To understand an atom or a molecule, physicists must not only know their internal structure, but also be able to describe the motion of the electrons. Due to the extremely high speed, this was not possible until now. Now, a European research team has developed such a measurement method. They report about it in Physical Review Letters 105, 053001.
At the level of atoms and molecules, our everyday conception of the world no longer works. An electron is usually thought of as a small particle. "That's it, too," says Prof. Marc Vrakking, Director at the Max-Born Institute for Nonlinear Optics and Short Pulse Spectroscopy (MBI) in Berlin. "But to understand it, sometimes we have to look at it from the quantum mechanical point of view and imagine it as a wave packet." Physicists can use this abstract idea to explain phenomena that later coincide with our everyday ideas.
Since one can not directly observe the motion of an electron because it is too fast, the European research team has measured the properties of the electron as a wave packet. Once they knew all the properties of this wave packet, they were able to derive from it the complete motion of the electron.
For the experiment, the researchers have used the principle of superposition of waves, the so-called interference. They have followed the same procedure as in experiments with light rays, in which regular light falls through two slits and on the screen behind light and dark stripes are visible. The rays of light behave like waves - meet two wave mountains on each other, resulting in a bright strip, a wave crest and a wave trough up and appear as a dark strip.