Quantum 2025 – scientific programme
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THU: Thursday Contributed Sessions
THU 5: QIP Implementations: Interfaces
THU 5.1: Talk
Thursday, September 11, 2025, 14:15–14:30, ZHG006
Quantum repeater applications with single trapped ions and single photons — •Pascal Baumgart, Max Bergerhoff, Jonas Meiers, Stephan Kucera, Christian Haen, and Jürgen Eschner — Universität des Saarlandes, Experimentalphysik, 66123 Saarbrücken
For the realization of large-distance quantum networks, quantum repeaters (QR) are needed to overcome the exponential loss of direct transmission by dividing a transmission link into asynchronously driven cells [1] and segments [2]. We report on the implementation of these QR building blocks with free-space-coupled photons from two 40Ca+ ions in the same Paul trap as quantum memories. Atom-photon entanglement is generated by controlled emission of single, separately fiber-coupled photons from the individually addressed ions. In the QR cell, entanglement is swapped from the ions to two asynchronously generated photons by a Mølmer-Sørensen gate and subsequent state detection [3], while in the QR segment, atom-atom entanglement is generated by a photonic Bell-state measurement.
In preparation for real-world QR applications, quantum communication protocols using a parametric down-conversion source of entangled photon pairs and a trapped-ion quantum memory, together with quantum frequency conversion, have been demonstrated over the 14.4 km Saarbrücken urban fiber link [4].
[1] D. Luong et al., Appl. Phys. B 122, 96 (2016)
[2] P. van Loock et al., Adv. Quantum Technol., 3: 1900141 (2020)
[3] M. Bergerhoff et al., Phys. Rev. A 110, 032603 (2024)
[4] S. Kucera et al., npj Quant. Inf. 10, 88 (2024)
Keywords: Trapped ion; Quantum repeater; Photon-photon entanglement; Atom-atom entanglement; Fiber link