Extending the quantum coherence of a qubit via engineering the noise spectrum of its environment*

Controlling the environment of a qubit to suppress decoherence is a key technique for modern quantum technologies. Such control can be either passive, via e.g. materials engineering, or active, via e.g. driving fields. Using a shallow defect center coupled to RF-driven surface spins, we demonstrate experimentally that spectral engineering of the spin bath enables improved qubit coherence. Results are in agreement with our quantitative model, and open the path to active decoherence protection using custom-designed waveforms applied to the environment rather than the qubit.