Experimental ancilla-assisted qubit transmission against correlated noise using quantum parity checking

We report the experimental demonstration of a transmission scheme which has the ability to transmit any state of a photonic qubit over unstabilized optical fibres, regardless of whether the qubit is known, unknown, or entangled to other systems. A high fidelity to the noiseless quantum channel was achieved by adding an ancilla photon after the signal photon within the correlation time of the fibre noise and by performing a measurement which computes the parity. Simplicity, the maintenance-free nature and robustness against path-length mismatches among the nodes make our scheme suitable for multi-user quantum communication networks.