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.

Reference: Z-J. Shu,  Z.-D. Zhang, Q.-Y. Cao,  P.-C. Yang,  M. B. Plenio, C. Mueller, J. Lang, N. Tomek, B. Naydenov, L. P. McGuinness, F. Jelezko, and J.-M. Cai, Unambiguous nuclear spin detection using engineered quantum sensing sequence,  Phys. Rev. A 96, 051402 [Rapid Communication] (2017) .