The invention relates to a processing device (1) comprising: —an input interface (2) receiving photons having first quantum states, —an encoder (3) generating a photon having a first fixed quantum state from a received electrical signal, —a transformer (4) transforming the first quantum state of a photon into a second quantum state, —a decoder (5) transforming the second quantum state of a photon into an electrical signal, —an output interface (6) delivering photons which have second quantum states and are intended for transmission, —and a switch (7) comprising three inputs connected respectively to the outputs of the input interface (2), encoder (3) and transformer (4), and three outputs connected respectively to the inputs of the output interface (6), decoder (5) and transformer (4), said switch selectively coupling at least one of its inputs to one of its outputs, depending on a received command.