Physicists Capture First-Ever Images of Atoms Interacting in Free Space

For the first time, physicists at MIT have succeeded in taking pictures of individual atoms as they freely interact in space, capturing visual evidence of quantum behaviors previously only predicted by theory. The breakthrough imaging technique reveals the mysterious dance of subatomic particles in unprecedented detail.

The research team, led by Professor Martin Zwierlein, has developed a method that allows them to observe quantum phenomena that have never been directly seen before. Their findings, published in the May 5 issue of Physical Review Letters, expose the hidden world of atom interactions that form the foundation of quantum mechanics.

“We are able to see single atoms in these interesting clouds of atoms and what they are doing in relation to each other, which is beautiful,” says Zwierlein, the Thomas A. Frank Professor of Physics at MIT.

To appreciate the scale of this achievement, consider that a single atom is approximately one-tenth of a nanometer in diameter – about one-millionth the thickness of a human hair. Yet unlike hair, atoms operate according to the strange rules of quantum mechanics, where precise position and velocity cannot be simultaneously known.

The MIT team’s approach differs dramatically from conventional atom imaging methods. Rather than simply capturing the shadow of an atom cloud, their technique – called “atom-resolved microscopy” – first contains atoms in a loose laser trap where they can move freely. The researchers then flash on a lattice of light that instantly freezes the atoms in position before illuminating them with a second laser. The resulting fluorescence reveals each atom’s exact location.

“The hardest part was to gather the light from the atoms without boiling them out of the optical lattice,” Zwierlein explains. “You can imagine if you took a flamethrower to these atoms, they would not like that. So, we’ve learned some tricks through the years on how to do this.”

What makes this method particularly valuable is its ability to capture atoms in mid-interaction. “It’s the first time we do it in-situ, where we can suddenly freeze the motion of the atoms when they’re strongly interacting, and see them, one after the other. That’s what makes this technique more powerful than what was done before,” says Zwierlein.

Visualizing Quantum Behaviors

The researchers applied their imaging technique to two different types of atoms: bosons (like sodium atoms) and fermions (like lithium atoms). These particle classifications represent fundamental divisions in quantum physics – bosons naturally attract, while fermions typically repel.

When imaging sodium bosons at very low temperatures, the team captured visual evidence of “bunching” – a quantum effect where bosons crowd together as they share the same quantum state, forming what’s known as a Bose-Einstein condensate. This state of matter earned MIT’s Wolfgang Ketterle a share of the 2001 Nobel Prize in Physics.

More significantly, the images reveal the wave-like nature of these particles, something first proposed by physicist Louis de Broglie in the early days of quantum mechanics. This wave-particle duality forms the cornerstone of our modern understanding of quantum physics.

“We understand so much more about the world from this wave-like nature,” Zwierlein notes. “But it’s really tough to observe these quantum, wave-like effects. However, in our new microscope, we can visualize this wave directly.”

When examining lithium fermions, the researchers observed another predicted but never-before-seen phenomenon – fermion pairing in free space. This pairing mechanism is believed to be fundamental to superconductivity, where electricity flows without resistance.

Bridging Theory and Reality

“This kind of pairing is the basis of a mathematical construction people came up with to explain experiments. But when you see pictures like these, it’s showing in a photograph, an object that was discovered in the mathematical world,” says study co-author Richard Fletcher, assistant professor of physics at MIT. “So it’s a very nice reminder that physics is about physical things. It’s real.”

The team’s paper appears alongside related work from two other research groups, including one led by Ketterle. Each group used similar imaging techniques, with Ketterle’s team visualizing enhanced pair correlations among bosons, while a group from École Normale Supérieure in Paris imaged noninteracting fermions.

The study is co-authored by MIT graduate students Ruixiao Yao, Sungjae Chi, and Mingxuan Wang, along with Fletcher.

Beyond Visualization

Conventional atom imaging methods have significant limitations. “These techniques allow you to see the overall shape and structure of a cloud of atoms, but not the individual atoms themselves,” Zwierlein notes. “It’s like seeing a cloud in the sky, but not the individual water molecules that make up the cloud.”

Looking ahead, the researchers plan to use their new imaging capability to investigate even more exotic quantum behaviors, particularly in the field of quantum Hall physics, where electrons display novel correlated behaviors in the presence of magnetic fields.

“That’s where theory gets really hairy — where people start drawing pictures instead of being able to write down a full-fledged theory because they can’t fully solve it,” Zwierlein says. “Now we can verify whether these cartoons of quantum Hall states are actually real. Because they are pretty bizarre states.”

The research received support from several organizations, including the National Science Foundation through the MIT-Harvard Center for Ultracold Atoms, the Air Force Office of Scientific Research, the Army Research Office, the Department of Energy, the Defense Advanced Projects Research Agency, a Vannevar Bush Faculty Fellowship, and the David and Lucile Packard Foundation.

For physicists, these images represent more than just technical achievements – they provide visual confirmation of quantum behaviors that have remained hidden from direct observation for decades, bringing us closer to understanding the mysterious quantum world that underlies our physical reality.