Introduction to Quantum Information: Part 4/7

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You enter a lightly device (mostly in a cylindric box shape), after pressing a few buttons on a computer, you are teleported somewhere else.
At least that's what they are showing in all the sci-fi movies, games, novels, etc.

In our imagination, teleportation is a transfer of matter from point A to point B.

That's why I'm sorry to say, but in quantum teleportation there is not a transfer of matter; only quantum information is transferred.
So, even if quantum teleportation has been proved experimentally ground-to-satellite (approximatively 500-1400km), you still cannot transfer yourself in Star Trek style.

This is quite a difficult problem to understand technically, but we will go through the main parts of the protocol to have an insight of its functioning.

Quantum teleportation involves three parties, commonly called: Alice (A), Bob (B), and Charlie (C).
The problem is to transfer an arbitrary unknown quantum state

from Charlie to Bob.
Charlie doesn't know Bob's position, but both Bob and Charlie share a channel of some kind with Alice.

In particular at the beginning of the protocol, Charlie and Alice share a quantum channel (e.g. a optical fiber), while Alice and Bob share a classical channel (e.g. internet connection) and an entangled pair, for example

The protocol runs as:

  • Charlie sends his unknown quantum state to Alice;
  • Alice entangles her part of the entangled pair (the one shared with Bob) and the qubit from Charlie;
  • Alice performs a measurement on the two qubits in her laboratory (the one she already had and the one from Charlie);
  • Alice communicate to Bob what measurement she performed and her outcome;
  • Bob applies a quantum gate to his qubit, according to the information from Alice;
  • Bob has now the unknown quantum state that was belonging to Charlie.

Some considerations: Charlie doesn't have his state anymore; Alice doesn't have it either because she performed a measurement on the state and therefore it has been destroyed (it is part of the weirdness of quantum measurements); Bob has a state from Charlie and he is sure that no leakage of information occurred and he is the only one having that state.

This feature about quantum teleportation is commonly used for the development of the quantum counterpart of blockchains!
If you are interested about quantum distributed system (hence the possibility to develop a blockchain using quantum mechanics, just let me know 😉)

That's all for today!
Stay tuned and see you in the next post! We will do some SUPERDENSE CODING!

Follow @maar to stay updated and to know more about the fascinating world of Quantum Information and Computation!