The Unbreakable Line Is Only as Honest as Its Ends

LAGOS — For ninety minutes on Sunday, the quantum-secured link serving a Lagos clearing house went dark, and the interruption offered an unusually plain lesson in what the technology does and does not promise. Q-Net secures a channel; it does not carry information faster than light, and it cannot repair a severed fiber. The fault was a mundane cut on a landing cable, but it forced traffic onto slower classical backups for the duration. "People imagine the quantum part as magic," said Dr. Wei-Lin Tan of the Singapore Institute, whose lab demonstrated a million-qubit processor over the backbone in September. "It is not magic. It is a very good lock on a very ordinary door." The distinction matters as more of the world's finance, relief logistics and migration records move onto the network. Roughly a dozen institutions rerouted during the Lagos gap; none reported a breach. The security held precisely because, for ninety minutes, nothing moved through the door at all.