Spin-bearing molecules offer modular building blocks for quantum technologies but typically lack mechanisms to optically initialize and read out the ground state spin, a crucial feature for single spin control in applications ranging from nanoscale sensing to secure communication. As a first step towards this goal, we recently translated the desired optical-spin interface into spin-triplet, transition metal-based complexes. We now use symmetry control of the host environment around a Cr4+ color center, Cr(o-tolyl)4 to generate noise-insensitive clock transitions, arising from non-zero transverse zero-field splitting that is absent in the isostructural, Sn(o-tolyl)4 host. This host-matrix engineering leads to spin-coherence times of more than 10 μs in a nuclear and electron-spin rich environment. Generalized cluster correlation expansion methods elucidate the effect of transverse anisotropy and the nuclear spin bath on magnetic field dependent coherence times. We demonstrate further enhancements of the optical-spin interface with five-fold enhancements in spin initialization and spin-lattice relaxation times. These results provide a general methodology to tune molecular color centers using both the intrinsic and extrinsic environment as initial steps towards nanoscale sensing in magnetically noisy, amorphous environments.

Optimizing the optical-spin interface of molecular color centers

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ACS Fall 2022

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