A direct GHz-clocked phase and intensity modulated transmitter applied to quantum key distribution

TL;DR

This paper presents a GHz-clocked, direct-modulation transmitter capable of implementing multiple QKD protocols with simple adjustments, enhancing multi-user quantum communication and potentially benefiting classical data transmission.

Contribution

The authors introduce a versatile, low-chirp, direct-modulation transmitter for quantum and classical communications that simplifies hardware requirements and supports multiple protocols.

Findings

Achieved secure key rates of up to megabits per second.

Demonstrated concurrent time-bin and phase modulation with phase randomization.

Secure key rate 1.60 times higher than purely phase-encoded BB84.

Abstract

Quantum key distribution (QKD), a technology that enables perfectly secure communication, has evolved to the stage where many different protocols are being used in real-world implementations. Each protocol has its own advantages, meaning that users can choose the one best-suited to their application, however each often requires different hardware. This complicates multi-user networks, in which users may need multiple transmitters to communicate with one another. Here, we demonstrate a direct-modulation based transmitter that can be used to implement most weak coherent pulse based QKD protocols with simple changes to the driving signals. This also has the potential to extend to classical communications, providing a low chirp transmitter with simple driving requirements that combines phase shift keying with amplitude shift keying. We perform QKD with concurrent time-bin and phase modulation, alongside phase randomisation. The acquired data is used to evaluate secure key rates for time-bin encoded BB84 with decoy states and a finite key-size analysis, giving megabit per second secure key rates, 1.60 times higher than if purely phase-encoded BB84 was used.