Fig. 1: Experimental testbed for quantum-classical coexistence in hollow core fibre.

a shows the setup for the coexistence of four classical channels and three entanglement-based quantum channels over 11.5 km HCF in a four-node quantum network. Purple components contain only quantum light, blue components contain only classical light, and orange components contain both quantum and classical light. b shows a scanning electron microscopy image of the Hollow Core fibre (HCF) cross-section29. c shows the classical communications system, consisting of a bandwidth-variable transponder (BVT) transmitter and receiver pair.