Abstract

One of the simplest protocols of quantum cryptography proposed so far is the one based on two nonorthogonal states.¹ In this protocol, the receiver cannot determine every bit because there is no way to distinguish non-orthogonal states completely. Another simple protocol² uses two orthogonal states, and the receiver can always discriminate between the two states that represent the bit values 0 and 1. In this protocol, however, the sender must mix the third states (vacuum states) in the bit stream to prevent eavesdropping. Thus the following question arises: do more simple protocols exist in which the sender switches between only two states and the receiver can obtain every bit value? Here we show that such a protocol does exist.³

© 1998 Optical Society of America