Researchers have been able to photograph the shadow of a single atom for the first time.

And this absorption imaging took five years of work. They basically wanted to investigate how few atoms are required to cast a shadow and they found it takes just one. At the heart of the effort is a super high-resolution microscope, which makes the atom's shadow dark enough to see. 

People still use optical microscopes in research?  Apparently so.  And the Griffith University team claims no other facility in the world has the capability for such extreme optical imaging. They did it by isolating it in a chamber and immobilizing it in free space using electrical forces. 

"We have reached the extreme limit of microscopy; you can not see anything smaller than an atom using visible light," Professor Dave Kielpinski of Griffith University's Centre for Quantum Dynamics in Brisbane, Australia. 

They trapped single atomic ions of the element ytterbium and exposed them to a specific frequency of light. Under this light the atom's shadow was cast onto a detector, and a digital camera was then able to capture the image. "By using the ultra hi-res microscope we were able to concentrate the image down to a smaller area than has been achieved before, creating a darker image which is easier to see," Kielpinski said. "If we change the frequency of the light we shine on the atom by just one part in a billion, the image can no longer be seen." 


Researchers photograph the shadow of a single atom for the first time. Credit: Griffith University

Research team member Dr Erik Streed said the implications of these findings are far reaching. "Such experiments help confirm our understanding of atomic physics and may be useful for quantum computing." 

Knowledge is nice, but are there any benefits for this kind of biomicroscopy?

"Because we are able to predict how dark a single atom should be, as in how much light it should absorb in forming a shadow, we can measure if the microscope is achieving the maximum contrast allowed by physics," said Streed. This is important if you want to look at very small and fragile biological samples such as DNA strands where exposure to too much UV light or x-rays will harm the material. 

We can now predict how much light is needed to observe processes within cells,under optimum microscopy conditions, without crossing the threshold and destroying them."

And this may get biologists thinking about things in a different way.

"In the end, a little bit of light just might be enough to get the job done."

Published in Nature Communications