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<jats:title>High fives and sixes for Americium ions</jats:title> <jats:p> You've probably heard of uranium and plutonium. Americium (Am) is less widely discussed outside chemistry circles, but the separation of this heavier radioactive element from nuclear waste streams is a major goal of fuel reprocessing research. The trouble is that trivalent Am ions are hard to tease apart from similarly charged lanthanide ions. Dares <jats:italic>et al.</jats:italic> now show that terpyridyl ligands appended to an electrode can promote the oxidation of trivalent Am ions to the pentavalent and hexavalent states (see the Perspective by Soderquist). These more highly charged ions should be easier to isolate for the subsequent use of the Am in next-generation nuclear reactors. </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="6261" page="652" related-article-type="in-this-issue" vol="350" xlink:href="10.1126/science.aac9217">652</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6261" page="635" related-article-type="in-this-issue" vol="350" xlink:href="10.1126/science.aad5131">635</jats:related-article> </jats:p>

<jats:title>Peeking into an exotic magnetic structure</jats:title> <jats:p> Cooling materials that contain magnetic interactions generally leads to an ordered magnetic state. In materials known as quantum spin liquids (QSLs), the geometry of the crystal lattice may prevent this ordered state from forming, even at absolute zero. The material herbertsmithite is thought to be a strong candidate for a QSL, but the nature of its ground state is still a mystery. Fu <jats:italic>et al.</jats:italic> measured shifts in the nuclear magnetic resonance signals of herbertsmithite to conclude that its ground state has a zero spin and is separated from the first excited state by an energy gap (see the Perspective by Furukawa). The results suggest that herbertsmithite is indeed a QSL. </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="6261" page="655" related-article-type="in-this-issue" vol="350" xlink:href="10.1126/science.aab2120">655</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6261" page="631" related-article-type="in-this-issue" vol="350" xlink:href="10.1126/science.aad3556">631</jats:related-article> </jats:p>

<jats:title>Filling a molecular lattice of light</jats:title> <jats:p> Cold atoms in optical lattices normally interact only when two of them occupy the same lattice site. More-complex interactions would expand the potential of the system for quantum simulation. A promising approach is to use polar molecules instead of atoms, which interact at much longer length scales. However, “packing” the lattice with molecules is tricky. Moses <jats:italic>et al.</jats:italic> introduced bosonic <jats:sup>87</jats:sup> Rb atoms and fermionic <jats:sup>40</jats:sup> K atoms into an optical lattice, combined them into molecules, and brought the molecules into their ground state, achieving a considerable lattice filling of 25%. </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="6261" page="659" related-article-type="in-this-issue" vol="350" xlink:href="10.1126/science.aac6400">659</jats:related-article> </jats:p>

<jats:title>What makes the gut microbiome stable?</jats:title> <jats:p> Classically, we think of our microbiome as stable, benign, and cooperative. Recent experimental work is beginning to unpick essential functions that can be attributed to the stable microbiota of humans. To be able to manipulate the microbiome to improve health, we need to understand community structure and composition and we need models to quantify and predict stability. Coyte <jats:italic>et al.</jats:italic> applied concepts and tools from community ecology to gut microbiome assembly. Independently developed models converged on a surprising answer: A high diversity of species is likely to coexist stably when the system is dominated by competitive, rather than cooperative, interactions. </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="6261" page="663" related-article-type="in-this-issue" vol="350" xlink:href="10.1126/science.aad2602">663</jats:related-article> </jats:p>