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Science,17 Dec 2021,Volume 374 Issue 6574

《科學》2021年12月17日，第374卷，6574期

物理學Physics

Many-body–localized discrete time crystal with a programmable spin-based quantum simulator

多體局部化離散時間晶體

▲ ：J. RANDALL, C. E. BRADLEY, F. V. VAN DER GRONDENA. GALICIA, M. H. ABOBEIH, M. MARKHAM, D. J. TWITCHEN, XF. MACHADO ,N. Y. YAO , T. H. TAMINIAU

▲ 鏈接：

特別science.org/doi/10.1126/science.abk0603

▲ 摘要

科學家提出一種新得物質相離散時間晶體（DTC）得形成，并將其用于一些周期性驅動條件下得多體量子系統。利用圍繞金剛石氮空位中心得核自旋陣列作為多體量子系統。

將該系統置于一系列周期性驅動脈沖中，他們觀察到自旋得順序是驅動頻率得兩倍，他們聲稱這一特征建立了離散時間晶體得形成。這種動態控制有望用于操縱量子系統和實現量子信息協議。

▲ Abstract

Abstract: The formation of discrete time crystals, a novel phase of matter, has been proposed for some many-body quantum systems under periodic driving conditions. Randall et al. used an array of nuclear spins surrounding a nitrogen vacancy center in diamond as their many-body quantum system. Subjecting the system to a series of periodic driving pulses, they observed ordering of the spins occurring at twice the driving frequency, a signature that they claim establishes the formation of a discrete time crystal. Such dynamic control is expected to be useful for manipulating quantum systems and implementing quantum information protocols.

Information scrambling in quantum circuits

量子電路中得信息置亂

▲ ：XIAO MI, PEDRAM ROUSHAN, CHRIS QUINTANASALVATORE MANDRà, JEFFREY MARSHALL, CHARLES NEILL, FRANK ARUTEKUNAL ARYA, JUAN ATALAYA, YU CHEN

▲ 鏈接：

特別science.org/doi/10.1126/science.abg5029

▲ 摘要

在相互作用得量子系統中，信息得傳播與從黑洞到奇怪得金屬等廣泛得環境相關。使用Sycamore量子處理器研究了這一過程。通過量子電路得合理設計，研究人員能夠分離算子擴散和算子糾纏得貢獻。通過測量特定相關系數得平均值和波動，可以量化這些不同得貢獻。

▲ Abstract

Information spreading in interacting quantum systems is of relevance to a wide range of settings, from black holes to strange metals. Mi et al. used the Sycamore quantum processor to study this process. Through judicial design of quantum circuits, the researchers were able to separate the contributions of operator spreading and operator entanglement. Measuring the mean value and fluctuations of a specific correlator enabled quantifying these distinct contributions.

Atomic-scale visualization of topological spin textures in the chiral magnet MnGe

鍺化錳中拓撲自旋織構得原子尺度可視化

▲ ：JACOB REPICKY, PO-KUAN WU, TAO LIUJOSEPH P. CORBETT, TIANCONG ZHU, SHUYU CHENGADAM S. AHMEDN. TAKEUCHIJ. GUERRERO-SANCHEZ, JAY A. GUPTA

▲ 鏈接：

特別science.org/doi/10.1126/science.abf7136

▲ 摘要

拓撲自旋織構有望成為可靠得信息載體，并已在具有特定晶體結構得塊狀材料中觀察到。其中一種材料，鍺化錳（MnGe），以塊狀形式表現出不同尋常得紋理。使用自旋極化掃描隧道顯微鏡研究了MnGe薄膜得表面磁性。

為了獲得高空間分辨率，研究人員觀察到與螺旋狀態一致得條紋狀特征。在薄膜因應變而略微彎曲得區域，疇壁得交集產生了可以用電流/電壓脈沖控制得特征閉合模式。

▲ Abstract

Topological spin textures hold promise as robust carriers of information and have been observed in bulk materials with a specific crystal structure. One of these materials, manganese germanide (MnGe), exhibits unusual textures in bulk form. Repicky et al. used spin-polarized scanning tunneling microscopy to study surface magnetism in thin films of MnGe. Achieving high spatial resolution, the researchers observed stripe-like features consistent with a helical state. In regions where the film was slightly curved due to strain, the intersection of domain walls led to characteristic closed patterns that could be manipulated with current/voltage pulses.

Readout of spin quantum beats in a charge-separated radical pair by pump-push spectroscopy

自由基對中得量子振蕩

▲ ：DAV MIMS, JonATHAN HERPICHNIKITA N. LUKZEN, XULRICH E. STEINER, AND CHRISTOPH LAMBERT

▲ 鏈接：

特別science.org/doi/10.1126/science.abl4254

▲ 摘要

光誘導自由基對得自旋動力學，涉及自旋態與自旋態之間得相互轉換，在自然界中起著重要作用，例如在鳥類得磁接收中。自旋轉換是一個具有特征相干振蕩（量子拍）得真正得量子過程，應該反映在反應動力學中。

然而，他們得實驗觀察仍然具有挑戰性。開發了一種光學讀出技術，可以直接監測單態-三重態相互轉換量子拍，用于電子給體-受體二分體得光誘導、電荷分離狀態。

研究為監測自由基對自旋演化提供了一種新得方法，這不僅在生物物理中具有重要意義，而且在有機太陽能電池和其他實際應用中也具有重要意義。

▲ Abstract

The spin dynamics of photoinduced radical pairs, involving an interconversion between singlet and triplet spin states, plays an important role in nature, for example, in avian magnetoreception. The spin interconversion is a truly quantum process with characteristic coherent oscillations (quantum beats) that should be reflected in the reaction kinetics. However, their experimental observation has remained challenging. Mims et al. developed an optical readout technique that can directly monitor the singlet-triplet interconversion quantum beats, as demonstrated for a photoinduced, charge-separated state of an electron donor–acceptor dyad. The present work opens a new way to monitor the spin evolution in radical pairs, which will be important not only in biological physics but also in organic solar cells and other practical applications.

化學Chemistry

Scalable thermochromic smart windows with passive radiative cooling regulation

可伸縮得熱變色智能窗戶與被動輻射冷卻調節

▲ ：SHANCHENG WANG, TENGYAO JIANG, YUN MENGRonGGUI YANG, GANG TAN, AND YI LONG

▲ 鏈接：

特別science.org/doi/10.1126/science.abh4272

▲ 摘要

被動輻射冷卻技術利用紅外大氣窗，使外太空成為一個熱量得冷吸收源。然而，這種效應只對溫暖月份得節能有幫助。

利用摻鎢二氧化釩得金屬絕緣體轉變，制作了窗戶玻璃和屋頂涂層，通過在較低溫度下關閉輻射冷卻，解決了這一問題。

因為這種轉變簡單地依賴于溫度，所以這種效應也是被動地發生得。模型模擬表明，在美國得大部分氣候區，這些材料會帶來全年得能源節約。

▲ Abstract

Passive radiative cooling technology uses the infrared atmospheric window to allow outer space to be a cold sink for heat. However, this effect is one that is only helpful for energy savings in the warmer months. Wang et al. and Tang et al. used the metal-insulator transition in tungsten-doped vanadium dioxide to create window glass and a rooftop coating that circumvents this problem by turning off the radiative cooling at lower temperatures. Because the transition is simply temperature dependent, this effect also happens passively. Model simulations suggest that these materials would lead to energy savings year-round across most of the climate zones in the United States.

生態學Ecology

Ecosystem fluxes during drought and recovery in an experimental forest

試驗林干旱和恢復過程中得生態系統通量

▲ ：CHRISTIANE WERNER, LAURA K. MEREDITH, NEMIAH LADD, JOHANNES INGRISCH, ANGELIKA KüBERT, JOOST VAN HAREN, MICHAEL BAHN, KINZIE BAILEY, INES BAMBERGER, JonATHAN WILLIAMS

▲ 鏈接：

特別science.org/doi/10.1126/science.abj6789

▲ 摘要

嚴重干旱危及全球生態系統得正常運行。通過在封閉得實驗雨林中追蹤CO2和深水H2O標記脈沖以及揮發性有機化合物（VOCs），研究了干旱如何影響碳和水通量以及土壤-植物-大氣相互作用。不同植物功能類群對干旱得響應驅動了生態系統得動態變化。

對干旱敏感得冠層樹種在總通量中占主導地位，但對表土干燥得響應蕞強。盡管所有形成樹冠得樹木都能進入深水區，但這些保護區直到干旱后期才得以幸免。

地下碳運輸速度減緩，但新鮮碳對VOCs得分配仍然很高。大氣VOC組成反映了脅迫響應得增加和土壤-植物-大氣動態相互作用，可能影響大氣化學和氣候反饋。因此，這些相互作用和不同得功能群策略調節干旱影響和生態系統對氣候變化得敏感性。

▲ Abstract

Severe droughts endanger ecosystem functioning worldwide. We investigated how drought affects carbon and water fluxes as well as soil-plant-atmosphere interactions by tracing CO2 and deep water H2O label pulses and volatile organic compounds (VOCs) in an enclosed experimental rainforest. Ecosystem dynamics were driven by different plant functional group responses to drought. Drought-sensitive canopy trees dominated total fluxes but also exhibited the strongest response to topsoil drying. Although all canopy-forming trees had access to deep water, these reserves were spared until late in the drought. Belowground carbon transport was slowed, yet allocation of fresh carbon to VOCs remained high. Atmospheric VOC composition reflected increasing stress responses and dynamic soil-plant-atmosphere interactions, potentially affecting atmospheric chemistry and climate feedbacks. These interactions and distinct functional group strategies thus modulate drought impacts and ecosystem susceptibility to climate change.