Quantum algorithm breakthrough

Feb 24, 2013

An international research group led by scientists from the University of Bristol, UK, and the University of Queensland, Australia, has demonstrated a quantum algorithm that performs a true calculation for the first time. Quantum algorithms could one day enable the design of new materials, pharmaceuticals or clean energy devices.

The team implemented the 'phase estimation algorithm'—a central quantum algorithm which achieves an exponential speedup over all classical algorithms. It lies at the heart of quantum computing and is a key sub-routine of many other important quantum algorithms, such as Shor's factoring algorithm and quantum simulations.

Dr Xiao-Qi Zhou, who led the project, said: "Before our experiment, there had been several demonstrations of quantum algorithms, however, none of them implemented the quantum algorithm without knowing the answer in advance. This is because in the previous demonstrations the were simplified to make it more experimentally feasible. However, this simplification of circuits required knowledge of the answer in advance. Unlike previous demonstrations, we built a full quantum circuit to implement the phase estimation algorithm without any simplification. We don't need to know the answer in advance and it is the first time the answer is truly calculated by a quantum circuit with a quantum algorithm."

Professor Jeremy O'Brien, director of the Centre for at the University of Bristol said: "Implementing a full without knowing the answer in advance is an important step towards practical quantum computing. It paves the way for important applications, including and quantum metrology in the near term, and factoring in the long term."

The research is published in .

Explore further: New imaging technique shows how cocaine shuts down blood flow in mouse brains

More information: 'Calculating unknown eigenvalues with a quantum algorithm' by Xiao-Qi Zhou, Pruet Kalasuwan, Timothy C. Ralph and Jeremy L. O'Brien in Nature Photonics. DOI: 10.1038/NPHOTON.2012.360

Related Stories

Quantum computing with recycled particles

Oct 23, 2012

A research team from the University of Bristol's Centre for Quantum Photonics (CQP) have brought the reality of a quantum computer one step closer by experimentally demonstrating a technique for significantly reducing the ...

Efficient distributed quantum computing

Feb 21, 2013

(Phys.org)—A quantum computer doesn't need to be a single large device but could be built from a network of small parts, new research from the University of Bristol has demonstrated. As a result, building ...

Madrid duo fire up quantum contender to Google search

Dec 14, 2011

(PhysOrg.com) -- Two Madrid scientists from The Complutense University think they have an algorithm that may impact the nature of the world's leading search engine. In essence, they are saying Hey, world, ...

Recommended for you

What time is it in the universe?

Aug 29, 2014

Flavor Flav knows what time it is. At least he does for Flavor Flav. Even with all his moving and accelerating, with the planet, the solar system, getting on planes, taking elevators, and perhaps even some ...

Breakthrough in light sources for new quantum technology

Aug 29, 2014

One of the most promising technologies for future quantum circuits are photonic circuits, i.e. circuits based on light (photons) instead of electrons (electronic circuits). First, it is necessary to create ...

User comments : 17

Adjust slider to filter visible comments by rank

Display comments: newest first

Tausch
1.7 / 5 (6) Feb 24, 2013
What answer does not depend on the question?
None of above?
j/k
Tausch
2 / 5 (4) Feb 24, 2013
Is there agreement with previous circuits?
javjav
4.6 / 5 (10) Feb 24, 2013
What answer does not depend on the question?

Politician answers. They never answer what they are asked for
LizR
2.9 / 5 (10) Feb 24, 2013
"An international research group led by scientists from the University of Bristol, UK, and the University of Queensland, Australia, has demonstrated a quantum algorithm that performs a true calculation for the first time."

Dr Xiao-Qi Zhou, who led the project, said: "Before our experiment, there had been several demonstrations of quantum algorithms, however, none of them implemented the quantum algorithm without knowing the answer in advance.


Are they suggesting that experimenters who already knew the prime factors of 15 cheated, and just published a paper _saying_ they'd done it?

How does knowing the answer in advance stop the quantum computer performing a "true calculation" ?

Not trying to detract from their achievement, but whenever someone starts dissing previous attempts at what they've achieved, I get a hackle-raising reaction. (Possibly this dates back to so-called improved versions of "Willy Wonka and the Chocolate Factory", "Psycho" and "Doctor Who"...)
tkjtkj
5 / 5 (1) Feb 24, 2013
quoting LizR : "How does knowing the answer in advance stop the quantum computer performing a "true calculation" "
As i misunderstand the article, knowing the answer allowed previous workers to 'tune' their process , nudging it more-efficiently towards the answer they wanted. These workers, however, in their own work, then ignored their own a priori knowledge of correctness of the result of their own assignment task they presented to the 'device'.
So, in their own minds, they did not 'tune' the algorithm.
Unfortunately, nothing about the algorithm,the problem, or the answer is presented (which, actually, might be parts of their own algorithm: the last step of which might be: 'deny all fudgings' ...
Now, the price they pay would be not knowing if their own algorithm's result is correct .. but then, nor do we.

Tausch
1 / 5 (4) Feb 24, 2013
lol
Fives for imagination and ingenuity.
Tausch
2 / 5 (4) Feb 24, 2013
As soon as an open access version is available I'll post again.
Still looking.
Meyer
5 / 5 (4) Feb 25, 2013
As soon as an open access version is available I'll post again.
Still looking.

Well there's this. http://arxiv.org/...76v1.pdf
Tausch
1 / 5 (2) Feb 25, 2013
Sign of thks is rating as well.
Tausch
1 / 5 (1) Feb 25, 2013
@DWorth
Refrain from rating levity. No comments on the article have been made yet.
Roach
5 / 5 (1) Feb 25, 2013
For everyone asking what difference knowing the answer makes. If I ask you how many beers are left in the case and you write an app to tell you how many are in there. you can write that app in such a way as to prevent obviously wrong answers, such as omitting values higher than 24. you can have a bad program that won't give you a wrong answer. it also wouldn't scale to answer how many beers are in my fridge? At the gas station, or in busch gardens. it's the difference between build a program that can count to ten or building a program that can count, and using it as a subroutine to count to any value you need. only more complex.
antialias_physorg
4.2 / 5 (5) Feb 25, 2013
Well there's this. http://arxiv.org/...76v1.pdf

If I'm reading the paper correctly (and I'm not at all sure that I am.) then the pre-knowledge of the answer in previous works has more to do with how the reading mechanism at the end was constructed (the one that transforms the qbits of the answer into regular bits).
It's not so much that this was 'hard coded' to give a certain result but that it would more easily read the expected result than any other (i.e. if the algorithm had 'failed' it wouldn't read anything. It would only read a result if the algorihm succeeded.)

but whenever someone starts dissing previous attempts

They're not dissing previous works. They are just showing that they have made an extension that will read any result equally well - not just the one that is expected.

Previous works were all about getting quantum calculations to work at all. This work is a step towards more general usefulness.
Tausch
1 / 5 (1) Feb 25, 2013
So far, I read an attempt in optics that asserted the successful implantation of IPEA was undermined by an aspect of the experiment that made the use of IPEA meaningless. The exact phase was known beforehand. Simply, you want to be in a position never to be able to decompose U with the information U provides. And suggestions are made to be in this position. Simple.
Yep. tkitkj misunderstood correctly.
Tausch
1 / 5 (2) Feb 25, 2013
implantation=implementation
quirk=quark
lol
Tausch
1 / 5 (1) Feb 25, 2013
Repost:
So far, I read an attempt in optics that asserted the successful implementation of IPEA was undermined by an aspect of the experiment that made the use of IPEA meaningless. The exact phase was known beforehand. Simply, you want to ever be in a position to be able to decompose U with the information U provides. And suggestions were made this. Simple.
Yep. tkitkj still misunderstood correctly.

Tausch
1 / 5 (1) Feb 25, 2013
Re/repost
Simply, you DON'T ever want to be in a position
to be able to decompose U with the information U provides. And suggestions were made to avoid this. Simple.

You'd never know this from my writing errors I have exhibited above.

jibbles
not rated yet Mar 02, 2013
so begins the slow death knell of r.s.a. encryption...