How close are we to building a quantum computer?

After trying to decipher the wiki article on this subject, I came to the conclusion that they have not yet built a quantum computer but they are actively working on it. I know its hard to predict the future but here are a few questions.

  1. Will these things be around one day?
  2. Will it be in the next 10, 20, 30 years or longer?

Nope, you came to the wrong conclusion.

Well, perhaps not - there are a number of prototype quantum computers that have been developed - they do actually work, but their information processing capabilities are limited.

The question of whether we will be able to build a large-scale quantum computer is still unanswered.

The post is interesting, but it didn’t even mention the problem that everyone expects a quantum computer to solve: factoring large integers and thereby breaking RSA cryptograms. Since a good implementation of RSA probably uses a 1000 digit (approximately 3000 bits) a quantum computer that can deal with that will need to maintain at least 3000 qubits and nothing in that post suggested that it was up to that. The last I heard (admittedly several years ago) is that the largest number they had factored was 15, which they discovered to be 3 times 5. I will believe it when I see it.

You don’t believe that 3x5=15? You are a skeptic! :smiley:

This company has been putting out a lot of hype but not many details. See here and here for some discussion from a quantum computation scientist.

Suffice to say, we are very very far away from building a quantum computer that can do anything useful. The current prototypes don’t scale up to be able to solve practical problems. There are skeptics who believe it cannot be done at all.

This guy also studies quantum computation and has a bit more positive opinion of D-Wave.

Most of the articles I have read, read like PR pieces. A company has claimed to have built one and has even demonstrated it, but since it’s essentially a “black box” there is no proof in it.

I don’t understand the first thing about quantum computers but that is not part of my question. From what has presented here, it is unlikely that I will be able to purchase one from Dell in the near future.
I had heard about them on various radio programs and was curious about their progress.
P.S. 16 qbits (whatever they are) doesn’t sound like a lot. Sounds like there is a long way to go!

I don’t know much about the specifics of D-Wave’s claim. That said, even if they do have a 16-qubit quantum computer, claims that they’ll soon extend this to hundreds or thousands of qubits are almost certainly nothing but hype. Scalability is a huge hurdle when it comes to quantum computation – essentially, the problem is that you want your qubits to interact with each other but not with the surrounding environment, and this becomes harder and harder to achieve the more qubits you have.

But as far as I can tell from reading news articles, D-Wave hasn’t even provided any evidence that they have a 16-qubit quantum computer. Apparently, their demo consisted of displaying a bunch of calculations that might just as well have been performed on a classical computer.

We’re very close to developing a quantum computer.

But we can’t tell how close.

To be more specific, we can tell how quickly we’re moving toward a solution, but we don’t know how close we are. If we knew how close we were, we wouldn’t be able to tell how quickly we’d get one.

You ruined the joke by examining it.

:smiley:

I don’t know if your are ever going to buy one from Dell or have one on your desk. They are completely unlike digital computers today and it isn’t clear that any individual would need one. That sound oddly like the early forecasts for digital computers but that is still the way it is looking now. Quantum computers simultaneously solve every outcome of hideously complex problems. That is good for mathematicians and security analysts but I that doesn’t mean it will be the best thing to play games and chat online with.

I should add that optical computers would be the most logical successors to our computers when development starts to run out of steam. There is lots of additional potential there.

I’m not sure exactly what you mean, but I don’t think this is true. The current state of knowledge is that the only thing that a (hypothetical) quantum computer could do that a digital computer can’t is factor numbers in polynomial time. Apart from that, the set of problems solvable by a quantum computer and a digital computer are the same, although a quantum computer can solve some of them a bit faster.

It is possible (but unlikely) that quantum computers are able to solve harder problems than factoring, but it is equally possible that an algorithm will be found that allows digital computers to be able to factor in polynomial time. Right now, whether quantum computers are significantly more powerful than digital computers is very much an open question.

Like laser fusion, quantum computers are 25 years off.

And will stay that way for the next century. :smiley:

Eleusis’ law: If “they” say new technology is 25 years away, that means not in our lifetime.

edit: believe it or not, I skimmed your first line, Exapno, and quickclicked quickreply.

But I did ask a similar question a few years ago, citing a paper which touted something like “artificial lungs by 2010”…

We are in agreement, but I didn’t mean to steal your thunder.

What you say is largely accurate in terms of why anyone is funding research on quantum computation - the vast majority of funding is coming either directly or indirectly from the military/intelligence agencies. However, there is one other very significant area in which quantum computers would be useful: simulating other quantum systems. In particular, cold atoms in optical lattices offer a very large number of qubits with relatively easily controlled interactions which could be used for simulating condensed matter systems.

Also, while the improvement is much less significant than in factorization, Grover’s Algorithm can be used to search very large databases in O(N^0.5) time, while classical computers can only manage O(N) time.

ET Clarify: Simulating quantum systems is (for complex systems) very demanding on classical computation time. Quantum computers are better because they can automatically include many quantum effects, rather than trying to include them by numerical solution of the Schrodinger equation.

Ah, I hadn’t thought of that. Good point.

That’s what I meant by “a bit faster”. It’s “only” a polynomial speed-up. :wink: