5 November 2026

Photo: UHH/Schauss

The illustration shows fermionic atoms of three flavors in an optical lattice. A quantum gas microscope can detect each atom individually with spatial resolution, making it possible to control interactions specifically.

For the first time, an international team of researchers from Germany, Thailand, India, China and United States has created a three-component Hubbard system with tunable interactions in the laboratory. In doing so, the team used a quantum gas microscope to make the individual atoms visible. The study, which was published in “Science”, provides an important foundation for future quantum simulations of nuclear physics and materials science.

Ultracold atoms are often employed to construct systems that resemble those found in solid-state physics. In this context, the fermionic atoms play the role of electrons in a solid. This system is unique in that it realizes a Hubbard model, which is one of the most important models for describing the interactions of fermions on a lattice. This approach is considered particularly promising for understanding high-temperature superconductivity.

The standard Hubbard model typically considers two spin states: spin-up and spin-down. A third component makes the system significantly more versatile, enabling researchers to investigate richer quantum mechanical phases.

Ultracold atoms in an optical lattice are an excellent platform for quantum simulations. The atoms in the lowest energy state of the lattice form a quantum system in which they tunnel from one lattice site to another, effectively swapping places. Identical fermions cannot occupy the same location, but if distinguishable fermions meet at a single location, a magnetic-field-dependent interaction energy arises.

Strong interactions prevent particles from 'flowing' freely

In the current study, the team led by Prof. Peter Schauss, who is conducting research at the University of Hamburg and in the Cluster of Excellence “CUI: Advanced Imaging of Matter”, realized for the first time a three-component Hubbard model using ultracold atoms with tunable interactions. The team also sought to detect fundamental states and phases in the experiment.

"It was particularly important to us to observe a so-called Mott state, in which the interactions suppress the double occupation of sites," says Schauss. In this case, strong interactions prevent particles from 'flowing' freely between lattice sites, leading to insulating behavior. Paradoxically, it is near Mott states that high-temperature superconductivity emerges.

The researchers used an instrument known as a quantum gas microscope, which can detect each individual atom with spatial resolution. By utilizing atoms in different internal states, the experiment was able to realize various types of fermions, allowing the team to ultimately use three distinct states. This results in a system that, while very different from the electrons on a lattice known from solid-state physics, resembles nuclear physics, where quarks can have three different colors.

The experimental realization was surprisingly stable

“It turned out that the experimental realization is surprisingly stable,” said Schauss. “Usually, one fears that three-body collisions could quickly destroy the system. Despite this potential danger, we were able to successfully carry out the measurements and observe a Mott insulator.” In addition, the researchers identified many other phases. These depend on the strength of the interactions between the three states in each case. For example, it was found that in the same system, both ferromagnetic correlations between two states and antiferromagnetic correlations between two others can occur.

In addition, the researchers developed a method of determining the number of triple-occupied lattice sites. The measured values agreed with the results of numerical calculations, performed by collaborators at Rice University. The researchers plan to refine the interactions in their model further in the long term so that they can study lattice models of quantum chromodynamics (QCD) in the laboratory.

Citation

Jirayu Mongkolkiattichai, Liyu Liu, Sohail Dasgupta, Kaden R. A. Hazzard, Peter Schauss

Quantum gas microscopy of three-flavor Hubbard systems

Science (2026)

DOI: 10.1126/science.adv1247