Ytterbium atoms have been used to make a very cold magnet
Carlos Clarivan/Science Photo Library

A new kind of quantum magnet is made up of atoms only a billionth of a degree warmer than absolute zero – and physicists aren’t certain how it behaves.

A regular magnet strongly repels or attracts magnetic objects depending on whether electrons inside it are in an “up” or a “down” quantum spin state, a property alike to having a north and south pole aligned in a particular direction. However, this isn’t the only property that can be used to make a magnet.

Kaden Hazzard at Rice University in Texas and his colleagues by making use of ytterbium atoms made a magnet based on a spin-like property that has six options, each labelled with a color.

The researchers enclosed the atoms in a vacuum in a small metal and glass box, and then used laser beams to cool them down. The push from the laser beam produces the most energetic atoms release some energy, which lowers the overall temperature, alike to blowing on a cup of tea.

The atoms ordered in lines and sheets reached about 1.2 nanokelvin, more than 2 billion times colder than interstellar space. For the atoms in three-dimensional arrangements, the situation is so complex that the researchers are still figuring out the finest way to measure the temperature.

Physicists have been very much interested in how atoms interact in exotic magnets like this because they suspect that alike interactions happen in high-temperature superconductors – materials that ideally conduct electricity. By better understanding what happens, they could make good superconductors.

There have been theoretical calculations about such magnets but they have failed to anticipate exact color state patterns or how magnetic exactly they can be, says co-author Eduardo Ibarra-García-Padilla. He says that he and his teammates carried out some of the finest calculations yet while they were analyzing the experiment, but could still only predict the colors of eight atoms at a time in the line and sheet configurations out of the thousands of atoms in the experiment.

Victor Gurarie at the University of Colorado Boulder state that the experiment was just cold enough for atoms to start “paying attention” to the quantum color states of their neighbors, a property that does not impact how they interact when warm. Because calculations are so difficult, similar future experiments may be the only technique for studying these quantum magnets, he says.

Journal reference: Nature Physics

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