Polarization-Controlled Dual-State Distribution of Bell and N00N Entanglement Over a Metro-Scale Commercial Quantum Network

Abstract: We report the first demonstration of multiphoton, dual state entanglement distribution over a metropolitan scale commercial fiber network, implemented on the EPB Bohr IV quantum network in Chattanooga, TN, using an all fiber optic experimental platform. Employing a spatially degenerate, continuous wave type II SPDC biphoton source and fully fiber coupled linear optics, we generated a 4 photon entangled state. Through polarization projective measurements on two locally retained photons, we then probabilistically heralded the remaining two photons into either a Bell state (particle particle entanglement) or a N00N state (mode-mode entanglement), which were then distributed to two spatially separated network nodes. Experimental verification confirmed successful entanglement distribution across the deployed network despite significant channel losses and limited source fidelity. These results highlight the versatility of our polarization controlled multi photon entanglement distribution over real world telecom infrastructure and lay the groundwork for future upgrades, including higher quality non degenerate photon sources, White Rabbit timing synchronization for true multi node entanglement, and active polarization control for enhanced fidelity and long term stability.