Danish and Czech scientists have collaborated to use continuous-variable quantum key distribution (CV-QKD) technology to achieve a co-fiber transmission distance of 120 kilometers for quantum signals and classical data. Their research results were published in the latest issue of Physical Review Letters, a journal published by the American Physical Society.
Quantum key distribution (QKD) leverages the properties of quantum mechanics to achieve highly secure confidential information transmission. The principle is that any eavesdropping perturbs the quantum state of the information being transmitted, and this perturbation is detected by electronic detection devices on both communicating parties, thus ensuring the security and reliability of the communication link.
However, practical deployment of QKD remains challenging. The key to achieving low-cost and scalable applications lies in integrating them into existing fiber optic networks that carry classical data. Quantum communication must share fiber optic infrastructure with classical data, but the noise introduced by classical channels severely limits the transmission distance and performance of QKD, limiting its maximum transmission distance to tens of kilometers.
Previous attempts to suppress interference by adding filters or allocating dedicated wavelengths complicate system integration. This study proposes a novel CV-QKD technology to address this challenge.
In the CV-QKD system, the sender loads randomly encoded information onto the amplitude and phase of the light wave, and the receiver generates a key by measuring the light wave. Both parties can use this electronic key to encrypt and decrypt information. Based on the principles of quantum physics, any eavesdropping will produce a detectable disturbance in the light wave, triggering a security alarm.
This research successfully suppressed the mutual interference between quantum signals and classical data. Unlike previous approaches, this technology does not require the addition of external filters or modifications to existing fiber networks. Instead, it cleverly activates the long-overlooked “built-in filtering” capability of the CV-QKD system. By optimizing the quantum signal transmission strategy, it ultimately achieved stable and reliable quantum key distribution over 120 kilometers of fiber fully loaded with classical data.
The research team emphasized that this latest breakthrough demonstrates that CV-QKD can provide a “plug-and-play” quantum security solution for long-distance fiber links, eliminating the need for additional filtering equipment or specific wavelength allocation, significantly simplifying upgrades to existing networks. Future improvements to error correction technology are expected to further increase the transmission distance and key generation efficiency of this system.
