  Nitrogen-vacancy centers in diamond show great potential as magnetic,
electric and thermal sensors which are naturally packaged in a bio-compatible
material. In particular, NV-based magnetometers combine small sensor volumes
with high sensitivities under ambient conditions. The practical operation of
such sensors, however, requires advanced quantum control techniques that are
robust with respect to experimental and material imperfections, control errors,
and noise. Here, we present a novel approach that uses Floquet theory to
efficiently generate smooth and simple quantum control pulses with tailored
robustness properties. We verify their performance by applying them to a single
NV center and by characterising the resulting quantum gate using quantum
process tomography. We show how the sensitivity of NV-ensemble magnetometry
schemes can be improved by up to two orders of magnitude by compensating for
inhomogeneities in both the control field and the spin transition frequency.
Our approach is ideally suited for a wide variety of quantum technologies
requiring high-fidelity, robust control under tight bandwidth requirements,
such as spin-ensemble based memories involving high-Q cavities.
