5. Applications and algorithms

5.1 Communication using super-dense coding

Super-dense coding is a quantum communication technique that allows more information to be transmitted than there are qubits in use, by exploiting quantum entanglement. We'll see, for example, that it enables two bits of information to be transmitted using a single qubit, which is impossible with conventional communication.

What's more, quantum entanglement offers a degree of security, as any attempt to intercept the message would disrupt the quantum state of the particles, which would be detectable. In fact, we could have the following scenario:

• Alice has a message for Bob. He asks her what her favorite pet is. Alice replies by sending a qubit |0> for "dog" and |1>...