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 T-2* from 2.7 +/- 0.1 to 15 +/- 1 mu s by dressing with a Omega/2 pi = 581 +/- 2 kHz mechanical Rabi field. Furthermore, we develop a model that quantitatively predicts the relationship between Omega and T-2* 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 Omega accessed here. We show that amplitude noise in Omega will dominate the dephasing for larger driving fields.