Interacting atoms at ultracold temperatures; credit to Sampson Wilcox, RLE@MIT."These effects occur at nanokelvin because we are working with dilute atomic gases. If you have a dense piece of matter, these same effects may well happen at room temperature."Martin Zwierlein
Individual atoms either avoiding each other or clustering in pairs has been observed for first time, according to researchers. Although atoms move at enormous speeds and are difficult to pin down at ambient temperatures, when they experience ultracold temperatures they slow down considerably, allowing for investigation into how they form exotic states of matter, such as superfluids, superconductors and quantum magnets.
Although it is impossible to model the behavior of high-temperature superconductors as the interactions between electrons are so strong, the team tried instead to develop a “quantum simulator” with atoms in a gas as replacements for electrons in a superconducting solid. As reported in Science [Cheuk et al Science (2016) DOI: 10.1126/science.aag3349], they cooled a gas of potassium atoms to several nanokelvins, and confined the atoms within a 2D sheet of an optical lattice developed. With high-resolution microscopy, they then took images of the cooled atoms located in the lattice.
The scientists had previously developed an experimental protocol for cooling a gas of atoms to near absolute zero before trapping them in a 2D plane of a lattice. At such temperatures, the atoms slowed down sufficiently for them to be captured in images as they interacted across the lattice.
In this study, by observing the correlations between the atoms’ positions, it was confirmed that single atoms interacted in strange ways due to their position. While some avoided each other, others bunched together with alternating magnetic orientations and others seemed to join, creating pairs of atoms next to empty spaces, called Pauli holes, correlating to the exclusion principle that no two electrons can occupy the same quantum state at the same time, and that electrons maintain a specific area of personal space.
Where the gas was more compressed, they noticed that the atoms were more amenable to having close neighbors, and were actually very tightly bunched and exhibited alternating magnetic orientations. They were also found to often hop on top of one another, creating pairs of atoms next to an empty lattice square, reminiscent of a mechanism proposed for high-temperature superconductivity where electron pairs resonating between adjacent lattice sites move through the material without friction if there is the right amount of empty space to allow it.
The group hopes the experiments will offer insight into the origins of superconducting behavior and help to identify the most effective conditions for superconductivity to arise in solids. As team leader Martin Zwierlein explains: “For us, these effects occur at nanokelvin because we are working with dilute atomic gases. If you have a dense piece of matter, these same effects may well happen at room temperature.”