Witnessing effective entanglement over a 2km fiber channel

TL;DR

This paper demonstrates a fiber-based continuous-variable quantum key distribution system that successfully witnesses effective entanglement over a 2km fiber channel by measuring conjugate quadratures and analyzing excess noise.

Contribution

It introduces a method to verify effective entanglement in a fiber-based CV-QKD system over a 2km distance, including the consideration of local oscillator effects.

Findings

Effective entanglement witnessed over 2km fiber channel.

Quantified channel attenuation and excess noise.

Validated the measurement approach for CV-QKD security.

Abstract

We present a fiber-based continuous-variable quantum key distribution system. In the scheme, a quantum signal of two non-orthogonal weak optical coherent states is sent through a fiber-based quantum channel. The receiver simultaneously measures conjugate quadratures of the light using two homodyne detectors. From the measured Q-function of the transmitted signal, we estimate the attenuation and the excess noise caused by the channel. The estimated excess noise originating from the channel and the channel attenuation including the quantum efficiency of the detection setup is investigated with respect to the detection of effective entanglement. The local oscillator is considered in the verification. We witness effective entanglement with a channel length of up to 2km.