Two-step quantum secure direct communication scheme with frequency coding<xref rid="cpb_26_3_030302fn1" ref-type="fn">*</xref> <fn id="cpb_26_3_030302fn1"> <label>*</label> <p>Project supported by the National Natural Science Foundation of China (Grant Nos. 11175094, 91221205, and 11547035) and the National Basic Research Program of China (Grant No. 2015CB921002).</p> </fn>

Two-step quantum secure direct communication scheme with frequency coding* *

Project supported by the National Natural Science Foundation of China (Grant Nos. 11175094, 91221205, and 11547035) and the National Basic Research Program of China (Grant No. 2015CB921002).

Zhao Xue-Liang¹, Li Jun-Lin¹, Niu Peng-Hao¹, Ma Hong-Yang², Ruan Dong^{1, †}

(color online) Three different frequencies’ direct sum in time domain. The dots represent every photon of the B-sequence. The number on the horizontal axis represents the photon number of B-sequence. The number on the vertical axis represents four different amplitudes.