For quantum technology to move into wider real-world applications, the development and use of devices that are small, stable, efficient, and relatively easy to fabricate are essential.
Miniaturized devices can make it easier to integrate devices into existing technologies and environments, as well as facilitate the development of portable mobile devices. Easy-to-manufacture devices can reduce production costs and accelerate the market adoption of quantum technology.
As the commercial potential of quantum technology is gradually recognized and explored, cost-effective, high-performance, and high-stability devices have become the object of pursuit by the industry.
Among them, quantum chips are not only the technical basis for the realization of quantum computers, but also the key factors to promote the development of quantum networks and quantum secure communications, and even the entire quantum technology and related applications.
At a time when the commercialization of quantum technology is accelerating, mastering the design and manufacturing technology of quantum chips will become an important symbol of the competitiveness of countries and enterprises. Whoever is the first to make a breakthrough in this technological race may have an advantage in the future technological and economic landscape.
Recently, the research group of Professor Zhou Qiang of the Institute of Basic and Advanced Research of the University of Electronic Science and Technology of China, the research group of Professor Sun Changzheng of the Department of Electronic Engineering of Tsinghua University, together with the Shanghai Institute of Microsystem and Information Technology of the Chinese Academy of Sciences and other institutions, have developed a gallium nitride quantum light source for the first time in the world. The research results were published in Physical Review Letters under the title "Quantum Light Generation based on GaN Microring toward Fully On-Chip Source".
（来源：Physical Review Letters）
At present, the field of quantum optics is developing rapidly, and it is expected to play an important role in quantum information technology in the future. One of the main challenges for further development in this area is how to convert larger desktop devices into more miniaturized microchip sizes.
The key to reducing the size of the device is to be able to develop and integrate quantum light sources on semiconductor chips, which is the core of integrating complete optical quantum circuits on a single chip.
In this study, the researchers used GaN materials for the first time to fabricate quantum light sources, and solved a series of problems such as the growth of high-quality GaN crystal films, waveguide sidewall and surface scattering losses, etc.
Although quantum light sources of materials such as gallium arsenide, indium phosphide, and silicon carbide have existed before, they are not suitable for achieving highly integrated photonic circuits due to their compatibility with mainstream technologies in the integrated circuit industry, cost, physical and chemical properties, and integration difficulty.
GaN materials have been widely used in various optical components due to their excellent physical properties, making them easier to integrate 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 of optical quantum technology.
In order to fabricate the GaN quantum light source, the research team first grew a thin film of gallium nitride on a sapphire substrate. Due to its good crystal properties and chemical stability, sapphire is often used as a substrate for the growth of other semiconductor materials.
Then, on the gallium nitride film, a ring structure with a diameter of 120 μm is etched. This ring-shaped structure allows photons (particles of light) to propagate within the ring, similar to how sound waves travel across the curved walls of the Whispering Gallery.
The researchers also etched a waveguide next to the ring structure to transmit the infrared laser. A waveguide is a physical structure used to limit and direct the propagation of light waves or electromagnetic waves. In the field of optics, waveguides play a key role in transmitting optical signals efficiently without dissipating them into the surrounding environment.
（来源：Physical Review Letters）
In the fabrication of gallium nitride quantum light sources, the role of the waveguide is to guide the infrared laser to the ring structure and transmit the new photons generated within the ring to provide the required optical signal for experiments and applications.
The coupling between the waveguide and the ring structure allows some laser photons to enter the ring structure from the waveguide. And when the wavelength of the photon is exactly an integer multiple of the circumference of the ring structure, it will resonate in the ring. The residence time of the particles in the ring is increased, allowing for effective optical processing or further optical experiments. This property is key to enabling 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.
In addition, the resonant photon pairs entering the ring may be annihilated by each other due to the four-wave mixing effect, and the result of annihilation is the generation of two new photons of a different wavelength than the original photon. The new resonant photon pairs can be controlled by adjusting the coupling strength to re-enter the waveguide from the ring. This allows researchers to externally detect and exploit these photons with specific quantum properties for further experiments and technical manipulations.
The research team verified that each pair of new photons generated by four-wave mixing is in a quantum entanglement state, proving that GaN can not only be successfully used to generate quantum light, but also has the same performance as other traditional quantum light source materials.
Therefore, gallium nitride has proven to be a "good quantum material platform", which provides more options for future quantum technology device materials, and also has a wide range of application prospects in the entire optical quantum field, which can be effectively used in quantum computing, quantum communication, quantum sensing and other fields.
Since gallium nitride is already widely used in optoelectronics and semiconductors, its application in the quantum domain may lead to the development of new devices, such as smaller and more efficient quantum chips and integrated optoelectronic systems.
As GaN quantum light source technology matures and validates, related industries are likely to experience growth and transformation, including quantum device manufacturing and quantum-secure communications. This not only affects the scientific community, but may also lead to market trends and investment directions.
Reference:
https://physics.aps.org/articles/v17/51
https://doi.org/10.1103/PhysRevLett.132.133603