p2

We now go one more final step to give a simplified outline of the actual teleportation process
according to Bennett et al. (1993). They propose a multistep procedure by which any quantum state |χ〉 of
a particle or a photon (that correspond to an N-state system) is to be teleported from one location to
another. For example, |χ〉 might be a two-level system that could refer to the polarization of a single
photon, the nuclear magnetic spin of a hydrogen atom, or the electronic excitation of an effective twolevel
atom. The following scenario outlines the q-Teleportation process in a very simplified way:
1. Prepare a pair of quantum subsystems |ϕ〉 and |ψ〉 in an EPR entangled state so that they are
linked together. |ϕ〉 and |ψ〉 are maximally entangled and together constitute a definite pure state
superposition even though each of them is maximally undetermined or mixed when considered
separately.
2. Transport |ϕ〉 to the location of the teleportation transmitter and transport |ψ〉 to the location of the
teleportation receiver. (In the technical literature the transmitter is called “Alice” and the receiver
is called “Bob.”) The transmitter and receiver can be many light years apart in space. Note that
the two subsystems are non-causally correlated via entanglement, but they contain no information
about |χ〉 at this point. The two subsystems represent an open quantum channel that is ready to
transmit information.
3. Now Alice brings the teleported state |χ〉 into contact with the entangled state |ϕ〉 and performs a
quantum measurement on the combined system |χ〉|ϕ〉. Bob and Alice have previously agreed
upon the details of the quantum measurement.
4. Using a conventional classical communication channel, Alice transmits to Bob a complete
description of the outcome of the quantum measurement she performed on |χ〉|ϕ〉.
5. Bob then subjects |ψ〉 to a set of linear transformations (i.e., suitable unitary rotations) that are
dictated by the outcome of Alice’s quantum measurement. The quantum subsystem Bob
originally first received is no longer in state |ψ〉 after the linear transformations because it is now
in a state identical to the original state |χ〉. Therefore, |χ〉 has in effect been teleported from Alice
to Bob.
Bennett et al. (1993) showed in their experimental work that this scheme requires both a conventional
communication channel and a non-causal EPR channel to send the state |χ〉 from one location to another.
In addition to this, a considerable pre-arrangement of entangled states and quantum measurement
procedures is required to make the process work. Bennett et al. (1993) analyzed the information flow
implicit in the process and showed that Alice’s measurement does not provide any information about the
quantum state |χ〉. All of the quantum state information is passed by the EPR link between the entangled
particle states |ϕ〉 and |ψ〉. We can think of the measurement results as providing the “code key” that
permits the EPR information to be decoded properly at Bob’s end. And because the measurement
information must travel on a conventional communications channel, the decoding cannot take place until
the code key arrives, insuring that no FTL teleportation is possible.
The q-Teleportation scheme teleports the state of a quantum system without having to completely
measure its initial state. The outcome of the process is that the initial quantum state |χ〉 is destroyed at
Alice’s location and recreated at Bob’s location. It is very important for the reader to understand that it is
the quantum states of the particles/photons that are destroyed and recreated in the teleportation process,
and not the particles/photons themselves. The quantum state or wavefunction contains the information on
the state of a particle, but is not a directly observable physical quantity like mass-energy. The quantum
information contained within a state is available in the form of probabilities or expectation values.
Approved for public release; distribution unlimited.
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