Continuous dynamical decoupling of a single diamond nitrogen-vacancy center spin with a mechanical resonator

Inhomogeneous dephasing from uncontrolled environmental noise can limit the coherence of a quantum sensor or qubit. For solid state spin qubits such as the nitrogen-vacancy (NV) center in diamond, a dominant source of environmental noise is magnetic field fluctuations due to nearby paramagnetic impurities and instabilities in a magnetic bias field. In this work, we use ac stress generated by a diamond mechanical resonator to engineer a dressed spin basis in which a single NV center qubit is less sensitive to its magnetic environment. For a qubit in the thermally isolated subspace of this protected basis, we prolong the dephasing time T₂^* from 2.7pm0.1 μs to 15pm1 μs by dressing with a Ω=581pm2 kHz mechanical Rabi field. Furthermore, we develop a model that quantitatively predicts the relationship between Ω and T₂^* in the dressed basis. Our model suggests that a combination of magnetic field fluctuations and hyperfine coupling to nearby nuclear spins limits the protected coherence time over the range of Ω accessed here. We show that amplitude noise in Ω will dominate the dephasing for larger driving fields.