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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, Sharma, Nand Lal, Joos, Raphael, Nawrath, Cornelius, Weber, Jonas H., Nie, Weijie, Bhayani, Ghata, Wagner, Lukas, Bisquerra, André, Geitz, Marc, Braun, Ralf-Peter, Hopfmann, Caspar, Simone Luca Portalupi, Becher, Christoph, Michler, Peter

Published May 23, 2024• 0 citations
arXivHTMLPDF

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 $F_{ϕ^+, conv}=0.972\pm0.003$) of the biexciton transition. As a step towards real-world applicability, high entanglement fidelities ($F_{ϕ^+, loop}=0.945\pm0.005$) 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 ($F_{ϕ^+, back}=0.903\pm0.005$). This further prepares the way for interfacing quantum light to various quantum memories.

DOI
10.48550/arxiv.2405.14557

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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.
A global quantum internet is based on scalable networks, which require reliable quantum hardware. Among them are quantum light sources providing deterministic, high-brightness, high-fidelity entangled photons and quantum memories with coherence times exceeding the millisecond range. Long-distance operation demands quantum light sources emitting at telecommunication wavelengths. A cornerstone for such networks is the demonstration of quantum teleportation. Here, we realize full-photonic quantum teleportation employing semiconductor quantum dots, which can fulfill all the aforementioned requirements. Two remote GaAs quantum dots, emitting in the near-infrared, are used: one as an entangled-photon pair source and the other as a single-photon source. During the experiment, the single photon is prepared in conjugate polarization states and interfaced with the biexciton emission of the entangled pair employing a polarization-selective Bell state measurement. This process teleports the respective polarization state onto the exciton emission of the entangled pair. The frequency mismatch between the triggered sources is erased using two polarization-preserving quantum frequency converters, enabling remote two-photon interference at telecommunication wavelengths, yielding a visibility of 30(1)%. A post-selected teleportation fidelity up to 0.721(33), significantly above the classical limit, demonstrates successful quantum teleportation between light from distinct sources. These results mark an important development for semiconductor-based quantum light sources.
Entangled light sources are considered as core technology for multiple quantum network architectures. Of particular interest are sources that are based on a single quantum system as these offer intrinsic security due to the sub-Poissonian nature of the photon emission process. This is important for applications in quantum communication where multi-pair emission generally compromises performance. A large variety of sources has been developed, but the generated photons remained far from being utilized in established standard fiber networks, mainly due to lack of compatibility with telecommunication wavelengths. In this regard, single semiconductor quantum dots are highly promising photon pair sources as they can be engineered for direct emission at telecom wavelengths. In this work we demonstrate the feasibility of this approach. We report a week-long transmission of polarization-entangled photons from a single InAs/GaAs quantum dot over a metropolitan network fiber. The photons are in the telecommunication O-band, favored for fiber optical communication. We employ a polarization stabilization system overcoming changes of birefringence introduced by 18.23 km of installed fiber. Stable transmission of polarization-encoded entanglement with a high fidelity of 91% is achieved, facilitating the operation of sub-Poissonian quantum light sources over existing fiber networks.
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.
On-demand indistinguishable single-photon sources are essential for quantum networking and communication. Semiconductor quantum dots are among the most promising candidates, but their typical emission wavelength renders them unsuitable for use in fiber networks. Here, we present quantum frequency conversion of near-infrared photons from a bright quantum dot to the telecommunication C-band, allowing integration with existing fiber architectures. We use a custom-built, tunable 2400 nm seed laser to convert single photons from 942 nm to 1550 nm in a difference-frequency generation process. We achieve an end-to-end conversion efficiency of ≃35%, demonstrate count rates approaching 1 MHz at 1550 nm with g(2)(0)=0.043(1), and achieve Hong-Ou-Mandel (HOM) visibilities of 60%. We expect this scheme to be preferable to quantum dot sources directly emitting at telecom wavelengths for fiber-based quantum networking.
On-demand sources of entangled photons for the transmission of quantum information in the telecom C-band are required to realize fiber-based quantum networks. So far, non-deterministic sources of quantum states of light were used for long distance entanglement distribution in this lowest loss wavelength range. However, they are fundamentally limited in either efficiency or security due to their Poissonian emission statistics. Here, we show on-demand generation of entangled photon pairs in the telecom C-band by an InAs/GaAs semiconductor quantum dot. Using a robust phonon-assisted excitation scheme we measure a concurrence of 91.4 %91.4\,\%91.4% and a fidelity of 95.2 %95.2\,\%95.2% to Φ+Φ^+Φ+. On-demand generation of polarization entangled photons will enable secure quantum communication in fiber-based networks. Furthermore, applying this excitation scheme to several remote quantum dots tuned into resonance will enable first on-demand entanglement distribution over large distances for scalable real-life quantum applications.