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<jats:title>Tightly tracking charge migration</jats:title> <jats:p> Electron transfer dynamics underlie many chemical and biochemical reactions. Erk <jats:italic>et al.</jats:italic> examined the charge migration between individual carbon and iodine atoms during dissociation of iodomethane (ICH <jats:sub>3</jats:sub> ) molecules (see the Perspective by Pratt). After initiating scission of the C-I bond with a relatively low-energy laser pulse, they introduced a higher-energy x-ray pulse to instigate ionization and charge migration. Delaying the arrival time of the x-ray pulse effectively varied the separation distance being probed as the fragments steadily drifted apart. The experimental approach should also prove useful for future studies of charge transfer dynamics in different molecular or solid-state systems. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6194" page="288" related-article-type="in-this-issue" vol="345" xlink:href="10.1126/science.1253607">288</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6194" page="267" related-article-type="in-this-issue" vol="345" xlink:href="10.1126/science.1255943">267</jats:related-article> </jats:p>

<jats:title>Iodine blooms as an oxidation catalyst</jats:title> <jats:p> Most catalysts for organic oxidation chemistry—whether biochemical or artificial—contain a transition metal like iron or palladium. Uyanik <jats:italic>et al.</jats:italic> now show that iodine can take the place of a metal in catalyzing efficient oxidative ring closures to make chromans—hexagonal rings incorporating oxygen that are perhaps best known as a constituent of the vitamin E structure (see the Perspective by Nachtsheim). The iodine is added as a salt with a chiral cation, which directs the reaction to form just one of two possible mirror-image variants of the product. Key to the success of the system was the addition of a base, which maintained the viability of an unstable, partially oxidized iodine intermediate critical to the reaction cycle. The results bode well for more general use of iodine salts as asymmetric oxidation-reduction catalysts. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6194" page="291" related-article-type="in-this-issue" vol="345" xlink:href="10.1126/science.1254976">291</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6194" page="270" related-article-type="in-this-issue" vol="345" xlink:href="10.1126/science.1257347">270</jats:related-article> </jats:p>

<jats:title>Improved perovskite photovoltaic performance</jats:title> <jats:p> A recent entry in the solar cell race is perovskite cells, named for the structure adopted by salt made from metal halides and organic cations that absorb the light and generate charges. The charges generated have to be transferred to a metal oxide (typically titanium oxide), and some of these charge carriers are lost in the transfer. Mei <jats:italic>et al.</jats:italic> made this process more efficient by growing a more crystalline perovskite with fewer defects inside porous versions of titanium and zirconium oxide. They added a second organic cation that stuck to the pore walls and directed the growth of the perovskite crystals. The improved solar cells operated for more than 1000 hours under full sunlight. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6194" page="295" related-article-type="in-this-issue" vol="345" xlink:href="10.1126/science.1254763">295</jats:related-article> </jats:p>

<jats:title>Extending the range of planar optics</jats:title> <jats:p> To build miniature optical devices, scientists are using silicon to replace bulky three-dimensional devices with flat versions. A patterned surface consisting of dense arrays of nanoscale silicon strips, which act as antennae, can be designed to work as transparent optical devices for the manipulation of light. Lin <jats:italic>et al.</jats:italic> used their versatile patterning technique to create a suite of planar optical elements. By patterning a 100-nm layer of silicon into a dense arrangement of nano-antennae, they were able to fabricate gratings, lenses, and axicons—a device that can add a shape to a propagating light beam. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6194" page="298" related-article-type="in-this-issue" vol="345" xlink:href="10.1126/science.1253213">298</jats:related-article> </jats:p>

<jats:title>Fault-tolerant quantum computing</jats:title> <jats:p> Quantum states can be delicate. Attempts to process and manipulate quantum states can destroy the encoded information. Nigg <jats:italic>et al.</jats:italic> encoded the quantum state of a single qubit (in this case, a trapped ion) over the global properties of a series of trapped ions. These so-called stabilizers protected the information against noise sources that can degrade the single qubit. The protocol provides a route to fault-tolerant quantum computing. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6194" page="302" related-article-type="in-this-issue" vol="345" xlink:href="10.1126/science.1253742">302</jats:related-article> </jats:p>

<jats:title>Bosons of a feather flit together</jats:title> <jats:p> Bosons are a type of particle that likes to congregate. This property has a major effect on the behavior of identical bosons. Kaufman <jats:italic>et al.</jats:italic> demonstrated quantum interference of two bosonic Rb atoms placed in two neighboring quantum wells (see the Perspective by Thompson and Lukin). They prepared the atoms in exactly the same state so that there would be no way to tell them apart except for which well each atom was in. They then monitored the probability of the two atoms still being in separate wells. At certain times, the probability had a characteristic dip signifying that the bosons preferred to be in the same well. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6194" page="306" related-article-type="in-this-issue" vol="345" xlink:href="10.1126/science.1250057">306</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6194" page="272" related-article-type="in-this-issue" vol="345" xlink:href="10.1126/science.1256529">272</jats:related-article> </jats:p>

<jats:title>A more simple route to metrology standards</jats:title> <jats:p> The time standards set by atomic clocks are usually the domain of national metrology laboratories. Li <jats:italic>et al.</jats:italic> modulated the phase of two closely spaced laser lines to generate a comb of stable and equally spaced frequencies. They then used that comb to generate stable microwaves. Being somewhat simpler than existing optical comb generation techniques and also tunable, the approach may offer a new era of metrology and precision timekeeping. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6194" page="309" related-article-type="in-this-issue" vol="345" xlink:href="10.1126/science.1252909">309</jats:related-article> </jats:p>

<jats:title>How the worm changes its tastes</jats:title> <jats:p> In associative learning, you link potentially unrelated things because you are exposed to them at the same time. Ohno <jats:italic>et al.</jats:italic> studied a simple associative learning task in the nematode worm <jats:italic>Caenorhabditis elegans</jats:italic> . They presented the worms with a taste substance while withholding food. After starving in the presence of the taste substance, the animals switched their behavior from being attracted to the taste to finding it aversive. A specific isoform of the insulin receptor is critical for this type of associative learning—at least in worms. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6194" page="313" related-article-type="in-this-issue" vol="345" xlink:href="10.1126/science.1250709">313</jats:related-article> </jats:p>

<jats:title>Circulating between different cycles</jats:title> <jats:p>Around a million years ago, large-scale ocean circulation changed dramatically during the switch from ∼41,000- to ∼100,000-year long glacial cycles. Pena and Goldstein analyzed the isotopic composition of neodymium in marine sediments from the South Atlantic. The results suggest how the contributions of deep water from northern and southern sources varied across the transition. The boundary between the two glacial states appears to have been marked by a dramatic weakening, perhaps even a shutdown, of deep-water currents.</jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6194" page="318" related-article-type="in-this-issue" vol="345" xlink:href="10.1126/science.1249770">318</jats:related-article> </jats:p>

<jats:title>Spinning up ocean circulation discretely</jats:title> <jats:p> Ocean eddies with diameters of tens to hundreds of kilometers are an important component of water transport on a global scale. Averaged over periods of many years, ocean circulation is regular and coherent enough to have been described as a conveyor belt. However, over shorter time scales, irregular, discrete events cause significant amounts of water movement—termed mesoscale eddies. Zhang <jats:italic>et al.</jats:italic> combined data from thousands of autonomous observational devices called ARGO floats with satellite data. The mesoscale eddies moved around as much ocean water as wind or deepwater currents. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6194" page="322" related-article-type="in-this-issue" vol="345" xlink:href="10.1126/science.1252418">322</jats:related-article> </jats:p>