Coherence times and Rabi oscillations in CaWO₄:Cr(5+) crystal

The coherence times of dopant pentavalent chromium ions in CaWO₄ single crystal (0.0006at.% Cr(5+)) were investigated both theoretically and experimentally. Temperature dependences of spin-lattice relaxation time T₁ and phase memory time T(M) were measured in the temperature range 6-30 K at high (94 GHz, W band) and low (3.5 GHz, S band) frequencies of electron spin resonance. It follows from T(M) calculations that phase relaxation of Cr(5+) ion arises mainly from magnetic dipole interactions between the chromium ions. Anomalously fast damping of Rabi oscillations is detected in both S- and W-band experiments. It is shown that this phenomenon is caused by microwave field inhomogeneity inside the resonator. Relations between the damping time of Rabi oscillations, Rabi frequency and the crystal sample size are obtained. Lumped-element resonators and smaller sample dimensions are suggested to lower spin dephasing during transient nutations.