Study Focuses on Effective Isolation of Ions in Optical and Electrostatic Traps

The results of a research team at the University of Freiburg’s Institute of Physics have been given a special place in the “Nature Photonics” journal: a supplementary “News & Views” article in the print version of the science journal focuses on the work of the team headed by Prof. Dr. Tobias Schätz, Dr. Leon Karpa, Julian Schmidt, and Alexander Lambrecht.

The researchers, in their article “Long lifetimes and effective isolation of ions in optical and electrostatic traps”, explain the technique they used to prevent the formerly unavoidable driven motion of trapped charged atoms.

Lasers of various wavelengths are used to cool the ions to a thousandth of a Kelvin at the start of an experiment. Credit: Julian Schmidt

The experiment starts by trapping individual Barium ions in a quadrupole ion trap, called a Paul trap. By using alternating electric fields, a quadrupole ion trap is able to store charged particles for days. However, this causes the ion to constantly swirl on a microscopic scale and execute a forced driven motion. This often results in undesirable side-effects. For instance, in current experiments with ultracold atoms, the ions heat up the neutral atoms’ bath, which is, in fact, far cooler, like an immersion heater, instead of being cooled. This makes the temperature to increase by a factor of 10,000. Even though this is only just a thousandth of a degree Celsius higher than absolute zero, it already causes heat death for sensitive quantum effects.

This is where the technique, which the team has been designing for its objectives since 2010, comes in: optical trapping of charged atoms. A very bright laser is used to trap the ion in its beam without making it move more. A few years back, this was only possible to optically trap ions for a few milliseconds. Now, due to the work of the Freiburg physicists, it is possible to trap charged atoms for similar timescales as neutral atoms in similar optical traps – a duration of several seconds is many times longer than is needed for experiments. Furthermore, the researchers have revealed that they can also isolate the ions effectively from the remaining outside world. Now, the team hopes to employ this technique to attain 10,000-times lower temperatures and monitor ultracold chemical processes where quantum effects will control the interaction of the particles.

In 2015, Tobias Schätz was awarded a Consolidator Grant from the European Research Council (ERC) for his technique to trap atoms and ions with light: www.pr.uni-freiburg.de/pm/2015/pm.2015-02-17.18.

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