A quantum repeater segment is a basic building block of a quantum repeater, generating buffered entanglement of quantum memories to connect quantum repeater cells. It also enables the connection between quantum computers. In the implementation we present here, photons emitted from two co-trapped free-space coupled $^{40}$ Ca $^+$ ions are converted to the telecom-C band and interfered after transmission over 440 $\,$ m of optical fiber (220 $\,$ m per arm), where a photonic Bell measurement is performed to create entanglement between the memories. With this scheme we generate an entangled $\left|Ψ^+\right\rangle$ Bell state with $\ge 68(8)\,$ % fidelity, highlighting trapped $^{40}$ Ca $^+$ ions as a promising quantum repeater hardware platform.A quantum repeater segment is a basic building block of a quantum repeater, generating buffered entanglement of quantum memories to connect quantum repeater cells. It also enables the connection between quantum computers. In the implementation we present here, photons emitted from two co-trapped free-space coupled $^{40}$Ca$^+$ ions are converted to the telecom-C band and interfered after transmission over 440$\,$m of optical fiber (220$\,$m per arm), where a photonic Bell measurement is performed to create entanglement between the memories. With this scheme we generate an entangled $\left|Ψ^+\right\rangle$ Bell state with $\ge 68(8)\,$% fidelity, highlighting trapped $^{40}$Ca$^+$ ions as a promising quantum repeater hardware platform.

quant-pharXiv:2606.12313Jun 11, 20260 citations

Trapping ions

Timo A. Nieminen

Nature PhotonicsOct 29, 201011 citations

^{40}

^+

ions are converted to the telecom-C band and interfered after transmission over 440

\,

m of optical fiber (220

\,

m per arm), where a photonic Bell measurement is performed to create entanglement between the memories. With this scheme we generate an entangled

\left|Ψ^+\right\rangle

Bell state with

\ge 68(8)\,

% fidelity, highlighting trapped

^{40}

^+

ions as a promising quantum repeater hardware platform.