Entanglement is a unique resource for quantum information processing, which allows for device-independent (DI) quantum communication protocols, such as Quantum Key Distribution and Quantum Random Number Generation. Loophole-free violation of Bell inequalities is a necessary condition for DI protocols. While timebin entanglement is promising for long-distance distribution over fiber optics, its most common implementation suffers from a post-selection loophole (PSL) which invalidates Bell non-locality tests. We present an implementation of a postselection-free “genuine” time-bin entanglement scheme working with 1550 nm biphotons with an estimated Bell violation of S = 2.56.
One of the most advanced technologies within the field of quantum mechanics is quantum key distribution (QKD), which allows the secure generation of secret keys among remote users. In order for QKD to be more widely adopted, it must be integrated into existing classical communication systems. However, this can be difficult due to the use of various technologies and channels in deployed networks. Recently, we developed a QKD network in the metropolitan area of Padova, which connects various nodes across the city through a combination of fiber and free-space links. By utilizing a modular design based on the iPOGNAC encoder and the Qubit4Sync method, we have realized portable and adaptable systems that operate in the C and O bands. This allowed us to deploy and test the compatibility of both research and commercial QKD systems by ThinkQuantum with classical communication over a variety of links, as well as their ability to switch between free-space and fiber connections. Finally, we developed and experimentally implemented complex network configurations such as star networks, where a fiber-based transmitter and free-space transmitter could operate with a single receiver.
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