Abstract
We put forward and demonstrate a controllable decoherence-assisted quantum key distribution scheme. The protocol is based on the possibility of introducing controllable decoherence to polarization qubits using the spatial degree of freedom of light. We show that our method reduces the amount of information that an eavesdropper can obtain in the BB84 protocol under the entangling probe attack. We demonstrate experimentally that Alice and Bob can agree on a scheme that gives low values of the quantum bit error rate, despite the presence of a large amount of decoherence in the transmission channel of the BB84 protocol.