编译 | 未玖
Nature, 15 June 2023, VOL 618, ISSUE 7965
《自然》2023年6月15日，第618卷，7965期
天文学Astronomy
Detection of phosphates originating from Enceladus’s ocean
从土卫二海洋中探测到磷酸盐
▲ 作者：Frank Postberg, Yasuhito Sekine, Fabian Klenner, Christopher R. Glein, Zenghui Zou, Bernd Abel, et al.
▲ 链接：
https://www.nature.com/articles/s41586-023-05987-9
▲ 摘要：
土星的卫星土卫二拥有一片全球冰封的海洋。卡西尼号宇宙飞船通过分析卫星低温火山羽流喷射到太空中的物质来研究海洋组成。卡西尼号宇宙尘埃分析仪对富含盐分的冰粒进行了分析，从而推断出海水中的主要溶质（Na 、K 、Cl–、HCO3–、CO32–）及其碱性pH值。
磷是生物必需元素中含量最低的一种，目前尚未在地球以外的海洋中检测到。早期的地球化学模型研究表明，在土卫二海洋和其他冰冷的海洋世界中，磷酸盐可能很稀缺。然而，最近对土卫二海洋矿物溶解度的模拟表明，磷酸盐可能相对丰富。
研究组展示了卡西尼号宇宙尘埃分析仪对土卫二喷射冰粒的质谱分析，显示了磷酸钠的存在。该观测结果及实验室模拟实验表明，在土卫二海洋中，磷较易以正磷酸盐的形式存在，卫星羽流形成海水中的磷浓度至少是地球海洋的100倍。
此外，地球化学实验和建模表明，如此高的磷酸盐丰度可能在土卫二上实现，也可能在原始二氧化碳雪线之外的其他冰冷海洋世界中实现，无论是在寒冷的海底还是在中等温度的热液环境中。在这两种情况下，主要驱动因素可能是在富含碳酸盐或碳酸氢根离子的中等碱性溶液中，磷酸钙矿物比碳酸钙矿物的溶解度更高。
▲ Abstract：
Saturn’s moon Enceladus harbours a global ice-covered water ocean. The Cassini spacecraft investigated the composition of the ocean by analysis of material ejected into space by the moon’s cryovolcanic plume. The analysis of salt-rich ice grains by Cassini’s Cosmic Dust Analyzer enabled inference of major solutes in the ocean water (Na , K , Cl–, HCO3–, CO32–) and its alkaline pH. Phosphorus, the least abundant of the bio-essential elements, has not yet been detected in an ocean beyond Earth. Earlier geochemical modelling studies suggest that phosphate might be scarce in the ocean of Enceladus and other icy ocean worlds. However, more recent modelling of mineral solubilities in Enceladus’s ocean indicates that phosphate could be relatively abundant. Here we present Cassini’s Cosmic Dust Analyzer mass spectra of ice grains emitted by Enceladus that show the presence of sodium phosphates. Our observational results, together with laboratory analogue experiments, suggest that phosphorus is readily available in Enceladus’s ocean in the form of orthophosphates, with phosphorus concentrations at least 100-fold higher in the moon’s plume-forming ocean waters than in Earth’s oceans. Furthermore, geochemical experiments and modelling demonstrate that such high phosphate abundances could be achieved in Enceladus and possibly in other icy ocean worlds beyond the primordial CO2snowline, either at the cold seafloor or in hydrothermal environments with moderate temperatures. In both cases the main driver is probably the higher solubility of calcium phosphate minerals compared with calcium carbonate in moderately alkaline solutions rich in carbonate or bicarbonate ions.
物理学Physics
Evidence for the utility of quantum computing before fault tolerance
在容错之前证明量子计算的实用性
▲ 作者：Youngseok Kim, Andrew Eddins, Sajant Anand, Ken Xuan Wei, Ewout van den Berg, Sami Rosenblatt, et al.
▲ 链接：
https://www.nature.com/articles/s41586-023-06096-3
▲ 摘要：
量子计算有望在某些问题上提供比经典计算更快的速度。然而，实现其全部潜力的最大障碍是这些系统固有的噪声。针对该挑战，人们广泛接受的解决方案是实现容错量子电路，但当前处理器无法实现。
研究组报道了在有噪声的127量子位处理器上的实验，演示了在超出Brute-Force经典计算范围内测量电路体积的精确期望值，并认为这代表了量子计算在前容错时期的实用性。该实验结果归功于这种规模的超导处理器在相干性和校准方面的进步，以及在如此大的设备上表征和可控操纵噪声的能力。
通过与精确可验证电路的输出进行比较，研究组确定了测量期望值的准确性。在强纠缠状态下，量子计算机提供了正确的结果，而诸如基于纯态的一维（矩阵乘积态，MPS）和二维（等距张量网络态，isoTNS）张量网络方法等主要经典近似都失效了。这些实验展示了实现Near-Term量子应用的基础工具。
▲ Abstract：
Quantum computing promises to offer substantial speed-ups over its classical counterpart for certain problems. However, the greatest impediment to realizing its full potential is noise that is inherent to these systems. The widely accepted solution to this challenge is the implementation of fault-tolerant quantum circuits, which is out of reach for current processors. Here we report experiments on a noisy 127-qubit processor and demonstrate the measurement of accurate expectation values for circuit volumes at a scale beyond brute-force classical computation. We argue that this represents evidence for the utility of quantum computing in a pre-fault-tolerant era. These experimental results are enabled by advances in the coherence and calibration of a superconducting processor at this scale and the ability to characterize and controllably manipulate noise across such a large device. We establish the accuracy of the measured expectation values by comparing them with the output of exactly verifiable circuits. In the regime of strong entanglement, the quantum computer provides correct results for which leading classical roximations such as pure-state-based 1D (matrix product states, MPS) and 2D (isometric tensor network states, isoTNS) tensor network methods break down. These experiments demonstrate a foundational tool for the realization of near-term quantum lications.
化学Chemistry
Transannular C–H functionalization of cycloalkane carboxylic acids
环烷烃羧酸的跨环C-H官能化
▲ 作者：Guowei Kang, Daniel A. Strassfeld, Tao Sheng, Chia-Yu Chen
