Ultrafast control of nuclear spins using only microwave pulses: Towards switchable solid-state quantum gates

We demonstrate the control of the α-proton nuclear spin, I $=1/2$, coupled to the stable radical {·}CH(COOH)₂, S $=1/2$, in a γ-irradiated malonic acid single crystal using only microwave pulses. We show that, depending on the state of the electron spin (mS=±1/2), the nuclear spin can be locked in a desired state or oscillate between mI=+1/2 and mI=-1/2 on the nanosecond time scale. This approach provides a fast way of controlling nuclear spin qubits and also enables the design of switchable spin-based quantum gates by addressing only the electron spin.