Abstract
The realization of isolated quantum systems within solid-state matrices is a pivotal challenge in quantum information science. This study demonstrates the existence of a "nano-vacuum" state in lithium-ion endohedral fullerene (Li(+)@C(60)·PF(6) (-)), where the encapsulated ion exhibits extreme magnetic isolation. Using ultrahigh field (18.79 T) solid-state NMR, we observed a (7)Li line width of ∼50 Hz that remains invariant under magic angle spinning (MAS), indicating that the ion undergoes ultrafast isotropic motion (τ(c) ≪ 10(-5) s), which completely averages quadrupolar interactions. Most significantly, we report a record-breaking spin-lattice relaxation time (T (1)) of approximately 1068 s. This extraordinary lifetime is rationalized by a "relaxation blockade" mechanism: the absence of spin-orbit coupling prevents phonon scattering, while the rapid "roaming" of Li(+) and the cooperative "plastic" rotation of external PF(6) (-) anions synergistically suppress dipolar and quadrupolar relaxation channels. These findings establish Li(+)@C(60) as a ″thermodynamically open but magnetically closed″ system, offering a robust platform for quantum sensing.