With all the press and hype in recent months surrounding potential discoveries (i.e., statistical verifications) of sub-atomic particles, such as the Higgs Boson, it is easy to forget one glaring fact: no one has ever seen or captured an image of a single atom.*
That is, until now. This week, a research team at Griffith University has been able to capture the “‘shadow” of a single atom — an ytterbium atom — using a super-high-resolution microscope.
The breakthrough achievement was accomplished through combining two different techniques: the first involves trapping, or holding, an atom in “free space” in a nano-scale chamber (and applying an electrical field to control it). The second technique involves bombarding the atomic ion with a highly specific frequency of light. This light causes the atom to cast a shadow onto a detector that is dark enough to digitally photograph (as a general rule in microscopy, the darker the image, the easier it is to see).
“We have reached the extreme limit of microscopy; you can not see anything smaller than an atom using visible light,” said Professor Dave Kielpinski of Griffith University’s Centre for Quantum Dynamics in Brisbane, Australia, in a press release.
Initially, the team had wanted to determine how many atoms were needed to cast such an atomic scale shadow. This successful experiment proved that it only takes one.
The remarkable achievement in extreme optical imaging overcomes what is known as the diffraction limit (or Abbe diffraction limit), wherein the optical resolution of an object can not be achieved when the object’s size is less that half the wavelength of the light source.
The technology used here is so precise that a variation in the light’s frequency by just one billionth would render the atom invisible.
In the same press announcement, Dr. Erik Streed, another research team member, discussed the implications and application of this breakthrough:
“Such experiments help confirm our understanding of atomic physics and may be useful for quantum computing.”
There is also great potential benefit here for the field 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. 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.”
The experiments were conducted over the past 5 years, and the results were published this week in Nature Communications, under the title: “Absorption imaging of a single atom ”
* Note: In 2009, researchers (Gross et al) were able to directly image the structure of a pentacene (5-carbon ring) molecule (also depicting its shadow) using Atomic Force Microscopy [see: Science, 28 August, 2009, pgs. 1110-1114]
Photo and cartoon diagram: Kielpinski/Streed, GriffithUniversity