Optics & Photonics

The quantum light source is now fully on-chip, allowing the quantum cloud to scale.

An entangled quantum light source that is fully integrated on a chip has been presented by an international team of researchers from Leibniz University Hannover (Germany), the University of Twente (Netherlands), and the start-up company QuiX Quantum. The study’s findings were presented in the journal Nature Photonics.

“Thanks to our breakthrough, we were able to reduce the size of the source by more than 1,000 times, enabling reproducibility, stability over a longer period of time, scaling, and possibly mass production. This multitude of attributes is expected for true applications like quantum processors,” says Prof. Dr. Michael Kues, head of the Foundation of Photonics and a board member of the Bunch of Greatness at Leibniz College Hannover.

“Our breakthrough enabled us to shrink the source size by a factor of 1,000, allowing for reproducibility, longer-term stability, scaling, and potentially mass-production. All of these properties are essential for real-world applications like quantum processors.”

Prof. Dr. Michael Kues, head of the Institute of Photonics, 

Quantum bits (qubits) are the essential building blocks of quantum computers and the quantum web. Light quanta (photons) produced by quantum light sources can be utilized as quantum bits. Because it can accommodate and arrange numerous elements on a single chip, on-chip photonics has emerged as a leading platform for processing optical quantum states. Photonic quantum computing systems are built using these extremely compact structures, which direct light onto the chip. The cloud already makes it possible to access these today. They could solve problems that conventional computers cannot because of their limited computing power. Quantum advantage is the name given to this advantage.

A chip that is less than the size of a one-euro coin houses the entire quantum light source. Using a novel “hybrid technology” that combines an indium phosphide laser and a silicon nitride filter on a single chip, the researchers were able to reduce the size of the light source by more than 1,000 times. The brand-new light source is reliable and effective, and it has the potential to power quantum computers and the quantum internet. Credit: Institute of Photonics/LUH

“Until now, quantum light sources required external, off-chip, and bulky laser systems, which limited their application in the field.” Institute of Photonics/LUH Hatam Mahmudlu, a Ph.D. student on Kues’s team, says, “However, we overcome these challenges by utilizing diverse integrated platforms and a novel chip design.” Their new invention, an electrically excited, laser-integrated photonic quantum light source, can produce frequency-entangled qubit states and fits entirely on a chip.

“Qubits are extremely sensitive to noise.” The chip should be driven by the laser field, totally liberated from clamor, requiring an on-chip channel. According to Dr. Raktim Haldar, a Humboldt fellow in Kues’s group, “Before, it was a major challenge to integrate a laser, filter, and cavity on the same chip because there was no unique material that was efficient for building these different components.”

The “hybrid technology,” which incorporates a silicon nitride cavity, a filter, and an indium phosphide laser into a single chip, was the key. Two photons are produced on the chip by a spontaneous nonlinear process involving a laser field. The phenomenon known as “superposition” occurs when both photons are entangled and capable of storing quantum information, and the colors of both photons are correlated. “Kues says that we achieve remarkable efficiencies and state qualities needed for use in quantum computers or the quantum internet.”

They fostered the new coordinated quantum light source (from left): With doctoral student Hatam Mahmudlu and Humboldt fellow Dr. Raktim Haldar, Prof. Dr. Michael Kues, head of the Institute of Photonics and board member of the Cluster of Excellence PhoenixD at Leibniz University Hannover, Credit: Sonja Smalian/PhoenixD.

“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,” says Sonja Smalian/PhoenixD. A step toward photon-based quantum advantage on a chip might be our tiny device. The quantum advantage could be achieved with such photonic systems on a chip even at room temperature, in contrast to Google, which currently uses super-cold qubits in cryogenic systems, claims Haldar.

The researchers likewise anticipate that their disclosure should assist with bringing down the creation expenses for uses. “We can envision that our quantum light source will before long be a central part of programmable photonic quantum processors,” says Kues.

The Institute of Photonics is led by Prof. Dr. Michael Kues, who also serves on the board of the Cluster of Excellence PhoenixD: Photonics, Optics, and Designing—DDevelopment across Disciplines at Leibniz College Hannover, Germany.

More information: Raktim Haldar, Fully on-chip photonic turnkey quantum source for entangled qubit/qudit state generation, Nature Photonics (2023). DOI: 10.1038/

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