Substrate Effects on Spin Lattice Relaxation in the Molecular Qubit CuPc

Molecular magnets can serve as qubits for quantum information system (QIS) applications where the molecule’s electron spin is used for storing information. To be functional in QIS applications, regular arrays of qubits supported on substrates need to exhibit long relaxation times. To address this challenge, we performed electronic structure calculations on a substrate-supported molecular magnet system, comprising copper(II) phthalocyanine(CuPc) on graphene, and examined changes in relaxation times using a spin lifetime proxy. We discuss how CuPc mechanically couples to graphene and what effect this coupling has on the molecule’s electronic structure and magnetic state. We compute the local vibrational modes for CuPc with and without graphene at the density functional theory level, and then, use these vibrational modes to calculate the variation in the g-tensor (our proxy for spin-lattice relaxation) for the molecule. Lastly, we analyze the changes in the g-tensor to understand how the coupling between the molecule and the surface will contribute to the spin-lattice relaxation times for the coupled substrate-qubit system.