Scientists from the University of Sydney in Australia and the University of Basel in Switzerland have for the first time demonstrated the ability to recognize and manipulate small amounts of interacting photons (light energy packets) that are highly correlated. This unprecedented achievement is an important milestone in the development of quantum technology. The research paper was published in the journal Nature Physics on the 20th. The concept of stimulated emission proposed by Einstein in 1916 laid the foundation for the emergence of lasers. In the new study, scientists observed stimulated emission of a single photon. Specifically, they can measure the direct time delay between a photon and a pair of bound photons scattered from a single quantum dot. Quantum dots are artificially created atoms. Researchers say this opens the door to manipulating so-called "quantum light". At the same time, this basic scientific research has opened the way for the progress of quantum enhancement measurement technology and photon quantum computing. The way light interacts with matter has attracted more and more research, such as interferometer using light to measure small changes in distance. However, the laws of quantum mechanics set a limit on the sensitivity of such devices: between the measurement sensitivity and the average number of photons in the measurement device. Researchers say the device they built creates a strong interaction between photons, allowing them to observe the difference between one photon and two photons interacting with it. They saw that one photon had a longer delay time than two photons. With this very strong photon photon interaction, two photons become entangled in the form of so-called two-photon bound states. The advantage of quantum light like this is that, in principle, it can use fewer photons to make more sensitive measurements with higher resolution. This is important for applications in biological microscopes, especially when the intensity of light can damage the sample and the characteristics that scientists need to observe are particularly small. Researchers say the new research represents a crucial first step towards using quantum light for practical purposes by demonstrating that photon bound states can be identified and manipulated. At the same time, the same principles can be applied to develop more efficient devices to provide photon bound states, which will have broad application prospects in biological research, advanced manufacturing, quantum information processing, and other fields. (Liao Xinshe)