18 May 2012

Quantum computing at ANU. Already knowing the answer helps

| johnboy
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The ANU informs us of progress by Dr André Carvalho, from the ARC Centre for Quantum Computation and Communication Technology and the Research School of Physics and Engineering, in the terrifying world of quantum computing by embracing noise.

“Most people have experienced some kind of computer error in their life – a file that doesn’t open, a CD that can’t be read – but we have ways to correct them. We also know how to correct errors in a quantum computer but we need to keep the noise level really, really low to do that,” he said.

“That’s been a problem, because to build a quantum computer you have to go down to atomic scales and deal with microscopic systems, which are extremely sensitive to noise.”

Surprisingly, the researchers found that the solution was to add even more noise to the system.

“We found that with the additional noise you can actually perform all the steps of the computation, provided that you measure the system, keep a close eye on it and intervene,” Dr Carvalho said.

“Because we have no control on the outcomes of the measurement – they are totally random – if we just passively wait it would take an infinite amount of time to extract even a very simple computation.

“It’s like the idea that if you let a monkey type randomly on a typewriter, eventually a Shakespearean play could come out. In principle, that can happen, but it is so unlikely that you’d have to wait forever.

“However, imagine that whenever the monkey types the right character in a particular position, you protect that position, so that any other typing there will not affect the desired character. This is sort of what we do in our scheme. By choosing smart ways to detect the random events, we can drive the system to implement any desired computation in the system in a finite time.”

Dr Carvalho said quantum information processing has the potential to revolutionise the way we perform computation tasks.

“If a quantum computer existed now, we could solve problems that are exceptionally difficult on current computers, such as cracking codes underlying Internet transactions.”

So two things:

1) If you already have the complete works of Shakespeare why are you trying to get the monkeys to re-type it? (That is how do you know if there’s a “correct” position to save if you don’t already know the outcome making the whole process useless)

2) The best example of uses for the technology is stealing our credit card numbers?

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The credit card example is raised because it’s an example of an encryption system that is currently beyond the reasonable code-cracking capability of the average punter with an off-the-shelf computer. The ability to either (a) factor (very) large numbers quickly and/or (b) mount a successful brute force attack (try every possible key that might have been used for the encryption) is still in the too-hard basket for the purposes of those who might be interested in the relatively small returns gained by cracking your credit card details, but it is mooted that a real, functioning quantum computer could pretty much trivialise such computational problems, rendering standard public key encryption as currently used for internet commerce fairly useless / insecure.

So, they need to add noise hey? The son of my neighbours plays in a death-metal band called Spermophage or some such nonsense, and they occasionally rehearse next door. They can provide all the noise any scientist would ever need in a thousand lifetimes.

I think that the last bit of the press release is a not-so-veiled appeal for funding from the Defence Signals Directorate.

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