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Record-Low Error Rate For Qubit Processor
An anonymous reader writes "Thanks to advances in experimental design, physicists at the National Institute of Standards and Technology have achieved a record-low probability of error in quantum information processing with a single quantum bit (qubit) — the first published error rate small enough to meet theoretical requirements for building viable quantum computers. 'One error per 10,000 logic operations is a commonly agreed upon target for a low enough error rate to use error correction protocols in a quantum computer,' said Kenton Brown, who led the project as a NIST postdoctoral researcher. 'It is generally accepted that if error rates are above that, you will introduce more errors in your correction operations than you are able to correct. We've been able to show that we have good enough control over our single-qubit operations that our probability of error is 1 per 50,000 logic operations.'"
One error per bit per 50,000 logic operations should be accurate enough for non-technical people.
The problem is that once you know what the error is, you don't know where the error is.
I mean, once you know where the error is, you don't know what the error is.
I mean, err... I'm not sure.
"They have some catching up to do"
Yea, that's the whole point of their efforts.
An important thing to recognize is that most of this experiment was done with a single qubit. Practical quantum computing will need to have this sort of error rate for thousands of qubits. The good news is that the methodology they used looks very promising. They used microwave beams rather than lasers to manipulate the ions. This has been I think suggested before but this may be the first successful use of that sort of thing. As TFA discusses, this drastically reduces the error rate as well as the rate of stray ions.
We are starting to move towards the point where quantum computers may be practical. But we're still a long way off. In the first few years of the last decade a few different groups successfully factored 15 as 3*5 using a quantum computer. (15 is the smallest number which is non-trivial to factor using a quantum computer since the fast factoring algorithm for quantum computers- Shore's algorithm- requires an odd composite number that is not a perfect power. It is easy to factor a perfect kth power a bit by looking instead at the kth root. And factoring an even number is easily reduced to factoring an odd number. So 15 is the smallest interesting case where the quantum aspects of the process matter.) Those systems used a classical NMR system http://en.wikipedia.org/wiki/Nuclear_magnetic_resonance_(NMR)_quantum_computing which has since been seen as too limited. There are now a lot of different ideas of other approaches that will scale better but so far they haven't been that successful.
One important thing to realize is that quantum computers will not magically solve everything. They can do a few things quite quickly such as factor large numbers. But they can't for example solve NP complete problems to the best of our knowledge, and it is widely believed that NP complete problems cannot be solved in polynomial time with a quantum computer. That is, it is believed that BQP is a proper subset of NP. Unfortunately, right now we can't even show that that BQP is a subset of NP, let alone that it is a proper subset. Factoring big integers is useful mainly for a small number of number theorists and a large number of other people who want to break cryptography. There are a few other cryptographic systems that can also be broken more easily by a quantum computer but there's not that much else. However, that is changing and people getting a better and better understanding of what can be done with quantum computers. A lot of the work has involved clever stuff involving using quantum computers to quickly calculate stuff related to Fourier series. Moreover, once we get even the most marginally useful quantum computers there will be a lot more incentive to figure out what sorts of practical things can be done with them.
So the upshot is that these are still a long way off, but they are coming. The way it looked in the late 1990s or early 2000s it was reasonable to think that the technical difficulties would make them never practical. They still are a long way from being practical but right now it doesn't look like there are any fundamental physical barriers and it looks like in the long run the problems that do exist will be solved.
It isn't at all clear that D-Waves system is using any sort of quantum entanglement at all. D-Wave has had a long history of massive hype. See e.g. http://www.scottaaronson.com/blog/?p=431. It isn't at all clear that D-Waves commercial system can do any of the things that we expect a quantum computer to do like say factor integers using Shor's algorithm http://en.wikipedia.org/wiki/Shor's_algorithm. It seems that D-Wave has made a fast computer but there's very little evidence that it actually is using quantum processes any more than a normal computer. You could call your laptop a quantum computer because quantum mechanics is used in determining how the transistors function and you might be close to what D-Wave is claiming. The key is whether there are entangled qubits that we can get info from, and D-Wave has shown little indication of that. They have had a handful of research papers that sort of point in that direction but it is very hard to separate the hype from what they've actually done.
The problem is that people are not generally aware of what a quantum computer would be useful for. Why should I care if there is a quantum computer sitting under my desk? How do I benefit from quantum algorithms?
There are indeed tangible benefits to quantum computing, beyond just attacking public key cryptosystems. As an example, quantum computers can speed up certain search algorithms, which is one of the promised commercial applications of a quantum computer.
Personally, I put quantum computers in the same technological category as fusion power. The world would be an exciting place if we had cold fusion, and we are just a few steps from having it...but those steps are measured in light years and involve practical and theoretical challenges that are hard to address. I have no doubt that some day, we will answer those questions and build fusion reactors and quantum computers, but I get the feeling that that day is pretty far off.
Palm trees and 8
Most early computing errors were caused by memory (not RAM as early technologies weren't random access) The shift from mercury delay lines to magnetic cores saw a serveral-orders-of-magnitude drop in error rates, and the associated increase in the viability of general purpose computing.
Sometimes the reason why no one laughs is not because they didn't get the joke.
Chances are pretty good that your Quantum Computer will be running at liquid helium temperatures, maybe 4 Kelvin or so. Your general purpose CPU won't. There have been projects to run CPUs at liquid-nitrogen temperatures, and that already tends to get into mechanical difficulties; you're probably not going to be running your overclocked Xeon down at 4K.
Also, the quantum computer isn't likely to be something you're pumping a lot of data through - you're more likely to set it up, have it magically give you a probably-correct answer, and feed that answer to another computer that figures out if it's actually correct and then does something with it. For instance, if you're using the QC as an oracle to factor large numbers, you'll have it give you the result, then let your general-purpose machine multiply the factors together to find out if they give the right result, and then you'll use a general-purpose machine to rip off the bank account whose private key you just cracked.
Bill Stewart
New Fast-Compression-only CPR http://preview.tinyurl.com/dy575ks
And of course you remember the joke -- why did they call it the Pentium instead of the 586? They added 100 to 486 and got 585.939434521165242233345, which wouldn't fit on the package.
Do not mock my vision of impractical footwear