1. Wang, C., Deng, F.-G., Li, Y.-S., Liu, X.-S., Long, G.L.: Quantum secure direct communication with high-dimension quantum superdense coding. Phys. Rev. A 71, 044305 (2005)
2. Zhu, A.-D., Xia, Y., Fan, Q.-B., Zhang, S.: Secure direct communication based on secret transmitting order of particles. Phys. Rev. A 73, 022338 (2006)
3. Zhang, W., Ding, D.-S., Sheng, Y.-B., Zhou, L., Shi, B.-S., Guo, G.-C.: Quantum secure direct communication with quantum memory. Phys. Rev. Lett. 118, 220501 (2017)
4. Chen, S.-S., Zhou, L., Zhong, W., Sheng, Y.-B.: Three-step three-party quantum secure direct communication. Sci. China Phys. Mech. Astron. 61, 1–5 (2018)
5. Liu, X.S., Long, G.L., Tong, D.M., Li, F.: General scheme for superdense coding between multiparties. Phys. Rev. A 65, 022304 (2002)