Optimizing spin qubit performance of lanthanide-based metal−organic frameworks

Lanthanide-based spin qubits are intriguing candidates for high-fidelity quantum memories owing to their spin-optical interfaces. Metal−organic frameworks (MOFs) offer promising solid-state platforms to host lanthanide ions because their bottom-up synthesis enables rational optimization of both spin coherence and luminescence. Here, we incorporated Nd³⁺ and Gd³⁺ into a La³⁺-based MOF with various doping levels and examined their qubit performance including the spin relaxation time (T₁) and phase memory time (T_m). Both Nd³⁺ and Gd³⁺ behave as spin qubits with T₁ exceeding 1 ms and T_m approaching 2 μs at 3.2 K under low doping levels. Variable-temperature spin dynamic studies unveiled spin relaxation and decoherence mechanisms, highlighting critical roles of spin-phonon coupling and spin-spin dipolar coupling. Accordingly, reducing the spin concentration, spin-orbit coupling strength, and ground spin state improves the qubit performance of lanthanide-based MOFs. These optimization strategies serve as guidelines for future development of solid-state lanthanide qubits targeting quantum information technologies.