Analysis of Atmospheric Continuous-Variable Quantum Key Distribution with Diverse Modulations.

Local oscillator (LO) acted as a reference to define the phase of quantum signals is necessary for coherent detection in continuous-variable quantum key distribution (CVQKD), and LO fluctuation caused by atmospheric channel brings the added excess noise into CVQKD. Here, we investigate the influence of atmospheric effects on the excess noise in free space CVQKD, and analyse the excess noise tolerance of systems with diverse modulations. And we obtain the critical condition that the excess noise related to LO remains constant under atmospheric effects. The results show that under general attacks, Gaussian-modulation which performs better in the short range propagation of high key rate has better excess noise tolerance than discrete-modulation that is propitious to distribute low key rate over distant propagation. Moreover, in discrete-modulation under collective attack, higher-order-state has higher secret key rate, better excess noise tolerance and longer propagation distance than lower-order-state. [ABSTRACT FROM AUTHOR]