

Two Big Steps Toward the Quantum Computer - wherkewitz
http://www.popularmechanics.com/technology/engineering/extreme-machines/two-big-steps-toward-the-quantum-computer-16682595

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rqebmm
This is all I can think of when I hear about this stuff:
[http://upload.wikimedia.org/wikipedia/commons/4/4e/Eniac.jpg](http://upload.wikimedia.org/wikipedia/commons/4/4e/Eniac.jpg)

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hcarvalhoalves
> But here's the tricky part. The scientists can put the rubidium atom in
> superposition, so that it is simultaneously in that energetic state and not
> in the energetic state. It's on and off. Because of this, the photon both
> does and does not enter the mirror, mingle, and gain its polarization
> change. And the photon, by virtue of having both changed and not changed,
> carries that superposition information and can bring it to a different atom-
> based qubit.

I know almost nothing about Quantum Mechanics, but this sounds amazingly
ingenious.

So what did they do, some sort of _parallel universe transistor_ where the
rubidium atom acts as the gate? If you assemble a processor out of this, will
it compute all possible computations _at the same time_? And, last but not
least... how do you make it converge to the computation you actually want?

Quantum computers make my head spin.

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tedsanders
Yeah, one interpretation of what a quantum computer does is that it performs
all computations in parallel. However... you run into problems when you try to
read the output of this computer. In order to read the output you must measure
a quantum state, and when this happens you only get to see one answer at
random, not all of them. And that's not really useful. But if you can design
an algorithm so that all of the parallel computations add together to form one
answer (i.e., get all the wrong answer's probabilities to cancel out), you can
get an exponential speed up. The key takeway is that quantum computers are not
faster for general problems - quantum computers are only faster for problems
where a special algorithm exists (like Shor's algorithm for factoring).

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callesgg
I was under the Belief that we currently have no way of adding the qbits
together. We can set a qbit and read it but we can't currently get the
particles in the quantum state to interact.

The article however paints another picture.

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sp332
Some groups have even been running Shor's algorithm on multi-qubit computers.
[https://en.wikipedia.org/wiki/Quantum_computer#Developments](https://en.wikipedia.org/wiki/Quantum_computer#Developments)
It requires the qubits to be entangled to do the computation, and in the later
ones (not IBM's 2001 work) the researchers did observe entanglement.

~~~
forgotprevpass
Technically, you can run Shor's algorithm on non quantum computers, with an
exponential speed up (but fully within capabilities of modern computing vs.
small quantities of qubits)

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bluejellybean
Here is a Google tech talk with Eric Ladizinsky that got posted a few days
ago.
[https://www.youtube.com/watch?v=eIEy1KHk0rk](https://www.youtube.com/watch?v=eIEy1KHk0rk)

Very interesting listen if you have the time

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m_mueller
IANAQP, but doesn't this article describe measuring the state of a quant?
Shouldn't measuring put a quant into a defined state, i.e. destroying its
superposition?

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SoftwareMaven
Measuring certainly would, but I don't think that's what it's describing.
Instead, I think it is describing connecting the qbits together and allowing
them all to share the same super-position through the entangled photon.

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cordite
Am I missing something? Isn't a quantum computer just a non deterministic
computation mechanism?

It feels wrong to suppose that answers come out in an "instant", or a mere one
step.

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IpxqwidxG
Continuum of Singularity, so to speak.

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chris_mahan
When two network quantum chips can communicate instantly (not at speed of
light--instantly) over infinite distances, using entangled atoms, then we can
ditch the tecos.

I'm so looking forward to that.

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thangalin
Chances are FTL communication is not possible.

[http://curious.astro.cornell.edu/question.php?number=612](http://curious.astro.cornell.edu/question.php?number=612)

[http://en.wikipedia.org/wiki/Superluminal_communication](http://en.wikipedia.org/wiki/Superluminal_communication)

The book, "Why E=mc^2" is an exceptional read. If I recall correctly, it
explains why light-speed is a universal limit:

[http://www.amazon.co.uk/Why-Does-mc2-Brian-
Cox/dp/0306819112](http://www.amazon.co.uk/Why-Does-mc2-Brian-
Cox/dp/0306819112)

~~~
jerf
Stating whether FTL communication is possible at all may require hedging.
Stating that it can't occur over quantum superposition does not, as I
understand it. The math is clear; there's no information traveling. It does
not matter how sophisticated our quantum computers get, there will not be any
FTL communication coming out of them.

If we could do that at all, we'd almost certainly be able to to it today,
anyhow. We have multi-q-bit QM computers, they just aren't of a practical size
for computation. But if FTL communication was possible, it would have been
done with them already.

