  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. Here, we leverage a robust approach based on Hong-Ou-Mandel
interference that allows us to circumvent these issues. First, we perform
high-fidelity quantum state tomographies of time-bin qubits with a short
temporal separation. Then, we certify intrasystem polarization-time
entanglement of single photons through a nonclassicality test. Finally, we
propose a robust and scalable protocol to generate and measure high-dimensional
time-bin quantum states in a single spatial mode. The protocol promises to
enable 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.
