Observing the coherent motion of electrons with an attosecond stopwatch


A significant effect Quantum Mechanics Electrons can exhibit interference effects. This interference is similar to waves that communicate in the ocean or electromagnetic waves that carry radio signals. Scientists were able to observe the quantum mechanical motion of electrons in an excited molecule with a device called an „attachlock”. This device measures the motion of electrons with an accuracy of hundreds of attoseconds (1 billionth of a second!). This measurement provides insight into how the coherent oscillation of charges inside a molecule exhibits interference effects on attosecond time scales.


The motion of electrons occurs on time scales so fast that they can only be measured with very short bursts of light (typically less than a femtosecond). Until now, sub-femtosecond measurements were only possible using intense UV sources produced by laser systems. To enable measurements that can distinguish electron movement between different atoms in a molecule, researchers need a source that extends these short pulses into the X-ray field. This new experimental method will enable the study of electron dynamics in complex molecules. This will improve our understanding of molecular physics and quantum chemistry.


The recent development of attosecond X-ray free-electron lasers has opened new avenues Super fast Science. In this experiment, the researchers used ultrafast X-ray pulses Coherent light source, a Department of Energy (DOE) user facility at SLAC National Accelerator Laboratory, creates coherent superposition of excited states in nitric oxide. These excited states are short-lived and decay through the Auger-Meitner process, where the excitation energy is released by ejecting a fast electron.

The researchers measured the Auger-Meitner decay process in the time-domain using the AttoClock, which is capable of measuring the arrival time of electrons with attosecond precision. The researchers observed that the time dependence of the decay is not a simple exponential function, but consists of exponential oscillations. These oscillations are a signature of coherent electron dynamics, specifically a quantum pulse between two coherently excited quantum states. This represents the first atomic site-specific observation of coherent electron motion in a molecule and the first time-domain experiment with attosecond resolution using an X-ray free-electron laser.

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This research was supported by the Department of Energy’s Office of Science, Basic Energy Sciences and Chemical Sciences, Geosciences, and Biology. Other funding sources include the SLAC National Accelerator Laboratory’s Laboratory Directed Research and Development Program; German Research Foundation, Federal Ministry of Education and Research and Max Planck Society, Germany; Engineering and Physical Sciences Research Council of the United Kingdom; Swiss National Science Foundation and National Center for Research-Molecular Ultrafast Science and technology; and the US National Science Foundation. This research used resources from the Linac Coherent Light Source, a DOE Office of Science user facility.

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