For the first time in physics history, scientists have developed a mathematical framework that allows them to visualize the precise shape of a single particle of light, known as a photon. This breakthrough, achieved by researchers at the University of Birmingham, represents a fundamental advance in our understanding of how light interacts with matter at the quantum level.
At its core, the research solves a problem that has puzzled quantum physicists for decades: how to accurately model the infinite possibilities of how light can interact with and travel through its environment. The team accomplished this by developing a new mathematical approach that groups these countless possibilities into distinct, manageable sets.
“The geometry and optical properties of the environment has profound consequences for how photons are emitted, including defining the photons shape, colour, and even how likely it is to exist,” explains Professor Angela Demetriadou from the University of Birmingham in a statement.
To understand the significance of this work, now published in Physical Review Letters, consider how light behaves in everyday situations. When sunlight passes through a stained glass window, its interaction with the glass creates beautiful colors. At the quantum level, these interactions become far more complex, with individual photons interacting with atoms and molecules in ways that previous mathematical models struggled to describe accurately.
The research team’s new approach, called “pseudomode transformation,” allows scientists to track precisely how light bounces around and interacts with matter in complex nanoscale systems. What makes this method particularly powerful is its ability to describe both what happens near the source of the light and how the energy travels out into the surrounding space.
“Our calculations enabled us to convert a seemingly insolvable problem into something that can be computed,” says Dr. Benjamin Yuen, the study’s first author. “And, almost as a bi-product of the model, we were able to produce this image of a photon, something that hasn’t been seen before in physics.”
To demonstrate their method, the researchers studied what happens when a quantum emitter (such as an atom or molecule) interacts with a tiny silicon sphere just one micrometer in diameter – about one-hundredth the width of a human hair. This seemingly simple system revealed a complex dance of quantum interactions that their new mathematical framework could precisely describe.
“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,” explains Dr. Yuen. “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.”