This site uses cookies. By continuing to use this site you agree to our use of cookies. To find out more, see our Privacy and Cookies policy.
Skip to the content

Share this

Free weekly newswire

Sign up to receive all our latest news direct to your inbox.

Physics on film

100 Second Science Your scientific questions answered simply by specialists in less than 100 seconds.

Watch now

Bright Recruits

At all stages of your career – whether you're an undergraduate, graduate, researcher or industry professional – can help find the job for you.

Find your perfect job

Physics connect

Are you looking for a supplier? Physics Connect lists thousands of scientific companies, businesses, non-profit organizations, institutions and experts worldwide.

Start your search today


Commercial quantum computer works, sort of

Is it or isn't it? The D-Wave 2X quantum processor (Courtesy: D-Wave Systems)

Is it or isn’t it? The D-Wave 2X quantum processor. (Courtesy: D-Wave Systems)

By Hamish Johnston

This morning I was speaking to quantum-entanglement expert Jian-Wei Pan, who shares the Physics World Breakthrough of the Year 2015 award for his work on quantum teleportation. Pan briefly mentioned research reported earlier this week by John Martinis, Hartmut Neven and colleagues at Google Research whereby a D-Wave 2X quantum computer was used to perform a computational task 100 million times faster than a classical algorithm.

This is a remarkable result, but does it mean that D-Wave’s controversial processors actually work as quantum computers? Some quantum-computing experts are urging caution in how the research is interpreted.

Based in Canada, D-Wave Systems is a commercial company that makes quantum processors based on superconducting circuits. The D-Wave 2X has more than 1000 such circuits, each representing a quantum bit (qubit) of information. Rather than being a quantum version of the universal processor in your laptop, the D-Wave 2X uses a protocol called quantum annealing to solve a very specific problem – how to find the global minimum value of a very complicated function.

The function can be thought of an energy landscape and the algorithm makes use of quantum-mechanical tunnelling to travel through the energy peaks and eventually find the lowest valley. The preprint from Google has the snappy title “What is the computational value of finite range tunnelling?” and looks at the special case where the energy peaks have a specific shape.

They found that the D-Wave 2X running quantum annealing is 100 million times faster at finding the global minimum than a conventional computer running a simulated annealing algorithm. In the latter, thermal fluctuations, rather than quantum tunnelling, allow the algorithm to “climb” over energy peaks.

Sounds great, but there are some important caveats, as MIT quantum-computer expert Scott Aaronson points out on his blog Shtetl-Optimized. It seems, for example, that there is another classical algorithm that can solve these problems just as fast as the D-Wave 2X. He also points out that because D-Wave 2X is designed specifically to solve this type of problem, its advantage may simply lie in its design rather than its “quantumness”. In other words, it’s just a well-designed classical computer.

I highly recommend reading Aaronson’s post, which was written after consulting Mathias Troyer of ETH Zurich, who is an expert on quantum annealing and has studied D-Wave’s processors. Also very illuminating is a post by Neven on the Google Research Blog called “When can quantum annealing win?”.

Physics World podcast: Quantum computing's challenges, triumphs and applications
Leading experts talk about their visions for the future of quantum computing
This text will be replaced

A few years ago I visited D-Wave’s headquarters in Vancouver and spoke to co-founder Geordie Rose. On the same trip I also talked to John Martinis and several other quantum-computing experts and put all of the conversations together into the above podcast. In it you will hear Rose explain how quantum annealing works and learn about Martinis’s vision for quantum computing.

Google and D-Wave are not the only organizations trying to build a quantum computer. Included in this year’s Physics World top 10 breakthroughs is the first ever silicon quantum logic gate, which was built by Andrew Dzurak, Menno Veldhorst and colleagues at the University of New South Wales and Keio University.


This entry was posted in General and tagged , . Bookmark the permalink.
View all posts by this author  | View this author's profile


  1. Jason Evans

    So this isn’t a quantum computer in the sense of something that can run Shor’s algorithm, right?

  2. jack curtis

    The Qubit-logic-gate architecture Shor’s algorithm relies upon is only 1 of 4 possible quantum-computer architectures, synthetic-annealing is another.


  • Comments should be relevant to the article and not be used to promote your own work, products or services.
  • Please keep your comments brief (we recommend a maximum of 250 words).
  • We reserve the right to remove excessively long, inappropriate or offensive entries.

Show/hide formatting guidelines

Tag Description Example Output
<a> Hyperlink <a href="">google</a> google
<abbr> Abbreviation <abbr title="World Health Organisation" >WHO</abbr> WHO
<acronym> Acronym <acronym title="as soon as possible">ASAP</acronym> ASAP
<b> Bold <b>Some text</b> Some text
<blockquote> Quoted from another source <blockquote cite="">IOP</blockquote>
<cite> Cite <cite>Diagram 1</cite> Diagram 1
<del> Deleted text From this line<del datetime="2012-12-17"> this text was deleted</del> From this line this text was deleted
<em> Emphasized text In this line<em> this text was emphasised</em> In this line this text was emphasised
<i> Italic <i>Some text</i> Some text
<q> Quotation WWF goal is to build a future <q cite="">
where people live in harmony with nature and animals</q>
WWF goal is to build a future
where people live in harmony with nature and animals
<strike> Strike text <strike>Some text</strike> Some text
<strong> Stronger emphasis of text <strong>Some text</strong> Some text