Hybrid single photon states: A resource for quantum communication and metrology

Photon polarization is usually exploited for quantum communication tasks as well as for roll angles measurements. However, it is also possible to encode information in other degrees of freedom of single photons like path or orbital angular momentum. When two or more degrees of freedom are exploited at the same time we refer to it as hybrid encoding. Single photon hybrid states encoded in polarization and orbital angular momentum show properties that make such states a useful resource in quantum communication and in roll angle measurements. In the first case they allow two users to communicate without sharing a reference frame even in presence of turbulences, in the second one they provide a sensitivity enhancement of optical non-contact angular measurements.