Secure Quantum Communication Scheme for Six-Qubit Decoherence-Free States

Noise is currently unavoidable in quantum communication environments. Eavesdroppers can exploit this issue by disguising themselves as channel noise to avoid detection during eavesdropping checks performed by legitimate communicants. This paper first proposes a new coding function comprising eight unitary operations for two orthogonal bases for six-qubit decoherence-free states. Subsequently, based on the coding function, the first deterministic secure quantum communication (DSQC) scheme for quantum channels with collective noise is developed. The developed DSQC is robust against both collective-dephasing noise and collective-rotation noise Senders can choose one of six-qubit decoherence-free states to encode their two-bit message, and receivers simply conduct Bell measurement to obtain the message. Analyses conducted verify that the proposed scheme is both secure and robust.