
Large-scale quantum chip validated - scotty79
http://news.usc.edu/#!/article/52818/large-scale-quantum-chip-validated/
======
gjm11
This is "validated" in a pretty weak sense.

I think the paper is (perhaps a slightly different version of) this one:
[http://arxiv.org/abs/1212.1739](http://arxiv.org/abs/1212.1739) in which the
researchers found evidence that favours the hypothesis "the D-Wave device is
doing quantum annealing" over the hypothesis "the D-Wave device is doing
classical simulated annealing".

That's very interesting scientifically (though it's not clear to me how far
they've ruled out _other_ basically-classical processes) but it's important to
notice what it isn't.

It _isn 't_ evidence that D-Wave's device can perform the operations usually
denoted by the phrase "quantum computing". (So far as I know, no one thinks it
can.) So, e.g., there is no known way to use it to break RSA encryption, no
matter how well it does the things it does.

It _isn 't_ evidence that there is any problem D-Wave's device can actually
solve faster than a classical computer.

It _isn 't_ evidence that there is any _useful_ problem D-Wave's device can
actually solve faster than a classical computer.

See [http://www.archduke.org/stuff/d-wave-comment-on-
comparison-w...](http://www.archduke.org/stuff/d-wave-comment-on-comparison-
with-classical-computers/) for some comparisons between the published
performance figures for D-Wave's device and simple software running on (one
core of) an ordinary laptop. The laptop comes up faster every time, even
solving _the exact problem D-Wave 's device is designed to solve_.

That doesn't rule out the possibility that there may be other instances of
that problem that D-Wave's device solves much faster than anything you can do
on a laptop (but no one seems to have found any) nor the possibility that some
future version of D-Wave's device may be much better because it scales better
(though Alex Selby's figures aren't particularly encouraging on that score).
But claims that D-Wave, _now_ , have a useful quantum computer don't look very
plausible.

~~~
jessriedel
> I think the paper is (perhaps a slightly different version of) this one:
> [http://arxiv.org/abs/1212.1739](http://arxiv.org/abs/1212.1739) in which
> the researchers found evidence that favours the hypothesis "the D-Wave
> device is doing quantum annealing" over the hypothesis "the D-Wave device is
> doing classical simulated annealing".

> (though it's not clear to me how far they've ruled out other basically-
> classical processes)

According to my colleagues at IBM Research, not far:

> A pair of recent articles concluded that the D-Wave One machine actually
> operates in the quantum regime, rather than performing some classical
> evolution. Here we give a classical model that leads to the same behaviors
> used in those works to infer quantum effects. Thus, the evidence presented
> does not demonstrate the presence of quantum effects.

[http://arxiv.org/abs/1305.4904](http://arxiv.org/abs/1305.4904)

~~~
mitmatt
The USC group has a response to Smolin and Smith which explains how some
quantitative features are still best explained by a simulated quantum
annealer: [http://arxiv.org/abs/1305.5837](http://arxiv.org/abs/1305.5837). So
there's still some potential for evidence of quantum effects (though "maybe
doing something nonclassical" is a far cry from all the marketing talk,
especially since annealing with stoquastic Hamiltonions with a fixed topology
is already a far cry from any known-to-be-useful quantum computing model).

~~~
jessriedel
Ooh, thanks. I think John and Graeme have been working on a second version,
presumably in response to this. The battle continues...

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Rickasaurus
The D-Wave is a quantum annealer not a multi-purpose quantum computer.

------
bsaul
There's something i don't get with this debate around "is this quantum or
classical" : i thought quantum computing meant breaking NP complexity. So, in
order to determine if it "is" quantum computing, one would suppose that any
big dataset would easily show the difference in computing time...

Now, if i understood correctly, the problem is that the algorithms compared
(aka annealing) are of statistical nature, so we're not actually comparing
"fully" NP complete algorithms, and so the expected difference is not as a big
as between an O(n) and an O(x^n)) algorithm.

Could someone here confirm if this is correct ?

~~~
lolcraft
Quantum computing means breaking Bounded Quantum Polynomial, not NP. Integer
factorization is in NP, and also in BQP; but some problems can just as well be
in NP and not in BQP. And NP-complete is not a subset of BQP, as far as anyone
knows.

~~~
dllthomas
Strictly, we don't actually know BQP is more powerful than P, right?

------
frisco
I've been thinking this for a while and have really come to believe it
recently, but I'd be amazed if the NSA didn't have quantum computing down,
either at scale or about to get there. Historically they've been, and similar
organizations are perceived to be, 5-10 years ahead of public technology, so
I'm going to go ahead and assume that all PKE is broken as far as the USG is
concerned.

I've heard from someone who'd know that a big driver of Google's purchase of
the D-Wave was that, "if there's going to be a crypto breakthrough, [Google]
would like to know about it early."

~~~
Osmium
You know, it's not impossible, but as someone who works in a field peripheral
to quantum computing I would be surprised. There are two types of problems in
science, the attrition kind where if you throw enough people and enough money
at it you'll get it to work and the breakthrough kind where nothing will
happen until some a-ha moment. I suspect quantum computing is more of the
latter right now; there are just too many outstanding issues for a large-scale
device. But who knows, I may be wrong.

Regarding D-Wave specifically, there's plenty of commentary around on what
they're doing...

~~~
chacham15
> There are two types of problems in science, the attrition kind where if you
> throw enough people and enough money at it you'll get it to work and the
> breakthrough kind where nothing will happen until some a-ha moment.

Thats interesting. What camp would you say flight fell under?

~~~
ewrwerwerw
Considering that it only took two guys to research,design, and build it I
would say the latter with a lot of grunt work.

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chacham15
Does this mean that I need to throw away my 2048-bit RSA key? Is 4096 bit at
all safer than 2048 from quantum computing?

~~~
pudquick
No.

No speed up when compared to a classical machine (for much cheaper) emulating
the exact same procedure:

[http://www.scottaaronson.com/blog/?p=1400](http://www.scottaaronson.com/blog/?p=1400)

------
damian2000
Anyone know how they program these?.. something like QCL?
[http://en.wikipedia.org/wiki/Quantum_programming](http://en.wikipedia.org/wiki/Quantum_programming)

~~~
teraflop
It doesn't run "programs" like a Turing or von Neumann machine does; it's not
even a universal quantum computer. It solves certain specific instances of an
optimization problem which, in the general case, is NP-hard.

~~~
IanChiles
Just to clarify, it's like a quantum ASIC?

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tehwalrus
As noted in the other thread on this story[1], this claim has already been
debunked by other physicists[2].

[1]
[https://news.ycombinator.com/item?id=5957232](https://news.ycombinator.com/item?id=5957232)
\- comment
[https://news.ycombinator.com/item?id=5957686](https://news.ycombinator.com/item?id=5957686)

[2] [http://arxiv.org/abs/1305.4904](http://arxiv.org/abs/1305.4904)

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LAMike
What's the coolest use-case for a quantum computer of the future?

~~~
raverbashing
I think if this really takes off we'll have a "quantum card" like a video card
for a PC

~~~
omegant
And for what use? (sincerely interested).

~~~
DanWaterworth
Same use as a graphics card... to show off and play games.

