Heterogeneous entanglement between a trapped ion and a solid-state quantum memory

Abstract

Hybrid quantum networks offer a promising architecture for scalable quantum information processing and a future quantum internet, as they can combine the complementary strengths of disparate physical platforms. While single-atom systems provide deterministic quantum logic gates, atomic ensembles enable large-capacity quantum storage. However, generating entanglement between such heterogeneous systems has remained an open challenge, primarily due to fundamental spectral mismatches and system complexity. Here, we demonstrate a hybrid quantum network that entangles a single trapped ${}^{171}\mathrm{Y}{\mathrm{b}}^{+}$ ion and a quantum memory based on ${}^{153}\mathrm{E}{\mathrm{u}}^{3+}:{\mathrm{Y}}_2\mathrm{Si}{\mathrm{O}}_5$ crystal over a 75-m separation. Using polarization-maintaining quantum frequency conversion, we map spin-photon entanglement onto a hybrid entanglement between a single spin qubit and a collective excitation of the quantum memory. The resulting entangled state achieves a fidelity of $(89.21\pm 2.23)\%$ and violates the CHSH-Bell inequality by 6 standard deviations ($S=2.328\pm 0.055$), confirming nonlocality between two heterogeneous nodes. This work establishes entanglement between a quantum processing module with a multiplexed quantum memory node, representing a key step toward a scalable, multifunctional quantum internet.