Quantum Frequency Conversion for Entangling Nodes in a Trapped Ion Network

Realizing distributed quantum computing (DQC) requires remote entanglement via single photons through optical fibers. The native visible wavelength photons from trapped barium ions—a leading qubit platform—suffer from prohibitive attenuation in commercial networks over kilometer-scale distances [1].  We address this challenge by developing a robust, field-deployable quantum frequency conversion [2] device converting 493 nm Ba+ photons to a telecom O-band frequency. We report high photon conversion efficiency and an optical noise floor sufficiently low to preserve high qubit fidelity, demonstrating the device’s viability as an interface between an ion-trap quantum processor and a commercial fiber-based quantum network. This interface enables distant barium ions to be entangled via a Bell state measurement of the converted photons. We further discuss our progress towards demonstrating long-distance DQC through a city-scale commercial optical fiber network.

[1] Saha, S. et al. Nat. Commun. 16, 2533 (2025).

[2] Kumar, P. Quantum Frequency Conversion. Opt. Lett. 1990, 15 (24), 1476−1478.