Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title><jats:p>Quantum electrodynamics (QED) is one of the most fundamental theories of physics and has been shown to be in excellent agreement with experimental results<jats:sup>1–5</jats:sup>. In particular, measurements of the electron’s magnetic moment (or <jats:italic>g</jats:italic> factor) of highly charged ions in Penning traps provide a stringent probe for QED, which allows testing of the standard model in the strongest electromagnetic fields<jats:sup>6</jats:sup>. When studying the differences between isotopes, many common QED contributions cancel owing to the identical electron configuration, making it possible to resolve the intricate effects stemming from the nuclear differences. Experimentally, however, this quickly becomes limited, particularly by the precision of the ion masses or the magnetic field stability<jats:sup>7</jats:sup>. Here we report on a measurement technique that overcomes these limitations by co-trapping two highly charged ions and measuring the difference in their <jats:italic>g</jats:italic> factors directly. We apply a dual Ramsey-type measurement scheme with the ions locked on a common magnetron orbit<jats:sup>8</jats:sup>, separated by only a few hundred micrometres, to coherently extract the spin precession frequency difference. We have measured the isotopic shift of the bound-electron <jats:italic>g</jats:italic> factor of the isotopes <jats:sup>20</jats:sup>Ne<jats:sup>9+</jats:sup> and <jats:sup>22</jats:sup>Ne<jats:sup>9+</jats:sup> to 0.56-parts-per-trillion (5.6 × 10<jats:sup>−13</jats:sup>) precision relative to their <jats:italic>g</jats:italic> factors, an improvement of about two orders of magnitude compared with state-of-the-art techniques<jats:sup>7</jats:sup>. This resolves the QED contribution to the nuclear recoil, accurately validates the corresponding theory and offers an alternative approach to set constraints on new physics.</jats:p>

<jats:title>Abstract</jats:title><jats:p>Topology in quantum many-body systems has profoundly changed our understanding of quantum phases of matter. The model that has played an instrumental role in elucidating these effects is the antiferromagnetic spin-1 Haldane chain<jats:sup>1,2</jats:sup>. Its ground state is a disordered state, with symmetry-protected fourfold-degenerate edge states due to fractional spin excitations. In the bulk, it is characterized by vanishing two-point spin correlations, gapped excitations and a characteristic non-local order parameter<jats:sup>3,4</jats:sup>. More recently it has been understood that the Haldane chain forms a specific example of a more general classification scheme of symmetry-protected topological phases of matter, which is based on ideas connected to quantum information and entanglement<jats:sup>5–7</jats:sup>. Here, we realize a finite-temperature version of such a topological Haldane phase with Fermi–Hubbard ladders in an ultracold-atom quantum simulator. We directly reveal both edge and bulk properties of the system through the use of single-site and particle-resolved measurements, as well as non-local correlation functions. Continuously changing the Hubbard interaction strength of the system enables us to investigate the robustness of the phase to charge (density) fluctuations far from the regime of the Heisenberg model, using a novel correlator.</jats:p>

<jats:title>Abstract</jats:title><jats:p>Missing heritability in genome-wide association studies defines a major problem in genetic analyses of complex biological traits<jats:sup>1,2</jats:sup>. The solution to this problem is to identify all causal genetic variants and to measure their individual contributions<jats:sup>3,4</jats:sup>. Here we report a graph pangenome of tomato constructed by precisely cataloguing more than 19 million variants from 838 genomes, including 32 new reference-level genome assemblies. This graph pangenome was used for genome-wide association study analyses and heritability estimation of 20,323 gene-expression and metabolite traits. The average estimated trait heritability is 0.41 compared with 0.33 when using the single linear reference genome. This 24% increase in estimated heritability is largely due to resolving incomplete linkage disequilibrium through the inclusion of additional causal structural variants identified using the graph pangenome. Moreover, by resolving allelic and locus heterogeneity, structural variants improve the power to identify genetic factors underlying agronomically important traits leading to, for example, the identification of two new genes potentially contributing to soluble solid content. The newly identified structural variants will facilitate genetic improvement of tomato through both marker-assisted selection and genomic selection. Our study advances the understanding of the heritability of complex traits and demonstrates the power of the graph pangenome in crop breeding.</jats:p>