Decoherence of Molecular Qubits: Insights From Quantum Many-Body Simulations*

Quantum properties of magnetic molecules will drive their applications in quantum information science. Electron spin decoherence time in such molecules depends strongly on molecular structure. A synthetic study of a series of vanadyl molecular qubits by Danna Freedman's group found that the decoherence time decreases as size of molecule increases.¹ To explain this counterintuitive experimental result and provide insights for decoherence in molecular qubits in general, we combine ab-initio electronic structure calculations and quantum many-body simulation to study hyperfine interactions between electron and hydrogen nuclear spins and their effects on electron spin decoherence. We show that, for an isolated molecule, decoherence is always incomplete, but the residual coherence decreases as the size of the molecule increases. This result explains the experimentally observed diffusion barrier for decoherence, also suggests a quantitative approach to connect molecular structure and diffusion barrier.
1. Graham, M. J. et al. JACS 2017, 139, 3196–3201