Hong-Ou-Mandel interference of spin-orbit hybrid entangled photons

Structured photons are a crucial resource in both classical and quantum technologies, particularly in spin-orbit hybrid photons, enabling various practical applications ranging from ultra-sensitive metrology techniques to quantum-enhanced information processing tasks. However, the two-photon interference of spin-orbit hybrid photons, which combines polarization modes and complex transverse spatial structures across the beam profile, remains unexplored. Here, we present an experimental observation of Hong-Ou-Mandel (HOM) interference of spin-orbit hybrid photons. The tunable q-plates that work as spin-orbit coupler devices are used to prepare various forms of spin-orbit hybrid entangled photons. By harnessing the match degree in the temporal domain, the coalescence and anti-coalescence effects resulting from the symmetric and anti-symmetric properties of the incident quantum states are observed. Moreover, we demonstrated the feasibility of quantum-enhanced photon polarization gears through HOM interference and theoretically analyze the noise-resilient advantages based on coherent HOM measurements. These results provide an alternative route toward quantum experiments with structured photons that allows for controlling their quantum interference in a compact, stable, and efficient way.