Predictable tuning of the zero field splitting parameter in molecular color centers via external electric fields

Molecular color centers (MCCs) have recently emerged as promising candidates for next-generation qubits owing to their modularity, tunability, and addressability. Among their most critical properties is the zero-field splitting (ZFS) parameter, which plays a pivotal role in qubit operation and in mitigating one of the intrinsic limitations of MCCs, the short coherence time (T₂). To date, the only proposed strategy for tuning ZFS has been chemically induced symmetry breaking via anisotropic host matrices. This approach, however, is time-consuming, and the resulting ZFS parameters remain close to a “black box,” lacking quantitative predictability.

Here, we computationally demonstrate that ZFS—particularly the rhombic zero field splitting parameter, E—can be tuned by applying external electric fields, thereby circumventing the need for chemical modifications. When the electric field is applied along the symmetry axis, the individual tensor elements of the ZFS and the resulting ZFS parameters exhibit a linear and thus predictable dependence on field strength. This establishes a predictive framework specifically for cases in which distortions occur along the symmetry axis and provides insights into practical design rules for achieving target ZFS values in MCC-based qubits.