Entanglement Swapping of Time-bin Qubits in Optical Fiber with Coexisting Classical Communication

• Optical fiber, initially installed worldwide for implementing standard internet communications, is now being used for deploying quantum networks with telecom-wavelength single photons. To maximize the bandwidth of existing fiber resources, quantum signals may have to coexist with classical light in the form of standard internet traffic. Noise photon generation from the comparatively stronger classical signal can degrade quantum fidelity, and the impact of this degradation on entanglement swapping operations has yet to be investigated. In this work, we present a study of entanglement swapping coexisting with classical signals in 10km of fiber. With two entangled-photon sources, a photon from each source is sent over a separate 5km fiber spool that simultaneously carries classical light. We study the impact of noise on entanglement distribution and Hong-Ou-Mandel interference. This work provides a pathway for designing next generation quantum networks that make full use of existing fiber infrastructure, allowing high fidelity and scalable quantum networking towards a global quantum internet.