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Advanced Quantum Technologies

Telecom C‐Band Source of Triggered Polarization‐Entangled Photon Pairs Combining High Coincidence Rates, Fidelities and Single‐Photon Purity

Raphael Joos, Mohamed Helal, Michal Vyvlečka, Lena Engel, Aditi Javali, Benjamin Breiholz, Ponraj Vijayan, Johannes Michl, Michael Jetter, Sven Höfling, Tobias Huber, Giora Peniakov, Simone Luca Portalupi, Peter Michler

Published May 1, 2026• 1 citation
Publisher

Abstract

ABSTRACT Many protocols of future quantum networks rely on the availability of entangled qubits which enable links among remote nodes due to their unique properties. Therefore, the efficient generation of entangled photons constitutes a key goal toward the implementation of such quantum networks. However, currently available sources are bound by intrinsic limitations, as for instance probabilistic nature of emission. Deterministic quantum emitters pose a potential solution for this issue, however, the maturity of their device platforms still needs to be improved for truly on‐demand emission. While record efficiencies are currently found at near‐infrared wavelengths, sources at telecommunication wavelengths will likely be the ideal choice for quantum networks. That motivates the development of efficient sources of entangled photons in the telecom regime. This work addresses that challenge presenting a telecom C‐band source of polarization entangled photons based on semiconductor quantum dots incorporated in a planar cavity structure. In this way, triggered emission of entangled photon pairs with a coincidence rate of (biexciton/exciton fiber‐coupled single‐photon count rates of /) combined with values of / is achieved. Full quantum state tomography of the two‐photon state demonstrates simultaneously entanglement fidelities of up to to the Bell state.

DOI
10.1002/qute.70317

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ABSTRACT Many protocols of future quantum networks rely on the availability of entangled qubits which enable links among remote nodes due to their unique properties. Therefore, the efficient generation of entangled photons constitutes a key goal toward the implementation of such quantum networks. However, currently available sources are bound by intrinsic limitations, as for instance probabilistic nature of emission. Deterministic quantum emitters pose a potential solution for this issue, however, the maturity of their device platforms still needs to be improved for truly on‐demand emission. While record efficiencies are currently found at near‐infrared wavelengths, sources at telecommunication wavelengths will likely be the ideal choice for quantum networks. That motivates the development of efficient sources of entangled photons in the telecom regime. This work addresses that challenge presenting a telecom C‐band source of polarization entangled photons based on semiconductor quantum dots incorporated in a planar cavity structure. In this way, triggered emission of entangled photon pairs with a coincidence rate of (biexciton/exciton fiber‐coupled single‐photon count rates of /) combined with values of / is achieved. Full quantum state tomography of the two‐photon state demonstrates simultaneously entanglement fidelities of up to to the Bell state.
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High Resolution Image Download MS PowerPoint Slide Entangled photon pairs at telecom wavelengths are essential for quantum communication, distributed computing, and quantum-enhanced sensing. The telecom O-band offers low chromatic dispersion and fiber loss, which is ideal for long-distance networks. Site-controlled nanowire quantum dots have emerged as a promising platform for generating single and entangled photons, offering high extraction efficiency and scalability. However, their operation has largely been restricted to the visible and first near-infrared (NIR-I) windows. Here, we demonstrate a bright source of entangled photon pairs in the telecom O-band based on site-controlled nanowire quantum dots. We measure a fine-structure splitting of 4.6 μeV, confirming suitability for high-fidelity polarization entanglement. Quantum-state tomography of the biexciton–exciton cascade reveals a maximum fidelity of 85.8 ± 1.1% to the Φ + Bell state and a maximum concurrence of 75.1 ± 2.1%. This work establishes nanowire quantum dots as viable entangled photon sources at telecom, advancing scalable quantum technologies for fiber-based networks.
Fiber-based quantum networks require on-demand sources of entangled photons in the telecom C-band for long distance information transfer. Historically, the field of in-fiber entanglement distribution has been dominated by photons provided via spontaneous processes. In recent years, semiconductor quantum dots have emerged as strong competitors in terms of generating single and entangled photons due to their promise of deterministic qubit generation in the NIR wavelength region. Here, we show the on-demand generation of polarization entangled photons in the telecom C-band based on InAs/GaAs quantum dots grown via metal-organic vapor-phase epitaxy. By employing a robust phonon-assisted two-photon excitation scheme, we are able to generate pairs of entangled photons with a concurrence of 91.4 ± 3.8 % and a maximum fidelity to the Bell state Φ+ of 95.2 ± 1.1 %.
For quantum light sources in everyday telecommunication networks, quantum science needs to be fully transformed into quantum technology. The first necessary step to move outside a well-controlled lab environment requires the use of quantum light sources operating in the technologically relevant telecom O- and C-band. This can be provided using epitaxial quantum dots as deterministic sources of quantum light. Particularly intriguing is that emitters operating at telecom wavelengths are rapidly catching up with their short wavelength counterparts in terms of performances. Here, we make a decisive step forward in the development of quantum communication networks: a state-of-the-art source of quantum light, a semiconductor quantum dot (QD), with record coincidence rate for entangled photon emission in the telecom C-band, is operated inside an optimized rack-based setup. This setup includes a tunable pulsed laser for the QD excitation (from quasi- to fully resonant excitation), all optics for the excitation filtering, and QD signal coupling into single-mode fibers. Overall, the setup allows for above 50%50\%50% transmission for both exciton and biexciton photons. These results show that quantum dots-based telecom light sources can now be transported and integrated into existing fiber infrastructures, an important step to demonstrate the feasibility of the upcoming quantum internet.
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 Fϕ+,conv=0.972±0.003F_{ϕ^+, conv}=0.972\pm0.003Fϕ+,conv​=0.972±0.003) of the biexciton transition. As a step towards real-world applicability, high entanglement fidelities (Fϕ+,loop=0.945±0.005F_{ϕ^+, loop}=0.945\pm0.005Fϕ+,loop​=0.945±0.005) 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 (Fϕ+,back=0.903±0.005F_{ϕ^+, back}=0.903\pm0.005Fϕ+,back​=0.903±0.005). This further prepares the way for interfacing quantum light to various quantum memories.
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 780 nm to telecom wavelengths. We show the preservation of polarization entanglement after QFC (fidelity to Bell state F ϕ + , c o n v =0.972±0.003) of the biexciton transition. As a step toward real-world applicability, high entanglement fidelities ( F ϕ + , l o o p =0.945±0.005) after the propagation of one photon of the entangled pair along a 35.8 km field-installed standard single mode fiber link are reported. Furthermore, we successfully demonstrate a second polarization-conserving QFC step back to 780 nm preserving entanglement ( F ϕ + , b a c k =0.903±0.005). This further prepares the way for interfacing quantum light to various quantum memories.