Towards the Quantum Internet: Prospects and Challenges of Efficient Entanglement Distribution Over Telecom Fibers

Network operators hold a significant asset in their widespread optical fiber networks and as quantum technologies advance, these operators will be ideally positioned to offer new streams of services in the context of the Quantum Internet. However, establishing a functional Quantum Internet requires diverse technological advancements, particularly in the efficient distribution of entanglement over optical fibers. Entanglement serves as the cornerstone for quantum protocols and technologies such as quantum repeaters, teleportation, sensing, and time synchronization. Nonetheless, as photons propagate through fiber, they encounter various impairments that can degrade entanglement quality. Specifically, polarization-entangled photons suffer from polarization drifts, which exhibit stochastic behavior and can reduce fidelity. In this paper, we examine the prospects of entanglement distribution for the Quantum Internet, presenting experimental campaigns that highlight both the challenges and solutions. We demonstrate the inherent instability of photon fidelity in field-deployed fibers and show how compensation schemes can effectively enhance entanglement transmission in urban fiber networks. Our findings include results from a four-day entanglement distribution experiment conducted over Deutsche Telekom's optical fiber network in Berlin, achieving an average Bell parameter and fidelity of 2.52 and 99.6%, respectively.