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arXiv · 2405.14557

High fidelity distribution of triggered polarization-entangled telecom photons via a 36km intra-city fiber network

Tim Strobel·Stefan Kazmaier·Tobias Bauer·Marlon Schäfer·Ankita Choudhary·Nand Lal Sharma·Raphael Joos·Cornelius Nawrath·Jonas H. Weber·Weijie Nie·Ghata Bhayani·Lukas Wagner·André Bisquerra·Marc Geitz·Ralf-Peter Braun·Caspar Hopfmann·Simone L. Portalupi·Christoph Becher·Peter Michler
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Abstract

Fiber-based distribution of triggered, entangled, single-photon pairs is a key requirement for the future development of terrestrial quantum networks. In this context, semiconductor quantum dots (QDs) are promising candidates for deterministic sources of on-demand polarization-entangled photon pairs. So far, the best QD polarization-entangled-pair sources emit in the near-infrared wavelength regime, where the transmission distance in deployed fibers is limited. Here, to be compatible with existing fiber network infrastructures, bi-directional polarization-conserving quantum frequency conversion (QFC) is employed to convert the QD emission from \unit[780]{nm} to telecom wavelengths. We show the preservation of polarization entanglement after QFC (fidelity to Bell state $F_{\phi^+, conv}=0.972\pm0.003$) of the biexciton transition. As a step towards real-world applicability, high entanglement fidelities ($F_{\phi^+, loop}=0.945\pm0.005$) after the propagation of one photon of the entangled pair along a \unit[35.8]{km} field installed standard single mode fiber link are reported. Furthermore, we successfully demonstrate a second polarization-conversing QFC step back to \unit[780]{nm} preserving entanglement ($F_{\phi^+, back}=0.903\pm0.005$). This further prepares the way for interfacing quantum light to various quantum memories.

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Tim Strobel, Stefan Kazmaier, Tobias Bauer, Marlon Schäfer, Ankita Choudhary, Nand Lal Sharma, Raphael Joos, Cornelius Nawrath, Jonas H. Weber, Weijie Nie, Ghata Bhayani, Lukas Wagner, André Bisquerra, Marc Geitz, Ralf-Peter Braun, Caspar Hopfmann, Simone L. Portalupi, Christoph Becher, Peter Michler. 2024-05-23. High fidelity distribution of triggered polarization-entangled telecom photons via a 36km intra-city fiber network. https://arxiv.org/abs/2405.14557

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