Calculations intended to feel out the interactions between light and the material that produces it may inadvertently describe the photon's outline, revealing its shape in unprecedented detail.
A new model, developed by physicists in the UK, provides a complete quantum description of the point at which light and matter engage, maintaining a picture of how that interaction continues to affect the particle as it zooms through a tangle of fields.
"Our calculations enabled us to convert a seemingly insolvable problem into something that can be computed," says theoretical physicist Ben Yuen of the University of Birmingham.
"And, almost as a byproduct of the model, we were able to produce this image of a photon, something that hasn't been seen before in physics."
With properties of both a wave rippling through an intangible ocean, and a massless object zooming along at the limit of speed itself, the photon's dual nature challenges our imagination.
Its existence is a riddle, something that can be represented with uncanny precision by the mathematics of probability but has no convenient analogy we can use to picture what that might look like in our world of shapes, sizes, and colors.
Yet some of light's qualities may translate into something familiar. Within its quantum coding – known as its wave function – lie rules dictating the boundaries of the photon's influence on its environment.
What we experience as the pale glow of a neon street sign or rays of sunshine on a summer's day are exchanges between atoms in the language of electromagnetism. As electrons shift in their orbits, they shout in corresponding units of energy known as photons.
Improvements in our technological ability to constrain and guide this electromagnetic conversation have revealed incredible complexities in light's passage through a material Universe.
This journey can no longer be understood as a one-way passage of energy from a point of emission to a destination; rather, its quantum nature preserves a kind of memory that continues to feed back along its path in what physicists called a non-Markovian dynamic.
"The geometry and optical properties of the environment has profound consequences for how photons are emitted, including defining the photon's shape, color, and even how likely it is to exist," says University of Birmingham theoretical physicist Angela Demetriadou.
To better understand these quantum rules of a photon's non-Markovian trip through time and matter, Yuen and Demetriadou developed a unique model that described the kind of open environment light would engage with immediately after being emitted by atoms in a nanoparticle of silicon.
Not only did their ground-up theory appear to capture the propagation of light from its starting point with unprecedented precision, it found definition in the "noise" of interactions that accurately described gradients of intensity of the field surrounding quanta of light.
As our desire for smaller, faster, more precise, and more sensitive technology increases, our need to accurately predict the quantum footprints photons leave in their wake will become increasingly important.
"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," says Yuen.
This research was published in Physical Review Letters.