Hybrid atomistic-parametric decoherence model for molecular spin qubits

Area of Science:

• Quantum Information Science
• Materials Science
• Physical Chemistry

Background:

• Solid-state molecular qubits offer potential for quantum computing but face challenges in understanding quantum coherence limits.
• The complex qubit environment hinders accurate prediction of relaxation (T1) and dephasing (T2) times.

Purpose of the Study:

• To develop a robust theoretical framework for predicting quantum coherence in molecular spin qubits.
• To investigate the impact of environmental noise, specifically lattice motion and magnetic field fluctuations, on qubit performance.

Main Methods:

• Utilized a random Hamiltonian approach incorporating molecular g-tensor fluctuations from molecular dynamics simulations.
• Constructed Redfield quantum master equations to model spin-lattice interactions and magnetic field noise.
• Investigated copper porphyrin qubits within a crystalline framework.

Main Results:

• Atomistic T1 predictions initially overestimated experimental data.
• Incorporating a magnetic field noise model, accounting for lattice nuclear spins, restored quantitative agreement with experimental T1 and T2 times.
• Identified field-dependent noise amplitudes (δB ∼ 10 μT - 1 mT) for the copper porphyrin system.

Conclusions:

• The developed dynamical methods accurately model open quantum system dynamics for molecular spin qubits.
• T1 relaxation scales as 1/B due to combined spin-lattice and magnetic noise, while T2 dephasing scales as 1/B² due to low-frequency magnetic noise.
• This work provides a pathway for designing and optimizing molecular spin qubits for quantum technologies.