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<jats:p> An ensemble of 40 ultracold atoms forms an entangled state when just one of the atoms is excited. <jats:named-content content-type="related-content"> [Also see Report by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6180" page="180" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1248905"> Haas <jats:italic>et al.</jats:italic> </jats:related-article> ] </jats:named-content> </jats:p>

<jats:p> Tough elastomers are created by adapting an approach previously used for hydrogels. <jats:named-content content-type="related-content"> [Also see Report by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6180" page="186" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1248494"> Ducrot <jats:italic>et al.</jats:italic> </jats:related-article> ] </jats:named-content> </jats:p>

<jats:title>Tripeptide Maternal Support</jats:title> <jats:p> In flowering plants, fertilization involves multiple gametes. The diploid zygote, which will form the embryonic plant, is surrounded by the often triploid endosperm, which provides a supportive and nourishing function. Working in <jats:italic>Arabidopsis</jats:italic> , <jats:bold> Costa <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6180" page="168" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1243005">168</jats:related-article> ; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6180" page="158" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1252985">Bayer</jats:related-article> </jats:bold> ) identified a trio of small signaling peptides that derive from the endosperm but that regulate growth of the embryo. RNA interference was used to down-regulate expression of all three peptides. Fertilization was not affected, but seed growth was. The peptides were critical for normal development of the suspensor, which tethers and nourishes the growing embryo. </jats:p>

<jats:title>Taking Flight</jats:title> <jats:p> Anyone who has tried to swat a fly knows that their powers of avoidance are impressive. Executing such rapid avoidance requires that the sensory recognition of an approaching threat be translated into evasive movement almost instantaneously. <jats:bold> Muijres <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6180" page="172" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1248955">172</jats:related-article> ) used high-speed videos and winged robots to show that flies respond to approaching threats by making rapid banked turns initiated through subtle wing changes over just a few wing beats. The rapid nature of the turns suggests the existence of dedicated sensory-motor circuits that allow the flies to respond within a fraction of a second. </jats:p>

<jats:title>Exposing a Hidden State</jats:title> <jats:p> Shining intense laser light on a material can temporarily alter its properties. The effect usually subsides after a few picoseconds, unless the system is trapped in a metastable state, in which case the transient period may last as long as microseconds. <jats:bold> Stojchevska <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6180" page="177" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1241591">177</jats:related-article> ) observed that, following exposure to a 35-femtosecond laser pulse, the layered dichalcogenide <jats:italic>1T</jats:italic> -TaS <jats:sub>2</jats:sub> entered a stable “hidden” state not present in the equilibrium phase diagram and stayed there indefinitely. The switch to the hidden state could be reversed by heat or a train of laser pulses. Because the switch alters the sample's conducting properties, the phenomenon might also lead to practical applications. </jats:p>

<jats:title>All Together Now</jats:title> <jats:p> In quantum entanglement, correlations between particles mean that the measurement of one determines the outcome of the other(s). Generally, when trying to exploit quantum entanglement, the larger the number of entangled particles, the better. However, the size of entangled systems has been limited. <jats:bold> Haas <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6180" page="180" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1248905">180</jats:related-article> , published online 27 March; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6180" page="160" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1251472">Widera</jats:related-article> </jats:bold> ) prepared a small ensemble of ultracold atoms into a collective entangled state. Starting from one internal quantum state, the system of cold atoms was excited with a weak microwave pulse leading to a small excitation probability. Because it is not known which atom is promoted into the excited state, the detection of one quantum of excitation projects the system into an entangled quantum state, called a W-state. A fast repeat-until-success scheme produced such W-states quasi-deterministically. Using such a technique was able to yield entangled states of more than 40 particles. The relatively large ensemble-entangled states could potentially in the future find use in quantum sensing or enhanced quantum metrology applications. </jats:p>

<jats:title>Mapping Stardust</jats:title> <jats:p> A galaxy's structure throughout time depends largely on its ability to convert the raw material of molecular clouds into stars. One of the most influential properties in determining star formation rates is the distribution of densities among individual molecular clouds, which can be described by a probability density function of volume densities. <jats:bold> Kainulainen <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6180" page="183" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1248724">183</jats:related-article> ) devised a method to quantify these distributions from empirical dust extinction maps of nearby clouds. The threshold for star formation in these observationally based calculations was significantly lower than theoretical predictions. </jats:p>

<jats:title>Toughening Up Elastomers</jats:title> <jats:p> Elastomers are soft polymer materials widely used in industry and daily life. Inspired by recent work on double-network hydrogels, <jats:bold> Ducrot <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6180" page="186" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1248494">186</jats:related-article> ; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6180" page="161" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1252389">Gong</jats:related-article> </jats:bold> ) designed interpenetrated network elastomers that contained isotropically prestretched chains as the first network. Double- and triple-network structures yielded elastomers with very high strength and toughness in comparison with the corresponding single networks. </jats:p>

<jats:title>Shutting Down Repair to Protect</jats:title> <jats:p> Cells repair DNA double-strand breaks (DSBs) by halting the cell cycle and activating the machinery involved in mending the breaks. However, during mitosis neither the DNA damage checkpoint nor DSB repair occur, apparently leaving the cell extremely vulnerable to DSBs. <jats:bold> Orthwein <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6180" page="189" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1248024">189</jats:related-article> , published online 20 March) found that the DSB response was blocked by the phosphorylation of two crucial repair factors, RNF8 and PB531, preventing their recruitment to the site of damage. Restoring DSB repair during mitosis caused end-to-end chromosome fusions, which are catastrophic for chromosome segregation and normal cell division, explaining why the repair machinery is shut down during cell division. </jats:p>