Atoms are too small to be seen with conventional microscopes let alone with the naked eye because they are far smaller than the wavelength of visible light. Although we know from the early experiments of J.J. Thomson that most of an atom’s mass is concentrated in a central nucleus surrounded by an orbit of electrons, we have no pictures of how individual atoms interact with their neighbors. Until now.

In a recent breakthrough, a team of MIT researchers led by Professor Martin Zwierlein have captured the first-ever images of individual atoms interacting freely in space. These images confirm behaviors of atoms that were previously only predicted by theory – in another stunning example of the triumph of human thought. Crucially, the new images line up well with the elusive quantum theory of matter, which predicts that entities such as photons behave as both particles and waves.

A Quick Review of Atomic Physics

Atoms are composite particles. An entire atom is classified as either a boson or a fermion based on the total number of its constituent elementary particles (protons, neutrons, and electrons). In theory, bosons attract, whereas fermions repel (the core theoretical framework is the spin-statistics theorem in relativistic quantum field theory but we will not get into that). What’s cool about the new imaging technique developed by the researchers is that it shows for the first time that nature is exactly what the theory predicts. In the picture below, bosons are shown bunched up, forming a wave, a phenomenon while on the left, we see fermions moving around freely instead of being bunched together.

The imaging results thus shows for the first time that bosons attract while fermions repel. This is exactly as predicted by the spin-statistics theorem and the implied Pauli Exclusion Principle (named after the theoretical physicist, Wolfgang Pauli). To use the jargon, fermions repel because they have non-integer spins and obey the Pauli exclusion principle while bosons attract because they have integer spins and do not obey the Pauli exclusion principle.

The new discovery solves one of the major challenges imposed by Heisenberg’s uncertainty principle. This principle predicts that it’s impossible to know both an atom’s exact position and its speed at the same time, which is why standard imaging techniques such as absorption images can only provide a blurry view of atomic interactions (they show atoms in a cloud but hide the atoms themselves). How did the new technique overcome this obstacle? In a nutshell, through the ingenious use of finely tuned lasers. Very roughly, the procedure is as follows. First, the researchers allow a cloud of atoms to move and interact freely. Then, they turn on a lattice of light that briefly freezes the atoms in their tracks. Lastly, they apply highly precise lasers to quickly illuminate the suspended atoms, creating an instantaneous picture of their positions before the atoms dissipate.

Practical Implications of the New Imaging Technique

The ability to visualize individual quantum interactions in real space, rather than relying on abstract mathematical models, has several practical implications. First, the direct observation of fermion pairing provides a visual blueprint for how electrons pair up in superconducting materials. A better understanding of this mechanism could lead to the development of materials that transmit energy and data without any loss of friction. Second and more speculatively, by providing a powerful new way to observe the quantum building blocks of the universe, this breakthrough is a significant leap forward that could advance future quantum technologies such as quantum computing.