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.