Breakthrough in quantum computing

Quantitative engineers at UNSW Sydney have made critical strides in the development of quantum computing technology, solving a problem that has long frustrated scientists and has so far represented a major roadblock to the development of the next generation of computers. The problem in question involves spinquots, which are the basic units of information in a silicon quantum processor. But first, what is a silicon quantum processor?

In classical computing, information is represented by electrical charges in silicon: in quantum computing, information will be transmitted through a “spin”, the property of an electron or atom that gives it magnetism.

So, a silicon quantum processor is the core of a quantum computer, and a “spin quantum” is a unit of information conveyed by the spin of the electrons in it. Confused yet?

The success the team has had concerns these spin-kits, which have traditionally been labor-intensive to control.

“Up to this point, controlling electron spin quits has depended on us delivering microwave magnetic fields by placing current through a wire right next to the qubit,” says Jarryd Pla, chief researcher.

“This presents some real challenges if we are to climb to the millions of quits that a quantum computer will need to solve globally significant problems, such as the design of new vaccines.”


Learn more: Quantum computing for the curious


“First, the magnetic fields fall very fast with distance, so we can only control those quits closest to the wire. That means we need to add more and more wires as we import more and more quits that would take up a lot of property on the chip. “

And because the chip has to operate at freezing cold temperatures, below -273 ° C, Pla says introducing more wires would generate too much heat in the chip, hampering the reliability of the quits.

“So, we’re back to just being able to control a few kbit with this wire technique.”

To avoid this problem, the team realized that they would need to reimagine the structure of the silicon chip. Instead of involving wires, they suggested generating a magnetic field from above the chip that could handle all the cubits at once.

The prospect of controlling all five at once using a magnetic field was first required in the 1990s, but so far no one has developed a practical way to do it.

“First we removed the wire next to the quits and then came up with a new way to deliver microwave-frequency magnetic control fields throughout the system. So, in principle, we could deliver control fields up to four million quits,” says Pla.

Andrew dzurak and jarryd pla behind a glass screen with fiery equations
Andrew Dzurak and Jarryd Pla, quantum engineers at UNSW. Credit: UNSW

Pla and the team then launched a new component directly over the silicon chip – a crystal prism called a dielectric resonator. When microwaves are directed at the resonator, it focuses the wavelength of the microwave down to a much smaller size.

“The dielectric resonator shrinks the wavelength below one millimeter, so we now have a very efficient conversion of microwave power into the magnetic field that controls the spins of all quits.

“There are two key innovations here. The first is that we don’t have to put a lot of power into getting a strong course of action for the quits, which seriously means we don’t generate a lot of heat. The second is that the field is very uniform. across the board, so that millions of quits all experience the same level of control. “

The team worked with UNSW Professor Andrew Dzurak, whose team over the past decade has demonstrated the first and most accurate quantum logic using the same silicon production technology used to make conventional computer chips.

“I was completely blown away when Jarryd came to me with his new idea,” Dzurak says, “and we immediately set to work to see how we could integrate it with the qubit chips my team had developed.

“We were overjoyed when the experiment proved successful. This problem of how to control millions of quits has worried me for a long time, because it was a major roadblock to building a full-scale quantum computer. “

The team hopes to use this new innovation to simplify the design of quantum computers.

“Removing the on-chip control wire frees up space for additional quits and all the other electronics needed to build a quantum processor. It makes the task of going to the next step of producing devices with a few dozen quits much simpler,” says Dzurak.

“While there are engineering challenges to solve before processors with a million cubits can be made, we are excited about the fact that we now have a way to control them,” says Pla.

Credit: UNSW Visual Content

This is not the first time that quantum engineers at UNSW Sydney have embarked on the journey to a quantum future: in April 2020, a team led by Dzurak published proof of concept a quantum processor unit that could allow quantum computers to work at 1.5 kelvins – 15 times hotter than quantum processors previously could work at (typically, quantum computers must be only fractions of a degree above absolute zero to operate), reducing the need for refrigeration equipment that costs millions dollars.

Quantum computers, when they become a practical, scalable reality, will enable an extraordinarily fast problem-solving, data-processing process that would require a typical computer much longer. Possible applications could range from creating innovative new ones medical treatments al prices of financial instruments.


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