Practical deterministic secure quantum communication in a lossy channel

Losses in a quantum channel do not allow deterministic communication. We propose a twoway six-state deterministic secure quantum communication scheme that is robust in a lossy channel. Our protocol can be used for two purposes: (a) establishment of a deterministic key, and (b) direct communication of a secret message. Our protocol is directly integrable with the decoy state method while achieving deterministic communication without using a quantum memory. In our protocol, a legitimate party has the control to assign a desired bit value to a successfully transmitted qubit in the public discussion step. Before the public discussion, no information is leaked to the eavesdropper (Eve) even if all the qubits are measured or prepared by her. Hence, our scheme is used as a quantum direct communication (QDC) protocol, to meet the quality of service requirement of swift data communication.We compare the security of our protocol against the photon number splitting attack in the absence of the decoy state method with two QDC protocols.We compute the success probability of Eve when our protocol is used as a multiparty key distribution scheme. We also propose the criteria to compute the efficiency of QDC protocols.