Intrinsic decoherence and Rabi oscillation damping of Mn 2+and Co 2+ electron spin qubits in bulk ZnO

We demonstrate by pulse EPR that two electron spin qubits in bulk ZnO, the Mn2+ and the Co2+ spin qubits, which have, respectively, long $(T_{2}(6\ \text{K})= 178\ \mu\text{s})$ and short $(T_{2}(1.7\ \text{K})= 9\ \mu\text{s})$ transverse spin coherence time T2 at low temperature, have however very short and similar Rabi oscillation damping times, on the order of $T_{R}\approx250\ \text{ns}$ at low temperature. A detailed study of Mn2+ spin qubits has shown that the main contribution to the Rabi oscilation damping rate is temperature independent and proportional to the Rabi frequency. This main contribution to the damping rate during coherent microwave manipulation of spins is interpreted as due to the changes of the dipolar couplings induced by the long microwave pulse used in this kind of EPR nutation experiment. Strategies are suggested for overcoming this problem of Rabi oscillation overdamping in future spin-based quantum computers