  A natural choice for quantum communication is to use the relative phase
between two paths of a single-photon for information encoding. This method was
nevertheless quickly identified as impractical for fibre-based communication
due to the requirement of a long stabilised interferometer to connect the
communicating parties. A modification based on single-photon time-bins has then
become widely adopted, with its practicability relying on trading the long
interferometer for two shorter local ones. It however, introduces a fundamental
loss, which increases with the dimension and that limits its application over
long distances. Here, we are able to solve this long-standing hurdle by
employing a few-mode fibre space-division multiplexing platform working with
orbital angular momentum modes. In our scheme, we maintain the practicability
provided by two short interferometers, while the quantum states are transmitted
through a few-mode fibre in a configuration that does not require temporal
post-selection, thus enabling a detection system without irreversible losses.
Our solution can be instantly deployed opening up new paths for the already
commercial phase-coding quantum communication systems.
