An efficient two-step quantum key distribution protocol with orthogonal product states

An efficient two-step quantum key distribution (QKD) protocol withorthogonal product states in the notimes n(ngeq3) Hilbert spaceis presented. In this protocol, the particles in the orthogonalproduct states form two particle sequences. The sender, Alice, firstsends one sequence to the receiver, Bob. After Bob receives the firstparticle sequence, Alice and Bob check eavesdropping by measuring afraction of particles randomly chosen. After ensuring the security ofthe quantum channel, Alice sends the other particle sequence to Bob.By making an orthogonal measurement on the two particle sequences,Bob can obtain the information of the orthogonal product states sentby Alice. This protocol has many distinct features such as greatcapacity, high efficiency in that it uses all orthogonal productstates in distributing the key except those chosen for checkingeavesdroppers.