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Light and matter can remain at separate temperatures even while interacting with each other for long periods, according to new research that could help scale up an emerging quantum computing approach in which photons and atoms play a central role.

In a theoretical study published in Physical Review Letters, a University at Buffalo-led team reports that interacting photons and atoms don’t always rapidly reach thermal equilibrium as expected.

Thermal equilibrium is the process by which interacting particles exchange energy before settling at the same temperature, and it typically happens quickly when trapped light repeatedly interacts with matter. Under the right circumstances, however, physicists found that photons and atoms can instead settle at different—and in some cases opposite—temperatures for extended periods.

For many years, cesium atomic clocks have been reliably keeping time around the world. But the future belongs to even more accurate clocks: optical atomic clocks. In a few years’ time, they could change the definition of the base unit second in the International System of Units (SI). It is still completely open, which of the various optical clocks will serve as the basis for this.

The large number of optical clocks that the Physikalisch-Technische Bundesanstalt (PTB), as a leading institute in this field, has realized could be joined by another type: an optical multi-ion clock with ytterbium-173 ions. It could combine the high accuracy of individual ions with the improved stability of several ions. This is the result of a cooperation between PTB and the Thai metrology institute NIMT.

The team led by Tanja Mehlstäubler reports on this in the current issue of the journal Physical Review Letters. The results are also interesting for quantum computing and, with a new look inside the atom, for fundamental research.

Imagine computer hardware that is blazing fast and stores more data in less space. That’s the promise of antiferromagnets, magnetic materials that do not interfere with each other and can switch states at high speed, opening the door to advanced computing and quantum applications.

Magnetism comes from unpaired electrons, tiny particles that orbit an atom’s nucleus. Each electron has a property called spin, which can point up or down. In standard ferromagnets, the atomic spins point in the same direction, creating a strong magnetic field. In antiferromagnets, neighboring spins point in opposite directions, canceling each other out and yielding no net magnetism.

Flipping individual spins in an antiferromagnet requires very little movement of magnetization, which allows ultrafast processing. Antiferromagnets can switch states trillions of times per second, compared with billions for ferromagnets. With net zero magnetism, antiferromagnets can be placed very close together without repelling or attracting each other, allowing more data to be stored in a small space.