A simple fix closes a major loophole in quantum encryption

Quantum key distribution promises unbreakable encryption, but real detectors have imperfections that hackers can exploit — including a "time-shift attack" that probes when photons arrive to learn secret information. Running on a gigahertz-clocked QKD system, a four-state countermeasure (long proven secure on paper) nearly fully recovers the secret key rate that the attack would otherwise destroy. The result gives hardware developers a practical, drop-in fix for one of the most significant known vulnerabilities in deployed quantum networks.