Improving Optical Traps for Ions

Lasers of various wavelengths are used to cool the ions to a thousandth of a Kelvin at the start of an experiment. (Source: J. Schmidt)

A research group from the Institute of Physics at the Uni­versity of Freiburg developed a new method to prevent the previously unavoi­dable driven motion of trapped charged atoms. The experiment begins by trapping indi­vidual Barium ions in a quadrupole ion trap, known as a Paul trap. A quadru­pole ion trap can store charged particles for days using alter­nating electric fields.

However this results in the ion constantly swirling on a micro­scopic scale and executing a forced driven motion. This often leads to unde­sirable side-effects. For example, in current experi­ments with ultra­cold atoms, the ions heat up the bath of neutral atoms – which is actually far cooler – like an immersion heater, instead of being cooled. This causes the tempera­ture to rise by a factor of 10,000. Although this is still barely a thousandth of a degree Celsius above absolute zero, it already leads to heat death for sensi­tive quantum effects.

This is where the method that the group has been deve­loping for its objectives since 2010 comes in: optical trapping of charged atoms. An extremely bright laser is used to trap the ion in its beam without compelling addi­tional movement. A few years ago it was only possible to optically trap ions for a few milliseconds. Thanks to the work of the Freiburg physi­cists, it is now possible to trap charged atoms for similar time­scales as neutral atoms in comparable optical traps – a lifetime of several seconds is several times longer than is required for experi­ments.

In addition, the researchers have shown that they can also isolate the ions ad­equately from the remaining outside world. The team now hopes to use this method to achieve 10,000-times lower tempera­tures and observe ultracold chemical processes in which quantum effects will dominate the inter­action of the particles. (Source: U. Freiburg)

Reference: A. Lambrecht et al.: Long lifetimes and effective isolation of ions in optical and electrostatic traps, Nat. Phot. 11, 704 (2017); DOI: 10.1038/s41566-017-0030-2

Link: Experimental Atomic, Molecular and Optical Physics, Univ. Freiburg, Freiburg, Germany

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