1 GBaud Continuous Variable Quantum Key Distribution Using Pilot Tone Assisted Heterodyne Detection

The major drawbacks of current CV-QKD systems are the achievable secret key rate or transmission distance. Moreover, most of the CV-QKD systems are based on homodyne detection and use a remotely transmitted local oscillator in time or polarization multiplex. This enhances the complexity of the transmitter and the receiver, limits the transmission distance and leaves a security loophole for a potential eavesdropper performing for example a local oscillator calibration attack. In this article, a CV-QKD system using a discrete 8-state phase modulation and a symbol rate of 1 GBd as well as a heterodyne detection with a real local oscillator is experimentally demonstrated. The excess noise, a crucial parameter limiting the achievable key rate and transmission distance, is studied.