Electron spin relaxation properties of atomic hydrogen encapsulated in octavinyl POSS cages

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/T 1 ${{T}_{1}}$ is analyzed in terms of a Raman process with a Debye temperature ofθ D = 145 ${{\theta }_{{\rm D}}=145}$ K and a thermally activated process withE a = 794 K ${{E}_{a}=794\hskip0.17em\hskip0.17em{\rm K}}$ (552 cm-1), whereas, the phase memory timeT M ${T_{\rm{M}} }$ shows the typical shortening behaviour atT < 150 ${T \char60 150}$ K observed for all methyl-containing derivatives. The hyperfine coupling of the cage29 ${^{29} }$ 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.

Long Electron Spin Coherence Times of Atomic Hydrogen Trapped in Silsesquioxane Cages

Encapsulated atomic hydrogen in cube-shaped octasilsesquioxane (POSS) cages of the Si8O12R8 type (where R is an organic group) is one of the simplest alternative stable systems to paramagnetic endofullerenes that have been regarded as key elements of spin-based quantum technologies. Apart from common sources of decoherence such as nuclear spin and spectral diffusion, all H@POSS species studied so far suffer from additional shortening of T2 at low temperatures due to methyl group rotations. Here we eliminate this factor for the first time by studying the smallest methyl-free derivative with R = H, namely, H@T8H8. By applying dynamical decoupling methods, we measure electron spin coherence times T2 up to 280 ± 76 μs at T = 90 K and observe a linear dependence of the decoherence rate 1/T2 on trapped hydrogen concentrations, which we attribute to the spin dephasing mechanism of instantaneous diffusion and a nonuniform spatial distribution of encapsulated H atoms.