1.Non-destructive state detection for quantum logic spectroscopy of molecular ions

http://www.nature.com/nature/journal/v530/n7591/full/nature16513.html

Subject terms:

Atomic and molecular interactions with photons
Quantum metrology

摘要

Precision laser spectroscopy of cold and trapped molecular ions is a powerful tool in fundamental physics—used, for example, in determining fundamental constants， testing for their possible variation in the laboratory, and searching for a possible electric dipole moment of the electron. However, the absence of cycling transitions in molecules poses a challenge for direct laser cooling of the ions, and for controlling， and detecting their quantum states. Previously used state-detection techniques based on photo-dissociation or chemical reaction are destructive and therefore inefficient, restricting the achievable resolution in laser spectroscopy. Here, we experimentally demonstrate non-destructive detection of the quantum state of a single trapped molecular ion through its strong Coulomb coupling to a well controlled, co-trapped atomic ion. An algorithm based on a state-dependent optical dipole force changes the internal state of the atom according to the internal state of the molecule. We show that individual quantum states in the molecular ion can be distinguished by the strength of their coupling to the optical dipole force. We also observe quantum jumps (induced by black-body radiation) between rotational states of a single molecular ion. Using the detuning dependence of the state-detection signal, we implement a variant of quantum logic spectroscopy of a molecular resonance. Our state-detection technique is relevant to a wide range of molecular ions, and could be applied to state-controlled quantum chemistry and to spectroscopic investigations of molecules that serve as probes for interstellar clouds.

Screenshot - 2016年03月02日 - 09时48分14秒.png

2.Possible light-induced superconductivity in K3C60 at high temperature

http://www.nature.com/nature/journal/v530/n7591/full/nature16522.html

Subject terms:

Superconducting properties and materials
Phase transitions and critical phenomena

摘要

The non-equilibrium control of emergent phenomena in solids is an important research frontier, encompassing effects such as the optical enhancement of superconductivity. Nonlinear excitation of certain phonons in bilayer copper oxides was recently shown to induce superconducting-like optical properties at temperatures far greater than the superconducting transition temperature, Tc (refs 4, 5, 6). This effect was accompanied by the disruption of competing charge-density-wave correlations, which explained some but not all of the experimental results. Here we report a similar phenomenon in a very different compound, K3C60. By exciting metallic K3C60 with mid-infrared optical pulses, we induce a large increase in carrier mobility, accompanied by the opening of a gap in the optical conductivity. These same signatures are observed at equilibrium when cooling metallic K3C60 below Tc (20 kelvin). Although optical techniques alone cannot unequivocally identify non-equilibrium high-temperature superconductivity, we propose this as a possible explanation of our results.

3.A pentanuclear iron catalyst designed for water oxidation

http://www.nature.com/nature/journal/v530/n7591/full/nature16529.html

Subject terms:

Coordination chemistry
Electrocatalysis

摘要

Although the oxidation of water is efficiently catalysed by the oxygen-evolving complex in photosystem II (refs 1 and 2), it remains one of the main bottlenecks when aiming for synthetic chemical fuel production powered by sunlight or electricity. Consequently, the development of active and stable water oxidation catalysts is crucial, with heterogeneous systems considered more suitable for practical use and their homogeneous counterparts more suitable for targeted, molecular-level design guided by mechanistic understanding. Research into the mechanism of water oxidation has resulted in a range of synthetic molecular catalysts, yet there remains much interest in systems that use abundant, inexpensive and environmentally benign metals such as iron (the most abundant transition metal in the Earth’s crust and found in natural and synthetic oxidation catalysts). Water oxidation catalysts based on mononuclear iron complexes have been explored, but they often deactivate rapidly and exhibit relatively low activities. Here we report a pentanuclear iron complex that efficiently and robustly catalyses water oxidation with a turnover frequency of 1,900 per second, which is about three orders of magnitude larger than that of other iron-based catalysts. Electrochemical analysis confirms the redox flexibility of the system, characterized by six different oxidation states between FeII5 and FeIII5; the FeIII5 state is active for oxidizing water. Quantum chemistry calculations indicate that the presence of adjacent active sites facilitates O–O bond formation with a reaction barrier of less than ten kilocalories per mole. Although the need for a high overpotential and the inability to operate in water-rich solutions limit the practicality of the present system, our findings clearly indicate that efficient water oxidation catalysts based on iron complexes can be created by ensuring that the system has redox flexibility and contains adjacent water-activation sites.

**a**, Redox flexibility arising from a multinuclear core. Multi-electron transfer to afford several oxidation states and electron rearrangement among valence tautomers enable the accumulation of positive charges required for water oxidation. **b**, Adjacent water-activation sites to promote intramolecular O–O bond formation. **c**, Ball-and-stick representations of the molecular structure (left) and the Fe5O core structure (right) of (**1**); the chemical structure of **L**H is also shown (bottom right). Three penta-coordinated iron centres are bridged by an oxygen atom in μ3-fashion to form a triangle structure, and two hexa-coordinated iron centres are connected to the triangle structure by six**L**s.

4.Timescales for detection of trends in the ocean carbon sink

http://www.nature.com/nature/journal/v530/n7591/full/nature16958.html

Subject terms:

Marine chemistry
Biogeochemistry

摘要

The ocean has absorbed 41 per cent of all anthropogenic carbon emitted as a result of fossil fuel burning and cement manufacture. The magnitude and the large-scale distribution of the ocean carbon sink is well quantified for recent decades. In contrast, temporal changes in the oceanic carbon sink remain poorly understood. It has proved difficult to distinguish between air-to-sea carbon flux trends that are due to anthropogenic climate change and those due to internal climate variability. Here we use a modelling approach that allows for this separation, revealing how the ocean carbon sink may be expected to change throughout this century in different oceanic regions. Our findings suggest that, owing to large internal climate variability, it is unlikely that changes in the rate of anthropogenic carbon uptake can be directly observed in most oceanic regions at present, but that this may become possible between 2020 and 2050 in some regions.

点评

首先注意这个文章的切入点，海洋是重要的碳库所以需要研究，已经有的结果主要是空间的分布而且目前定量的很好了。但是时间的分布结果没有多少。所以作者去做这个研究，那么研究的核心是什么——其实是如何区分出人类活动的结果和非人类活动的结果。当然这个论文其实给出的是一个不确定结果在大部分的海洋上我们是无法准确区分两者的。现在回过头来想标题中**Timescales **这个词用的确实准确。

5.Third-party punishment as a costly signal of trustworthiness

http://www.nature.com/nature/journal/v530/n7591/full/nature16981.html

Subject terms:

Social evolution
Evolutionary theory
Economics
Psychology

摘要

Third-party punishment (TPP), in which unaffected observers punish selfishness, promotes cooperation by deterring defection. But why should individuals choose to bear the costs of punishing? We present a game theoretic model of TPP as a costly signal of trustworthiness. Our model is based on individual differences in the costs and/or benefits of being trustworthy. We argue that individuals for whom trustworthiness is payoff-maximizing will find TPP to be less net costly (for example, because mechanisms that incentivize some individuals to be trustworthy also create benefits for deterring selfishness via TPP). We show that because of this relationship, it can be advantageous for individuals to punish selfishness in order to signal that they are not selfish themselves. We then empirically validate our model using economic game experiments. We show that TPP is indeed a signal of trustworthiness: third-party punishers are trusted more, and actually behave in a more trustworthy way, than non-punishers. Furthermore, as predicted by our model, introducing a more informative signal—the opportunity to help directly—attenuates these signalling effects. When potential punishers have the chance to help, they are less likely to punish, and punishment is perceived as, and actually is, a weaker signal of trustworthiness. Costly helping, in contrast, is a strong and highly used signal even when TPP is also possible. Together, our model and experiments provide a formal reputational account of TPP, and demonstrate how the costs of punishing may be recouped by the long-run benefits of signalling one’s trustworthiness.

点评

这个文章很有意思，核心要点是:

Specifically, we introduce a game theoretic model of TPP as a costly signal of trustworthiness: if you see me punish selfishness, it can signal that I will not be selfish to you. Our model involves a partner-choice19
game with two roles. In each interaction, the ‘Signaller’ decides whether to send one or more costly signals; then the ‘Chooser’ decides whether to partner with the Signaller.

也就是第三方惩罚事实上表明了一个态度——我会对你更好。