
Commercial quantum computer leaves PC in the dust - ColinWright
http://www.newscientist.com/article/dn23519-commercial-quantum-computer-leaves-pc-in-the-dust.html
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shadowmint
I wish there was more detail on this comparison, I'm looking forward to the
presentation.

That a custom specialized computing device performed better than a _desktop
computer_ doesn't sound particularly compelling to me.

Aren't the dwave machines like super computers? Would you _expect_ them to be
that much faster than a _desktop_?

Sounds weird to me.

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IgorCarron
Let me make a simple observation here:

In the Paper of Catherine McGeoch and her co-author Cong Wang, they write:

"...As a case in point, our second project compares the V5 hardware chip used
in our first study to a V6 chip that became operational after the study was
completed. V6 is three to five times faster than V5, and can solve problems as
large as n = 502...."

In other words, during the time it took to set up the algorithm and perform
the study, Moore's law had been able to enable a classical approach to go five
times faster. I am a big supporter of anything that does quantum computing but
one should never lose sight of Moore's law.

[http://nuit-blanche.blogspot.com/2013/05/randomized-thoughts...](http://nuit-
blanche.blogspot.com/2013/05/randomized-thoughts-and-around-blogs-in.html)

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swombat
So, basically, as soon a someone builds one of those optimised for factoring
primes, all our encryption methods are finished, as is the Bitcoin economy,
right?

Assuming the contents of the article are true (which is possible), how long
before that happens? A few years? A decade?

~~~
pja
Pretty much: Quantum Computers (QCs) can factor numbers (Shor's algorithm) and
calculate discrete logarithms in polynomial time. I don't know whether there's
an algorithm for hash-calculation that will let someone dominate the BitCoin
hashing chain with a QC though.

On the other hand, no one actually knows whether it's possible to build a
quantum computer with enough q-bits that will stay coherent for long enough to
carry out the calculation: as you add q-bits, noise becomes more and more of a
problem. You can add error correction, but that makes keeping all the q-bits
coherent harder because now you've got even more of them! At the moment, no-
one knows (unless the NSA has built one and isn't telling!) which effect is
going to win out as the number of q-bits increases.

(You can't use a smaller QC to simulate a slower version of a larger one,
unlike in the non-quantum computing world: if you need to factor a 1024 bit
number and you only have a 1000 bit QC you can't do it, as I understand
things.)

Note that Quantum Computers don't help as much with symmetric encryption,
unless someone comes up with a much better algorithm. They let you effectively
halve the key-space, which is a fairly big deal, but you can get back to the
same level of difficulty by doubling up the size of your keyspace: a 256-bit
AES key provides roughly the protection of a 128-bit key in a quantum
computing world. This is different to public-key encryption, where you can
double the key size, but if your opponent has a quantum computer with enough
q-bits, they can still break your new key in reasonable time.

~~~
shadowmint
I actually thought that error correction codes were largely considered to
solve the problem of decoherence, at least theoretically.

(aka.
[http://www.google.com.au/url?sa=t&rct=j&q=&esrc=...](http://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&ved=0CEUQFjAD&url=http%3A%2F%2Fwww.theory.caltech.edu%2Fpeople%2Fpreskill%2Fph229%2Fshor_error.ps&ei=SMqQUaKNK8XmiAfs-4HQDA&usg=AFQjCNEVRTSN2PNKgUKy1Sr-2mFDLEHPpQ&sig2=wng6eCmyuiGIpnp6e15GrQ&bvm=bv.46340616,d.aGc&cad=rja)
or perhaps more easily explained @
<http://en.wikipedia.org/wiki/Quantum_error_correction>)

~~~
pja
As I understand things (and I'm not anything close to being an expert, just an
interested outsider with enough of a physics education to be dangerous), you
can add q-bits to cope with errors introduced by decoherence, but whether
these codes work depends quite finely on the error rate. So if you can manage
to keep the error rate low enough, then everything will be fine.

If it turns out that the error rate depends (for physical reasons) on the the
size of the system, then for some size of QC, adding error correcting q-bits
will be counter-productive. Given that (in public) no-one has made a QC with
more than a handful of coherent q-bits, no-one really knows where the limits
are: it might well be that error-correction lets you build arbitrary sized
coherent QCs, or there might be insurmountable physical limits that prevent
that from happening. I look forward to people finding out! It's a fascinating
new experimental field of physics.

------
Eliezer
Probably not what it seems. <http://www.scottaaronson.com/blog/?p=954>

~~~
greenmountin
There's a theorist from ETH who also has been working with the D-Wave
computers, and visited Scott at MIT last week. There should be a new post
about it soon, I'm sure it will be mostly cold water.

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bhitov
D-Wave has a history of 'exaggeration'. I'd take anything they say with a
grain of salt.

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nraynaud
I don't know why, I keep thinking about the Great Oil Sniffer Hoax. They
really should show the stuff now.

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NamTaf
I wrote a bunch of words about this [1] when it surfaced 4 days ago, but this
NS article contains a bit more info. I'm really excited to see this
presentation now.

Yes they've talked themselves up previously but if they're willing to front up
with the evidence that they have something going on, I'm willing to give them
the benefit of the doubt. After all, there's something to be said when the
combined intellect of Google is willing to sink money in to your device.

[1]: <https://news.ycombinator.com/item?id=5679278>

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Ygg2
Title is misleading. An analogy would be submarines leave cars in the dust.

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zeus13i
I really wish there was more information in this article.

~~~
tristanj
Her website (linked in the article) has a copy of the paper.

<http://www.cs.amherst.edu/ccm/cf14-mcgeoch.pdf>

Quoting her paper, she used the D-Wave computer to solve instances of three
NP-Hard problems: Quadratic Unconstrained Binary Optimization (QUBO); Weighed
Maximum 2-Satis ability (W2SAT), and the Quadratic Assignment Problem (QAP).
She then compared the runtime with current software libraries run on Intel
Xenons.

~~~
zeus13i
Cheers! I missed that link.

------
ohwp
Related: When I first heard about quantum computers I thought a bit would be a
value of 0 to 1 (or 0V to 5V or something like that). I still am very curious
if such a computer could exist and would be useful. For example to do very
quick raytracing. Although inaccurate (I assume) it could still be very
useful.

~~~
czr80
<http://en.wikipedia.org/wiki/Analog_computer>

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ColinWright
There's another submission about this now:
<https://news.ycombinator.com/item?id=5700155>

Not sure if it gives more details, or if the different perspective will help,
but I thought it worth the cross-link.

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larrydag
I'm a bit confused by this article. Is it comparing computers or comparing
algorithms? CPLEX is software to run linear and mixed-integer optimization
algorithms. CPLEX is not a computer. Perhaps I misunderstood the article.
Could you not run CPLEX on the D-Wave computer?

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kriro
Free lunches in search and optimization are the tastiest.
[https://en.wikipedia.org/wiki/No_free_lunch_in_search_and_op...](https://en.wikipedia.org/wiki/No_free_lunch_in_search_and_optimization)

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tiziano88
I doubt that I would be able to buy a D-Wave for 2000$ (or whatever the price
of the "high-end desktop computer" they used in the comparison is). This
entire comparison seems just a joke to me.

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mikecane
I keep scratching my head over articles about the D-Wave. Is this ever going
to be something we'll see in our homes or are too many qubits required for
generalized, popular use?

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bsaul
I suppose it's a bit too early to be relevant, but does anyone knows what's
the gain in term of price at this point ?

~~~
Devilboy
They sell for $10 million. Is that what you mean?

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easytiger
wouldn't it be more fair to compare to an FPGA solution for those problem
sets?

~~~
Devilboy
Sure but that's not the point here. The important thing is that this quantum
computer actually WORKS. In 2 years classical computers will be maybe 5 times
faster. But this quantum computer will be 1000s of times faster (at these
specific problems) so very soon any comparison will be irrelevant.

~~~
easytiger
also i'm pretty sure if we used a computer of the same size as the quantum one
(a fairly large room) it may also have been a different story)

