  Surfaces enable useful functionalities for quantum systems, e.g. as
interfaces to sensing targets, but often result in surface-induced decoherence
where unpaired electron spins are common culprits. Here we show that the
coherence time of a near-surface qubit is increased by coherent radio-frequency
driving of surface electron spins, where we use a diamond nitrogen-vacancy (NV)
center as a model qubit. This technique is complementary to other methods of
suppressing decoherence, and importantly, requires no additional materials
processing or control of the qubit. Further, by combining driving with the
increased magnetic susceptibility of the double-quantum basis we realize an
overall fivefold sensitivity enhancement in NV magnetometry. Informed by our
results, we discuss a path toward relaxation-limited coherence times for
near-surface NV centers. The surface spin driving technique presented here is
broadly applicable to a wide variety of qubit platforms afflicted by
surface-induced decoherence.
