Encapsulated Atomic Hydrogen in Octamethyl-POSS Cages: A Pulsed EPR Study

Encapsulated atomic hydrogen in polyhedral oligomeric silsesquioxane (POSS) cages is a promising candidate for spin-based quantum technologies. Key parameters such as spin relaxation times and magnetic interactions with surrounding electron and nuclear spins can be typically probed with advanced electron paramagnetic resonance (EPR) methods. Here we present a detailed pulsed EPR study of the species H@Si₈O₁₂R₈ with R=CH₃, namely encapsulated atomic hydrogen in the octamethyl POSS derivative. The temperature dependence of the spin-lattice relaxation rate 1/ $$ is analyzed in terms of a Raman process with a Debye temperature of $$ K and a thermally activated process with $$ (552 cm^-1), whereas, the phase memory time $$ shows the typical shortening behaviour at $$ K observed for all methyl-containing derivatives. The hyperfine coupling of the cage $$ Si nuclei is measured by hyperfine sublevel correlation (HYSCORE) spectroscopy and is found to fulfil the so-called "matching condition" at the low-field EPR transition. The potential of this paramagnetic molecule to perform one-qubit quantum operations is probed by room-temperature Rabi oscillations.