Telecom single photons from a trapped Ba+ ion

Long-distance fiber-based quantum networks require photons at telecommunication wavelengths that can be exchanged to interconnect qubits. Trapped ions are excellent candidates for quantum networks because of their long coherence times [1], high fidelity two-qubit gates [2], and the ability to generate entangled photons [3]. But virtually all trapped ions have strong optical dipole transitions at UV and visible wavelengths making the photons incompatible for long-distance fiber-based networks. Here, we demonstrate the first frequency conversion of visible photons emitted from a trapped barium ion into the telecom C-band. We use a two-stage conversion setup with  37% and 52% end-to-end conversion efficiency in the first and second stage respectively. We show that frequency conversion preserves the quantum nature of the emitted photons via second-order correlation measurements [4]. This approach could enable trapped ion quantum computers to communicate over long distances using a fiber network [5].

[1] Pengfei Wang et al.. Nat. Commun. 12, 233 (2021)

[2] C. J. Ballance et al. Phys. Rev. Lett. 117, 60504 (2016)

[3] James D. Sivern et al. Appl. Opt. 56, B222-B230 (2017)

[4] John Hannegan et al. in progress 

[5] John Hannegan, et al. arXiv:2101.04236 (2021).