1) BENNETT & CO. IDEAQuantum Teleportation is a quantistic process by whom a quantum state Getting acquainted with the original BBCJPW idea you can't but notice its simplicity. Let's take three 2-level quantum system, for example three photons with their polarizations:
is the state of the first one (that is commonly called a quantum-bit),
is the entangled state (commonly called EPR-pair) of the other two and represents the quantistic
channel. Particles 1 and 2 enter the Alice box at point A, particle 3 instead enters Bob box at point
B. We wish to teleport the state
So Alice tells Bob, via the classic channel, which of the 4 eigenstates she found. With this
information Bob can use his box to make one of 4 possible unitary transformations on photon 3
which, entering the box in an arbitrary state, will leave it exactly in the state i) Teleportation is not a fax (or a cloning machine): if you want to measure the state of a
quantistic system you can't help projecting the system itself in one of its eigenstates. This means that
in the very moment Alice measures the state ii) You can't gain any direct information on the teleported state: this definitely is the secret that
grants the final success. After Bell measurement on the state (*) The quantistic channel is the quantistic nonlocal interaction and it an be substitued by a classic interaction, like Spin-Flip in NMR: the ormer is istantaneous, the latter has got a delay time. |
is transferred from one
place A to another distant place B without using direct transfer of the matter to whom the state is
attached. This is achieved by setting two channels between the points A and B, a classic channel
and a quantistic one(*): the former tells you how use the latter in order to reconstruct the initial state
.
from photon 1 to photon 3. To this end Alice uses her box to
perform a Bell-operator measurement on particles 1 and 2. The Bell operator has the following 4
eigenstates: 
: "transport
complete, capt. Kirk!" - said doct.Scotty- Worth of noting are the following points:
she destroys it, but gains some indirect informations
to perfectly reconstruct the state at Bob's position.
Alice can just tell Bob which of the
4 couples 
, 
she gets, but not the exact values of 
and 
. Rather than a measure in the
usual meaning of the word Bell measure is rather the correct way to use the quantistic channel
represented by the entangled photons: the less you know about the state, the better you can beam it
up. This striking feature becomes clearer dealing briefly with some definitions like classical
teleportation and fidelity.