https://www.sciencedaily.com/releases/2022/09/220922124427.htm

Typically, quantum communication systems "write" information onto a photon's spin angular momentum. In this case, photons carry out either a right or left circular rotation, or form a quantum superposition of the two known as a two-dimensional qubit. It's also possible to encode information onto a photon's orbital angular momentum -- the corkscrew path that light follows as it twists and torques forward, with each photon circling around the center of the beam. When the spin and angular momentum interlock, it forms a high-dimensional qudit -- enabling any of a theoretically infinite range of values to be encoded into and propagated by a single photon.

Qubits and qudits, also known as flying qubits and flying qudits, are used to propagate information stored in photons from one point to another. The main difference is that qudits can carry much more information over the same distance than qubits, providing the foundation for turbocharging next generation quantum communication.