I am looking into securing our data center interconnects using Quantum Key Distribution. Can this be done using the standard fiber we already have in the ground, or does QKD require specialized dark fiber and expensive quantum repeaters to work over distances greater than 100km?
3 answers
You can use existing fiber, but there are significant "co-propagation" challenges. Since QKD relies on single photons, any classical data traffic on the same fiber can drown out the quantum signal due to Raman scattering. Most successful deployments use "Dark Fiber" where the quantum channel is completely isolated. As for distance, 100km is roughly the current limit for terrestrial fiber before the signal attenuates too much. To go further in 2023/2024, you'd either need "Trusted Nodes"—which are essentially secure vaults where the keys are decrypted and re-encrypted—or wait for commercial quantum repeaters which are still in development.
If we use Trusted Nodes to extend the QKD range, doesn't that create a massive security vulnerability at each node, essentially defeating the "unbreakable" promise of quantum physics?
We are looking at Photonic Integrated Circuits (PICs) to help with this. They aim to shrink the QKD hardware down to a chip level, making it much cheaper to deploy across existing nodes.
Matthew is right. The miniaturization of quantum components into PIC chips is going to be the "Ethernet moment" for the quantum internet, making it accessible for standard enterprise racks.
Daniel, you are 100% correct. Trusted Nodes are the "weakest link" in current quantum networks. If an adversary compromises the node, they can intercept the keys. This is why the industry is pushing so hard for "Quantum Repeaters" and satellite-based QKD. Satellites can bypass the fiber attenuation by sending photons through the vacuum of space, allowing for thousands of kilometers of coverage. Until repeaters are mature, you have to balance the physics-based security of QKD with the physical security of your node locations.