A theory posited by University of Birmingham researchers explores the nature of photons in unprecedented detail to show how they are emitted by atoms or molecules and shaped by their environment. The theory explains how light and matter interact at the quantum level and allows researchers to define the precise shape of a single photon. The nature of this interaction leads to infinite possibilities for light to exist and propagate through its surrounding environment. However, this limitless possibility makes the interactions exceptionally difficult to model. This is a challenge that quantum physicists have been working on for decades. By grouping these possibilities into distinct sets, the researchers were able to create a model that describes not just the interactions between the photon and the emitter, but also how the energy from that interaction travels into the distant “far field.” At the same time, they were able to use their calculations to produce a visualization of the photon itself. “Our calculations enabled us to convert a seemingly insolvable problem into something that can be computed. And, almost as a by-product of the model, we were able to produce this image of a photon, something that hasn’t been seen before in physics,” said first author Benjamin Yuen, a professor in the University of Birmingham’s School of Physics and Astronomy. The shape of a single photon according to a new theory presented by researchers at the University of Birmingham. Courtesy of the University of Birmingham/Benjamin Yuen. The work opens new avenues of research in quantum physics and materials science. By being able to precisely define how a photon interacts with matter and with other elements of its environment, scientists can design new nanophotonic technologies that could change secure communications securely, pathogen detection, or the control of chemical reactions at a molecular level. “The geometry and optical properties of the environment has profound consequences for how photons are emitted, including defining the photons shape, color, and even how likely it is to exist,” said co-author, professor Angela Demetriadou, also at the University of Birmingham. “This work helps us to increase our understanding of the energy exchange between light and matter, and secondly to better understand how light radiates into its nearby and distant surroundings,” Yuen said. “Lots of this information had previously been thought of as just ‘noise’ — but there’s so much information within it that we can now make sense of, and make use of. By understanding this, we set the foundations to be able to engineer light-matter interactions for future applications, such as better sensors, improved photovoltaic energy cells, or quantum computing.” The research was published in Physical Review Letters (www.doi.org/10.1103/PhysRevLett.133.203604).