Re: Quantum Cryptography can not work

On 2007-03-02, Unruh <unruh-spam@xxxxxxxxxxxxxx> wrote:
Can't quantum teleportation be used to get around this?

Well, you do have to exchange the original entangled pairs. But otherwise
yes. If your shared secret is entangled pairs then the communication
channel can be any classical channel.

So, basically, if you were trying to build a network where end-to-end
communications can be encrypted using QC, but without having to have
something that can let there be a direct end-to-end transmission of,
say, a photon (e.g., you don't want to have to have a fiber link
directly to the other party), would the following work?

You build a network, much like current networks. You have end points
and routers. End points connect to routers, and routers connect to
other routers and to end points.

A connection between two adjacent nodes consists of a classical
connection, plus something that generates entangled pairs and sends them
to the nodes.

If you need an entangled pair at end points A and Z, and the route from
A to Z is A -> R1 -> R2 ... -> Rn -> Z, then A and R1 get an entangled
pair (which they can do because they have a direct link). R1 and R2 use
quantum teleportation to teleport that to R2, so now A and R2 have an
entangled pair, and so on, until A and Z have an entangled pair.

Note that each link could have a large buffer of entangled pairs, so
generating and distributing the entangled pairs would not have to be a
bottleneck.
.

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