International Team Engineers Silicon Chip for Quantum Information Processing

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BRISTOL, England, Aug. 24, 2018 — An international team led by the University of Bristol has demonstrated the ability to control two qubits of information within a single silicon chip. This programmable two-qubit quantum processor could be used as a tool to perform quantum information experiments and could facilitate the use of silicon photonics for future photonic quantum processors.

To encode the qubits, the researchers used large-scale silicon photonic circuits to guide photons along waveguides. The quantum processor was fabricated with CMOS-compatible processing and comprises more than 200 photonic components.

Two-qubit quantum processor. Courtesy of Xiaogang Qiang/University of Bristol. Image is for single use only to illustrate this story and must not be archived.
Waveguides guide photons in silicon, much like an optical fiber. Spirals of these waveguides are used to generate photons that are then routed around the processor circuit to perform different tasks. Courtesy of Xiaogang Qiang/University of Bristol.

The researchers programmed the device to implement 98 different two-qubit unitary operations, a two-qubit quantum approximate optimization algorithm, and efficient simulation of Szegedy-directed quantum walks.

“What we’ve demonstrated is a programmable machine that can do lots of different tasks,” said researcher Xiaogang Qiang.

“It’s a very primitive processor, because it only works on two qubits, which means there is still a long way before we can do useful computations with this technology,” said Qiang. "But what is exciting is that the different properties of silicon photonics that can be used for making a quantum computer have been combined together in one device. This is just too complicated to physically implement with light using previous approaches."


The team believes that its small device built from silicon could be scaled up in a cost-effective way, and emphasizes the importance of building quantum computers from technology that will allow precision on a very large scale. It sees integrated photonics as an alternative to bulky optical elements that could be too large and unstable to be used for the large, complex circuits that will be needed to build quantum computers.

“We need to be looking at how to make quantum computers out of technology that is scalable,” said researcher Jonathan Matthews. "We think silicon is a promising material to do this, partly because of all the investment that has already gone into developing silicon for the microelectronics and photonics industries."

The small quantum processor has become a tool for further research, said the team, who has used the device to implement several different quantum information experiments using almost 100,000 different reprogrammed settings.

“Since there’s been so much research and investment in silicon chips, this innovation might be found in the laptops and smartphones of the future,” said University of Queensland professor Timothy Ralph. “This is just the beginning; we’re just starting to see what kind of exponential change this might lead to.”

The research was published in Nature Photonics (doi: 10.1038/s41566-018-0236-y).

Published: August 2018
The term quantum refers to the fundamental unit or discrete amount of a physical quantity involved in interactions at the atomic and subatomic scales. It originates from quantum theory, a branch of physics that emerged in the early 20th century to explain phenomena observed on very small scales, where classical physics fails to provide accurate explanations. In the context of quantum theory, several key concepts are associated with the term quantum: Quantum mechanics: This is the branch of...
integrated photonics
Integrated photonics is a field of study and technology that involves the integration of optical components, such as lasers, modulators, detectors, and waveguides, on a single chip or substrate. The goal of integrated photonics is to miniaturize and consolidate optical elements in a manner similar to the integration of electronic components on a microchip in traditional integrated circuits. Key aspects of integrated photonics include: Miniaturization: Integrated photonics aims to...
integrated optics
A thin-film device containing miniature optical components connected via optical waveguides on a transparent dielectric substrate, whose lenses, detectors, filters, couplers and so forth perform operations analogous to those of integrated electronic circuits for switching, communications and logic.
Research & TechnologyeducationEuropeAsia-PacificOpticswaveguidesCommunicationsquantumsilicon photonicsintegrated photonicsintegrated opticsquantum information processingUniversity of BristolUniversity of QueenslandEuro News

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