A quantum magnet is 3 billion times colder than interstellar space, scientists discover

This discovery could help scientists build high-temperature superconductors or insulators.
Fabienne Lang

"Japanese and U.S. physicists have used atoms about 3 billion times colder than interstellar space to open a portal to an unexplored realm of quantum magnetism," explained a Rice University press release – where the study's U.S. scientists are based.

That sentence belongs in a sci-fi movie, but it also belongs right here in real life.

What the scientists uncovered is a new kind of quantum magnet that is made out of atoms just a billionth of a degree warmer than absolute zero – the unattainable temperature where all motion stops – as NewScientist described.

The study was published in the journal Nature Physics on September 1.

Matter colder than deep space

Rice University's Kaden Hazzard, the corresponding theory author of the study, explained in the press release that the team based in Kyoto, led by study author Yoshiro Takahashi, used lasers to cool its fermions, atoms of ytterbium, (particles that include things like electrons and are one of two types of particles that all matter is made of). Ultimately, they created a magnet based on a spin-like property that has six color-labelled options.

The team cooled the particles down to such low temperatures because "the physics starts to become more quantum mechanical, and it lets you see new phenomena," said Hazzard.

Ultimately, the quantum behaviors of atoms become much more evident when they are cooled within a fraction of a degree of absolute zero. By using lasers to cool atoms down, it's easier to observe them as their movements become restricted to optical lattices. These lattices are 1D, 2D, and 3D channels of light that can be used as quantum simulators capable of solving complex problems that conventional computers can't solve.

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A quantum magnet is 3 billion times colder than interstellar space, scientists discover
An artist’s conception of the complex magnetic correlations

Takahashi’s lab in Japan used these optical lattices to simulate a Hubbard model, a regularly-used quantum model used to investigate the magnetic and superconducting behavior of materials.

As the team explained in the press release, "The Hubbard model simulated in Kyoto has special symmetry known as SU(N), where SU stands for special unitary group — a mathematical way of describing the symmetry — and N denotes the possible spin states of particles in the model."

Ytterbium atoms have six possible spin states, and the Kyoto simulator is the first to reveal magnetic correlations in an SU(6) Hubbard model, which are impossible to calculate on a computer.

Study co-author Eduardo Ibarra-García-Padilla, a graduate student in Hazzard's research group, said "the Hubbard model aims to capture the minimal ingredients to understand why solid materials become metals, insulators, magnets or superconductors."

Ibarra-García-Padilla further explained: "To have the capability to engineer it in a laboratory is extraordinary. If we can understand this, it may guide us to making real materials with new, desired properties."

Physicists have long been interested in how atoms interact in exotic magnets like this because they imagine similar interactions occur in high-temperature superconductors – materials that perfectly conduct electricity. By better understanding what happens, they could put together better superconductors, for instance.

These experiments carried out in Kyoto open doors for physicists to learn how these complex quantum systems operate by directly watching them in action.

The results are the first observations of particle coordination in an SU(6) Hubbard model, Hazzard said.

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