

Scientists achieve critical steps to building first practical quantum computer - Errorcod3
http://phys.org/news/2015-04-scientists-critical-quantum.html

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swordswinger12
>If a quantum computer could be built with just 50 quantum bits (qubits), no
combination of today's TOP500 supercomputers could successfully outperform it.

I would really, really like to know how they came up with this.

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titanomachy
I agree, without more info that's a pretty meaningless statement. What if the
quantum computer takes minutes to complete a single operation?

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rurban
why? 2^50 is a pretty high number.

calculating with 2^50 states at once in one cycle certainly outperforms any
known super computer, even if a cycle costs 1s. It does not however.

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titanomachy
2^50 is the upper bound on the size of the solution space that can be searched
by a 50-bit quantum computer. If that same solution space were divided up
amongst the hundreds of thousands of cores in the world's largest
supercomputers, the solution could be found in much less than 1 second, or
indeed much less than 1 cycle of any computer, quantum or otherwise.

Anyway, whatever "cycle" means in a quantum computer, it would take much more
than 1 cycle to search the whole solution space. Assuming your problem is in
BQP you still have to iterate until error is within acceptable limits.

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omgitstom
It is interesting that they visualized bit flip and phase/sign flip error with
two dead birds in:

[http://cdn.phys.org/newman/gfx/news/hires/2015/3-scientistsa...](http://cdn.phys.org/newman/gfx/news/hires/2015/3-scientistsac.jpg)

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geoelectric
That's because they're killing both birds with one stone, metaphorically
speaking.

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omgitstom
exactly!

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heimatau
This is just mind boggling. Quantum related things is one of the reasons I
decided to go back to college. I'm just lost in a vortex of unknowing. Props
to IBM research team for being able to find the errors within the system.

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Animats
This is a very strange field. D-Wave is shipping quantum computers designed to
do optimization problems, and yet nobody is really sure if they work.

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marcosdumay
The D-Wave is not a quantum computer by the usual meaning of that term.

It's only a "quantum computer" by a definition created by their market
department. A definition that also classifies as "quantum computer" the one
you have on your desk.

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jdjdps
That's not entirely fair. D wave is attempting to use quantum effects anneal
to solutions faster than a classical computer would. It's not what we would
usually think of as a quantum computer, but its in the right ball park. No?

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marcosdumay
Well my desktop also uses quantum effects. So did valve computers at the time,
thus, I don't think anybody ever built a "classical computer".

Yes, that's the definition they use on their site. No, I don't think applying
it verbatim to my computer is unfair.

Ok, they created a different kind of classical computer. One that may be able
to solve some kinds of problems better, like a specialized computer often
does. Yes, it could have been huge (but wasn't - too bad). But it's not a
quantum computer, and their marketing is dishonest.

