Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Innovative computer under scrutiny

18.03.2014

D-Wave – a special computing machine with this name has been getting computer scientists and physicists talking for a number of years now.

The Canadian technology company of the same name is advertising the machine as a quantum computer. However, whether or not the machine does in fact use quantum effects is the subject of controversial debate amongst experts in the field. If it does, then this would make D-Wave the world's first commercially available quantum computer.

The company sold its system to illustrious customers, piquing the interest of the scientific community and of bloggers and journalists even further. For example, the very first machine was sold to the US arms manufacturer Lockheed Martin in 2011, which provided it to the University of Southern California in Los Angeles for tests. Last year, Google purchased the second machine. D-Wave can solve certain mathematical problems referred to as optimization problems by searching for and finding the state of lowest energy in a system. That is why the technology is of interest to this company.

Analogue device, not a quantum computer

But the question of whether or not D-Wave does in fact use quantum effects is not the only disputed aspect of the machine. Scientists and bloggers have also expressed doubt as to whether the machine can be accurately described as a computer at all. There are also different opinions regarding whether or not it can compute faster than a traditional computer. To find answers to these questions, Matthias Troyer, a professor at the Institute for Theoretical Physics at ETH Zurich, worked together with colleagues at the University of Southern California in Los Angeles and tested the system located there.

In their study, which has now been published in the journal Nature Physics, the Swiss-American team of researchers comes to a conclusion that is not clear cut. On the one hand, the scientists confirm that D-Wave does in fact use quantum effects. However, in other areas the researchers are more critical: "D-Wave is an analogue device, a prototype that can be used to solve optimization problems. It would be more accurate to describe it as a programmable quantum simulation experiment", says Professor Troyer, an internationally recognized expert in the field. "D-Wave is certainly not a universal quantum computer."

Quantum effects, but only momentarily

The researchers came to their conclusions by writing thousands of computing problems of differing complexity and solving each of these one thousand times on three systems: once on D-Wave and twice on a simulation programme for optimization problems that ran on a traditional computer. The simulation programme ran in two modes, where one took quantum effects into consideration and one did not. For each task, the scientists made a note of how often which system delivered the right solution. It turned out that D-Wave behaves in the same manner as the simulation that accounted for quantum effects but differently from the simulation that did not.

The scientists were amazed by this result, because the quantum effects of D-Wave are extremely short-lived, lasting only a few billionths of a second. Physicists describe this as coherence time. Because it generally takes around 500 times longer to solve an optimization problem, most experts assumed that the quantum effects with D-Wave simply could not play any role. And yet they do, as the results of the researchers have shown. "It appears that the quantum effects do not necessarily have to be coherent all of the time in order to have a significance", explains Troyer.

Not faster than a traditional computer

When one considers that research into quantum computers is carried out primarily because of the promise of hugely accelerated computing speeds, then another conclusion arrived at by the researchers is particularly significant, namely that D-Wave is not faster than a traditional computer.

The speed of D-Wave is the subject of intense debate amongst experts in the field, particularly since a publication by a computer scientist at Amherst College caused uproar in May of last year. According to the publication, depending on the computing problem, D-Wave is several thousands of times faster than a traditional computer. The researcher examined a version of D-Wave that almost corresponds to the current version, in existence for one year, with a computing capacity of 512 quantum bits (qubits). By contrast, the study carried out by the researchers from ETH Zurich is based on a predecessor version with 108 qubits.

"Not only have we demonstrated that a traditional computer is faster than the 108-bit version of D-Wave", Troyer responds. "We also used a traditional computer to solve the same problems that can be solved by the new 512-qubit version or hypothetically even higher-performing machines." When these findings are compared with those of the researcher from Amherst College, it becomes clear that D-Wave is consistently slower than a traditional computer for the tests performed. According to Troyer, the problem with the Amherst study is that it compared fast algorithms for D-Wave with slower algorithms for traditional computers. "We developed optimized algorithms for traditional computers. This allows us to match even the current 512-qubit version of D-Wave", explains Troyer. "Nobody knows at present whether a future quantum system like D-Wave with more qubits will offer any advantages over traditional systems. This is an important question, and we are currently using experiments on the 512-qubit machine to find the answer."

[Box:] Quantum annealing with D-Wave

An imperfect crystal structure made of metals or glass can be improved by heating the material until it glows and then cooling it in a controlled environment. In the hot material, the atoms have a certain freedom of movement and can realign in a more refined crystal lattice. This craft technique is thousands of years old and called annealing. A comparable method has also been in use for the past 30 years in computer science as an optimization process and is called annealing as well.

A typical question that can be answered using this method is the search for the lowest point of a landscape. To understand this better, it is possible to imagine a thought experiment where a sphere located in a landscape is subjected to jolts depending on temperature. At high temperatures, the sphere can hop around the entire landscape. The lower the temperature, the harder it is for the sphere to cross mountains. If an experiment is repeated several times, starting with high temperatures and slowly cooling, at the end of the experiments the sphere will frequently be found at the lowest point of the landscape.

When the D-Wave system solves an optimization problem, it uses a similar procedure. In addition, quantum physics and thus tunnel effects also have a role to play: the sphere (remaining with the above example) is also in a position to tunnel underneath the mountains in the landscape. With D-Wave, however, it is not spheres that are moving. Instead, individual superconducting circuits act as quantum simulations or artificial atoms. For this purpose, the system must be cooled to temperatures of almost absolute zero. The circuits simulate the spin of atoms. There is the spin "up" and the spin "down" as well as (because quantum physics plays a role) superposition of the spins, the state of "both up and down". In the D-Wave circuits, the spins are simulated by the direction in which the electrical current is flowing. Physicists call the optimization procedure used by D-Wave "quantum annealing".

###

Literature reference

Boixo S, Rønnow TF, Isakov SV, Wang Z, Wecker D, Lidar DA, Martinis JM, Troyer M: Evidence for quantum annealing with more than one hundred qubits. Nature Physics, 2014, 10: 218-224, doi: 10.1038/nphys2900 [http://dx.doi.org/10.1038/nphys2900]

ETH News & Media Relations | EurekAlert!
Further information:
http://www.ethz.ch

Further reports about: D-Wave ETH landscape quantum computer quantum effects temperatures

More articles from Information Technology:

nachricht Deep Learning predicts hematopoietic stem cell development
21.02.2017 | Helmholtz Zentrum München - Deutsches Forschungszentrum für Gesundheit und Umwelt

nachricht Sensors embedded in sports equipment could provide real-time analytics to your smartphone
16.02.2017 | University of Illinois College of Engineering

All articles from Information Technology >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Stingless bees have their nests protected by soldiers

24.02.2017 | Life Sciences

New risk factors for anxiety disorders

24.02.2017 | Life Sciences

MWC 2017: 5G Capital Berlin

24.02.2017 | Trade Fair News

VideoLinks
B2B-VideoLinks
More VideoLinks >>>