Secure Deterministic Communication without Entanglement

We propose a protocol for deterministic communication that does not make use of entanglement. It exploits nonorthogonal states in a two-way quantum channel to attain unconditional security and high efficiency of the transmission. We explicitly show the scheme is secure against a class of individual attacks regardless of the noise on the channel. Its experimental realization is feasible with current technology.

Figure 1

Scheme of the communication protocol.

Figure 2

Mutual information vs detection probability in individual attacks. The descent curve represents Alice and Bob mutual information ${\mathcal{I}}_{AB}$. The crescent curves are Alice-Eve mutual information ${\mathcal{I}}_{AE}$ (dotted line) and Bob-Eve mutual information ${\mathcal{I}}_{BE}$ (dashed line).