Physicists capture images of atoms that have ever interacted in free space

MIT physicists successfully took photos of individual atoms freely interacting in space for the first time, capturing visual evidence of quantum behavior previously predicted only by theory. Breakthrough imaging technology reveals the mysterious dance of subatomic particles in unprecedented detail.

A research team led by Professor Martin Zwierlein has developed a method that allows them to observe quantum phenomena that have never been seen directly before. Their discovery, published in a physical review letter on May 5, exposed the hidden world of atomic interactions that form the basis of quantum mechanics.

“We were able to see individual atoms in these interesting clouds of atoms, and the things they influenced each other, which was beautiful,” said Zwierlein, a professor of physics at MIT.

To appreciate the scale of this achievement, consider that an atom is about one tenth of its diameter – about one million thickness of human hair. However, unlike hair, atoms operate according to the strange rules of quantum mechanics, where the exact position and speed cannot be known at the same time.

The MIT team’s approach is very different from conventional atomic imaging methods. Their technology does not simply capture the shadow of atomic clouds, but rather a technique called “atomic resolution microscopy” that first contains atoms in a loose laser trap that can move freely. The researchers then flashed on the lattice of light, which immediately freezes atoms and then illuminates them with a second laser. The resulting fluorescence reveals the exact position of each atom.

“The most difficult part is collecting light from the atoms without boiling it out of the optical lattice,” Zwierlein explained. “You can imagine that if you brought the flamethrower of these atoms to these atoms, they wouldn’t be like that. So, over the years, we’ve learned some tips.”

What makes this approach particularly valuable is its ability to capture atoms in the midterm. “This is the first time we’ve done it in situ, where we can suddenly freeze the motion of atoms when they interact strongly and see them, one by one. That’s what makes this technology more powerful than before.”

Visualize quantum behavior

The researchers applied their imaging technology to two different types of atoms: bosons (such as sodium atoms) and fermions (such as lithium atoms). These particle classifications represent the fundamental split in quantum physics – bosons naturally attract, while fermions usually repel.

When the sodium boson was imaged at very low temperatures, the team captured visual evidence of the “beam”, a quantum effect where the bosons share the same quantum state, forming the so-called boson condensate. This state of matter has given MIT’s Wolfgang Ketterle a share of the 2001 Nobel Prize in Physics.

More importantly, these images reveal the fluctuating properties of these particles, which was 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 have a lot more understanding of the world from this wave-like nature,” Zwierlein notes. “But it’s really difficult to look at these quantums, wave-like effects. But in our new microscope, we can visualize this wave directly.”

When the researchers examined lithium fermions, they observed another predicted but never seen phenomenon – the Fermion pairing in free space. This pairing mechanism is believed to be the basis of superconductivity, with current flowing without resistance.

Bridge theory and reality

“This pairing is the foundation of mathematical architecture, and people come up with the basis for explaining experiments. But when you see a picture like this, it shows an object found in a mathematical world in the photo,” said Richard Fletcher, co-author of the study. “So, it’s a good reminder that physics is about physical things. It’s real.”

The team’s papers appear along with the work of two other research groups, including a research group led by Ketterle. Each group used similar imaging techniques, Ketterle’s team visualized enhanced pair correlations between bosons, while a group from école Normale Supérieure in Paris imaged non-interactive fermions.

The study was written by MIT graduate students Ruixiao Yao, Sungjae Chi and Mingxuan Wang along with Fletcher.

Beyond visualization

Conventional atomic imaging methods have significant limitations. “These technologies allow you to see the overall shape and structure of atomic clouds, rather than the overall shape and structure of a single atom itself,” Zwierlein notes. “It’s like seeing clouds in the sky, rather than the single water molecules that make up the clouds.”

Going forward, researchers plan to use their new imaging capabilities to study more exotic quantum behaviors, especially in the field of quantum Hall physics, where electrons show novel related behaviors in the presence of magnetic fields.

“That’s where the theory is really furry – people start drawing pictures instead of being able to write mature theories because they can’t solve it completely,” Zwierlein said. “Now, we can verify whether these quantum hall countries’ comics are really real. Because they are very strange states.”

The study has received support from multiple organizations, including through the MIT-Harvard Ultracold Atoms, the Air Force Office of Scientific Research, the Army Research Office, the Department of Energy, the Defense Advanced Program Research Bureau, the Vannevar Bush Teacher Scholarship, and the David and Lucile Packard Foundation.

For physicists, these images not only represent technological achievements, but also provide visual confirmation of quantum behavior that has been unavailable for decades, giving us a greater understanding of the mysterious quantum world based on our physical reality.