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

We demonstrate the control of the alpha-proton nuclear spin, I=1/2, coupled to the stable radical CH(COOH)2, S=1/2, in a gamma-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 and efficient way of controlling nuclear spin qubits and also enables the design of switchable spin-based quantum gates by addressing only the electron spin.