Secret key rate of multi-ring M-APSK continuous variable quantum key distribution

Abstract

Discrete modulation continuous variable quantum key distribution (DM-CV-QKD) is highly considered in real implementations to avoid the complexity of Gaussian modulation (GM), which is optimum in terms of the key rate. DM-CV-QKD systems usually consider M-symbol phase shift keying (M-PSK) constellations. However, this type of constellation cannot reach transmission distances and key rates as high as GM, limiting the practical implementation of CV-QKD systems. Here, by considering M-symbol amplitude and phase shift keying (M-APSK) constellations, we can approximate GM. Indeed, considering finite-size effects, 4 ring 64-APSK can reach 52.0 km, only 7.2 km less than GM and 282% the maximum achievable transmission distance for 8-PSK.

Theoretical development of discrete-modulated continuous-variable quantum key distribution

“…The lower bound of the secret key rate of CV-QKD with an arbitrary modulation is secure against collective attacks under the asymptotic regime. (Almeida et al, 2021) applies this method to the M-QPSK type considering finite-size effects.…”

“…The amplitude and phase shift keying (APSK) type (Almeida et al, 2021) is likely a multi-ring of PSK type. The states in each ring have the same amplitude, and adjacent states have the same phase difference.…”

Impact of Shot Noise Estimation on the Secret Key Rate of a CV-QKD System

“…In ( 4), χ BE describes the Holevo bound that majors the amount of information that Eve can gain on Bob's recovered states, being obtained through equation ( 5) in [Almeida et al 2021]. For the results presented in this work ⟨n⟩ was set at 1.91 photons per symbol, η was measured at 0.72 and ϵ thermal was assumed to be 0.35 SNU.…”

Polarization diverse true heterodyne receiver for continuous variable quantum key distribution

“…Coherent-state CV-QKD typically encodes the information in the phase and amplitude of weak coherent states, thus allowing for implementation with current modulation methods and telecom-based equipment [1,7]. The first implementations of CV-QKD protocols were carried out by using a transmitted local oscillator (LO) setup [8].…”