Under the spotlight: Scientists sketch the shape of a photon
“Our calculations enabled us to convert a seemingly insolvable problem into something that can be computed."
Photons are massless, chargeless particles that zoom along at the speed of light and can only be identified by their interactions with matter.
Humans will never be able to "see" these elementary units of light, let alone capture them in a glass bottle to be studied.
But scientists from the University of Birmingham think they've worked out the "precise shape of a single photon" in a discovery that could inspire the creation of tiny light-manipulating machines.
A study published in Physical Review Letters examines these individual particles of light in "unprecedented detail" to show how "they are emitted by atoms or molecules and shaped by their environment". This work allowed them to produce an image depicting the shape of a photon - which looks like the sort of psychedelic pattern more associated with an ayahuasca session deep in the jungle rather than sober experimentation in a laboratory.
First author Dr Benjamin Yuen, in the University’s School of Physics, explained: “Our calculations enabled us to convert a seemingly insolvable problem into something that can be computed. 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.”
The infinite possibilities of photons
Yuen and his team examined how photons are emitted by atoms or molecules and then shaped by their environment.
The nature of this interaction "leads to infinite possibilities" for light to exist and then travel through its surrounding environment at the speed of light.
However, its interactions are "exceptionally hard to model", posing a conundrum that quantum physicists have spent decades trying to unravel.
The Birmingham team's paper presents a new way to model the way in which light interacts with matter in complex photonic systems, like nanophotonic devices (tiny structures that manipulate light).
Instead of relying on traditional approximations, it turns continuous light modes into a simpler, discrete set called “pseudomodes.” This method makes it easier to accurately describe how light behaves and travels.
By grouping these possibilities into distinct sets, the Birmingham team were able to produce a model that describes not only the interactions between the photon and the emitter, but also how the energy from that interaction travels into the distant "far field".
T hey were able to use their calculations to produce a visualisation of the photon itself.
Dr Benjamin Yuen, added: “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. 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.”
Let there be light
It is hoped that the work will open new avenues of research for quantum physicists and material science. The ability to precisely define how a photon interacts with matter and other aspects of the environment could allow scientists to design
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 (tiny devices that manipulate light) that could "change the way we communicate securely, detect pathogens, or control chemical reactions at a molecular level", among many other use cases.
Co-author Professor Angela Demetriadou, also from the University of Birmingham, said: “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.”
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