A six-node Quantum Key Distribution network is now live in the Randstad, running over deployed telecom fibre that links three data centres. This trial moved MDI-QKD out of the lab and onto infrastructure operators already run.
The challenge
Most QKD results are produced on spooled fibre in a temperature-controlled room. Deployed fibre behaves differently: it drifts with the weather, it is shared with classical traffic, and it is spliced by people who are not thinking about single photons. The question for this trial was simple. Does a multi-node, quantum-secured key exchange hold up on the infrastructure that is already in the ground?
The network
Six nodes were placed across three data centres and two street cabinets, connected by 214 kilometres of deployed single-mode fibre. Each link carried quantum and classical channels on the same strand, with the classical traffic left at its normal power level rather than turned down for the experiment.
Node layout
Four nodes acted as key endpoints, two as trusted relays. The relays hold key material in a hardware security module and forward it hop by hop, which is what makes a metropolitan span practical today without a quantum repeater.
Key management
All six nodes were driven by a single Quantum Domain Controller. Keys were delivered to the encryptors over ETSI GS QKD 014, so the network encryptors on either side needed no modification.
What we measured
Over eleven months of continuous operation the network produced a stable secret key rate on every link, with the quantum bit error rate staying inside the range that keeps the security proof valid. Two fibre cuts and one planned maintenance window interrupted service; in each case the affected link resumed key exchange without manual intervention.
What it means for operators
The result that matters is not the peak key rate. It is that the network ran unattended, on live fibre, alongside production traffic, for the better part of a year. That is the bar an operator applies to any new equipment in the estate, and it is the bar quantum key distribution has to clear before it becomes an ordinary line item.
Next steps
The trial continues with two additional nodes and a second operator joining in the next phase. The full measurement data and the network topology are available on request.
