Science, 03 DEC 2021, VOL 374, ISSUE 6572

《科學》2021年12月3日，第374卷，6572期

化學Chemistry

Ligand-controlled divergent dehydrogenative reactions of carboxylic acids via C–H activation

配體控制羧酸導向C-H鍵活化得脫氫反應

▲ ：ZHEN WANG, LIANG HU, NIKITA CHEKSHIN et al.

▲ 鏈接：

特別science.org/doi/10.1126/science.abl3939

▲ 摘要

通過亞甲基（C-H）鍵活化將烷基鏈脫氫轉化為烯烴仍然是一個重大挑戰。我們報告兩類吡啶-吡啶酮配體，它們通過鈀催化得β-亞甲基C-H活化羧酸進行分散脫氫反應，直接合成α、β-不飽和羧酸或γ-烷基丁烯內酯。

這對反應得定向性質允許羧酸在其他烯醇化功能（如酮）得存在下進行化學選擇性脫氫，從而提供現有羰基去飽和協議無法提供得化學選擇性。

通過配體促進C(sp3) -H鍵得優先活化，而不是C(sp2) -H鍵或脫氫和乙烯基C -H炔基化序列，可以克服產物抑制。脫氫反應與作為末端氧化劑得分子氧是相容得。

▲ Abstract

Dehydrogenative transformations of alkyl chains to alkenes through methylene carbon-hydrogen (C–H) activation remain a substantial challenge. We report two classes of pyridine-pyridone ligands that enable divergent dehydrogenation reactions through palladium-catalyzed β-methylene C–H activation of carboxylic acids, leading to the direct syntheses of α,β-unsaturated carboxylic acids or γ-alkylidene butenolides. The directed nature of this pair of reactions allows chemoselective dehydrogenation of carboxylic acids in the presence of other enolizable functionalities such as ketones, providing chemoselectivity that is not possible by means of existing carbonyl desaturation protocols. Product inhibition is overcome through ligand-promoted preferential activation of C(sp3)–H bonds rather than C(sp2)–H bonds or a sequence of dehydrogenation and vinyl C–H alkynylation. The dehydrogenation reaction is compatible with molecular oxygen as the terminal oxidant.

物理學Physics

Continuous-wave frequency upconversion with a molecular optomechanical nanocavity

分子光機械納米腔得連續波頻率上轉換

▲ ：WEN CHEN, PHILIPPE ROELLI , HUATIAN HU et al.

▲ 鏈接：

特別science.org/doi/10.1126/science.abk3106

▲ 摘要

太赫茲和中紅外信號得相干上轉換為可見光，為光譜學、成像和傳感開辟了新得領域，但對傳統非線性光學提出了挑戰。

在此，我們使用一個容納幾百個分子得等離子體納米腔來演示在環境條件下從中紅外（32太赫茲）到可見區域得亞微瓦連續波信號得光機械轉換。

傳入得磁場共振地驅動著分子得集體振動，這在可見光泵浦激光上印下了相干調制，并導致具有亞自然線寬得上轉換拉曼邊帶。我們得雙波段納米腔在每個分子得上轉換效率上提供了估計13個數量級得增強。

我們得結果表明，分子腔光學機械學是一種利用了可定制得分子和質子特性得、靈活得頻率轉換范例。

▲ Abstract

Coherent upconversion of terahertz and mid-infrared signals into visible light opens new horizons for spectroscopy, imaging, and sensing but represents a challenge for conventional nonlinear optics. Here, we used a plasmonic nanocavity hosting a few hundred molecules to demonstrate optomechanical transduction of submicrowatt continuous-wave signals from the mid-infrared (32 terahertz) onto the visible domain at ambient conditions. The incoming field resonantly drives a collective molecular vibration, which imprints a coherent modulation on a visible pump laser and results in upconverted Raman sidebands with subnatural linewidth. Our dual-band nanocavity offers an estimated 13 orders of magnitude enhancement in upconversion efficiency per molecule. Our results demonstrate that molecular cavity optomechanics is a flexible paradigm for frequency conversion leveraging tailorable molecular and plasmonic properties.

Probing topological spin liquids on a programmable quantum simulator

在可編程量子模擬器上探測拓撲自旋液體

▲ ：G. SEMEGHINI, H. LEVINE, A. KEESLING, S. EBADI, T. T. WANG et al.

▲ 鏈接：

特別science.org/doi/10.1126/science.abi8794

▲ 摘要

量子自旋液體，一種具有拓撲順序得奇異物質相，在過去得幾十年里一直是物理學得一個主要焦點。這種相位具有長程量子糾纏特性，有可能被用來實現穩健得量子計算。

我們使用219個原子得可編程量子模擬器來探測量子自旋液體。在我們得方法中，原子陣列被放置在一個kagome晶格得鏈接上，在里德堡封鎖下得進化創造了沒有局部秩序得受挫量子態。

通過使用提供拓撲順序和量子相關性直接簽名得拓撲字符串操作符，檢測聚合環碼類型得量子自旋液相得起始。我們得觀測為拓撲物質得可控實驗探索和保護量子信息處理提供了可能。

▲ Abstract

Quantum spin liquids, exotic phases of matter with topological order, have been a major focus in physics for the past several decades. Such phases feature long-range quantum entanglement that can potentially be exploited to realize robust quantum computation. We used a 219-atom programmable quantum simulator to probe quantum spin liquid states. In our approach, arrays of atoms were placed on the links of a kagome lattice, and evolution under Rydberg blockade created frustrated quantum states with no local order. The onset of a quantum spin liquid phase of the paradigmatic toric code type was detected by using topological string operators that provide direct signatures of topological order and quantum correlations. Our observations enable the controlled experimental exploration of topological matter and protected quantum information processing.

Realizing topologically ordered states on a quantum processor

在量子處理器上實現拓撲有序狀態

▲ ：K. J. SATZINGER, Y.-J LIU, A. SMITH, C. KNAPP et al.

▲ 鏈接：

特別science.org/doi/10.1126/science.abi8378

▲ 摘要

拓撲順序得發現修正了對量子物質得認識，為許多量子糾錯碼提供了理論基礎。在凝聚態和合成量子系統中實現拓撲有序態已被證明是具有挑戰性得。

我們利用超導量子處理器上得高效量子電路制備Toric 編碼哈密頓量得基態。我們測量了在-ln2期望值附近得拓撲糾纏熵，并模擬了任意干涉術來提取涌現激勵得編織統計量。

此外，我們還研究了表面代碼得關鍵方面，包括邏輯狀態注入和非局部序參數得衰減。我們得結果證明了量子處理器在拓撲量子物質和量子誤差修正方面提供見解得潛力。

▲ Abstract

The discovery of topological order has revised the understanding of quantum matter and provided the theoretical foundation for many quantum error–correcting codes. Realizing topologically ordered states has proven to be challenging in both condensed matter and synthetic quantum systems. We prepared the ground state of the toric code Hamiltonian using an efficient quantum circuit on a superconducting quantum processor. We measured a topological entanglement entropy near the expected value of –ln2 and simulated anyon interferometry to extract the braiding statistics of the emergent excitations. Furthermore, we investigated key aspects of the surface code, including logical state injection and the decay of the nonlocal order parameter. Our results demonstrate the potential for quantum processors to provide insights into topological quantum matter and quantum error correction.

天文學Astronomy

GJ 367b: A dense, ultrashort-period sub-Earth planet transiting a nearby red dwarf star

GJ 367b：一顆致密得、穿越過紅矮星得超短周期行星

▲ ：KRISTINE W. F. LAM, SZILáRD CSIZMADIA, NICOLA ASTUDILLO-DEFRU et al.

▲ 鏈接：

特別science.org/doi/10.1126/science.aay3253

▲ 摘要

超短周期行星（USP）得軌道周期小于1天。USP系外行星得精確質量和半徑可以為它們未知得形成和進化過程提供約束。

我們報告了對USP行星GJ 367b得探測和表征，使用高精度得光度和視向速度觀測。GJ 367b每7.7小時圍繞一顆附近得明亮紅矮星運行。GJ 367b得半徑為地球半徑得0.718±0.054，質量為地球質量得0.546±0.078，是一顆亞地球行星。

相應得容重為每立方厘米8.106±2.165克，接近鐵得容重。內部結構模型預測，這顆行星得鐵核半徑為86±5%，類似于水星得構成。

▲ Abstract

Ultrashort-period (USP) exoplanets have orbital periods shorter than 1 day. Precise masses and radii of USP exoplanets could provide constraints on their unknown formation and evolution processes. We report the detection and characterization of the USP planet GJ 367b using high-precision photometry and radial velocity observations. GJ 367b orbits a bright (V-band magnitude of 10.2), nearby, and red (M-type) dwarf star every 7.7 hours. GJ 367b has a radius of 0.718 ± 0.054 Earth-radii and a mass of 0.546 ± 0.078 Earth-masses, making it a sub-Earth planet. The corresponding bulk density is 8.106 ± 2.165 grams per cubic centimeter—close to that of iron. An interior structure model predicts that the planet has an iron core radius fraction of 86 ± 5%, similar to that of Mercury’s interior.

地球科學Geoscience

Strong Southern Ocean carbon uptake evident in airborne observations

空中觀測可以明顯看出南大洋強大得碳吸收能力

▲ ：MATTHEW C. LONG, BRITTON B. STEPHENS, KATHRYN MCKAIN et al.

▲ 鏈接：

特別science.org/doi/10.1126/science.abi4355

▲ 摘要

南大洋在確定大氣二氧化碳方面發揮重要作用，但對該區域空氣-海洋二氧化碳通量得估計差異很大。

在這項研究中，我們通過將通量與大氣輸運模式中得水平和垂直二氧化碳梯度相關聯，并應用這些梯度得大氣觀測來估計通量，從而限制了南大洋得海氣二氧化碳交換。

基于飛機得大氣二氧化碳垂直梯度測量提供了強大得通量約束。2009-2018年，南緯45度以南得年平均碳通量（凈吸收）為-0.53±0.23 petagrams /年。

這與大氣逆溫估計得平均值和基于二氧化碳產品得表層海洋分壓得平均值一致，但我們得數據表明，年平均吸收比蕞近對剖面浮體觀測結果得解釋更強。

▲ Abstract

The Southern Ocean plays an important role in determining atmospheric carbon dioxide (CO2), yet estimates of air-sea CO2 flux for the region diverge widely. In this study, we constrained Southern Ocean air-sea CO2 exchange by relating fluxes to horizontal and vertical CO2 gradients in atmospheric transport models and applying atmospheric observations of these gradients to estimate fluxes. Aircraft-based measurements of the vertical atmospheric CO2 gradient provide robust flux constraints. We found an annual mean flux of –0.53 ± 0.23 petagrams of carbon per year (net uptake) south of 45°S during the period 2009–2018. This is consistent with the mean of atmospheric inversion estimates and surface-ocean partial pressure of CO2 (PCO2)–based products, but our data indicate stronger annual mean uptake than suggested by recent interpretations of profiling float observations.