How a Quantum Physicist Invented New Code to Achieve What Many Thought Was Impossible

Quantum Computer Code Concept

Dr. Benjamin Brown from the University of Sydney has developed a new error-correcting code for quantum computers. By adapting a 3D code to a 2D framework, he has freed up more hardware for useful calculations and provided a new approach for designing better quantum microchips.

Error suppression opens pathway to universal quantum computing.

A scientist at the University of Sydney has achieved what one quantum industry insider has described as “something that many researchers thought was impossible.”

Dr. Benjamin Brown from the School of Physics has developed a type of error-correcting code for quantum computers that will free up more hardware to do useful calculations. It also provides an approach that will allow companies like Google and IBM to design better quantum microchips.

Dr Benjamin Brown

Dr. Benjamin Brown is a Research Fellow at the University of Sydney Nano Institute and School of Physics. Credit: University of Sydney

He did this by applying already known code that operates in three dimensions to a two-dimensional framework.

“The trick is to use time as the third dimension. I’m using two physical dimensions and adding in time as the third dimension,” Dr. Brown said. “This opens up possibilities we didn’t have before.”

His research is published today (May 22, 2020) in Science Advances.

“It’s a bit like knitting,” he said. “Each row is like a one-dimensional line. You knit row after row of wool and, over time, this produces a two-dimensional panel of material.”

Fault-tolerant quantum computers

Reducing errors in quantum computing is one of the biggest challenges facing scientists before they can build machines large enough to solve useful problems.

“Because quantum information is so fragile, it produces a lot of errors,” said Dr. Brown, a research fellow at the University of Sydney Nano Institute.

Professor Stephen Bartlett

Professor Stephen Bartlett leads the quantum information theory group at the University of Sydney. He is also Associate Dean for Research in the Faculty of Science. Credit: University of Sydney

Completely eradicating these errors is impossible, so the goal is to develop a “fault-tolerant” architecture where useful processing operations far outweigh error-correcting operations.

“Your mobile phone or laptop will perform billions of operations over many years before a single error triggers a blank screen or some other malfunction. Current quantum operations are lucky to have fewer than one error for every 20 operations — and that means millions of errors an hour,” said Dr. Brown who also holds a position with the ARC Centre of Excellence for Engineered Quantum Systems.

“That’s a lot of dropped stitches.”

Most of the building blocks in today’s experimental quantum computers — quantum bits or qubits — are taken up by the “overhead” of error correction.

“My approach to suppressing errors is to use a code that operates across the surface of the architecture in two dimensions. The effect of this is to free up a lot of the hardware from error correction and allow it to get on with the useful stuff,” Dr. Brown said.

Dr. Naomi Nickerson is Director of Quantum Architecture at PsiQuantum in Palo Alto, California, and unconnected to the research. She said: “This result establishes a new option for performing fault-tolerant gates, which has the potential to greatly reduce overhead and bring practical quantum computing closer.”

Path to universal computation

Start-ups like PsiQuantum, as well as the big technology firms Google, IBM, and Microsoft, are leading the charge to develop large-scale quantum technology. Finding error-correcting codes that will allow their machines to scale up is urgently needed.

Dr. Michael Beverland, a senior researcher at Microsoft Quantum and also unconnected with the research, said: “This paper explores an exciting, exotic approach to perform fault-tolerant quantum computation, pointing the way towards potentially achieving universal quantum computation in two spatial dimensions without the need for distillation, something that many researchers thought was impossible.”

Two-dimensional codes that currently exist require what Dr. Beverland refers to as distillation, more precisely known as ‘magic-state distillation’. This is where the quantum processor sorts through the multiple computations and extracts the useful ones.

This chews up a lot of computing hardware just suppressing the errors.

“I’ve applied the power of the three-dimensional code and adapted it to the two-dimensional framework,” Dr. Brown said.

Dr. Brown has been busy this year. In March he published a paper in the top physics journal Physical Review Letters with colleagues from EQUS and the University of Sydney. In that research he and colleagues developed a decoder that identifies and corrects more errors than ever before, achieving a world record in error correction.

“Identifying the more common errors is another way we can free up more processing power for useful computations,” Dr. Brown said.

Professor Stephen Bartlett is a co-author of that paper and leads the quantum information theory research group at the University of Sydney.

“Our group at Sydney is very focused on discovering how we can scale up quantum effects so that they can power large-scale devices,” said Professor Bartlett, who is also Associate Dean for Research in the Faculty of Science.

“Dr. Brown’s work has shown how to do this for a quantum chip. This type of progress will enable us to go from small numbers of qubits to very large numbers and build ultra-powerful quantum computers that will solve the big problems of tomorrow.”


“A fault-tolerant non-Clifford gate for the surface code in two dimensions” by Benjamin J. Brown, 22 May 2020, Science Advances.
DOI: 10.1126/sciadv.eaay4929

“Fault-Tolerant Thresholds for the Surface Code in Excess of 5% under Biased Noise” by David K. Tuckett, Stephen D. Bartlett, Steven T. Flammia and Benjamin J. Brown, 30 March 2020, Physical Review Letters.
DOI: 10.1103/PhysRevLett.124.130501

This research was supported by the University of Sydney Fellowship Program and the Australian Research Council via the Centre of Excellence in Engineered Quantum Systems (EQUS) project number CE170100009.

For the PRL paper, access to high-performance computing resources was provided by the National Computational Infrastructure (NCI), which is supported by the Australian Government, and by the Sydney Informatics Hub, which is funded by the University of Sydney.

24 Comments on "How a Quantum Physicist Invented New Code to Achieve What Many Thought Was Impossible"

  1. Bob Schaserling | May 22, 2020 at 2:49 pm | Reply

    I guess it is just me. I have been building fault tolerant computing systems for decades. Didn’t think it was a big deal.

  2. Now, now… Don’t get all tangled up over small qubits…

  3. Toni Christina | May 22, 2020 at 4:54 pm | Reply

    Waite, Waite, don’t tell me, you’re a physicist.

  4. No, but I play one during lockdown.

  5. As noted fault tolerance was invented the day faults were, however fail through is just an extended failure.

    This changes not one single thing, logic remains supreme.

    • just wait until dr. Benjamin Brown find a way to use mass as a tool to resist the change in time and add this functionality to the system.

  6. Quantum Erlang?

  7. To be or not to be at fault, that is the entanglement

  8. Christ, they should disable the comment section. And you should all be ashamed of yourselves.

  9. Richard Pizzoferrato | May 23, 2020 at 4:27 am | Reply

    I have spent my entire life in Computer Enginerring…… detection, correction, reporting, recovery, pulling signal out of overwhelming noise.

    studying errors, creating errors, documenting errors……. and speculating on errors in The Mystical Marvelous Machines, Giant Electronic Intelligence of the future (there is always one) not quite there yet… and now errors in the human genome their consequences, their identification…

    There is only one quantum computer and it is in our mind…… defined by the human genome..

    Have fun, all…

    • Achievement unlocked: you just invented the Table and the Matrix. Reading this, it kinda seems that there are very few that do any research on quantum computing. So nobody thought about adding time all these years? Interesting.

  10. Patrick Phelps | May 23, 2020 at 7:46 am | Reply

    I have spent my entire life being grossly ignorant of such things as quantum computing. So, from a layman’s point of view, if I understand this correctly, we are attempting to greatly reduce the number of errors associated with this technology? As the article points out, even though it could be eons before a cell phone blanks out, how could we trust ANY results, EVER? I would hate to be on board a star ship that is reliant upon a system that is “mostly” error-free!

    • If we thought from the beginning of technology that we had to have error-free computing, we would never have gotten off the ground. If we were aware of how many errors Windows actually had at the beginning, it probably would never have been put to market. Even today Windows 10, as well as Apple devices, have faults that could have stopped them from being released if we had to have error-free computation.

    • Haha, very interesting. Makes me think about how many times I have been on board airplanes with systems that are “mostly” error-free.

  11. Am I the only one that thinks it’s a hoot that a Dr. Brown is using three dimensional code using time as the third dimension? I can’t wait til he bops his head on a toilet and comes up with the flux capacitor!

  12. Renaissance musketeer | May 23, 2020 at 10:15 am | Reply

    Quantum computing starts at 4 dimensions, with first three
    X, Y, Z, and then Time..

  13. …and Dr. Brown has a beautiful smile, too. This article reminds me of the story of John Nash, portrayed on screen by Russell Crowe in “A Beautiful Mind”. I think there should be more touting of scientists to encourage young people to grow up thinking of science as a career choice.

  14. Quantum computing? Who needs it..
    On the other hand… it sure would be nice to have my own personal, Real-time Fractal Animation G2. enerator to monkey around with…

  15. peter cameron | May 23, 2020 at 7:43 pm | Reply

    Are ‘errors’ anything other than unwanted phase shifts that cause loss of coherence between qbits, loss of entanglement?
    Phase shifts are caused by impedances. To what extent are quantum computer designers paying attention to impedance matching?
    To what extent are matching aware designers also aware of impedance quantization? quantum Hall impedance is well known, made accessible by its scale invariance, a topological property shared with all inverse square potentials. Unless one knows where to look, scale dependent impedance quantization is not so obvious. However, with some thought it becomes clear that quantization applies to both topological and geometric impedances. Given that ields are quantized in quantum field theory, it is unavoidable that impedances are likewise quantized.

  16. I’m confused. How the hell do you “code time in 1 dimension, and space in 2 dimensions, in order to get rid of errors” like *what does that even mean*

  17. This technology don’t work in 3 dimension. They don’t know wet.

  18. Patrick G Tracy | May 24, 2020 at 11:13 am | Reply

    “Useful problems?”

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