Laser Pulse Reveals Quantum Phase in Electrons

Events that appear to happen instantaneously now can be resolved to a resolution of 10 attoseconds, enabling scientists to look at phenomena that happens on the order of attoseconds (10^-18 s), previously far too fast to measure.

Researchers at Vienna University of Technology's (TU Vienna) Photonics Institute fired short laser pulses at an atom. The waves of light pass through the atom, affecting its electric field. This causes the atom to ionize and lose an electron. The exact moment when the electron is removed from the atom is impossible to identify because the electron exists as a superposition of possible electron interactions at different points in time. In quantum mechanics, a single particle can be treated as a particle or a wave, and this ambiguity allows electrons to interfere with each other when these probabilities combine, creating a rapidly changing quantum phase, such as waves on the surface of water.

Markus Kitzler (left) and Xinhua Xie. (Image: TU Vienna)

“These quantum mechanical wave-interferences give us information about the initial quantum state of the electron during the ionization process,” said Joachim Burgdörfer of the Institute for Theoretical Physics at the university, whose team collaborated with the Photonics Institute.

To measure the interferences inside the atom, the researchers used a laser beam that contained two wavelengths. The pulse could be customized for the individual atom and the quantum phase of the electron inside the atom could be measured against the beat defined by the laser pulse, an atomic attribute that had not been measurable until now.

“This quantum phase that we can measure now also tells us about the electron’s energy states inside the atom and about the precise position at which the ionization took place,” said Markus Kitzler of the Photonics Institute.

For more information, visit: www.tuwien.ac.at/en