Making Next Generation Quantum Computers Even More Powerful


Three resonators operating at different frequencies read a 3×3 matrix of quantum dots. Credit: © Harald Homulle 2022 EPFL

EPFL engineers have developed a method to read multiple qubits – the smallest unit of quantum data – at the same time. Their method paves the way for a new generation of even more powerful quantum computers.

“IBM and Google currently have the most powerful quantum computers in the world,” explains Professor Edoardo Charbon, head of the Advanced Quantum Architecture Laboratory (AQUA Lab) at EPFL’s Faculty of Engineering. “IBM has just unveiled a 127 qubit machine, while Google’s is 53 qubit machine.” The possibilities to make quantum computers even faster are limited, however, due to an upper limit on the number of qubits. But a team of engineers led by Charbon, in collaboration with British researchers, has just developed a promising method to overcome this technological barrier. Their approach can read qubits more efficiently, which means more of them can be packed into quantum processors. Their findings appear in Electronic Nature.

Biochemistry and cryptography

Quantum computers don’t work like the computers we’re used to. Instead of having a separate processor and memory chip, the two are combined into a single unit called a qubit. These computers use quantum properties like superposition and entanglement to perform complex calculations that ordinary computers could never do in a reasonable amount of time. Potential applications of quantum computers include biochemistry, cryptography, etc. The machines used by research groups now have around ten qubits.

“Our challenge now is to interconnect more qubits in quantum processors – we’re talking hundreds, if not thousands – in order to increase the processing power of computers,” says Charbon.

The number of qubits is currently limited by the fact that there is not yet a technology that can read all qubits quickly. “To further complicate matters, qubits operate at temperatures close to absolute zero, or -273.15oC, ”says Charbon. “This makes them even more difficult to read and control. What engineers usually do is run machines at room temperature and control each qubit individually.

“It’s a real breakthrough”

Andrea Ruffino, a doctoral student at the Charbon laboratory, has developed a method for simultaneously and efficiently reading nine qubits. In addition, its approach could be extended to larger qubit matrices. “Our method is based on the use of the time and frequency domains,” he explains. “The basic idea is to reduce the number of connections by making three qubits work with a single link. “

EPFL doesn’t have a quantum computer, but that didn’t stop Ruffino. He found a way to emulate qubits and perform experiments under almost the same conditions as a quantum computer. “I incorporated quantum dots, which are nanoscale semiconductor particles, into a transistor. It gave me something that works the same as qubits, ”says Ruffino.

He is the first AQUA Lab doctoral student to study this subject for his thesis. “Andrea has shown that his method works with integrated circuits on ordinary computer chips and at temperatures approaching those of a qubit,” Charbon explains. “This is a real breakthrough that could lead to large integrated qubit matrix systems with the necessary electronics. The two types of technologies could work together in a simple, efficient and repeatable way.

Reference: “A cryo-CMOS chip that integrates silicon quantum dots and multiplexed dispersive reading electronics” by Andrea Ruffino, Tsung-Yeh Yang, John Michniewicz, Yatao Peng, Edoardo Charbon and Miguel Fernando Gonzalez-Zalba, December 27, 2021 , Electronic Nature.
DOI: 10.1038 / s41928-021-00687-6


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