Spin physics in solid helium: Experimental results and applications

We have observed optical pumping signals from Cs atoms trapped in solid⁴He. While the longitudinal electronic spin relaxation timeT₁ is found to be in the range of 1–2 s, the transverse relaxation timeT₂, as inferred from magnetic resonance linewidths has a lower bound of 150 s, and is determined by magnetic field inhomogeneities. We present a quantitative discussion of how paramagnetic species trapped in solid He might be used in a highly sensitive search for permanent atomic electric dipole moments.