To advance quantum technology towards broader practical applications, it is essential to develop and utilize devices that are compact, stable, efficient, and relatively easy to manufacture.

Miniaturized devices can make it easier to integrate equipment into existing technologies and environments, and also facilitate the development of portable mobile devices. Devices that are easy to manufacture can reduce production costs and accelerate the market promotion of quantum technology.

As the commercial potential of quantum technology is gradually recognized and exploited, devices that are cost-effective, high-performance, and highly stable have become the target of the industry.

Among these, quantum chips are not only the technical foundation for realizing quantum computers but also a key factor in promoting the development of quantum networks, quantum secure communication, and even the entire field of quantum technology and related applications.

At present, as the commercialization process of quantum technology accelerates, mastering the design and manufacturing technology of quantum chips will become an important sign of competitiveness for countries and enterprises. Whoever can take the lead in this technological competition may occupy an advantageous position in the future technological and economic landscape.Recently, the research team led by Professor Zhou Qiang from the Basic and Frontier Research Institute of University of Electronic Science and Technology, in collaboration with Professor Sun Changzheng's team from the Department of Electronic Engineering at Tsinghua University and other institutions such as the Shanghai Institute of Microsystem and Information Technology of the Chinese Academy of Sciences, has for the first time internationally developed a gallium nitride (GaN) quantum light source. The related research findings, titled "Quantum Light Generation based on GaN Microring toward Fully On-Chip Source," have been published in Physical Review Letters.

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The field of quantum optics is rapidly developing and is expected to play a significant role in future quantum information technology. One of the main challenges for further development in this field is how to transform larger desktop-sized devices into more miniaturized microchip dimensions.

The key to achieving a reduction in device size is the ability to develop and integrate quantum light sources on semiconductor chips, which is the core of achieving a complete integrated photonic quantum circuit on a single chip.

In this study, researchers have, for the first time, used gallium nitride material to manufacture a quantum light source, solving a series of challenges such as the growth of high-quality GaN crystal thin films, waveguide sidewall and surface scattering losses.

Although there have been quantum light sources made of materials such as aluminum gallium arsenide, indium phosphide, and silicon carbide before, they are not suitable for realizing highly integrated photonic circuits due to factors such as compatibility with mainstream integrated circuit industry technology, cost, physical and chemical properties, and integration difficulty.Gallium nitride (GaN) materials, due to their excellent physical properties, have been widely used in various optical components and are more easily integrated with existing silicon-based processes. This compatibility allows GaN quantum light sources to be integrated with other electronic and optoelectronic components (such as sensors, processors, etc.) on silicon chips, making them more suitable for building complex quantum circuits on a single chip. This helps to reduce production costs, thereby accelerating the commercialization process of quantum photonic technology.

To manufacture the GaN quantum light source, the research team first grew a layer of GaN thin film on a sapphire substrate. Sapphire is often used as a substrate for growing other semiconductor materials due to its good crystal properties and chemical stability.

Then, on the GaN thin film, a ring structure with a diameter of 120μm was etched. This ring structure allows photons (particles of light) to propagate within the ring, similar to the way sound waves propagate on the curved walls of a whispering gallery.

Researchers also etched a waveguide next to the ring structure to transmit infrared laser light. A waveguide is a physical structure used to confine and guide the propagation of light waves or electromagnetic waves. In the field of optics, waveguides play a very crucial role, as they can effectively transmit light signals without causing light waves to dissipate into the surrounding environment.

In the manufacturing of the GaN quantum light source, the role of the waveguide is to guide the infrared laser to the ring structure and to transmit the newly generated photons out of the ring, providing the required light signals for experiments and applications.The coupling between waveguides and ring structures allows some laser photons to enter the ring structure from the waveguide. When the photon's wavelength is exactly an integer multiple of the ring structure's circumference, resonance occurs within the ring. At this time, the photon's residence time in the ring increases, thereby enabling effective optical processing or further optical experimental operations. This characteristic is key to achieving optical quantum information processing and other advanced optical functions. Without resonance, photons may quickly escape from the ring or gradually decay as they propagate within the ring.

Additionally, the resonant photon pairs entering the ring may annihilate each other due to the four-wave mixing effect. The result of the annihilation is the creation of two new photons with different wavelengths from the original photons. The new resonant photon pairs can be controlled by adjusting the coupling strength and re-enter the waveguide from the ring. In this way, researchers can detect and utilize these photons with specific quantum properties externally for further experiments and technical operations.

The research team verified that each pair of new photons generated through four-wave mixing is in a quantum entangled state, proving that gallium nitride can not only be successfully used for generating quantum light but also has comparable performance to other traditional quantum light source materials.

Therefore, gallium nitride has been proven to be a "good quantum material platform," providing more options for materials for future quantum technology devices and having a broad application prospect in the entire field of optical quantum, which can be effectively used in the fields of quantum computing, quantum communication, and quantum sensing.

Since gallium nitride has already been widely used in the fields of optoelectronics and semiconductors, its application in the quantum field may lead to the development of new types of devices, such as smaller and more efficient quantum chips and integrated optoelectronic systems.As the technology of gallium nitride quantum light sources matures and is validated, the related industries may experience growth and transformation, including quantum device manufacturing and quantum secure communication. This will not only impact the scientific research community but may also lead market trends and investment directions.