Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title><jats:p>Lithium-rich oxide cathodes lose energy density during cycling due to atomic disordering and nanoscale structural rearrangements, which are both challenging to characterize. Here we resolve the kinetics and thermodynamics of these processes in an exemplar layered Li-rich (Li<jats:sub>1.2–<jats:italic>x</jats:italic></jats:sub>Mn<jats:sub>0.8</jats:sub>O<jats:sub>2</jats:sub>) cathode using a combined approach of ab initio molecular dynamics and cluster expansion-based Monte Carlo simulations. We identify a kinetically accessible and thermodynamically favourable mechanism to form O<jats:sub>2</jats:sub> molecules in the bulk, involving Mn migration and driven by interlayer oxygen dimerization. At the top of charge, the bulk structure locally phase segregates into MnO<jats:sub>2</jats:sub>-rich regions and Mn-deficient nanovoids, which contain O<jats:sub>2</jats:sub> molecules as a nanoconfined fluid. These nanovoids are connected in a percolating network, potentially allowing long-range oxygen transport and linking bulk O<jats:sub>2</jats:sub> formation to surface O<jats:sub>2</jats:sub> loss. These insights highlight the importance of developing strategies to kinetically stabilize the bulk structure of Li-rich O-redox cathodes to maintain their high energy densities.</jats:p>

<jats:title>Abstract</jats:title><jats:p>Spin qubits defined by valence band hole states are attractive for quantum information processing due to their inherent coupling to electric fields, enabling fast and scalable qubit control. Heavy holes in germanium are particularly promising, with recent demonstrations of fast and high-fidelity qubit operations. However, the mechanisms and anisotropies that underlie qubit driving and decoherence remain mostly unclear. Here we report the highly anisotropic heavy-hole <jats:italic>g</jats:italic>-tensor and its dependence on electric fields, revealing how qubit driving and decoherence originate from electric modulations of the <jats:italic>g</jats:italic>-tensor. Furthermore, we confirm the predicted Ising-type hyperfine interaction and show that qubit coherence is ultimately limited by 1/<jats:italic>f</jats:italic> charge noise, where <jats:italic>f</jats:italic> is the frequency. Finally, operating the qubit at low magnetic field, we measure a dephasing time of <jats:inline-formula><jats:alternatives><jats:tex-math>$${T}_{2}^{* }$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> </mml:msubsup> </mml:math></jats:alternatives></jats:inline-formula> = 17.6 μs, maintaining single-qubit gate fidelities well above 99% even at elevated temperatures of <jats:italic>T</jats:italic> &gt; 1 K. This understanding of qubit driving and decoherence mechanisms is key towards realizing scalable and highly coherent hole qubit arrays.</jats:p>

<jats:title>Abstract</jats:title><jats:p>Solid-state spin–photon interfaces that combine single-photon generation and long-lived spin coherence with scalable device integration—ideally under ambient conditions—hold great promise for the implementation of quantum networks and sensors. Despite rapid progress reported across several candidate systems, those possessing quantum coherent single spins at room temperature remain extremely rare. Here we report quantum coherent control under ambient conditions of a single-photon-emitting defect spin in a layered van der Waals material, namely, hexagonal boron nitride. We identify that the carbon-related defect has a spin-triplet electronic ground-state manifold. We demonstrate that the spin coherence is predominantly governed by coupling to only a few proximal nuclei and is prolonged by decoupling protocols. Our results serve to introduce a new platform to realize a room-temperature spin qubit coupled to a multiqubit quantum register or quantum sensor with nanoscale sample proximity.</jats:p>