Long Electronic Spin Relaxation Times of Cs Atoms in Solid4He

We report on optical pumping of Cs atoms implanted in a matrix of solid ${}^4$He at 1.6 K. Longitudinal spin relaxation times $T_l$ of 1–2 s have been measured using the “relaxation in the dark” method for magnetic holding fields in the range 0.01–1 G, for which no significant field dependence was found. Zero-field level-crossing resonances in longitudinal and transverse fields (ground-state Hanle effect) and conventional optical-rf double resonance of Cs atoms in solid ${}^4$He have been detected.