By Sascha Brodsky
Publication Date: 2026-03-19 12:00:00
One strange property of quantum information is that it cannot be copied.
Classical information can be duplicated perfectly and infinitely. Copy a file, and you have two identical files. At the quantum level, this is false. A quantum state is disturbed the moment you try to measure or copy it. Bennett has a way of explaining this that tends to stop people cold.
“Quantum information,” he said to IBM, is “ like the information in a dream. As soon as you start trying to tell somebody about your dream, you begin to forget the dream, and you only remember what you said about it. The public version can be copied, but it’s not the same as the dream.”
What Bennett and his collaborators grasped was that this limitation was actually a tool. If quantum information cannot be copied, it cannot be secretly copied either. An eavesdropper who intercepts a quantum-encoded message necessarily disturbs it, leaving a trace. That is the premise behind quantum cryptography, which is…
