For a clearer understanding of the problem of transfer of quantum information, Let's say, that Alice has some part of the quantum state |Ψ|, and she wants to send to Bob, located on certain distance, the same part in the same State. I see, that there is a possibility to send Bob a particle directly. But suppose, What channel of communications between Alice and Bob is not very good for keeping the necessary quantum coherence, or let's say, that the transfer would take too long and this will cause the, that |Ψ| become more complex or large object. So, What should be the strategic behavior of Alice's and Bob's?
As noted above, There is no such measurements, that would be Alice by |Ψ|, that would have been sufficient to reconstitute them to Bob, because the State of a quantum system can never be fully determined by measurements. Quantum systems so elusive, as they can be in a superposition of multiple States at one time. Measurement of a quantum system is accurate only in one of these States, and this will be one of the key provisions of the proposed model. We can demonstrate this important quantum property, taking a single photon, which may have horizontal or vertical polarization, tagged conditions |↔| and | |. It can even have a total superposition of the two polarization States. (1)
|Ψ|= α|↔|+ b| |
where α and β are two complex numbers, satisfying |α|² |β|² = 1
Given this sample in the more general case, We can replace State |↔| and | | in the equation (1) on |0| and |1| , who represent States of any quantum system in two States. Superposition |0| and |1| called qubits (qubits), they have important new features, imposed by quantum physics in information science .
If the photon is able to |Ψ> passes through a polarizing beam disintegrant (the reflection device horizontally or vertically polarized photons), It is found in the reflected (the passed) Ray with probability |α|²(|β|²). The differentiation of the general condition of the |Ψ| It is possible to predict how the path to the |↔| , and on the way | | Depending on the measure. We believe, that the laws of quantum mechanics, in particular, the postulate (projection) forecast of this kind, Alice's makes it impossible for accurate measurement |↔|, i.e.. Unable to obtain all the information, that is needed for the reconstruction of the State.
The concept of quantum teleportation
Although tenet prediction in quantum mechanics seems to be sufficient for Alice's attempts to ensure the right transition from Bob in the State |↔| (as the equivalent of taking teleportacionnoj information from Alice to Bob (P.G.)), However,, This became possible after the work of Bennett and others. , who were able to accurately predict the teleportation State |↔| from Alice to Bob. During the teleportation Alice will destroy (own? P.G.) quantum state at the time of admission Bob (new P.g.) quantum state (sent it? P.G.), and at the same time, neither Bob, no Alice did not have accurate information about the status of |↔|. A key role in the scheme of teleportation are further tangled pair of particles, the first are Alice and Bob.
Suppose, particle 1, that Alice wishes to teleport, is in a State of
|Ψ|1 = a|↔|1 + b| |1 (Figure 1a), and entangled pair of particles 2 and 3, manipulated, Alice and Bob, possess the status of (2)
|Ψ-|2 3=1/√2 |↔|2 | |3 – | |2 |↔|3