Now is a good moment to introduce Alice and Bob (not their real names): our two protagonists who always need to communicate with each other. These two play the major role in many communication dramas, though they remain rather lacking in character development.
This time Alice is sending quantum states to Bob, and Bob does his best to identify them correctly by choosing appropriate measurements.
Let us start with a simple observation: if a quantum state of the carrier of information is described by a state vector in a
But can Alice and Bob do better than that?
Can Alice send more than
The answer is no.