9.2 GHz Clock Transition in a Lu(II) Molecular Spin Qubit Arising from a Massive 3467 MHz Hyperfine Interaction*

Molecular spin qubits are attractive targets for next-generation quantum technologies [1] due to their intrinsic tunability via coordination chemistry techniques, enabling precise control of the relevant spin degrees of freedom and the possibility for massive scale-up via self-assembly. Here, we demonstrate chemical control of the degree of s-orbital mixing into the spin-bearing d-orbital associated with a series of spin-½ La(II) and Lu(II) molecules. Increased s-orbital character reduces spin-orbit coupling and enhances the electron-nuclear Fermi contact interaction. Both outcomes are beneficial for quantum applications: the former reduces spin-lattice relaxation, while the latter gives rise to a record molecular hyperfine interaction for Lu(II) that, in turn, generates a massive 9 GHz hyperfine clock transition and an order of magnitude increase in phase memory time [2]. These findings suggest new strategies for development of molecular quantum technologies, similar to trapped ion systems.

[1] Gaita-Ariño et al., Nat. Chem. 11, 301 – 309 (2019); https://doi.org/10.1038/s41557-019-0232-y

[2] Kundu et al., ChemRxiv 14399333 (Apr 2021). https://doi.org/10.26434/chemrxiv.14399333.v1