Design Rules to Engineer the Spin Structure of Cr4+ Molecular Qubits via Matrix Modularity

Using a multi-level computational approach we predict the zero-field splitting (ZFS) parameters of Cr(IV) molecular qubits with unprecedented accuracy, obtaining results in excellent agreement with experiments. We then apply the pro-tocol to Cr(IV) molecular color centers embedded in non-isostructural tin host matrices. We show that by simply altering the matrix composition, one can effectively modify the relative energies of the spin sub-levels, thus enabling a fine-tuning of the qubit’s magnetic anisotropy for optimal performance in quantum technologies. We identify two effects influencing matrix design: the molecular symmetry of the qubit and the presence of inhomogeneous electrostatic fields arising from the chemical composition of the matrix. Finally, we compute spin-coherence times and discuss their sensitivity to the ma-trix environment through the ZFS parameters. Our work provides predictive strategies for tailoring the spin structure and coherence properties of molecular color centers through a rational control of their matrix environment.