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How a quantum physicist invented a new code to achieve what many thought was impossible



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Error suppression opens the way to universal quantum computing.

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

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

Dr. Benjamin Brown

Dr. Benjamin Brown is a 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 works in three-dimensional to a two-dimensional frame.

“The trick is to use time as the third dimension. I use two physical dimensions and over time add as the third dimension, ”Dr. Brown. “This opens up opportunities we didn’t have before.”

His research is published today (May 22, 2020) in Scientific progress.

“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. “

Error-tolerant quantum computers

Reducing quantum computation errors is one of the biggest challenges that researchers face before they can build machines large enough to solve useful problems.

“Because quantum information is so fragile, they produce a lot of error,” Dr. Brown, a researcher at the University of Sydney Nano Institute.

Professor Stephen Bartlett

Professor Stephen Bartlett heads the quantum information theory group at the University of Sydney. He is also associate professor of research at the Faculty of Science. Credit: University of Sydney

It is impossible to completely eradicate these errors, so the goal is to develop a “fault-tolerant” architecture where useful processing operations far outweigh error-correction operations.

“Your mobile phone or laptop performs billions of operations for many years before a single error triggers a blank screen or other malfunction. Current quantum operations are lucky with fewer than one error for every 20 operations – and that means millions of errors per hour, ”Dr. Brown, who also holds a position at the ARC Center of Excellence for Engineered Quantum Systems.

“It’s a lot of fallen stitches.”

Most of the building blocks of today’s experimental quantum computers – quantum bits or qubits – are occupied by the “overhead” of error correction.

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

Dr. Naomi Nickerson is director of quantum architecture at PsiQuantum in Palo Alto, California, and is not associated with the research. She said: “This result establishes a new opportunity to perform fault-tolerant gates, which have the potential to greatly reduce costs and bring practical quantum computing closer.”

Path to universal calculation

Start-ups such as PsiQuantum as well as major technology companies Google, IBM and Microsoft are leading the way in developing large-scale quantum technology. It is urgent to find error correction codes that allow their machines to scale.

Dr. Michael Beverland, a senior scientist at Microsoft Quantum and also unrelated to the research, said: “This paper explores an exciting, exotic approach to performing fault-tolerant quantum computation and points to the path to potentially achieving universal quantum computation in two spatial dimensions without the need for distillation, something that many researchers thought was impossible. “

Two-dimensional codes currently available 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 calculations and extracts the useful ones.

This chewing a lot of computer hardware just suppresses the errors.

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

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

“Identifying the more common errors is another way we can release more processing power for useful calculations,” Dr. Brown.

Professor Stephen Bartlett is the co-author of this article and heads the quantum information theory research group at the University of Sydney.

“Our group in Sydney is very focused on discovering how we can scale up quantum effects so that they can operate large units on a large scale,” said Professor Bartlett, also associate dean of research at the Faculty of Science.

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

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references:

“A Fault Tolerant Non-Clifford Gate to the Two-Dimensional Surface Code” by Benjamin J. Brown22 May 2020, Scientific progress.
DOI: 10.1126 / sciadv.eaay4929

“Fault-tolerant Surface Code Limits in 5% Surplus Noise Surplus,” by David K. Tuckett, Stephen D. Bartlett, Steven T. Flammia, and Benjamin J. Brown, March 30, 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 through the Center of Excellence in Engineered Quantum Systems (EQUS) project number CE170100009.

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




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