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Trapped! New cooling method for charged particles

Transmission of cooling power between two Penning traps

PTBnews 1.2022
Especially interesting for

fundamental research

quantum technology

A new method to cool protons by means of laser-cooled ions – in this case, beryllium ions – has been successfully implemented for the first time worldwide. What is new about this method is that the cooling power can now be transmitted via a resonant electric circuit, covering an enhanced distance of 9 cm from one trap to the other. In this way, the proton in one of the traps can be cooled down to much lower temperatures than previously.

The particles are stored inside the golden structure in the center. The setup is hollow inside and similar to a stack of washers of different sizes. (Picture credits: Stefan F. Sämmer/JGU Mainz)

To be able to perform precise measurements on single ions, these ions must be enclosed and stored in a trap and must move as little as possible. Energy is removed from the charged particles to reach this state, which leads to their cooling down. Thanks to this indirect laser cooling method, the research team of the BASE collaboration project has been able to lower the temperature by a factor of approx. 10 compared with the results obtained by the previously best method of cooling protons. In this way, they have reached a temperature of a few kelvins – close to absolute zero.

Another advantage of the new double- trap cooling method is that it can also be used on antimatter particles. In a single-trap cooling system, matter and antimatter would mutually destroy each other. This new setup therefore allows a precise comparison between protons and antiprotons – and thus investigations of the fundamental issue as to why there is more matter than antimatter in the universe.

Whereas previous indirect cooling methods required distances of 0.1 mm or less between the particles to be cooled and the beryllium ions, the new method is able to transmit the cooling power over a spatial divide and a distance of 9 cm. This sets the stage for more in-depth research projects and allows the Lamor and cyclotron frequency to be measured precisely and disturbance-free. The BASE collaboration would, moreover, like to perform such measurements in its search for dark matter with the help of antimatter, too.

In the future, it should become possible to cool the particles still more and even getting them closer to absolute zero, where freezing prevents any motion. The particles could then be entirely controlled in all degrees of freedom. For this purpose, it is planned to use quantum logic techniques. Such methods of quantum manipulation are being developed by the Leibniz Universität Hannover and PTB within the BASE collaboration project.

Christian Ospelkaus
QUEST Institute at PTB
Phone: +49 531 592-4740
Opens local program for sending emailchristian.ospelkaus(at)ptb.de

Scientific publication

M. Bohman, V. Grunhofer, C. Smorra et al.: Sympathetic cooling of a trapped proton mediated by an LC circuit. Nature 596, 514–518 (2021)