Quantum coherence of S = ½ transition metal-based quantum bits (qubits) is often governed by the coupling of electron spin to molecular vibrations. Yet, a general model for understanding coherence of molecular qubits from fundamental chemical principles has not been established. Here a general ligand field theory model is outlined to describe coherence properties of S = ½ transition metal complexes. We show that the spin-phonon coupling term for a given vibrational mode is related to the coherence of the complex, and is dependent on: 1) the identity of the metal, 2) the magnitude and gradient in the ligand field excited state energy, and 3) the covalency of the ligand–metal bonds. From an extensive series of density functional theory (DFT) and time-dependent DFT calculations calibrated to a range of experimental data, we show that spin phonon coupling terms of minimalistic high symmetry complexes of Cu(II) and V(IV) translate to and correlate with experimentally observed quantum coherence properties of modern molecular qubits of different ligand sets, geometries, and coordination numbers. The results can be used to estimate the coherence lifetime of any S = ½ molecular qubit candidate and guide the discovery of room temperature coherent materials for quantum information processing.

Dynamic ligand fields of molecular qubits: Decoherence through spin-phonon coupling

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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