  The orbital angular momentum, OAM, of photons offers a suitable support to
carry the quantum data of multiple users. We present two novel 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 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.
