the tunneling is dominated by the fluctuations at the leads. This regime is characterized by an elevated zero-bias tunneling alongside a universal power-law decay at high energies. Furthermore, local tunneling measurements in this regime show a unique spatial dependence that marks the formation of plasmonic standing waves in the wire. Our result offers a tunable method by which to control the boundary effects and measure the interaction strength (Luttinger parameter) within the wire.

Tunneling into a Finite Luttinger Liquid Coupled to Noisy Capacitive Leads

Antonio Štrkalj et al.

Phys. Rev. Lett. 122, 126802 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.126802

2H−TaS₂中壓力誘導的電荷密度波

崩塌和希格斯模式可見性

The pressure evolution of the Raman active electronic excitations of the transition metal dichalcogenides 2H−TaS2 is followed through the pressure phase diagram embedding incommensurate charge-density-wave and superconducting states. At high pressure, the charge-density wave is found to collapse at 8.5 GPa. In the coexisting charge-density-wave and superconducting orders, we unravel a strong in-gap superconducting mode, attributed to a Higgs mode, coexisting with the expected incoherent Cooper-pair breaking signature. Thelatter remains in the pure superconducting state reached above 8.5 GPa. Our report constitutes a new observation of such Raman active Higgs mode sincethe long-standing unique case 2H−NbSe2.

Pressure-Induced Collapse of the Charge Density Wave and Higgs Mode Visibility in 2H−TaS₂

Romain Grasset et al.

Phys. Rev. Lett. 122, 127001 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.127001

C₉H₁₈N₂CuBr₄中平面耦合自旋階梯的

Higgs模式及其觀測

[編輯推薦] 利用大尺度量子蒙特卡羅模擬，金屬-有機化合物C₉H₁₈N₂CuBr₄中的Higgs模式可被理解為一個強各項異性（伊辛）極限下雙磁振子束縛態。

C₉H₁₈N₂CuBr₄是一種二維近量子臨界的自旋1/2 two-leg階梯化合物，具有弱的易軸交換各向異性。近期，極化非彈性中子散射實驗在C₉H₁₈N₂CuBr₄中發現了Higgs模式。本文中，作者利用大尺度量子蒙特卡羅模擬，從理論上研究了這種平面耦合自旋階梯系統的動力學自旋結構因子，能夠在一個自洽的量子自旋模型內，定量描述中子散射實驗數據。結果顯示，在磁激勵作用下，該系統可以從具有完全SU(2)對稱性的各向同性極限演化到主導易軸交換作用的伊辛極限。同時發現，Higgs模式在海森堡極限處存在過阻尼現象，而在伊辛區域則演化成一個雙磁振子束縛態。相反，對於弱耦合類的階梯化合物，同樣的模態會發生凝聚，併產生量子無序相。（劉錢）

Higgs Mode of Planar Coupled Spin Ladders and its Observation in C₉H₁₈N₂CuBr₄

T. Ying et al.

Phys. Rev. Lett. 122, 127201 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.127201

XXZ自旋鏈中自旋擴散

和超擴散的動力學理論

We address the nature of spin transport in the integrable XXZ spin chain, focusing on the isotropic Heisenberg limit. We calculate the diffusion constant using a kinetic picture based on generalized hydrodynamics combined with Gaussian fluctuations: we find that itdiverges, and show that a self-consistent treatment of this divergence gives superdiffusion, with an effective time-dependent diffusion constant that scalesas D(t)∼t1/3. This exponent had previously been observed inlarge-scale numerical simulations, but had not been theoretically explained. We briefly discuss XXZ models with easy-axis anisotropy Δ>1. Ourmethod gives closed-form expressions for the diffusion constant D in the infinite-temperature limit for all Δ>1. We find that D saturates at large anisotropy, and diverges as the Heisenberg limit is approached, as D∼(Δ−1)−1/2.

Kinetic Theory of Spin Diffusion and Superdiffusion in XXZ Spin Chains

S. Gopalakrishnan and R. Vasseur

Phys. Rev. Lett. 122, 127202 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.127202

亞鐵磁性GdFeCo合金中的低磁阻尼

本文中，作者在較大溫度區間內研究了由稀土-過渡金屬組成的亞鐵磁材料的吉爾伯特阻尼參數α。作者根據外場驅動磁疇壁的運動速度，得到體系的α。結果顯示，在該類體系中，α低至10

Low Magnetic Damping of Ferrimagnetic GdFeCo Alloys

D. Kim et al.

Phys. Rev. Lett. 122, 127203 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.127203

利用X射線磁圓二色性在高磁場下

同時觀察到亞鐵磁鉺鐵石榴石鉺L_2,3

帶邊處Er和Fe子晶格的磁矩

Strohm等人在鉺鐵石榴石中進行了磁圓二色性實驗，發現鉺L

Simultaneous Observation of the Er- and Fe-Sublattice Magnetization of Ferrimagnetic Er3Fe5O12 in High Magnetic Fields Using X-Ray Magnetic Circular Dichroism at the Er L2,3 Edges

C. Strohm et al.

Phys. Rev. Lett. 122, 127204 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.127204

強各向異性亞鐵磁體HoFe₅Al₇中

一階場誘導相變的微觀本質

Gorbunov等人對亞鐵磁體HoFe₅Al₇進行了X射線磁圓二色實驗以追蹤在脈衝磁場誘導相變過程中單個磁矩的旋轉。作者在基態附近觀測到 Ho和Fe的磁矩同時、逐步地旋轉，並藉助子晶格間通過弱交換作用耦合的各向異性亞鐵磁雙子晶格模型解釋了這個現象。他們在補償點附近發現了兩個相變。額外的磁矩跳躍反映出外加磁場與子晶格間交換場作用相反時，Ho磁矩的變化。（李松）

Microscopic Nature of the First-Order Field-Induced Phase Transition in the Strongly Anisotropic Ferrimagnet HoFe₅Al₇

D. I. Gorbunov et al.

Phys. Rev. Lett. 122, 127205 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.127205

摻雜釩鈣鈦礦中缺陷誘導的

軌道極化和軌道序的坍塌

We explore mechanisms of orbital-order decay in the doped Mott insulators R1−x(Sr,Ca)xVO3 (R=Pr,Y,La) caused by charged (Sr,Ca) defects. Our unrestricted Hartree-Fock analysis focuses on the combined effect of random charged impurities and associated doped holes up to x=0.5. The study is based on a generalized multiband Hubbard model for the relevant vanadium t2g electrons and includes the long-range (i) Coulomb potentials of defects and (ii) electron-electron interactions. We show that the rotation of t2g orbitals, induced by the electric field of defects, is a very efficient perturbation that largely controls the suppression of orbital order in these compounds. We investigate the inverse participation number spectra and find that electron states remain localized on few sites even in the regime where orbital order is collapsed. From the change of kinetic and superexchange energy, we can conclude that the motion of doped holes, which is the dominant effect for the reduction of magnetic order in high-Tc compounds, is of secondary importance here.

Defect-Induced Orbital Polarization and Collapse of Orbital Order in Doped Vanadium Perovskites

A. Avella, A. Oleś, and P. Horsch

Phys. Rev. Lett. 122, 127206 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.127206

反鐵磁金屬EuMnBi₂中

磁壓電效應的觀察

Shiomi等人實驗研究了最近預測的具有低晶體對稱性的磁性金屬的磁壓電效應。77K時在具有反鐵磁性Mn磁矩的EuMnBi

Observation of a Magnetopiezoelectric Effect in the Antiferromagnetic Metal EuMnBi₂

Y. Shiomi et al.

Phys. Rev. Lett. 122, 127207 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.127207

單層MoS₂中塞曼場誘導的谷敏感光電流

[編輯推薦語]：利用外磁場與電子能帶的特定特徵的相互影響操控二維材料MoS₂中的光電響應。

利用圓偏振光可以在單層過渡金屬二硫化物中產生特定的谷自旋激發。對谷自由度的操控是該領域的核心問題。目前實驗上已經可以對谷指標進行測量和操控，但主要侷限在純光學手段。這個工作中，Zhang等人發現，當單層MoS

Zeeman-Induced Valley-Sensitive Photocurrent in Monolayer MoS₂

Xiao-Xiao Zhang et al.

Phys. Rev. Lett. 122, 127401 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.127401

激子磁體中的集體模式：

動力學平均場研究

Geffroy等人進行了雙能帶Hubbard模型中關於動態磁化率的動力學平均場研究。通過改變模型參數，他們分析了正常和有序相中的雙粒子激發，即激子凝聚。有序相中的雙粒子動力學平均場理論能譜揭示了由連續對稱性的自發破缺引起的無能隙Goldstone模式。他們還觀察到有能隙的希格斯模式，其特徵在於相邊界處的能隙消失。自旋磁化率中觀察到的定性變化可以用作鑑定激子凝聚的實驗探測手段。（方子明）

Collective Modes in Excitonic Magnets: Dynamical Mean-Field Study

D. Geffroy et al.

Phys. Rev. Lett. 122, 127601 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.127601

單粒子量子點發射器中的相互作用效應

與電荷量子化

We discuss a theoretical model of an on-demand single-particle emitter that employs a quantum dot, attached to an integer or fractional quantum Hall edge state. Via an exact mapping of the model onto the spin-boson problem we show that Coulomb interactions between the dot and the chiral quantum Hall edge state, unavoidable in this setting, lead to adestruction of precise charge quantization in the emitted wave packet. Our findings cast doubt on the viability of this setup as a single-particle source of quantized charge pulses. We further show how to use a spin-boson master equation approach to explicitly calculate the current pulse shape in this setup.

Interaction Effects and Charge Quantization in Single-Particle Quantum Dot Emitters

G. Wagner et al.

Phys. Rev. Lett. 122, 127701 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.127701

軟物質與交叉科學

波狀泊肅葉流中湧現的吸引子

觸發生物細胞的分選

微流是控制粒子動力學的重要工具。一個重要的例子是生物細胞的分選，其依賴於可變形細胞橫向移動到流線的能力。經典的結果是，軟微粒子在通過直的微管道的流中總是遷移到其中心的吸引子處。在這篇快報中，Laumann等人彙報了通過波狀管道的流從根本上改變了總體圖像。這導致了另一種共存的軟粒子吸引子的湧現。它的湧現和偏離中心的位置取決於邊界調製和粒子特性。軟粒子的相對跨流遷移被解析的考慮，無界流的斯托克斯動力學模擬和有界流的格子玻爾茲曼模擬來解釋。例如，新穎的偏離中心的吸引子可用於在診斷中分離不同大小和彈性的細胞，這通常是細胞健康狀態的指示。

Emerging Attractor in Wavy Poiseuille Flows Triggers Sorting of Biological Cells

Matthias Laumann, et al.

Phys. Rev. Lett. 122, 128002 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.128002

複雜大分子旋轉對稱

破缺的廣義Flory理論

Kelly等人報道了在具有分支和環路的複雜大分子的最簡模型中自發旋轉對稱破缺。隨著自排斥強度的增加，轉變發生。在轉變點，密度分佈從各向同性轉變為各向異性。作者使用變分平均場理論來分析這種轉變，該理論將吉布斯－波戈留波夫－費因曼不等式與拉普拉斯矩陣的概念相結合。破缺對稱態的密度分佈由拉普拉斯矩陣的特徵值和特徵向量確定。在物理上，這反映了當排斥相互作用產生內部張力時，潛在的拓撲結構在確定大分子密度方面的作用越發重要。最終，變分自由能地貌發展成一個具有多個競爭的極小值的複雜結構。

Generalized Flory Theory for Rotational Symmetry Breaking of Complex Macromolecules

Josh Kelly, et al.

Phys. Rev. Lett. 122, 128003 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.128003

在運動接觸線處的受限液體的結晶狀排序

液體溶脹的軟彈性體和固體表面之間的摩擦取決於受限液體的狀態。為了測量受限液體的物理狀態，Nanjundiah等人使用界面敏感的和頻產生光譜技術來探測接觸區域。作者發現，當把十五烷－溶脹的聚（二甲基硅氧烷）透鏡浸沒在藍寶石襯底上的線性烷烴（十五烷）中進行滑動（摩擦）和拉脫（粘附）實驗時，液體的結晶狀排序僅在接觸線處發生，作者預測到最高的剪切力也在接觸線處。這種十五烷分子的結晶狀結構是短暫的，並顯示阿倫尼烏斯溫度依賴性具有異常長的弛豫時間（數百秒）和活化能（50千焦/摩），該值是塊狀十五烷液體的兩倍，溫度比塊狀熔化溫度（T_m= 9°C）高14到70°C。這種非尋常的長壽命結晶狀排序可以解釋為什麼這些系統相比於使用十五烷體積粘度（流體動力潤滑）的預測值顯示出更高的摩擦係數（邊界潤滑）。

Crystalline like Ordering of Confined Liquids at the Moving Contact Line

Kumar Nanjundiah, et al.

Phys. Rev. Lett. 122, 128004 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.128004

由尺寸分散球體形成的複雜晶體

膠體很少是完全均勻的，卻遵循尺寸、形狀和電荷的分佈。這種分散度可以是固有的（靜態的）或隨時間發展和變化（動態的）。儘管研究歷史悠久，但非均勻顆粒結晶和晶體形成的條件仍然不是很清楚。在本文中，Bommineni等人演示了，如果壓縮得足夠慢，具有高斯半徑分佈和高達19％的分散度的硬球總是結晶，並且它們的結晶方式驚人的複雜。作者通過加速事件驅動模擬來獲得該結果，該模擬具有描述靜態分散度的粒子交換步驟和描述動態分散度的粒子尺寸調整步驟。作者在高於6％的分散度發現了AB₂Laves相，AB₁₃相和Frank-Kasper相的區域。 Frank-Kasper區域包括與Pearson符號oS276近似的準晶體。作者的研究結果與軟物質和合金中的有序現象有關。

Complex Crystals from Size-Disperse Spheres

Praveen K. Bommineni,

Phys. Rev. Lett. 122, 128005 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.128005

堵塞作為多重臨界點

發生堵塞轉變時，體積模量B的不連續跳變是抗壓縮球體的臨界接觸網絡形成的結果。Liarte等人引入了具有潛在欠協調抗壓彈簧格子的格子模型，並允許向該彈簧格子中添加次近鄰彈簧。在這些模型中，堵塞轉變作為一種終止一系列剛性滲流轉變的多重臨界點而湧現。發生堵塞時用臨界網絡替換欠協調格子，可以忠實地描述堵塞及其與剛性滲流的關係。

Jamming as a Multicritical Point

Danilo B. Liarte, et al.

Phys. Rev. Lett. 122, 128006 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.128006

細胞中的擴散電泳：細胞中依賴於代謝的

顆粒輸運的一般非平衡、非馬達機制

人們對細胞質瞭解的越多，就越發意識到細胞質是非均勻的，而且是高度異質的。在任何異質溶液中，濃度梯度都存在，並且由於一種被稱為擴散電泳的機制，顆粒沿著這些梯度上下運動。Sear估計在代謝活躍的細胞內，只要顆粒的尺寸有至少幾十納米，顆粒的動力學就可以被擴散電泳強烈加速。較小物體（如單個蛋白）的動力學則基本不受影響。

Diffusiophoresis in Cells: A General Nonequilibrium, Nonmotor Mechanism for the Metabolism-Dependent Transport of Particles in Cells

Richard P. Sear

Phys. Rev. Lett. 122, 128101 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.128101

隨機語言模型

許多複雜的生成系統使用語言來創建結構化對象。 DeGiuli考慮了一個由加權並與上下文無關的語法定義的隨機語言模型。隨著語法權重的分佈變寬，作者發現了該模型經歷了從句子與噪聲無法區分的隨機相到攜帶非平凡信息的組織相的轉變。這標誌著語言中深層結構的湧現，並且可以通過能量和熵之間的競爭來理解。

Random Language Model

E. De Giuli

Phys. Rev. Lett. 122, 128301 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.128301

具有奇怪粘度的流體中的拓撲波

Fluids in which both time reversal and parity are broken can display a dissipationless viscosity that is odd under each of these symmetries. Here, we show how this odd viscosity has a dramatic effect on topological sound waves in fluids, including the number and spatial profile of topological edge modes. Odd viscosity provides a short-distance cutoff that allows us to define a bulk topological invariant on a compact momentum space. As the sign of odd viscosity changes, a topological phase transition occurs without closing the bulk gap. Instead, at the transition point, the topological invariant becomes ill defined because momentum space cannot be compactified. This mechanism is unique to continuum models and can describe fluids ranging from electronic to chiral active systems.

Topological Waves in Fluids with Odd Viscosity

Anton Souslov, et al.

Phys. Rev. Lett. 122, 128001 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.128001

對比分別具有極性和可極化

溶劑的電解液的介電特性

We examine the static dielectric constant of electrolyte solutions with a polar and/or polarizable small-molecule solvent using a classical field-theoretic approach. We compute corrections to the dielectric constant and screening length due to intra- and intermolecular correlations via a renormalized one-loop approximation, accounting for the excluded volume of both solvent and electrolyte. In the salt-free case, we verify the one-loop theory by comparison with full numerical solutions of the field theory. The one-loop theory predicts either a nonlinear dielectric decrement or increment with increasing salt, depending on whether the fluid correlations are dominated by the dipolar or polarizable nature of the solvent. These contrasting regimes of nonlinear dielectric behavior are consistent with experimental trends in high- and low-dielectric constant electrolyte solutions.

Contrasting Dielectric Properties of Electrolyte Solutions with Polar and Polarizable Solvents

Douglas J. Grzetic, et al.

Phys. Rev. Lett. 122, 128007 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.128007

通過可調的具有吸引力的單尖端

引導棒狀粒子的液晶自組織

Dispersions of rodlike colloidal particles exhibit a plethora of liquid crystalline states, including nematic, smectic A, smectic B, and columnar phases. This phase behavior can be explained by presuming the predominance of hard-corevolume exclusion between the particles. We show here how the self-organization of rodlike colloids can be controlled by introducing a weak and highly localized directional attractive interaction between one of the ends of the particles. This has been performed by functionalizing the tips of filamentous viruses by means of regioselectively grafting fluorescent dyes onto them,resulting in a hydrophobic patch whose attraction can be tuned by varying thenumber of bound dye molecules. We show, in agreement with our computer simulations, that increasing the single tip attraction stabilizes the smectic phaseat the expense of the nematic phase, leaving all other liquid crystalline phases invariant. For a sufficiently strong tip attraction, the nematic state may be suppressed completely to get a direct isotropic liquid-to-smectic phase transition. Our findings provide insights into the rational design of building blocks for functional structures formed at low densities.

Directing Liquid Crystalline Self-Organization of Rodlike Particles through Tunable Attractive Single Tips

Andrii Repula, et al.

Phys. Rev. Lett. 122, 128008 (2019)

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.128008

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