Entanglement of trapped-ion qubits separated by 230 meters

Entanglement-based quantum networks hold out the promise of new capabilities for secure communication, distributed quantum computing, and interconnected quantum sensors. However, only a handful of elementary quantum networks have been realized to date. I will present results from our prototype network, in which two calcium ions are entangled with one another over a distance of 230 m, via a 520 m optical fiber channel linking two buildings [1]. The ion-ion entanglement is based on ion-photon entanglement mediated by coherent Raman processes in optical cavities. Fidelities of up to (88.0+2.2−4.7)% are achieved with respect to a maximally entangled Bell state, with a success probability of 4×10⁻⁵. We will examine the strengths of trapped ions in a quantum-network setting and the role that cavities can play as quantum interfaces at network nodes. In ongoing work, we aim to extend this result to metropolitan-scale distances, enabled by quantum-frequency conversion to telecom wavelengths [2].

[1] V. Krutyanskiy, M. Galli et al., Phys. Rev. Lett. 130, 050803 (2023)

[2] V. Krutyanskiy et al., Phys. Rev. Lett. 130, 213601 (2023)