Cryogenic chip is a big step to scale up Quantum Computing

Through the Microsoft partnership with the university, Professor David Reilly and colleagues invented a device 40 times colder than deep space to directly control thousands of qubits, the building blocks of quantum technology.

Scientists and engineers from the University of Sydney and Microsoft Corporation have opened the next chapter in quantum technology with the invention of a single chip that can generate control signals for thousands of qubits, the building blocks of quantum computers.

“To unlock the potential of quantum computer, machines will have to drive thousands, if not millions, of qubits,” said Professor David Reilly, a chip designer who works with Microsoft and the University of Sydney.

“The world’s largest quantum computers currently operate with only 50 or so qubits,” he said. “This small scale is partly due to limitations in the physical architecture driving the qubits.”

“Our new chip puts an end to those limits.”

The results were published in Nature Electronics.

Cryogenic chip platform in situ

The cryogenic chip platform in situ in a dilution refrigerator. The device can operate at 0.1 Kelvin. Credit: University of Sydney

Most quantum systems require quantum bits, or qubits, to operate at temperatures near absolute zero (-273.15 degrees). This is to prevent them from losing their ‘quantumness’, the nature of matter or light that quantum computers need to perform their specialized calculations.

In order for quantum devices to do anything useful, they need instructions. That means sending and receiving electronic signals to and from the qubits. With the current quantum architecture, many wires are involved.

“Today’s machines create a beautiful array of wires to control the signals; they look like an inverted gilded bird’s nest or chandelier. They are beautiful, but fundamentally impractical. It means we can’t scale the machines to perform useful calculations. There is a real input-output bottleneck,” said Professor Reilly, also principal investigator at the ARC Center for Engineered Quantum Systems (EQUS).

Microsoft Senior Hardware Engineer, Dr. Kushal Das, a co-inventor of the chip, said: “Our device takes care of all those cables. With just two wires carrying information as input, it can generate control signals for thousands of qubits.

“This changes everything for quantum computing.”

David Reilly

Professor David Reilly from the School of Physics at the University of Sydney holds a joint position at Microsoft Corporation. Credit: University of Sydney

The control chip was developed at the Microsoft Quantum Laboratories at the University of Sydney, a unique industrial-academic partnership that is changing the way scientists tackle technical challenges.

“Building a quantum computer is perhaps the most challenging engineering task of the 21st century. This cannot be achieved by working with a small team in a university lab in one country, but it needs the scale provided by a global technology giant like Microsoft,” said Professor Reilly.

“Through our partnership with Microsoft, we not only proposed a theoretical architecture to overcome the input-output bottleneck, we also built it.

“We demonstrated this by designing a custom silicon chip and linking it to a quantum system,” he said. “I can say with confidence that this is the most advanced integrated circuit ever built to operate at deep cryogenic temperatures.”

If realized, quantum computers promise to revolutionize information technology by solving problems beyond the reach of classical computers in fields as diverse as cryptography, medicine, finance, artificial intelligence and logistics.

Energy budget

Quantum computers are at a similar stage to classical computers in the 1940s. Machines like ENIAC, the world’s first electronic computer, needed control rooms to perform every useful function.

It has taken decades to overcome the scientific and technical challenges that now allow billions of transistors to fit inside your cell phone.

“Our industry faces perhaps even greater challenges in taking quantum computing beyond the ENIAC stage,” said Professor Reilly.

“We need to develop very complex silicon chips that operate at 0.1 Kelvin,” he said. “That’s an environment 30 times colder than deep space.”

dr. Sebastian Pauka’s PhD research at the University of Sydney involved much of the work pairing quantum devices with the chip. He said: “Working in such cold temperatures means we have an incredibly low energy budget. If we try to put more power into the system, we overheat.”

To achieve their result, the scientists from Sydney and Microsoft built the most advanced integrated circuit to operate at cryogenic temperatures.

“We did this by designing a system that works close to the qubits without interfering with their activities,” said Professor Reilly.

“Current qubit control systems are, as it were, meters away from the action. They usually exist at room temperature.

“In our system, we don’t have to get rid of the cryogenic platform. The chip is right there with the qubits. This means less power and higher speeds. It is a real control system for quantum technology.”

Quantum Machine Full Stack

‘The full stack’ needed for a useful quantum machine: Professor David Reilly is working with Microsoft scientists worldwide to realize a fault-tolerant universal quantum computer. The device he invented is located at the interface between classical and quantum systems. Credit: Microsoft

Years of engineering

“Finding out how to control these devices takes years of engineering,” said Professor Reilly. “We started this device four years ago when the University of Sydney partnered with Microsoft, Australia’s largest investment in quantum technology.

“We have built many models and design libraries to capture the behavior of transistors at deep cryogenic temperatures. Then we had to build devices, verify them, characterize them and finally connect them with qubits to see them work in practice.”

Vice Chancellor and Director of the University of Sydney, Professor Stephen Garton, said: “The entire university community is proud of Professor Reilly’s success and we look forward to many years of continued partnership with Microsoft.”

Professor Reilly said the field has now fundamentally changed. “It’s not just about ‘here’s my qubit’. It’s about how you build all the layers and all the technology to build a real machine.

“Our partnership with Microsoft allows us to work with academic rigor, with the advantage of quickly putting our results into practice.”

The Deputy Vice Chancellor (Research), Professor Duncan Ivison, said: “Our partnership with Microsoft was about realizing David Reilly’s inspired vision to enable quantum technology. It’s great to see that vision come true.”

Professor Reilly said, “If we had just stayed in academia, this chip would never have been built.”

The Australian scientist said he won’t stop there.

“We’ve just started this new wave of quantum innovation,” he said. “The great thing about the collaboration is that we don’t just publish a paper and move on. We can now move forward with the blueprint to realize quantum technology on an industrial scale.”

Reference: “A cryogenic CMOS chip for generating multi-qubit control signals” by SJ Pauka, K. Das, R. Kalra, A. Moini, Y. Yang, M. Trainer, A. Bousquet, C. Cantaloube, N Dick, GC Gardner, MJ Manfra and DJ Reilly, January 25, 2021, Nature Electronics.
DOI: 10.1038/s41928-020-00528-y

This research was supported by Microsoft Corporation and the Australian Research Council Center of Excellence for Engineered Quantum Systems. We acknowledge the facilities and scientific and technical assistance of the Research and Prototype Foundry, a Core Research Facility at the University of Sydney, and part of the Australian National Fabrication Facility (ANFF).

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