  Sensing, localising and identifying individual nuclear spins or frequency
components of a signal in the presence of a noisy environments requires the
development of robust and selective methods of dynamical decoupling. An
important challenge that remains to be addressed in this context are spurious
higher order resonances in current dynamical decoupling sequences as they can
lead to the misidentification of nuclei or of different frequency components of
external signals. Here we overcome this challenge with engineered quantum
sensing sequences that achieve both, enhanced robustness and the simultaneous
suppression of higher order harmonic resonances. We demonstrate experimentally
the principle using a single nitrogen-vacancy center spin sensor which we apply
to the unambiguous detection of external protons.
