China Launches Quantum Communications Satellite

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I wonder if the military people around the world will take that as a challenge to try to crack it Ala Alan Turning in WW2.

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This is the science forum, not the racism forum.

I don't understand how it would work. How would a single photon be sent through the atmosphere to a ground station without ever interacting with anything else? Or do they send lots of photons and somehow communicate back which particular ones they have received?

Originally posted by twhitehead
I don't understand how it would work. How would a single photon be sent through the atmosphere to a ground station without ever interacting with anything else? Or do they send lots of photons and somehow communicate back which particular ones they have received?

They don't HAVE to be visible photons, maybe they are using longer wavelengths like IR or lower, maybe even high gigahertz waves. It has to be SOME kind of photon, the only question is the wavelength.

Originally posted by sonhouse
They don't HAVE to be visible photons,

I realise that, but the question still stands. Can you send photons of any kind, from space to a receiver without any interaction, or am I misunderstanding something?

Originally posted by twhitehead
I realise that, but the question still stands. Can you send photons of any kind, from space to a receiver without any interaction, or am I misunderstanding something?

It might be like you said, millions of photons simultaneously and the ones intact used at the other end.

I know it is possible to send this kind of photon through optical fiber at least a hundred kilometers which of course is a lot milder transmission media than atmosphere but the Chinese have claimed to be able to do so.

Of course they may be just lying and having a belly laugh at the hooplaw generated.

Originally posted by sonhouse
Of course they may be just lying and having a belly laugh at the hooplaw generated.

I am sure it is genuine, its just that I don't understand it. I'll have to do some research.

Originally posted by twhitehead
I am sure it is genuine, its just that I don't understand it. I'll have to do some research.

Maybe there is a paper in there somewhere.

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This is a joint project with Austria.

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It has to be experimental so I don't think either China or Austria knows the outcome yet since it IS experimental. It's not like they have some boiler plate solution in hand. This is science not warfare.

Originally posted by twhitehead
I don't understand how it would work. How would a single photon be sent through the atmosphere to a ground station without ever interacting with anything else? Or do they send lots of photons and somehow communicate back which particular ones they have received?

There already has been relatively long distance work like this:

http://phys.org/news/2012-09-km-physicists-quantum-teleportation-distance.html

Laser beam through the atmosphere 143 km apart.