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

TL;DR

This paper demonstrates the first entanglement between a trapped ion and a solid-state quantum memory over 75 meters, confirming nonlocality and advancing hybrid quantum network development.

Contribution

It introduces a method to generate and verify entanglement between a single trapped ion and a solid-state quantum memory across a significant distance.

Findings

Achieved 89.21% fidelity in hybrid entanglement.

Violates CHSH-Bell inequality by 6 standard deviations.

First demonstration of ion-solid state entanglement over 75 meters.

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 $\mathrm{^{171}Yb^{+}}$ ion and a quantum memory based on $\rm ^{153}Eu^{3+}\colon\!Y_2SiO_5$ 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.