Researchers Measure Quantum Phase of Electrons

Researchers at the Vienna University of Technology are now able to study an electron’s removal from an atom by a powerful laser beam with a time resolution of below 10 as.

The researchers have succeeded in experimentally observing the process of ionization of an atom and the process of generation of a free electron in detail. These results provide valuable insight about the electrons in an atom, including the time progression of the quantum phase of the electron, meaning that the beat of oscillation of the quantum waves.

In the study, short laser pulses are shot at atoms. When the atom hit by the laser pulse, the electric field surrounding the atom gets changed and removes an electron from the atom. However, the exact time of this electron removal cannot be identified.

Markus Kitzler, one of the researchers from the Photonics Institute at TU Vienna, informed that the removal of electron has not taken place at one time point during the interplay with the laser pulse, indicating the presence of a superposition of multiple processes just as in quantum mechanics. The removal of a single electron takes place in various points in time, thus forming an intricate wave pattern.

Joachim Burgdorfer, a Professor at Institute for Theoretical Physics, TU Vienna, stated that these quantum mechanical wave-interferences provide data pertaining to an electron’s initial quantum state in the ionization process. Burgdorfer’s team closely worked with the researchers at the Photonics Institute.

The quantum phase modifies quickly when the electrons’ wave cycle is very short. It is possible to get information about the quantum phase of an electron through the combination of complex theoretical calculations and high precision measurements. To make these measurements, a laser beam comprising two different wavelengths is used. Accurately customized laser pulses are used to measure an electron’s quantum phase inside the atom prior to its removal by the laser.

This quantum phase measurement provides information about the energy state of an electron inside the atom and the exact point at which ionization occurred, said Kitzler. For this purpose, the researchers had to perform the quantum phase measurement at an accuracy of below 10 as, which is the atomic process timescale.


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