Optimizing the spin qubit performance of lanthanide-based metal–organic frameworks†

Abstract

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 at low doping levels. Variable-temperature spin dynamic studies unveiled spin relaxation and decoherence mechanisms, highlighting the 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 the future development of solid-state lanthanide qubits targeting quantum information technologies.