Suppression of spin-bath and low-frequency noise for submegahertz ac magnetometry based on a doubly dressed spin qubit in diamond

We experimentally demonstrate a protocol that effectively suppresses low-frequency noise, including the qubit-bath interaction in diamond. This enables the detection of ac signals below 1 MHz with an increased signal-to-noise ratio of up to approximately 17. The method is based on ac magnetometry with single- and doubly dressed states, which are adiabatically transferred from the initial bare qubit states via concatenated continuous dynamical decoupling. We compare the dressed-state protocols with a conventional pulsed dynamical decoupling method, XY16. This work paves an alternative way toward the sensitive detection of weakly coupled nuclear spins in low-field NMR experiments and submegahertz ac magnetometry.