Figure 4: Evaluation of the multi-photon rate.
From: Deterministic secure quantum communication using a single d-level system
(a) In the case that Eve inserts a spy photon in each signal, the multi-photon rate 
versus the original multi-photon rate 
. (b) Increase rate Ir of multi-photon rate versus 
. (c) In the case that Eve inserts a spy photon in a signal with probability s, 
versus 
and s. (d) Increase rate Ir of multi-photon rate versus 
and s.
