
Chinese satellite is one giant step for the quantum internet - jonbaer
http://www.nature.com/news/chinese-satellite-is-one-giant-step-for-the-quantum-internet-1.20329
======
xgbi
> Eventually, quantum teleportation in space could even allow researchers to
> combine photons from satellites to make a distributed telescope with an
> effective aperture the size of Earth — and enormous resolution. “You could
> not just see planets,” says Kwiat, “but in principle read licence plates on
> Jupiter’s moons.”

Uh, what? What does entangled photons have to do with interferometry-based
astronomy? Can somebody explain to me how this could be achieved?

~~~
Strilanc
It lets you bypass some classical limits. It's a well known idea. For example,
John Preskill mentioned entangled telescopes in a non-technical talk back in
February [1].

A specific case is "NOON" states [2]:

> _NOON states are an important concept in quantum metrology and quantum
> sensing for their ability to make precision phase measurements when used in
> an optical interferometer._

\---

Here's an example that doesn't exactly use entanglement, but does use quantum
stuff to give you the general flavor. Suppose you have an optical setup like
this:

    
    
              B
              |
              v
        A --> ◩ -----> D1
              |
              |
              v
              D2
    

When a photon is emitted from A, or B, it passes through a beam splitter then
continues on to the two detectors and triggers one of them. If the detectors
are classical, then there's no way for you to distinguish whether A or B
emitted the photon. Both are a 50/50 split. But if the detectors can store
their readings at various times as quantum information and keep that
information coherent, then you can bring the stored qubits together, simulate
un-applying the beam splitter, and voila! The same basic idea applies to
telescopes: photons from different sources spread out in slightly different
ways, and we can undo some of that spreading with quantum computation.

1:
[https://youtu.be/lN8zT_Yk5sg?t=3m58s](https://youtu.be/lN8zT_Yk5sg?t=3m58s)

2:
[https://en.wikipedia.org/wiki/NOON_state](https://en.wikipedia.org/wiki/NOON_state)

~~~
24gttghh
Thanks, I actually understood that!

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frandroid
So what if someone decided to DOS quantum communications by spying on all of
them? You don't need to be successful at deciphering the communications; you
just need to tamper with many of them to make a whole bunch untrusted, and
eventually others stop trusting the whole channel because most messages have
false interception positives.

~~~
OldSchoolJohnny
Exactly what I was thinking, if it's easy to tell they've been intercepted by
a third party that infers it's possible to do it so what's to stop a DOS
attack making it useless?

~~~
jcoffland
> if it's easy to tell they've been intercepted by a third party that infers
> it's possible to do it so

This is a logical fallacy. Furthermore, it says nothing about how difficult a
DOS attack would be to perform.

------
gradinafrica
This is a pretty interesting article! I have some questions, though:

1\. What properties of space facilitate quantum experiments more than
terrestrial environments? Reduced gravity? Vacuums?

2\. How does the satellite create pairs of entangled photons? I missed the
memo that we could control entanglement...

3\. When two photons are entangled, what kinds of properties about them are
useful to observe/control, that give us information about or control of the
twin? All I can think of are positional properties like position, speed,
acceleration, etc...

~~~
tim333
1\. Yeah space so nothing disturbs the photons

2\. "heart of their satellite is a crystal that produces pairs of entangled
photons" (see [https://en.wikipedia.org/wiki/Spontaneous_parametric_down-
co...](https://en.wikipedia.org/wiki/Spontaneous_parametric_down-conversion))

3\. Mostly polarization

------
justicezyx
Wonderful achievement, kudos to Chinese scientists and engineers who
pioneering this breakthrough.

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dajomu
What about the interference from the trisolarians?

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tkinom
Does speed of communicate with entangled photons travel faster than speed of
light?

For example if we have the device that encode/decode voice with entangled
photons and put that on Moon, Mars, does that form of communication has any
delay like normal electronic communication would?

~~~
zitterbewegung
No, it doesn't see the No Communication theorem.
[https://en.wikipedia.org/wiki/No-
communication_theorem](https://en.wikipedia.org/wiki/No-communication_theorem)

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bennalle
Could these satellites have any implications for Facebook's drone and Google's
Loon internet connectivity projects?

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abroter
deploy GFW is the next step

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bglazer
The original Nature article is here: [http://www.nature.com/news/chinese-
satellite-is-one-giant-st...](http://www.nature.com/news/chinese-satellite-is-
one-giant-step-for-the-quantum-internet-1.20329)

This is a reprint.

~~~
sctb
Thanks, we updated the link from
[http://www.scientificamerican.com/article/chinese-
satellite-...](http://www.scientificamerican.com/article/chinese-satellite-is-
one-giant-step-for-the-quantum-internet/), which pointed to this.

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frozenport
This is a transparent attempt to develop a military communication system that
bipassses US suvalience.

------
known
Does Chinese have "Golden Eye"

