Magnetic and electric properties of alkali atoms in solid helium

The magnetic properties of alkali atoms implanted in crystalline 4 He matrices are extremely sensitive to the symmetry of the local trapping sites. For Cs atoms trapped in the body-centered-cubic phase of 4 He spin relaxation times up to 1 s have been observed. In the hexagonal-close-packed phase on the other hand the Cs spins are readily depolarized and a number of phenomena specific for this phase, such as zero-field magnetic resonance spectra, forbidden transitions and anomalous hyperfine shifts have been observed in magnetic resonance experiments with optical detection. Our present interest focuses on spin perturbations of implanted Cs atoms by strong (30 kV/cm) external electric fields. These perturbations are measured as shifts of the magnetic resonance lines using a phase-sensitive optical magnetic resonance technique.