Figure 2: Theoretical comparison between the performance of different CV-QKD protocols.
From: Continuous variable quantum key distribution with modulated entangled states
(a) Secret key rate as a function of distance (corresponding to a loss of 0.2 dB per km) for a fixed excess noise of 0.1 SNU. (1) Ideal coherent state protocol with 100 SNU modulation. The shaded region illustrates the regime accessible with coherent state protocols. (2) and (3) Squeezed state protocol with 3 dB and 10 dB squeezing, respectively (without additional modulation). (4) and (5) Our proposed protocol with 3 dB and 10 dB of squeezing, respectively, and 100 SNU modulation. The red arrows indicate the improvement of our proposed protocol compared with the squeezed state protocol with no modulation. For all protocols, the added noise to Bob's data is optimized and β=1. (b) Maximal tolerable channel noise versus the initial antisqueezed variance. The channel loss is set to 10 dB (corresponding to a distance of 50 km). (1) Ideal coherent state protocol with asymptotically large modulation. The shaded region illustrates the regime accessible with coherent state QKD. (2) Squeezed state protocol without additional modulation. (3) New combined squeezed state protocol with 100 SNU of coherent modulation without the gain. This is also the performance obtained for highly impure squeezed states. (4) Our proposed optimized protocol with 100 SNU coherent modulation and optimized gain factor. For all protocols, the added noise to Bob's data is optimized and β=1.
