Robust Approach for Time-Bin-Encoded Photonic Quantum Information Protocols.

Quantum states encoded in the time-bin degree of freedom of photons represent a fundamental resource for quantum information protocols. Traditional methods for generating and measuring time-bin-encoded quantum states face severe challenges due to optical instabilities, complex setups, and timing resolution requirements. To circumvent these issues, we leverage an approach based on Hong-Ou-Mandel interference and we propose and demonstrate a robust and scalable protocol to generate and measure arbitrary high-dimensional time-bin quantum states. We experimentally implement the protocol in a photonic setup reaching high-fidelity quantum state tomographies of two- and three-dimensional quantum states encoded in time bins with short temporal separation. We also certify intrasystem polarization-time entanglement of single photons through a nonclassicality test. The demonstrated approach enables access to high-dimensional states and tasks that are practically inaccessible with standard schemes, thereby advancing fundamental quantum information science and opening applications in quantum communication.