
A Reality Check on Quantum Computers - wellokthen
https://www.wsj.com/articles/a-reality-check-on-quantum-computers-11575041271
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abdullahkhalids
> The most profound issue, however, concerns the meaning of quantum supremacy.
> After all, it doesn’t take qubits to solve important quantitative problems
> faster than any classical computer. Any carbon atom can “calculate” the
> solution of a very important practical problem—how does carbon
> behave?—simply by doing its thing.

The author [1] is trivializes the notion of computational machine. Calculating
using a classical/quantum computer vs doing the experiment, differ in at least
two important respects.

(1) Computers are fully programmable while experimental setups are usually
specific to calculating a choice few parameters. The universality of various
computational models implies exactly this: a well designed physical machine
can simulate any other physical system, assuming you have the correct model of
the system. A carbon-spectra calculating experimental setup does not have this
universal programmability.

(2) A computer often yields the correct answer with a lot fewer resources,
again assuming your model of the simulated system is correct. This is because,
a well designed computation can ignore unneeded part of the model, which the
experimental system must include. In fact, computers are precisely useful
where we can get such an advantage, and useless where we can't. As the author
points out this is not possible for some carbon atoms, and it also is not
possible for medical drugs. But it is possible for a wide variety of other
systems - say rockets to the moon.

[1] a Nobel prize winner, so take my words with a grain of salt.

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orbifold
I think he is well aware of this. The current quantum device Google build is
however not much different than a sufficiently complex other physics
experiment and so far they have not been able to demonstrate that it is
capable of fault-tolerant error-corrected computation (which they basically
won't be able to do in the foreseeable future).

~~~
jessriedel
Everyone agrees that Sycamore isn't fault tolerant, but I don't think many
people agree that it is "not much different than a sufficiently complex other
physics experiment". Here's a test: do you think there is _any_ device that
could be achieve quantum supremacy without being fault tolerant? If not, then
your complaint isn't specific to Sycamore at all.

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KKKKkkkk1
Wikipedia blurb about the author:

 _Frank Anthony Wilczek ( /ˈwɪltʃɛk/;[2] born May 15, 1951) is an American
theoretical physicist, mathematician and a Nobel laureate. He is currently the
Herman Feshbach Professor of Physics at the Massachusetts Institute of
Technology (MIT), Founding Director of T. D. Lee Institute and Chief Scientist
Wilczek Quantum Center, Shanghai Jiao Tong University (SJTU), Distinguished
Origins Professor at Arizona State University (ASU) and full Professor at
Stockholm University._

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neonate
[http://archive.is/p5DAW](http://archive.is/p5DAW)

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mathattack
I’ve noticed that the MBA crowd (including some friends!) who jumped into the
Bitcoing bandwagon at 10K are now hawking Quantum Computing.

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barbecue_sauce
How does one hawk Quantum Computing?

~~~
LeftHandPath
People riding the bandwagon and generally talking about it like they're in on
it when they don't know what a qubit or bell state is (or how to read braket
notation).

It's a similar line to AI - if the people talk about it like it has the
potential to (and eventually will) destroy the world, they probably don't know
much about it (in that case they're conflating sentience with intelligence,
and ignoring the word "artificial).

The people who are working on it right now will - like with AI - tell you that
it's in its infancy, that its current applications are more limited than they
are made to appear in pop-culture, and that (generally) things are harder and
take longer than people pretend.

Which is exactly what the author of the WSJ article is getting at (because
he's not a hawker - he knows):

> "There’s little doubt that, in the long run, computers that exploit quantum
> features of matter will dramatically enhance our ability to address useful
> problems. But we’re not there yet, nor is success guaranteed. For the
> foreseeable future we will have, at best, a “quantum advantage” in well-
> chosen applications, not “quantum supremacy” along a broad front."

~~~
perl4ever
"It's a similar line to AI - if the people talk about it like it has the
potential to (and eventually will) destroy the world"

Surely we can all agree that it doesn't take human or better intelligence to
destroy the world.

...how about a nice game of chess?

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false-mirror
I'm disappointed that this article doesn't answer my only real question about
quantum computers: What does a reasonable expectation look like? What is the
range of potential performance gains?

I understand that this is the frontier and no one has any definite answers,
but I hear everything from "trivial" improvements to "insta-crack AES-256"
(thousands of trillion trillion trillion trillions times faster).

Does anyone have a well informed upper/lower bound estimate?

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ahelwer
Quantum computers won't insta-crack AES. They only give a square-root speedup
for symmetric crypto (so you can double the key length for equivalent
security) with Grover's algorithm. It's public-key crypto algorithms based on
prime factorization or the descrete log problem which will be broken by
Shor's. However, running Shor's algorithm on production key sizes requires a
_huge_ quantum computer (with millions of qbits) and Scott Aaronson says he
would be "astounded" if this was accomplished within the next decade.

Improvements are believed to be exponential when simulating physical quantum
systems.

~~~
nestorD
This.

Quantum computing have be designed to solve a single problem : the simulation
of quantum systems on a classical computer is very slow, lets build a quantum
computer so that it will be fast.

It might seem like a fringe use case but it matters (a lot) to industrials and
researchers in a wide variety of topics.

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waheediqbal
The first generation of Quantum Computers are nothing more than a huge
scientific experiment.

~~~
leereeves
Companies like Rigetti are betting on making money by building quantum
computers.

Whether they prove to be right or wrong, their motives aren't primarily
scientific.

~~~
nosianu
Or, not exactly unheard of, they aim at finding a buyer for themselves well
before a time when it may become clear whether the product would really be
viable or not. In those cases the product is the company itself and they don't
need to have a finalized working and useful real product. Works especially
well in "hype" topics where hope can more easily win against common sense (of
the buyer).

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euroPoor
What does this article really ‘reality check’? The editor’s understanding of
quantum computing?

~~~
DebtDeflation
I think the intent is to reality check some of the marketing coming out of
Google/IBM/Intel/Rigetti that seem to be trying to imply that quantum
computers actually exist today (as opposed to laboratory science experiments
which are what actually exist now) and are just a few years away from
commercialization after which some form of Moore's Law will take hold. I've
seen a number of Pop Sci articles that say things like "today's quantum
computers fill an entire room like 1960s mainframes" or "today's leading edge
quantum computers contain 53 qubits, experts say we'll need n-qubits to solve
x problem which is intractable on a classical computer". All of this is
intended to imply we just need to figure out how to shrink these existing
quantum computers down while expanding the number of qubits available and
we're about to have a quantum repeat of the PC Revolution. Nothing could be
further from the truth.

