Abstract: A quantum processor is provided according to one embodiment of the present invention. The quantum processor uses propagating microwave photons as flying qubits, encoded in a dual-rail configuration. The dual-rail configuration is characterised by the fact that one photon encodes a qubit, and one photon at most is present in a transmission line. The quantum processor comprises single-qubit gates and two-qubit gates for performing state operations on the qubits. The single-qubit gates comprise directional couplers and phase shifters, while the two-qubit gates comprise electronic circuits including LC oscillators and Josephson junctions. The quantum processor further comprises a single microwave photon generation circuit and a microwave photon detector circuit.