Teleportation in theory...

In science fiction novels, teleportation is a common phenomenon. A person enters a special booth, presses a button... and is instantly transported to the other side of the galaxy. This will likely be possible in the future. But for now, when physicists speak of teleportation, they mean objects much smaller than a human being—individual particles. They mean transporting an exact copy of a particle over a distance and reproducing it in another location. This isn't easy, because according to quantum mechanics, we can't know the full quantum state of a particle (the uncertainty principle prohibits this). And any intervention (including measurement) irreversibly changes the particle being studied. So how is this achieved?

This was first achieved by American Charles Bennett of the IBM research center in Yorktown Heights, USA, in the early 1990s. He created a character named Alice who wanted to faithfully transmit a photon instantly, over a long distance, to Bob. Bennett gave Alice the following advice:

Take a pair of entangled photons. Let one stay with you, and the other go to Bob. This is a necessary pair of intermediaries for such teleportation. Now all that's needed is for the photon we want to teleport to be entangled with Alice's photon. At that moment, all the properties of that photon will immediately transfer to Bob's photon—via the chain of the strange quantum bond connecting the three photons. As soon as Alice entangles her two photons, Bob's photon will become an exact copy of each of them.