Photonic spatial Bell-state analysis for robust quantum secure direct communication using quantum dot-cavity systemsBao-Cang Ren, Hai-Rui Wei, Ming Hua, Tao Li and Fu-Guo DengEur. Phys. J. D, 67 2 (2013) 30DOI: https://doi.org/10.1140/epjd/e2012-30626-x