Re: How to detect interception
"detecting the state of one of the photons has no influence whatsoever on the other"
This is a common mistake when talking about quantum entanglement. Observing the state of an entangled photon instantly collapses the entanglement--the photons are no longer entangled. Even disturbing one of the photons will almost certainly collapse the entanglement, which is one of many reasons but probably the most important, that quantum computers are so difficult to build. Almost anything will cause quantum entanglement to collapse. Since it is possible to know when photons (or other particles) are entangled, without actually observing the photons themselves, hiding the fact that someone is snooping becomes nearly impossible. Entanglement is a "quantum weirdness" that has no classical counterpart.