High Fidelity Distribution of Telecom Polarization Entangled Photons through a 7.7 Km Antiresonant Hollow-Core Fiber

Antiresonant hollow-core fibers are a novel type of optical fiber with unparalleled characteristics, unattainable with solid-core fibers. In particular, antiresonant hollow-core fibers are characterized by vacuum-like propagation speed, suppressed dispersion and nonlinear optical effects and, recently, even ultra-low propagation loss. In recent years, the development of a type of antiresonant hollow-core fiber, called Nested Antiresonant Nodeless Fiber (NANF) has seen tremendous improvements, and applications in both classical and quantum communications have been suggested. While encouraging results over meter long distances have been shown, the distribution of polarized entangled photons over inner-city distances through antiresonant hollow-core fibers has not been demonstrated yet. This could be a game changer for the development of quantum networks, which leverage entanglement for the distribution of secret keys, and more in the long term, in a quantum internet scenario. In this work, an experimental investigation of entanglement distribution through a NANF with an overall length of 7.72 km is presented. Remarkably, substantial reduction of latency (about 13 μs) and suppressed chromatic dispersion (about one order of magnitude) of the studied NANF compared to a telecom single-mode fiber (Corning's SMF28) of equal length are measured for different bandwidths of the distributed entangled photons. Moreover, by encoding entanglement in polarization, high fidelity (>95%) distribution of narrow-bandwidth entangled photons is demonstrated. This result paves the way to the exploitation of NANF as a superior transmitting medium for quantum technology applications relying on the distribution of entanglement encoded in polarization over inner-city distances.