# Re: Quantum Cryptography can not work

"Joseph Ashwood" <ashwood@xxxxxxx> writes:

"Unruh" <unruh-spam@xxxxxxxxxxxxxx> wrote in message
news:ert8ge\$m6u\$2@xxxxxxxxxxx
"Joseph Ashwood" <ashwood@xxxxxxx> writes:
The limitation of Quantum Cryptography has nothing to do with your
arguments, the problem is in routing. Just to enable my home router to
work
with quantum cryptography would require making the router larger than my
apartment because of the connection requirements. For single hop
connections
it is a wonderful solution, for multiple hop connections it is entirely
infeasible.

???
I certainly have no idea what you are talking about.

Work through the size of the cabling required for the router.
The router requires 1 cable for each simultaneous connection to avoid
collision and pollution.
Home routers take some number of milliseconds to look up and make the
connection for the next hop.
Assuming the cable is a vacuum, the router will require
299792458*lookup_time_in_seconds of cable for each open connection
For a 1 ms router the router would require ~299792 meters of fiber optic
cable for each connection
Home routers generally support on the order of 1000 simultaneous
connections.
This means 299792458 linear meters of fiber
Assuming fiber optic cable with a face of 1 mm^2 (small cable), the cable
volume would be 299792 m^3
A 500m^2 building (large for a house) would have to be 600 meters tall to
accomodate the router, about half again taller that the Empire State
Building

Again I have no idea what you are going on about. You can store the state
of the light in a local quantum system until you have decided on what to do
with it. The packer would be a classical packet with the address tag, and a
single quantum bit ( photon) you would store the classical stuff, and then
store the quantum state. Then you would read the address and decide where
to send it on to-- ether the next router or to the local machine-- exactly
like a classical router.
Now if you wanted you could store that single bit photon into an optical
waveguide, as you suggest, while you figure out what to so with it, or
store it in an atom, or store it in a slow light material, or....

Quantum memories do not have to be waveguides.
Note that your router at home doe snot take 1 second to figure out where to
send the packet on to. At least I hope not. So why store the photon for a

I'm certain on such a large volume of cable the pricing would not be in
accordance with current pricing, but I certainly wouldn't want that bill.

Unless a way is found to pipeline them in the cable at absolutely absurd
levels (which I cannot rule out) such routing becomes entirely infeasible.
For a small number of connections (<~5) that do not require routing Quantum
Cryptography is a possible option, but as it grows it starts becoming
completely absurd.

??? Your model is what is absurd I am afraid.

Joe

.

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