Measurement-Device-Independent Entanglement Quantification in a Fully Connected Time-Bin Quantum Network

Fully connected quantum networks enable scalable quantum communication, yet reliable entanglement characterization without trusting measurement devices remains challenging. Here we experimentally demonstrate measurement-device-independent (MDI) entanglement verification and quantification in a time-bin-encoded fully connected quantum network. Using a broadband periodically poled lithium niobate on insulator source combined with dense wavelength-division multiplexing, we distribute all six pairwise entangled links among four users over an end-to-end separation of 20 km. MDI measurements are realized by encoding the trusted input states in the polarization degree of freedom of the same photons carrying the distributed time-bin entanglement, thereby eliminating the need for independently prepared trusted photons. We show that both entanglement verification and quantification are obtained from the MDI measurements. Our results demonstrate the practical integration of resource-efficient MDI characterization into a fully connected time-bin quantum network, providing a scalable approach for reliable entanglement characterization in large-scale quantum networks.