Atomic processes take place on extremely short time scales. Measurements at the Vienna University of Technology (TU Vienna) can now visualize these processes.

Markus Kitzler (left) und Xinhua Xie

A strong laser beam can remove an electron from an atom--a process which takes place almost instantly. At the Vienna University of Technology, this phenomenon could now be studied with a time resolution of less than ten attoseconds (ten billionths of a billionth of a second). Scientists succeeded in watching an atom being ionized and a free electron being “born.” These measurements yield valuable information about the electrons in the atom, which up until now hasn't been experimentally accessible, such as the time evolution of the electron’s quantum phase--the beat to which the quantum waves oscillate.

Wave-like Quantum Interference

In the experiment, short laser pulses are fired at atoms. Each laser pulse can be described as a light wave--the wave sweeps over the atom, and therefore, the electric field around the atom changes. The electric field rips an electron away from the atom--but the precise moment at which this happens cannot be defined. “The electron is not removed from the atom at one point in time during the interaction with the laser pulse. There is a superposition of several processes, as it is often the case in quantum mechanics,” says Markus Kitzler from the Photonics Institute at TU Vienna. One single electron leaves the atom at different points in time, and these processes combine, much like waves on a water surface, combining to a complex wave pattern.

“These quantum mechanical wave-interferences give us information about the initial quantum state of the electron during the ionization process,” says Professor Joachim Burgdörfer (Institute for Theoretical Physics, TU Vienna), whose research team closely collaborated with the experimentalists at the Photonics Institute.