Quantum Light Source Completely On-chip, Bringing Scalability to the Quantum Cloud

Insider Summary

• An international research team reports in Nature Photonics that they demonstrated an entangled quantum light source that is fully integrated for the first time on a chip.
• Progress allowed the team to “shrink source size by a factor of over 1000, enabling reproducibility, stability over longer periods of time, scalability, and the possibility of mass production.”
• The team includes scientists from Leibniz University Hannover (Germany), University of Twente (Netherlands), and startup QuiX Quantum.
• Image: Artistic illustration of a quantum light source integrating with a chip to produce entangled photons.

PRESS RELEASE — An international team of researchers from Leibniz University Hannover (Germany), University of Twente (Netherlands) and startup QuiX Quantum have presented the first fully integrated entangled quantum light source on a chip.

“Our breakthrough allows us to shrink source size by a factor of over 1000, enabling reproducibility, stability over longer periods, scalability and potential for mass production. All of these characteristics are necessary for real-world applications such as quantum processors,” said Prof. Dr. Michael Kues, head of the Institute of Photonics, and member of the board of the Cluster of Excellence PhoenixD at Leibniz University Hannover.

Quantum bits (qubits) are the basic building blocks of quantum computers and the quantum internet. Quantum light sources produce light quanta (photons) that can be used as quantum bits. On-chip photonics has become the leading platform for optical quantum state processing because it is compact, powerful, and makes it possible to accommodate and organize multiple elements on a single chip. Here, light is directed onto the chip via a very compact structure, which is used to build photonic quantum computing systems. It is already accessible today via the cloud. Implemented in a scalable manner, they can accomplish tasks that are inaccessible to conventional computers due to their limited computing capacity. This advantage is called a quantum advantage.

“Until now, quantum light sources required bulky, off-chip, external laser systems, which limited their use in the field. However, we overcome these challenges through new chip designs and by exploiting different integrated platforms,” ​​said Hatam Mahmudlu, Ph.D. students on the Cookies team. Their new development, a laser-integrated, electrically excited photonic quantum light source, fits completely on a chip and can emit frequency-entangled qubit states.

“Qubits are very susceptible to noise. The chip must be driven by the laser field, completely free of noise, requiring an on-chip filter. Previously, integrating lasers, filters and cavities on the same chip was a huge challenge because there was no unique efficient material to manufacture these different components,” said Dr. Raktim Haldar, a Humboldt researcher in the Kues group.

The key is ‘hybrid technology’ which attaches a laser made of indium phosphide, a filter and a cavity made of silicon nitride and fuses them into a single chip. On the chip, in a spontaneous nonlinear process, two photons are created from the laser field. Each photon covers a range of colors simultaneously, which is called a ‘superposition’, and the colors of the two photons are correlated, that is, the photons are entangled and can store quantum information. “We achieved the extraordinary efficiency and quality required for applications in quantum computers or the quantum internet,” said Kues.

“Now we can integrate the laser with other components on a chip so that the entire quantum source is smaller than a one euro coin. Our tiny device can be considered a step towards quantum superiority on a chip with photons. Unlike Google, which currently uses supercooled qubits in cryogenic systems, quantum superiority can be achieved with such a photonic system on a chip even at room temperature,” said Haldar. The scientists also expect their invention to help lower the cost of producing apps. “We can envision that our quantum light source will soon become a fundamental component of programmable photonic quantum processors,” said Kues. The results of the research were published in the journal Nature Photonics.

Prof. Dr. Michael Kues is head of the Institute of Photonics and a board member of the Cluster of Excellence PhoenixD: Photonics, Optics, and Engineering – Innovation cross Disciplines at Leibniz University Hannover, Germany. The PhoenixD research cluster comprises about 120 scientists working on the new integrated optics. The German Research Foundation (DFG) is funding PhoenixD with around 52 million euros from 2019 to 2025. Raktim Haldar is an Alexander von Humboldt Research Fellow at the Institute of Photonics, and Hatam Mahmudlu is a doctoral student on the Kues team. This research was funded by the Federal Ministry of Education and Research (BMBF) and the European Research Council (ERC).