by Jérémy Ribeiro
Have you ever dreamt about teleportation? You wonder if it is possible, or if we can use it to travel faster than light, or at least to communicate instantaneously. Then you are at the good place. Here I will explain what quantum teleportation is. Behind this very attractive name that reminds us of science fiction, a communication protocol is hidden which uses the mysterious quantum mechanics.
Why do I talk about quantum teleportation ?
I wanted to write about this protocol because we hear a lot about it and a lot of information and explanations can be found about it. But sometimes those are partially wrong, or are a complete nonsense. For example we can read that quantum teleportation is an instantaneous transfer of information at a distance which respects special relativity… Well this is a contradiction.
These misconceptions of the protocol are not surprising since it relies on one of the most ununderstandable and less well understood phenomenon of quantum mechanics: the famous entanglement.
That’s why I will try to clarify what this notorious quantum teleportation actually is. For that I will have to introduce a little bit of quantum mechanics. Therefore there will be some mathematical expressions, but I’ll guide you through it to make you understand what is going on. It shouldn’t be too difficult since you should have already seen all the mathematical concepts in high school (vectors), and I think it is worth it and permits to really understand what quantum teleportation is.
So what is that quantum teleportation ?
The first thing to understand is that we only teleport a quantum state (we will call it ), and not a particle nor any other kind of matter. Only information is transmitted from one place to another. So somehow we will scan the physical system in the first place (which will destroy the state), send the information (by phone, internet or any other way of communication) to an other place and there reconstruct the state. But to do that there are some obstacles. The main obstacle the “scanning phase” is not trivial since we cannot (by the law of quantum mechanics) get all the
information on a state by measuring it, as I will explain later, but only partial information. To overcome that we will need to use a correlated state which will somehow compensate the lack of information.