KRAKEN Technique Reveals Quantum Electron States Dependence on Source Material

Researchers at Lund University in Sweden have developed a novel method, named KRAKEN, for measuring the quantum state of electrons emitted from atoms under high-energy light pulses. This technique allows for the precise determination of how "quantum" an electron appears.The study opens new perspectives in understanding the interaction of light and matter at the quantum level. The method builds upon the principle of photoelectron spectroscopy but goes further by measuring not only the classical properties of a photoelectron, such as its speed, but also its complete quantum state.David Busto, a lecturer in atomic physics and one of the study's authors, explains that their technique allows reconstructing a complex three-dimensional object by taking multiple two-dimensional images from different angles, similar to how a brain CT scan works. For this, researchers use a pair of laser pulses of different colors to "photograph" and reconstruct the quantum state of an electron layer by layer.Experiments conducted on helium and argon atoms showed that the quantum state of a photoelectron depends on the type of material from which it is emitted. This discovery could have far-reaching consequences for various scientific fields, including atmospheric photochemistry and the study of systems for collecting solar energy, such as solar panels or photosynthesis in plants.The new methodology also links two different fields of science: attosecond physics and spectroscopy on one hand, and quantum information and quantum technologies on the other. This fits into the context of the "second quantum revolution," which aims to manipulate individual quantum objects to exploit their full potential in various applications.While the KRAKEN technique does not directly lead to the creation of new quantum computers, it provides physicists with access to knowledge about the quantum state of photoelectrons, which will allow to fully exploit their quantum properties for future applications. This may help uncover processes occurring in a material after electron emission, which is especially important for studying the properties of new materials.Researchers hope that in the future their method will allow tracing how the quantum properties of electrons evolve in time from a quantum to a classical state, which may shed light on fundamental questions of quantum mechanics and its connection to the macroscopic world.