Quantum Science Satellite (Mozi)

[Kryten]

 The Chinese have launched the first satellite for quantum communications, Mozi, into a 600km sun-synchronous orbit. The satellite is designed to facilitate transmission of entangled photons from a ground station in Beijing to one in Vienna; this would allow quantum key encrypted communications over about 7,000km, versus the current record of a few hundred kilometres over fibre. The satellite is also intended to demonstrate quantum teleportation over this distance, again compared to current records of a few hundred kilometres. According to one of the physicists on the team, the satellite could be followed by others if successful, allowing transmission of quantum information across the globe.

[insert_name]

Is the entanglement experiment a FTL comms test, I heard that somewhere but it wasn't a very credible source and I am doubtful for hopefully obvious reasons.

[K^2]

19 minutes ago, insert_name said:

Is the entanglement experiment a FTL comms test, I heard that somewhere but it wasn't a very credible source and I am doubtful for hopefully obvious reasons.

No, entanglement is used for light-speed (or slower) communication. What it lets you do instead is send quantum data over a classical channel. This can be used for teleportation and encryption, as stated in Kryten's post.

There is actually a rather infamous No-Communication Theorem in Quantum Mechanics that states that while effect of entanglement is apparently instant, it cannot be used for FTL communication.

[RainDreamer]

I wonder if quantum computer require much more hardening against cosmic radiation considering how sensitive the q-bits are.

[PB666]

http://www.bbc.com/news/world-asia-china-37091833

[Kryten]

3 hours ago, RainDreamer said:

I wonder if quantum computer require much more hardening against cosmic radiation considering how sensitive the q-bits are.

It isn't handling q-bits, only entangled photons. There's not a lot of real cross-over between quantum cryptography like this and quantum computing.

[K^2]

Technically, an entangled pair is two qbits. And there is actually crossover once you start talking about breaking encryption. An arms race waiting to happen, in fact.

But yeah, at this stage, rad hardening isn't an issue, since sat doesn't need to hold on to data for any amount of time, and photons don't age.

[PB666]

26 minutes ago, K^2 said:

Technically, an entangled pair is two qbits. And there is actually crossover once you start talking about breaking encryption. An arms race waiting to happen, in fact.

But yeah, at this stage, rad hardening isn't an issue, since sat doesn't need to hold on to data for any amount of time, and photons don't age.

 

Who else thinks that this is going to be hard to do, at least create a data stream?

 

[K^2]

It's not as hard as it sounds. There are existing methods to amplify one of the entangled photon pair via lasers/masers for example. At that point, satellite itself can be just a mirror. The trick is then to have it be a very finely tunable mirror that lets you bounce that beam precisely and without significant losses. But that's a mechanical/electrical engineering problem, which you can always solve by throwing enough money at it. The Quantum side is easy for once.

Not that it makes it less impressive. Just less amazing.

[Kryten]

The sat isn't just a bent-pipe relay, it's also set up to produce it's own entangled photons and transit them to both ground stations. More info here.

[K^2]

Fair. But that merely shifts weight of the amplifiers to the sat. Tech remains exactly the same. The challenge is to take a single photon and turn it into an avalanche of photons while preserving entanglement. A laser already does this, so long as distance you are trying to send the beam to is within the laser's coherence length.

Hm. I wonder if this can be leveraged for some sort of point-to-point communication, though. Having a pair producing sat in orbit does allow for some interesting practical uses. I can see why it's getting funding.