编译 | 李言

Nature,  12 October 2023, Volume 622 Issue 7982

《自然》2023年10月12日，第622卷，7982期

天文学Astronomy

A planetary collision afterglow and transit of the resultant debris cloud

行星碰撞的余辉和产生的碎片云凌日

▲ 作者：Matthew Kenworthy, Simon Lock et al.

▲ 链接：

https://www.nature.com/articles/s41586-023-06573-9

▲ 摘要：

在此，我们报告对大约3亿年前的年轻类太阳恒星ASASSN-21qj的综合观测：与黑体温度1000开尔文一致的红外增亮和持续约1000天的恒星的4%的光度，与持续约500天的复杂和深度、波长依赖的光学日食进行部分重叠。

此次日食开始于红外增亮后的2.5年，这意味着它的轨道周期至少为2.5年。这些观测结果与2颗质量为地球数倍至数十倍的系外行星在距离中心恒星2-16个天文单位的地方发生碰撞后的情况是一致的。

这样的撞击产生了一个炙热的、高度延伸的撞击后遗迹，其产生的亮度可以解释红外观测结果。撞击碎片后的凌日，被轨道运动分解，导致主星日食产生。

▲ Abstract：

Here we report combined observations of the young (about 300 million years old), solar-like star ASASSN-21qj: an infrared brightening consistent with a blackbody temperature of 1,000 Kelvin and a luminosity that is 4 percent that of the star lasting for about 1,000 days, partially overlapping in time with a complex and deep, wavelength-dependent optical eclipse that lasted for about 500 days. The optical eclipse started 2.5 years after the infrared brightening, implying an orbital period of at least that duration. These observations are consistent with a collision between two exoplanets of several to tens of Earth masses at 2-16 astronomical units from the central star. Such an impact produces a hot, highly extended post-impact remnant with sufficient luminosity to explain the infrared observations. Transit of the impact debris, sheared by orbital motion into a long cloud, causes the subsequent complex eclipse of the host star.

A super-massive Neptune-sized planet

一颗海王星大小的超大质量行星

▲ 作者：Luca Naponiello, Luigi Mancini et al.

▲ 链接：

https://www.nature.com/articles/s41586-023-06499-2

▲ 摘要：

这里我们展示了凌日行星TOI-1853 b的观测结果，它的半径为地球半径的3.46±0.08倍，每1.24天绕一颗矮星运行一次。这颗行星的质量是地球的73.2±2.7倍，几乎是目前已知的海王星大小行星的2倍，密度为9.7±0.8克每立方厘米。

这些数字让我们认为TOI-1853 b在海王星沙漠之中，这意味着重元素占据了它的大部分质量。TOI-1853 b的特性给传统的行星形成和演化理论提出了一个难题。它可能是几次原行星碰撞产生的结果，也可能是一颗最初高离心率的行星向其母恒星迁移后的最终状态。

▲ Abstract：

Here we show observations of the transiting planet TOI-1853 b, which has a radius of 3.46 ± 0.08 Earth radii and orbits a dwarf star every 1.24 days. This planet has a mass of 73.2 ± 2.7 Earth masses, almost twice that of any other Neptune-sized planet known so far, and a density of 9.7 ± 0.8 grams per cubic centimetre. These values place TOI-1853 b in the middle of the Neptunian desert and imply that heavy elements dominate its mass. The properties of TOI-1853 b present a puzzle for conventional theories of planetary formation and evolution, and could be the result of several proto-planet collisions or the final state of an initially high-eccentricity planet that migrated closer to its parent star.

物理学Physics

State estimation of a physical system with unknown governing equations

对未知控制方程物理系统的状态评估

▲ 作者：Kevin Course & Prasanth B. Nair

▲ 链接：

https://www.nature.com/articles/s41586-023-06574-8

▲ 摘要：

在此，我们提出了一种用马尔科夫决策过程进行随机变分推理的再参数化技巧。这种技巧可以使用近似贝叶斯方法进行状态估计，其中控制系统随时间演变的方程部分或完全未知。

与传统的状态评估技术相比，我们的方法从近似贝叶斯的角度同时学习数学模型中的缺失项和状态评估。这一发展使状态估计方法能够应用于目前被证明无法解决的问题。最后，虽然我此次专注于状态评估，但这里所做的随机变分推理的进展适用于机器学习中更广泛的问题。

▲ Abstract：

Here we present a reparametrization trick for stochastic variational inference with Markov Gaussian processes that enables an approximate Bayesian approach for state estimation in which the equations governing how the system evolves over time are partially or completely unknown. In contrast to classical state-estimation techniques, our method learns the missing terms in the mathematical model and a state estimate simultaneously from an approximate Bayesian perspective. This development enables the application of state-estimation methods to problems that have so far proved to be beyond reach. Finally, although we focus on state estimation, the advancements to stochastic variational inference made here are applicable to a broader class of problems in machine learning.

High-fidelity parallel entangling gates on a neutral-atom quantum computer

中性原子量子计算机上的高保真平行纠缠门

▲ 作者：Simon J. Evered, Dolev Bluvstein et al.

▲ 链接：

https://www.nature.com/articles/s41586-023-06481-y

▲ 摘要：

在此，我们报告以99.5%的保真度在多达60个原子上并行实现的双量子比特纠缠门，这一数值超过了表面码的纠错阈值。我们的方法使用的是基于最优控制的快速单脉冲门，同时利用原子暗态来减少散射，并改进里德堡激发和原子冷却。

我们使用基于重复门应用的几种方法对保真度进行基准测试，表征物理误差源并概述未来的改进。最后，我们概括了设计涉及FC碰碰胡老虎机法典-提高赢钱机率的下注技巧量子比特的纠缠门的方法，并且通过实现低误差的三量子比特门进行展示。

▲ Abstract：

Here we report the realization of two-qubit entangling gates with 99.5% fidelity on up to 60 atoms in parallel, surpassing the surface-code threshold for error correction. Our method uses fast, single-pulse gates based on optimal control, atomic dark states to reduce scattering and improvements to Rydberg excitation and atom cooling. We benchmark fidelity using several methods based on repeated gate applications, characterize the physical error sources and outline future improvements. Finally, we generalize our method to design entangling gates involving a higher number of qubits, which we demonstrate by realizing low-error three-qubit gates.　

High-fidelity gates and mid-circuit erasure conversion in an atomic qubit

原子量子比特中的高保真门和中电路擦除转换

▲ 作者：Shuo Ma, Genyue Liu et al.

▲ 链接：

https://www.nature.com/articles/s41586-023-06438-1

▲ 摘要：

在此，我们展示了一个在171Yb中利用原子核自旋的长寿命亚稳态的新中性原子量子位。较长的相干时间和对里德堡态的快速激发使得保真度分别为0.9990(1)和0.980(1)的单量子比特门和双量子比特门成为可能。重要的是，大部分门错误会导致量子比特子空间向基态的衰减。

通过对这些错误进行快速的中电路检测，我们将它们转换为擦除错误；在检测过程中，计算空间中剩余量子位的诱导错误概率小于10⁻⁵。我们的研究建立了亚稳态171Yb，一个可以实现容错量子计算的、有前景的平台。

▲ Abstract：

Here we demonstrate a new neutral atom qubit using the nuclear spin of a long-lived metastable state in 171Yb. The long coherence time and fast excitation to the Rydberg state allow one- and two-qubit gates with fidelities of 0.9990(1) and 0.980(1), respectively. Importantly, a large fraction of all gate errors result in decays out of the qubit subspace to the ground state. By performing fast, mid-circuit detection of these errors, we convert them into erasure errors; during detection, the induced error probability on qubits remaining in the computational space is less than 10⁻⁵. This work establishes metastable 171Yb as a promising platform for realizing fault-tolerant quantum computing.

生态学Ecology

Ongoing declines for the world’s amphibians in the face of emerging threats

世界两栖动物数量因新威胁持续下降

▲ 作者：Jennifer A. Luedtke, Janice Chanson et al.

▲ 链接：

https://www.nature.com/articles/s41586-023-06578-4

▲ 摘要：

在此，我们评估8011种列入国际自然保护联盟濒危物种红色名录的物种后，报告第二次全球两栖动物评估的结果。我们发现两栖动物是最受威胁的脊椎动物（40.7%的物种在全球受到威胁）。最新的红色名录指数显示，全球两栖动物的状况正在恶化，尤其是蝾螈和新热带地区的物种。

1980年至2004年间，91%的状况恶化是由疾病和栖息地丧失造成的。目前气候变化的影响越来越令人担忧，自2004年以来已经造成39%的状况恶化。其次是栖息地丧失（37%）。尽管物种恢复的迹象促使人们立即采取保护行动，但仍迫切需要增加投入以扭转目前的趋势。

▲ Abstract：

Here we report the findings of the second Global Amphibian Assessment, evaluating 8,011 species for the International Union for Conservation of Nature Red List of Threatened Species. We find that amphibians are the most threatened vertebrate class (40.7% of species are globally threatened). The updated Red List Index shows that the status of amphibians is deteriorating globally, particularly for salamanders and in the Neotropics. Disease and habitat loss drove 91% of status deteriorations between 1980 and 2004. Ongoing and projected climate change effects are now of increasing concern, driving 39% of status deteriorations since 2004, followed by habitat loss (37%). Although signs of species recoveries incentivize immediate conservation action, scaled-up investment is urgently needed to reverse the current trends.