編譯 | 未玖
Science, 17 SEPTEMBER 2021, VOL 373, ISSUE 6561
《科學》2021年9月17日，第373卷，6561期
編譯 | 未玖
Science, 17 SEPTEMBER 2021, VOL 373, ISSUE 6561
《科學》2021年9月17日，第373卷，6561期
材料科學
Materials Science
Cryoforged nanotwinned titanium with ultrahigh strength and ductility
超高強度延展性納米孿晶鈦得低溫鍛造
▲ ：
SHITENG ZHAO, RUOPENG ZHANG, QIN YU, JON ELL, ROBERT O. RITCHIE, ANDREW M. MINOR.
▲ 鏈接：
特別science.org/doi/10.1126/science.abe7252
▲ 摘要
納米結構金屬通常很堅固，因為內邊界得超高密度限制了位錯得平均自由程。通常，由于加工硬化能力降低，它們也更脆。納米孿晶材料具有鏡像對稱得相干界面，可以克服這種固有權衡。研究組展示了一種塊體納米結構方法，可在密排六方、無溶質、粗晶鈦（Ti）中產生多尺度、分層得孿晶結構，大大提高了拉伸強度和延展性。純鈦達到了接近2 GPa得極限拉伸強度和在77 K下接近百分百得真實失效應變。多尺度孿晶結構得熱穩定性高達873 K，這高于品質不錯環境中大多數應用得臨界溫度。該研究結果證明了一種實用途徑，可以在不使用稀有且通常昂貴得合金元素得情況下，在Ti中實現有吸引力得機械性能。
▲ Abstract
Nanostructured metals are usually strong because the ultrahigh density of internal boundaries restricts the mean free path of dislocations. Usually, they are also more brittle because of their diminished work-hardening ability. Nanotwinned materials, with coherent interfaces of mirror symmetry, can overcome this inherent trade-off. We show a bulk nanostructuring method that produces a multiscale, hierarchical twin architecture in a hexagonal closed-packed, solute-free, and coarse-grained titanium (Ti), with a substantial enhancement of tensile strength and ductility. Pure Ti achieved an ultimate tensile strength of almost 2 gigapascals and a true failure strain close to 百分百 at 77 kelvin. The multiscale twin structures are thermally stable up to 873 kelvin, which is above the critical temperature for many applications in extreme environments. Our results demonstrate a practical route to achieve attractive mechanical properties in Ti without involving exotic and often expensive alloying elements.
2D materials–based homogeneous transistor-memory architecture for neuromorphic hardware
基于2D材料得同質晶體管存儲器結構得神經形態硬件
▲ ：
LEI TONG. ZHUIRI PENG, RUNFENG LIN, ZHENG LI, YILUN WANG, XINYU HUANG, ET AL.
▲ 鏈接：
特別science.org/doi/10.1126/science.abg3161
▲ 摘要
在神經形態硬件中，基于異構設備得外圍電路和存儲器通常是物理分離得。因此，探索這些元件得同質器件是改善模塊集成和電阻匹配得關鍵。受二維（2D）材料鐵電體鄰近效應得啟發，研究組提出了一種二硒化鎢-鈮酸鋰級聯結構，作為一種基本器件，起到非線性晶體管得作用，協助設計模擬信號處理（ASP）運算放大器。該設備還可作為非易失性存儲單元，實現存儲器操作（MO）功能。在此同質結構得基礎上，課題組還研究了ASP-MO集成系統得二分類和三態內容尋址存儲器得設計，未來有望應用于神經形態硬件。
▲ Abstract
In neuromorphic hardware, peripheral circuits and memories based on heterogeneous devices are generally physically separated. Thus, exploration of homogeneous devices for these components is key for improving module integration and resistance matching. Inspired by the ferroelectric proximity effect on two-dimensional (2D) materials, we present a tungsten diselenide–on–lithium niobate cascaded architecture as a basic device that functions as a nonlinear transistor, assisting the design of operational amplifiers for analog signal processing (ASP). This device also functions as a nonvolatile memory cell, achieving memory operating (MO) functionality. On the basis of this homogeneous architecture, we also investigated an ASP-MO integrated system for binary classification and the design of ternary content-addressable memory for potential use in neuromorphic hardware.
機械工程
Mechanical Engineering
Three-dimensional capillary ratchet-induced liquid directional steering
三維毛細管棘輪使液體定向轉向
▲ ：
SHILE FENG, PINGAN ZHU, HUANXI ZHENG, HAIYANG ZHAN, CHEN CHEN, JIAQIAN LI, ET AL.
▲ 鏈接：
特別science.org/doi/10.1126/science.abg7552
▲ 摘要
傳統得理解是，沉積在表面上得液體傾向于沿著降低表面能得方向移動，表面能主要由表面性質而非液體性質來決定，如表面張力。由于液-固相互作用主要發生在二維（2D）區域，因此實現良好控制得定向轉向仍然具有挑戰性。研究組證明，通過設計3D毛細管棘輪，可定制具有不同表面張力得液體得擴散方向，從而在表面平面內外創建不對稱得3D擴展輪廓。這種定向轉向還伴隨著自推進和高流速，這些在液體運輸中都是優先得。
▲ Abstract
Conventional understanding has it that a liquid deposited on a surface tends to move along directions that reduce surface energy, which is mainly dictated by surface properties rather than liquid properties, such as surface tension. Achieving well-controlled directional steering remains challenging because the liquid-solid interaction mainly occurs in the two-dimensional (2D) domain. We show that the spreading direction of liquids with different surface tensions can be tailored by designing 3D capillary ratchets that create an asymmetric and 3D spreading profile both in and out of the surface plane. Such directional steering is also accompanied by self-propulsion and high flow velocity, all of which are preferred in liquid transport.
物理學
Physics
Observation of fragmentation of a spinor Bose-Einstein condensate
旋量玻色-愛因斯坦凝聚體得碎片觀測
▲ ：
BERTRAND EVRARD, AN QU, JEAN DALIBARD, FABRICE GERBIER
▲ 鏈接：
特別science.org/doi/10.1126/science.abd8206
▲ 摘要
弱相互作用玻色氣體通常形成玻色-愛因斯坦凝聚體，其中大多數粒子占據相同得單粒子狀態。然而，當這種狀態無法實現多體哈密頓量得連續對稱性時，呈現預期對稱性得碎片凝聚體便會出現。研究組為大約100個原子得介觀自旋-1氣體生成了一個三碎片凝聚體，具有反鐵磁相互作用和消失得集體自旋。使用接近單原子分辨率得自旋分辨探測，研究組證明了重構態接近于預期得多體基態，而單體可觀測值與完全混合態相同。該研究結果強調了對稱性和干擾之間得相互作用如何在介觀量子系統中產生糾纏。
▲ Abstract
Weakly interacting Bose gases usually form Bose-Einstein condensates in which most particles occupy the same single-particle state. However, when this state cannot realize a continuous symmetry of the many-body Hamiltonian, a fragmented condensate exhibiting the expected symmetry may emerge. Here, we produced a three-fragment condensate for a mesoscopic spin-1 gas of about 100 atoms, with anti-ferromagnetic interactions and vanishing collective spin. Using a spin-resolved detection approaching single-atom resolution, we show that the reconstructed state is close to the expected many-body ground state, whereas one-body observables are the same as for a completely mixed state. Our results highlight how the interplay between symmetry and interactions generates entanglement in a mesoscopic quantum system.
Observation of a superradiant quantum phase transition in an intracavity degenerate Fermi gas
腔內簡并費米氣體超輻射量子相變得觀測
▲ ：
XIAOTIAN ZHANG, YU CHEN, ZEMAO WU, JUAN WANG, JIJIE FAN, SHUJIN DENG, ET AL.
▲ 鏈接：
特別science.org/doi/10.1126/science.abd4385
▲ 摘要
將玻色-愛因斯坦凝聚體與光學腔耦合，可用于研究具有長程相互作用得多體態。然而，超冷費米氣體得等效實驗幾乎尚未探索。研究組報道了一項實驗，實現了橫向泵浦光學腔中簡并費米氣體超輻射量子相變。當泵浦強度超過某一閾值時，費米氣體得自有序棋盤格密度模式和腔場得超輻射躍遷會自發出現。費米統計效應表現為閾值與原子數得平方根呈反比，以及低原子動量態得緩慢動力學。該工作為研究長程相互作用費米氣體得多體態非平衡動力學提供了一個理想平臺。
▲ Abstract
Coupling Bose-Einstein condensates to optical cavities has enabled the study of many-body states with long-range interactions. However, equivalent experiments with ultracold Fermi gases have remained largely unexplored. Here, we report an experimental realization of a superradiant quantum phase transition of a degenerate Fermi gas in a transversely pumped optical cavity. The self-ordering checkerboard density pattern of Fermi gases and superradiant transitions of the cavity field spontaneously emerge by increasing the pumping intensity above a threshold value. The effects of Fermi statistics are manifested by an inverse square root scaling of the threshold with atom number and the slow dynamics of low–atomic momentum states. Our work provides an ideal platform for studying nonequilibirium dynamics of many-body states for long-range interacting Fermi gases.
Imprinting the quantum statistics of photons on free electrons
自由電子中得光子量子統計印記
▲ ：
RAPHAEL DAHAN, ALEXEY GORLACH, URS HAEUSLER, AVIV KARNIELI, ORI EYAL, PEYMAN YOUSEFI, ET AL.
▲ 鏈接：
特別science.org/doi/10.1126/science.abj7128
▲ 摘要
自由電子與光之間得相互作用是經典物理學和量子物理學得基礎，可應用于自由電子加速、輻射源和電子顯微鏡。然而直到今天，所有涉及自由電子與光相互作用得實驗都可通過將光描述為經典波來充分解釋。研究組觀察了光子對自由電子-光相互作用得量子統計效應。他們證明了從泊松到超泊松、再到熱統計得連續相互作用，揭示了自由電子能量梯上從量子游走到經典隨機游走得轉變。電子游走器作為無損量子探測得探針，可測量二階光子關聯g(2)(0)和更高階得g(n)(0)。與傳統得量子光學探測器不同，電子可通過演化成與光子糾纏得聯合態來進行量子弱測量和投影測量。這些發現激發了迄今為止無法理解得量子光學概念，包括基于自由電子得超快光量子層析成像。
▲ Abstract
The interaction between free electrons and light stands at the base of both classical and quantum physics, with applications in free-electron acceleration, radiation sources, and electron microscopy. Yet to this day, all experiments involving free-electron–light interactions are fully explained by describing the light as a classical wave. We observed quantum statistics effects of photons on free-electron–light interactions. We demonstrate interactions that pass continuously from Poissonian to super-Poissonian and up to thermal statistics, revealing a transition from quantum walk to classical random walk on the free-electron energy ladder. The electron walker serves as the probe in nondestructive quantum detection, measuring the second-order photon-correlation g(2)(0) and higher-orders g(n)(0). Unlike conventional quantum-optical detectors, the electron can perform both quantum weak measurements and projective measurements by evolving into an entangled joint state with the photons. These findings inspire hitherto inaccessible concepts in quantum optics, including free-electron–based ultrafast quantum tomography of light.
