The Basics of BB84

As with any subject, an introductory treatment simply leads to more questions about how something works. The key to understanding why QKD is possible is rooted in the Heisenberg uncertainty principle, which states that a measurement of a quantum system will affect the behavior of that system. An uninvited listener will disturb the transmitted photon polarizations, and any receiver can detect this effect. Use this material to understand how BB84 can detect the presence of a listener on a quantum channel.