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

Abstract

We demonstrate the control of the $\ensuremath{\alpha}$-proton nuclear spin, $I$ $=1/2$, coupled to the stable radical \ensuremath{\cdot}CH(COOH)${}_{2}$, $S$ $=1/2$, in a $\ensuremath{\gamma}$-irradiated malonic acid single crystal using only microwave pulses. We show that, depending on the state of the electron spin (${m}_{S}=\ifmmode\pm\else\textpm\fi{}1/2$), the nuclear spin can be locked in a desired state or oscillate between ${m}_{I}=+1/2$ and ${m}_{I}=\ensuremath{-}1/2$ 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.