Mechanism of Electron Spin Decoherence in a Partially Deuterated Glassy Matrix

Long
electron spin coherence lifetimes are essential for applications
in quantum information science and electron paramagnetic resonance,
for instance, for nanoscale distance measurements in biomolecular
systems using double electron–electron resonance. We experimentally
investigate the decoherence dynamics under the Hahn echo sequence
of the organic radical d18-TEMPO in a
variably deuterated frozen water:glycerol matrix. The coherence time
(phase memory time) TM scales with proton
concentration as [1H]−0.65. For selectively
deuterated matrices, decoherence is accelerated in the presence of
proton clustering, that is, substantial short-range density in the
proton–proton radial distribution functions (<3 Å).
Simulations using molecular dynamics and many-body spin quantum dynamics
show excellent agreement with experiment and show that geminal proton
pairs such as CH2 and OH2 groups are major decoherence
drivers. This provides a predictive tool for designing molecular systems
with long electron spin coherence times.