Two-step quantum direct communication protocol using the Einstein-Podolsky-Rosen pair block

TLDR

The authors propose a quantum secure direct communication protocol that employs blocks of Einstein‑Podolsky‑Rosen (EPR) pairs. The protocol uses an ordered set of N EPR pairs split into a checking sequence and a message‑coding sequence; after verifying channel security by randomly measuring a fraction of particles in random bases, Alice encodes the secret message onto the coding sequence, sends it to Bob, who then combines the sequences to recover the message, with additional discussion of noisy‑channel issues. The scheme is secure because an eavesdropper cannot obtain both sequences simultaneously.

Abstract

A protocol for quantum secure direct communication using blocks of Einstein-Podolsky-Rosen (EPR) pairs is proposed. A set of ordered N EPR pairs is used as a data block for sending secret message directly. The ordered N EPR set is divided into two particle sequences, a checking sequence and a message-coding sequence. After transmitting the checking sequence, the two parties of communication check eavesdropping by measuring a fraction of particles randomly chosen, with random choice of two sets of measuring bases. After insuring the security of the quantum channel, the sender Alice encodes the secret message directly on the message-coding sequence and sends them to Bob. By combining the checking and message-coding sequences together, Bob is able to read out the encoded messages directly. The scheme is secure because an eavesdropper cannot get both sequences simultaneously. We also discuss issues in a noisy channel.