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The distribution of entanglement between the nodes of a quantum network will allow new advances e.g. in long-distance quantum communication, distributed quantum computing and quantum sensing. But the realisation of large-scale quantum networks is faced with the same problem of its classical counterpart: the attenuation in optical fibres. The quantum repeater has been introduced in quantum communication to solve this same problem, since the amplification of quantum states is not possible without a critical decrease in the qubit fidelity due to the no-cloning theorem. The nodes of such a quantum repeater are matter systems that should efficiently interact with quantum light, allow entanglement with photons (ideally at telecommunication wavelengths) and serve as a quantum memory allowing long-lived, faithful and multiplexed storage of (entangled) quantum bits.
In this talk, after introducing the current efforts tand architectures for a quantum internet, I will describe our recent progress towards the realisation of quantum repeater nodes with multiplexed ensemble-based quantum memories, using cryogenically-cooled rare-earth ion doped solids. They can be considered a solid-state version of an atomic ensemble, with billions of ions trapped inside a crystalline matrix. They have long been used as a powerful platform for light-matter interaction due to their long coherence times at cryogenic temperatures and great potential for massive multiplexing, which can be harnessed for quantum communication. I will describe how we have employed this system to demonstrate the basic requirements for a quantum repeater node, namely the generation of light-matter entanglement, the demonstration of remote matter-matter entanglement between two memories and the implementation of quantum teleportation with active feedforward. Finally, I will explain our current work towards deploying our system outside of the laboratory environment, and how we plan to build quantum processing nodes using single rare-earth ions in nanoparticles.
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• D. Lago-Rivera et al., Telecom-heralded entanglement between multimode solid-state quantum memories, Nature 594, 37 (2021).
• J. V. Rakonjac et al., Entanglement between a Telecom Photon and an On-Demand Multimode Solid-State Quantum Memory. Phys. Rev. Lett. 127, 210502 (2021).
• J. V. Rakonjac et al., Storage and Analysis of Light-matter Entanglement in a Fiber-integrated System. Science Advances 8, eabn3919 (2022).
• A. Ortu, et al. Multimode capacity of atomic-frequency comb quantum memories. Quantum Sci. Technol. 7, 035024 (2022).
• D. Lago-Rivera et al., Long-distance multiplexed quantum teleportation from a telecom photon to a solid-state qubit. Nature Communications 14, 1889 (2023).
• J. V. Rakonjac et al., Transmission of light-matter entanglement over a metropolitan network. arXiv 2304.05416 (2023).
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