Record quantum computing result for Sydney teams

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Unprecedented work has been achieved through the theoretical work of physicists at the Sydney Nano Institute and the School of Physics, which has reduced errors in semiconductor spin qubits, a type of building block for quantum computers.

Experimental results from engineers at the University of New South Wales showed error rates as low as 0.043%, lower than all other qubits. The joint research paper of the Sydney and UNSW teams was published this week in Nature Electronics and is the cover of the newspaper for April.

"It is necessary to reduce the errors in quantum computers before they can be turned into useful machines," said Professor Stephen Bartlett, corresponding author of the paper.

"Once exploited on a large scale, quantum computers could well keep their promise of solving problems beyond the capacity of the most important supercomputers." This could help humanity solve chemistry, drug design and technology problems. # 39; industry. "

There are many types of quantum bits, or qubits, ranging from those using trapped ions, superconducting loops, or photons. A "spin qubit" is a quantum bit that encodes information based on the quantized magnetic direction of a quantum object, such as an electron.

Australia, and Sydney in particular, claims to be a world leader in quantum technology. The recent announcement of funding for the creation of a Sydney Quantum Academy underscores Australia's enormous opportunity to build a quantum economy based on the world's largest concentration of quantum research groups here in Sydney.

No practice without theory

Although quantum computing has recently focused on material progress, none of these advances have been possible without the development of quantum information theory.

The Quantum Theory Group of the University of Sydney, led by Professors Stephen Bartlett and Steven Flammia, is one of the world leaders in quantum information theory. It enables teams of engineers and experimenters from around the world to achieve the hard physical progress needed to make quantum computing a priority. reality.

The work of the Sydney Quantum Theory Group was essential to the outcome of the world record published in Nature Electronics.

Professor Bartlett said: "Because of the very low error rate, the UNSW team needed very sophisticated methods to be able to even detect errors.

"With such low error rates, we needed data processing that took days and days to collect statistics and highlight occasional errors."

Professor Bartlett stated that once errors have been identified, they must be characterized, eliminated and re-characterized.

"Steve Flammia's group is a world leader in the theory of error characterization, which has been used to achieve this result," he said.

The Flammia group recently demonstrated for the first time an improvement in quantum computers with codes designed to detect and eliminate errors in logic gates, or switches, using the IBM Q quantum computer.

Professor Andrew Dzurak, who heads the UNSW research team, said: "Working with Professors Bartlett and Flammia and their team has been invaluable in helping us understand the types of errors that we are seeing in our silicon-CMOS qubits at UNSW.

"Our lead experimenter, Henry Yang, worked closely with them to achieve this remarkable 99.957% fidelity, which shows that we now have the world's most accurate semiconductor qubit."

Professor Bartlett said that Henry Yang's world record will probably last a long time. He added that the UNSW team and others would work on the establishment of two-qubit matrices and higher levels of silicon-CMOS.

Fully operational quantum computers will require millions, if not billions, of qubits to function. The design of low error qubits is now an essential step for scaling up such devices.

Professor Raymond Laflamme is President of Quantum Information at the University of Waterloo in Canada and did not participate in the study. He said: "As quantum processors become more widespread, the Bartlett Group at the University of Sydney has developed an important tool for evaluating them, allowing us to characterize quantum gate accuracy and give physicists to distinguish between consistent errors leading to unprecedented control of qubits ".

Overall impact

The joint Sydney University-UNSW result comes shortly after an article from the same team of quantum theory with experimenters at the Niels Bohr Institute in Copenhagen.

This result, published in Nature Communications, allows the exchange of remote information between electrons via a mediator, which improves the prospects for a larger-scale architecture in quantum spin-qubit computers.

The result was significant because it allowed the distance between quantum dots to be large enough for integration into more traditional microelectronics. Physicists from Copenhagen, Sydney and Purdue in the United States collaborated to achieve this goal.

Professor Bartlett said: "The main problem is that the interaction of quantum dots requires a ridiculous distance between them, at nanometers.But at this distance, they get in the way, making the device too difficult to adjust to perform useful calculations. "

The solution was to allow entangled electrons to convey their information via a "pool" of electrons, further away from them.

"It's a bit like having a bus, a great mediator that allows the interaction of far spins." If you can allow more spin interactions, quantum architecture can shift to two-dimensional provisions. "

Associate Professor Ferdinand Kuemmeth of the Niels Bohr Institute of Copenhagen said: "We discovered that a large elongated quantum dot between the left and right points was at the origin of an exchange Coherent spin states, in the billionth of a second, without moving electrons out of their points.

Professor Bartlett said, "This result fascinates me as a theorist, that is, it frees us from the constraining geometry of a qubit that relies solely on its closest neighbors."

Bureau of Global Engagement

The story of this experiment goes back a decade through an American IARPA program led by Professor Charlie Marcus, a co-author who was then at Harvard before moving to Copenhagen.

Professor Bartlett said: "We all went to Copenhagen to participate in a workshop on this problem in 2018. Thomas Evans, co-author of the paper, stayed there for two months, with the support of the Bureau of the World Health Organization. global commitment, OGE also supported Dr. Arne Grimsmo, who was working on another project. "

He said that the experience and our discussions were well advanced by the time we received the EMB funding. But it was this workshop and its funding that allowed the Sydney team to travel to Copenhagen to plan the next generation of experiments based on this outcome.

Professor Bartlett said, "This method allows us to separate the quantum dots a bit further, making them easier to adjust separately and make them work together.

"Now that we have this mediator, we can start planning a two-dimensional array of these pairs of quantum dots."