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arXiv:2603.05836

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

Chen-Xu Wang, Yi-Yang Wang, Tian-Xiang Zhu, Qing-Quan Yao, Peng-Jun Liang, Yuan-Cong Li, Zi-Peng Liu, Ran He, Yong-Jian Han, Jin-Ming Cui, Zong-Quan Zhou, Yun-Feng Huang, Chuan-Feng Li, Guang-Can Guo

quant-phphysics.atom-phSubmitted Mar 6, 2026• Announced Mar 9, 2026• 1 citation
v1 · Mar 6, 2026v2 · Oct 14, 2026
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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.

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27 pages,16 figures,2 tables

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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 171Yb+\mathrm{^{171}Yb^{+}}171Yb+ ion and a quantum memory based on 153Eu3+ ⁣: ⁣Y2SiO5\rm ^{153}Eu^{3+}\colon\!Y_2SiO_5153Eu3+:Y2​SiO5​ 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±2.23)%(89.21 \pm 2.23)\%(89.21±2.23)% and violates the CHSH-Bell inequality by 6 standard deviations (S=2.328±0.055S = 2.328 \pm 0.055S=2.328±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.
Different quantum systems possess different favorable qualities. On the one hand, ensemble-based quantum memories are suited for fast multiplexed long-range entanglement generation. On the other hand, single-atomic systems provide access to gates for processing of information. Both of those can provide advantages for high-rate entanglement generation within quantum networks. We develop a hybrid architecture that takes advantage of these properties by combining trapped-ion nodes and nodes comprised of spontaneous parametric down conversion photon pair sources and absorptive memories based on rare-earth ion ensembles. To this end, we solve the central challenge of matching the different bandwidths of photons emitted by those systems in an initial entanglement-generation step. This enables the parallel execution of multiple probabilistic tasks in the initial stage. As a particular example, we show that our approach can lead to a significant speed-up for the fundamental task of creating ion-ion entanglement over hundreds of kilometers in a quantum network.
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Long-range quantum information processing will require the integration of different technologies to form hybrid architectures combining the strengths of multiple quantum systems. In this work, we propose a hybrid networking architecture designed to improve entanglement rates in quantum networks based on trapped ions. Trapped ions are excellent candidates as network nodes, but photon losses make long-distance networking difficult. To overcome some losses and extend the range of trapped-ion-based networks, we propose including neutral-atom-based nondestructive single-photon detection and single-photon storage in between networking nodes, forming a hybrid network. This work builds on recently demonstrated optical frequency conversion of single photons emitted by trapped ions. We derive the average two-node entanglement rate for this proposed network architecture as a function of distance. Using reasonable experimental parameters, we show that this proposed quantum network can generate remote entanglement rates up to a factor of 100 larger than that of an equivalent homogeneous network at both near-IR and C-band wavelengths for distances up to 50 km.
Increasing the number of qubits that can be controlled in a quantum system represents an essential challenge to the field of quantum computing. Quantum networks consisting of nodes for local information processing and photonic channels to distribute entanglement between different nodes represent a promising modular approach to achieve this scaling. Trapped atomic ions are an ideal candidate for quantum network nodes, with long-lived identical qubit memories that can be locally entangled through their Coulomb interaction and remotely entangled through photonic channels. In this work I will first discuss our established toolkit for using 171Yb+ and 138Ba+ ions individually or together within a quantum node. Next I will show how the 138Ba+ toolkit has been extended to allow for quantum operations in the 52D3/2 manifold. I will then demonstrate how we can generate ion-photon entanglement as a resource to connect separate nodes with a focus on some important improvements which will allow us to implement it as part of a larger network. These improvements include first the use of separate memory (171Yb+ ) and photon generating (138Ba+ ) ions. Additionally, the use of separate atomic lines within 138Ba+ for excitation and collection allows us to preserve integrity of this photonic interface by ensuring the purity of the single photons that are produced. To this end I demonstrate a single-photon source for quantum networking based on a trapped 138Ba+ ion with a single photon purity of g2(0) = (8.1 ± 2.3) × 10−5 without background subtraction. Trade-offs between the photonic generation rate and the memory-photon entanglement fidelity for the case of polarization photonic qubits are also examined and optimized by tailoring the spatial mode of the collected light. These techniques should be useful in constructing larger ion-photon networks.
The quantum internet -- in synergy with the internet that we use today -- promises an enabling platform for next-generation information processing, including exponentially speed-up distributed computation, secure communication, and high-precision metrology. The key ingredients for realizing such a global network are the distribution and storage of quantum entanglement. As ground-based quantum networks are likely to be based on existing fiber networks, telecom-wavelength entangled photons and corresponding quantum memories are of central interest. Recently, 167Er3+\rm^{167}Er^{3+}167Er3+ ions have been identified as a promising candidate for an efficient, broadband quantum memory at telecom wavelength. However, to date, no storage of entangled photons, the crucial step of quantum memory using these promising ions, 167Er3+\rm^{167}Er^{3+}167Er3+, has been reported. Here, we demonstrate the storage and recall of the entangled state of two telecom photons generated from an integrated photonic chip based on a silicon nitride micro-ring resonator. Combining the natural narrow linewidth of the entangled photons and long storage time of 167Er3+\rm^{167}Er^{3+}167Er3+ ions, we achieve storage time of 1.936 μμμs, more than 387 times longer than in previous works. Successful storage of entanglement in the crystal is certified by a violation of an entanglement witness with more than 23 standard deviations (-0.234 ±\pm± 0.010) at 1.936 μμμs storage time. These results pave the way for realizing quantum networks based on solid-state devices.