Robust AC vector sensing at zero field with pentacene

Quantum sensors have long shown promise in sensitively detecting microwave-range signals, but practical applications are still limited by the sensor performance and its ability to work in rugged conditions. Here we focus on pentacene molecules as quantum sensors since they are compatible with a wide range of environments, can be embedded in organic materials, and can operate at room temperature and in the absence of a strong static magnetic field. In particular, we demonstrate Rabi-type sensing on a confocal microscopy set-up with pentacene molecules doped into naphthalene crystals. We show we can evade previous sensitivity limits on Rabi sensing using pentacene by lengthening the rotating-frame coherence time by over five times with a Solomon-echo inspired protocol. In the regime of interest, this gives a corresponding fivefold sensitivity enhancement. Moreover, we can reconstruct the spatial vector of the magnetic field by using the two transitions intrinsic to pentacene and two orientations of pentacene molecules in our solid-state matrix. We achieve a sensitivity of under 1 μT/√Hz for the amplitude of microwave frequency in each cartesian direction.