Ultracold atoms and ultrafast lasers

July 6, 2018, University of Hamburg
Ultracold atoms and ultrafast lasers
Ultrashort laser pulses for studying the strong-field ionization of ultracold atoms. Credit: UHH/Wessels

Two separate research fields have been united in Hamburg for the very first time. Ultrashort laser pulses enable us to observe and manipulate matter on very short time scales, whereas ultracold atoms permit experiments with high precision and controllability. Scientists from Universität Hamburg have united the two research fields and succeeded in observing the emergence of ions in ultracold atoms. Their findings have been published in the new scientific journal Communications Physics.

More than a century ago, Albert Einstein published his theoretical work on the photo-effect, which fundamentally describes the photoionization of matter, or the process of dissolving electrons from by using . This discovery earned him a Nobel Prize in 1921. However, it turns out that the process is very complicated in detail. Up until now it has been nigh impossible to carry out experimental measurements of the absolute probability, e.g., the percentage of atoms ionized after light irradiation. The teams of scientists led by Prof. Dr. Markus Drescher and Prof. Dr. Klaus Sengstock have uniquely combined expertise in with phenomena of ultrafast physics, which has opened up a fundamentally new experimental approach.

Ultrashort pulses can be so intense that they rip atoms apart. This process is called strong-field ionization and the details depend on the energy and color of the laser light. Up until now, it was not always possible to know which ionization regime dominates. The scientists have now succeeded in observing this in detail by using ultracold atoms. As there is hardly any atomic motion after the ionization process, it is possible to accurately measure the regimes.

The scientists used laser light to cool rubidium atoms to ultracold temperatures of 100 nanokelvins, only slightly above absolute zero temperature of -273.15° Celsius. An intense ultrashort laser pulse illuminated parts of the cloud of for a very short time of 215 femtoseconds (a femtosecond is one millionth of one billionth of a second) and ionized a fraction of the atoms. The remaining atomic density was imaged onto a camera so that the amount of ionized atoms could be accurately measured.

In particular, the scientists observed that the atomic bond in an optical light field is modified so fast that the atomic shell cannot follow the oscillation of the light field. During ionization the atom thus absorbs multiple light particles (photons) simultaneously. "The presented work paves the way towards further experiments using for creating ions and electrons in ultracold atomic samples," lead author Philipp Wessels from Prof. Sengstock's group explains. "This leads to precise measurements of ultrafast processes by using ultracold atoms, because these systems can be controlled extremely well experimentally." The results can also be used to help realize quantum computers based on ultracold ions. Such computers may solve certain problems faster than conventional ones.

Parallel to these experiments, an international collaboration with Prof. Nikolay Kabachnik (Moscow State University) and Prof. Andrey Kazansky (Ikerbasque, Spain) calculated the theoretically. The scientists modelled the quantum mechanical interaction between atom and laser field, with the following result: the theoretical predictions are in perfect agreement with the measured data.

Explore further: Quantum mechanics: entanglements in ultracold atomic clouds

More information: Philipp Wessels et al. Absolute strong-field ionization probabilities of ultracold rubidium atoms, Communications Physics (2018). DOI: 10.1038/s42005-018-0032-5

Related Stories

Quantum mechanics: entanglements in ultracold atomic clouds

June 27, 2018

A system's state is characterised as entangled or quantum correlated if two or more particles cannot be described as a combination of separate, independent states but only as a whole. Researchers at the Kirchhoff Institute ...

Detecting the shape of laser pulses

May 17, 2018

A team of researchers at the Center for Relativistic Laser Science, within the Institute for Basic Science (IBS) have developed a method to measure the shape of laser pulses in ambient air. Unlike conventional strategies, ...

Quantum LEGO—building ultracold molecules

June 12, 2018

Cooling matter is not easy. Atoms and molecules have the tendency to jump around, to rotate and to vibrate. Freezing these particles by slowing them down is a complicated process. For individual atoms, physicists have figured ...

Attoseconds break into atomic interior

February 27, 2018

A newly developed laser technology has enabled physicists in the Laboratory for Attosecond Physics (jointly run by LMU Munich and the Max Planck Institute of Quantum Optics) to generate attosecond bursts of high-energy photons ...

Cooling with the coldest matter in the world

November 24, 2014

Physicists at the University of Basel have developed a new cooling technique for mechanical quantum systems. Using an ultracold atomic gas, the vibrations of a membrane were cooled down to less than 1 degree above absolute ...

Recommended for you

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.