Rack‐Integrated Quantum Dot‐Based Source of Single and Entangled Photons at Telecom C‐Band

Bringing quantum light sources into real‐world telecommunication networks requires moving beyond the laboratory and developing sources that operate at the telecom C‐band. Epitaxial quantum dots (QDs) provide deterministic sources of quantum light at these wavelengths. Here, we demonstrate an important step toward quantum communication networks: a state‐of‐the‐art semiconductor QD source, exhibiting a record coincidence rate for entangled‐photon emission in the telecom C‐band, integrated into an optimised rack‐based setup exhibiting remote controle. This setup includes a tunable pulsed laser for QD excitation, enabling operation from quasi‐resonant to resonant two‐photon excitation, all‐optical excitation suppression, and QD signal coupling into single‐mode fibres. Overall, the setup achieves more than 65% transmission for both exciton and biexciton photons. To demonstrate the usability of our stand‐alone source, we transmit single photons through a deployed 36 km‐long fibre link and verify that their single‐photon purity is preserved. Moreover, based on the measured entangled‐photon pair rate, we estimate that the source could enable entangled QKD protocols with a projected secret key rate 3.4 cps after 150 km of optical fibres. These results demonstrate the potential of quantum‐dot‐based telecom light sources for integration into existing fibre infrastructures, paving the way toward the realisation of a quantum internet.