Spin Relaxation Times of Copper Phthalocyanine (CuPc) Qubits diluted in Diamagnetic Zinc Phthalocyanine (ZnPc) Host Matrices

We report on electron paramagnetic resonance (EPR) measurements of powder CuPc prepared in a solid-state complex, ZnPc. The free electron spin of CuPc constitutes a two-state quantum system that may potentially be a candidate as a quantum bit (qubit) for quantum computing applications [1]. We test whether the CuPc electron spin increases its spin dephasing time, T₂, when the exchange interactions between adjacent CuPc qubits is reduced by diluting CuPc molecules in a zinc phthalocyanine (ZnPc) host matrix [2] at concentrations of 0%, 1%, 5%, and 10%, which modifies the average distance between CuPc molecules. ZnPc is a diamagnetic molecule that nominally does not exhibit an EPR signal and, also, the dominant Zn isotopes are I=0. We study the system using continuous wave and pulsed EPR, and we find similar results to previous studies on CuPc in liquid host matrices, T₂ on the order of 1 µs observed for both, CuPc as well as another yet unidentified paramagnetic center that is likely due to an admixture to the ZnPc matrix. We also study the temperature dependence of the EPR signals between 5 K and room temperature. [1] M.Warner et. al, Nature, 503, 504(2013). [2] S.Seelan, et. al, Journal of Molecular Catalysis A: Chemical, 168, 61(2001).