Figure 4
\(\mu_{3}=\mu_{2}\) in backward the channel. The dashed red line shows the performance of the forward channel with Alice transmitting \(\mu_{1}=0.36\). Its maximal distance is 134 km. The dotted green line shows the performance of the backward channel with Bob transmitting \(\mu _{3}=\mu_{2}\). Its maximal distance is 84 km. The solid blue line shows the SQKD secure bit with \(\mu_{1}=0.36\) and \(\mu_{3}=\mu_{2}\). Its maximal distance is 86 km. Therefore, the SQKD transmission distance is 84 km