# Breaking the system-frequency limitation of quantum key distribution

## TL;DR

This paper introduces a new protocol and techniques to overcome bandwidth limitations in quantum key distribution, enabling higher secret key rates without increased device costs or security compromises.

## Contribution

The authors propose a comprehensive countermeasure and new protocol that break the bandwidth-limited secret key rate barrier in quantum key distribution.

## Key findings

- Achieved lowest correlated deviation compared to similar works.
- Successfully broke the bandwidth-limited secret key rate barrier.
- Demonstrated practical feasibility with an experimental setup.

## Abstract

Enhancing the system performance has been the primary mission in the domain of quantum key distributions in recent years. Higher performance necessitates a higher repetition frequency, which is, however, strictly limited by the bandwidth. Excessive increase in the repetition frequency is not justifiable since it leads to misaligned and correlated modulation, resulting in compromised security and significant errors. Meanwhile, replacing devices with higher bandwidth means more technique challenges and more expense, which is detrimental to practical implementations. In this work, we propose a comprehensive countermeasure to overcome the bandwidth limitation. We present a new protocol addressing the aforementioned loopholes to ensure security and achieve superior performance compared to previous approaches. Additionally, we address the challenges associated with characterizing and mitigating the correlations by developing two techniques. An experiment setup is completed in this work, whose result indicates that our technique achieves the lowest correlated deviation in all similar works and our proposal breaks the bandwidth-limited secret key rate, thus releasing people from the trade-off between performance and cost, paving the way for practical applications.