Are there really functioning quantum computers?

Question

I saw this video on youtube on quantum computing. It says that a company called dwavesys has already made commercially available quantum computer. I checked on the website and it exists. I thought that this was still in theory and quantum computers are a distant future.
If what the video says is true, then the whole Public Key Infrastructure will collapse, right?

Answer 1

Yes, a fully functional quantum computer could solve the hard problems that are at the root of Public Key cryptography. And yes, D-Wave Systems have indeed produced a machine that seems to have some characteristics of quantum computing. But D-Wave have yet to demonstrate that their computer meets all the criteria of quantum computing needed to solve problems like the RSA problem or the discrete logarithm problem.

In fact some experts doubt if the D-Wave computer should be considered a quantum computer at all. MIT Associate Professor Scott Aaronson wrote on his blog:

For me, three crucial points to keep in mind are:

(1) D-Wave still hasn’t demonstrated 2-qubit entanglement, which I see as one of the non-negotiable “sanity checks” for scalable quantum computing. In other words: if you’re producing entanglement, then you might or might not be getting quantum speedups, but if you’re not producing entanglement, then our current understanding fails to explain how you could possibly be getting quantum speedups.

(2) Unfortunately, the fact that D-Wave’s machine solves some particular problem in some amount of time, and a specific classical computer running (say) simulated annealing took more time, is not (by itself) good evidence that D-Wave was achieving the speedup because of quantum effects. Keep in mind that D-Wave has now spent ~$100 million and ~10 years of effort on a highly-optimized, special-purpose computer for solving one specific optimization problem. So, as I like to put it, quantum effects could be playing the role of “the stone in a stone soup”: attracting interest, investment, talented people, etc. to build a device that performs quite well at its specialized task, but not ultimately because of quantum coherence in that device.

(3) The quantum algorithm on which D-Wave’s business model is based — namely, the quantum adiabatic algorithm — has the property that it “degrades gracefully” to classical simulated annealing when the decoherence rate goes up. This, fundamentally, is the thing that makes it difficult to know what role, if any, quantum coherence is playing in the performance of their device. If they were trying to use Shor’s algorithm to factor numbers, the situation would be much more clear-cut: a decoherent version of Shor’s algorithm just gives you random garbage. But a decoherent version of the adiabatic algorithm still gives you a pretty good (but now essentially ”classical”) algorithm, and that’s what makes it hard to understand what’s going on here.

So at least for now there is no practical quantum computer in existence that would undermine Public Key cryptography nor is one expected in the near future. Some experts believe that it's still a long way off.

BTW, for a great analysis of the impact of a future quantum computer on cryptography I would recommend Matthew Green's blog post on this subject.

Answer 2

Sort of, a couple unis have made experimental quantum processors but they haven't managed to match the power of a pocket calculator yet.