# Long-distance continuous-variable quantum key distribution using separable Gaussian states

## TL;DR

This paper proposes a novel long-distance continuous-variable quantum key distribution scheme using separable Gaussian states, enhancing security and transmission range by mitigating eavesdropping through state separability.

## Contribution

The authors introduce a tunable CVQKD protocol utilizing separable Gaussian states, enabling longer distances and higher noise tolerance compared to existing methods.

## Key findings

- Achieves longer transmission distances in CVQKD.
- Tolerates higher excess noise levels.
- Reduces vulnerability to eavesdropping.

## Abstract

Continuous-variable quantum key distribution (CVQKD) is considered to be an alternative to classical cryptography for secure communication. However, its transmission distance is restricted to metropolitan areas, given that it is affected by the channel excess noise and losses. In this paper, we present a scheme for implementing long-distance CVQKD using separable Gaussian states. This tunable QKD protocol requires separable Gaussian states, which are squeezed and displaced, along with the assistance of classical communication and available linear optics compoments. This protocol originates from the entanglement of one mode and the auxiliary mode used for distribution, which is first destroyed by local correlated noises and restored subsequently by the interference of the auxillary mode with the second distant separable correlated mode. The displacement matrix is organized by two six-dimensional vectors and is finally fixed by the separability of the tripartite system. The separability between the ancilla and Alice and Bob's system mitigates the enemy's eavesdropping, leading to tolerating higher excess noise and achieving longer transmission distance.