Spatially-resolved coherence of organic molecular spins at room-temperature

Abstract: Molecular spins are a versatile platform for quantum sensing. Not only are the spin-bearing molecules themselves widely tunable, they are also capable of being used as sensors as crystals, films and in solution. Using thin-films offers the advantages of high doping ratios and the ability to control the thickness with nanometre precision, however they also introduce disorder to the system. High proximity sensing can also be realised by using micro- and nano-crystals, however in many solid-state systems this leads to a reduction in coherence. In this paper we combine room-temperature optically detected coherent control of molecular spins and microscopy to image the coherence properties of both thin-films and micro-crystals of pentacene doped p-terphenyl. In thin-films we find large amounts of variation in both the contrast and coherence times, leading to a variability in the magnetic field sensitivity of approximately 7.6 %. Applying the technique to micro-crystals shows much lower sensitivity variability (1.3 %), and we find no evidence of coherence loss toward the edge of the crystal. Finally we perform optically-detected coherent control on a nano-crystal, showing minimal loss in coherence and contrast compared to the bulk crystal, with a coherence time of 1.09 μs and a contrast of 25 %.