Quantum key distribution – BB84

Let's introduce BB84, the acronym that's Charles Bennett and Gilles Brassard developed in 1984 valid for QKD.

Now that we have learned about the properties of Q-Mechanics, we can use them to describe a technique for distributing bits (or better, quantum bits) through a quantum channel.

To describe what a quantum bit, also known as a qubit, is, we have to refer to the "quantum unit information" that's carried by qubits. Like traditional bits, (0) and (1), qubits are mathematical entities subject to calculation and operations.

We will use a bi-dimensional vectorial complex space of unitary length to define a qubit. So, we can say that a qubit is a unitary vector acting inside of a two-dimensional space. So far, we can think of a qubit as a polarized photon, similar to the entanglement experiment we looked at in the previous section. I have already introduced the notation to represent the qubits inside "bra...