Photoluminescent Rare-Earth Qubits Embedded in a Metal–Organic Framework as Candidates for Optical Quantum Memories

Optical quantum memories enable long-distance quantum information distribution, which is critical for establishing the global quantum Internet. Rare-earth qubits are promising candidates due to their spin-optical interfaces with excellent spin coherence and optical properties. When doped into inorganic solids, they display relatively long excited-state lifetimes and, in turn, low storage efficiencies, which are difficult to optimize via material design. Metal–organic frameworks (MOFs) allow fine-tuning of spin coherence and excited-state lifetimes through rational design of coordination environments, thereby offering alternative platforms to host rare-earth qubits. By incorporating Nd3+ and Yb3+ into an oxalate-based MOF, we develop frameworks that exhibit spin decoherence time exceeding 5 μs at 3.4 K, near-infrared and/or telecommunication-band photoluminescence, and excited-state lifetimes up to 150 μs. These materials hold promise with long storage times and high storage efficiencies. Spin dynamics analysis reveals design principles to further improve coherence, promoting the development of rare-earth MOFs for quantum information science.