Coherence enhancement of solid-state qubits by local manipulation of the electron spin bath

The performance of qubit-based technologies can be strongly limited by environmental sources of noise and disorder that cause decoherence. Qubits used in quantum sensing are usually very close to the host surface to enhance their coupling to external targets. This leaves them vulnerable to the effects of the surrounding noisy electron spin bath near the surface, which is very challenging to eliminate. Here we developed an efficient method to engineer the immediate electrostatic environment of nitrogen vacancy centre qubits located several nanometres beneath the diamond surface. We adopt a ‘pull-and-push’ strategy for near-surface charge manipulation using the strong local electric field of an atomic force microscope tip. Our technique is particularly effective for extremely shallow nitrogen vacancy centres, increasing their spin echo time by up to 20 fold. This corresponds to an 80-fold enhancement in the potential sensitivity for detecting individual external proton spins. Our work not only represents a step towards overcoming a fundamental restriction to applications of shallow nitrogen vacancy centres for quantum sensing but may also provide a general route for enhancing the coherence of solid-state qubits.