Coherent spin dynamics in gadolinium-doped CaWO4 crystal
  We report the first observation of Rabi oscillations in the spin-7/2 ensemble of trivalent gadolinium ions hosted in CaWO$_4$ single crystal. A number of transitions within the lowest electronic multiplet $^8S_{7/2}$ of Gd$^{3+}$ ion are studied using a combination of continuous-wave and pulsed electron paramagnetic resonance spectroscopy. The corresponding Rabi damping curves and the spin coherence times are detected at varying strengths of the microwave field. These data are well reproduced by a theoretical model which accounts for the intrinsic inhomogeneity of the microwave field within the microwave resonator and the magnetic dipole interactions in the diluted spin ensemble. The results indicate that the studied 8-level ground manifold of Gd$^{3+}$ ion can represent an effective three qubit quantum system. 
E. I. Baibekov, M. R. Gafurov, D. G. Zverev, I. N. Kurkin, A. A.   Rodionov, B.Z. Malkin, B. Barbara
cond-mat.mes-hall cond-mat.mtrl-sci