Quantum multiplexing with the orbital angular momentum of light

The orbital angular momentum (OAM) of photons offers a suitable support to carry the quantum data of multiple users. We present two optical setups that send the information of n quantum communication parties through the same free-space optical link. Those qubits can be sent simultaneously and share path, wavelength, and polarization without interference, increasing the communication capacity of the system. The first solution, a qubit combiner, merges n channels into the same link, which transmits n independent photons. The second solution, the OAM multiplexer, uses controlled-not (CNOT) gates to transfer the information of n optical channels to a single photon. Additional applications of the multiplexer circuits, such as quantum arithmetic, as well as connections to OAM sorting are discussed.