All-mechanical coherence protection and fast control of a spin qubit

In a phononic quantum network, quantum information is stored and processed within stationary nodes defined by solid-state spins, and phonons carry the information between nodes. Phonons have a number of benefits in comparison to photons, including smaller device footprints, reduced crosstalk, long cavity lifetimes at low temperatures and coupling to both solid-state spins and electromagnetic waves. Previous results on multiple platforms have demonstrated enhanced interactions between a phononic cavity and a stationary qubit. However an outstanding issue is the compatibility between the spin’s coupling to the resonant phononic cavity and the simultaneous use of pulse sequences to suppress low-frequency environmental noise. Here we demonstrate all-mechanical coherence protection of a silicon–vacancy spin in diamond. Optical initialization, quantum operations and readout are performed in a dressed basis, which is protected from low-frequency noise and compatible with a phononic cavity. We additionally show a Rabi frequency reaching 800 MHz, which enables ultrafast quantum control. Our results establish a basis for high-fidelity, phonon-mediated quantum gates and represent a crucial advance towards robust on-chip quantum phononic networks.