Semi-empirical Haken-Strobl model for molecular spin qubits

Understanding the physical processes that determine the relaxation T 1 and dephasing T 2 times of molecular spin qubits is critical for envisioned applications in quantum metrology and information processing. Recent spin-echo measurements of solid-state molecular spin qubits have stimulated the development of quantum mechanical models for predicting intrinsic qubit timescales using first-principles electronic structure methods. We develop an alternative semi-empirical approach to construct Redfield quantum master equations for molecular spin qubits using a stochastic Haken-Strobl theory for a central spin with fluctuating gyromagnetic tensor due to spin-lattice interaction and fluctuating local magnetic field due to interactions with lattice spins. Using two vanadium-based spin qubits as case studies, we compute qubit population and decoherence times as a function of temperature and magnetic field, using a bath spectral density parametrized with a small number of T 1 measurements. The theory quantitatively agrees with experimental data over a range of conditions beyond those used to parameterize the model, demonstrating the generalization potential of the method. The ability of the model to describe the temperature dependence of the ratio T2/T1 is discussed and possible applications for designing novel molecule-based quantum magnetometers are suggested.

Automated summary

Understanding the physical processes that determine the relaxation and dephasing times of molecular spin qubits is crucial for their applications in quantum metrology and information processing. Recent spin-echo measurements in solid-state molecular spin qubits have led to the development of quantum mechanical models for predicting qubit timescales. In this study, a semi-empirical approach is used to construct Redfield quantum master equations for molecular spin qubits, taking into account the effects of spin-lattice interaction and interactions with lattice spins. The model is validated using two vanadium-based spin qubits, and it demonstrates good agreement with experimental data over a wide range of conditions. The model's ability to describe the temperature dependence of the T2/T1 ratio is discussed, and potential applications for designing molecule-based quantum magnetometers are suggested.