Photoluminescent rare-earth qubits embedded in a metal−organic framework as candidates for optical quantum memories

Optical quantum memories enable long-distance distribution of quantum information, which is critical for establishing global quantum internet. Rear-earth qubits are promising candidates for optical quantum memories because they can provide 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 offer alternative solid-state 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 the promise for optical quantum memories with long storage times and high storage efficiencies. Spin dynamic analysis reveals design principles to further improve coherence, which would promote the development of rare-earth MOFs for quantum information science.