  A novel secure communication protocol is presented, based on an entangled
pair of qubits and allowing asymptotically secure key distribution and
quasi-secure direct communication. Since the information is transferred in a
deterministic manner, no qubits have to be discarded. The transmission of
information is instantaneous, i.e. the information can be decoded during the
transmission. The security against arbitrary eavesdropping attacks is provided.
In case of eavesdropping attacks with full information gain, the detection rate
is 50% per control transmission. The experimental realization of the protocol
is feasible with relatively small effort, which also makes commercial
applications conceivable.
