Real-Time Imaging of Quantum Transitions in Graphene

Researchers from the University of Regensburg, Philipps University of Marburg and Forschungszentrum Jülich combined attosecond-scale laser pulses with a photoemission momentum microscope to track electrons in atomically thin graphene. The method expands the momentum area accessible at sub-cycle resolution by more than 100 times compared with earlier approaches. By delivering intense, rapidly changing electric fields, the experiment drove electrons across graphene’s energy gap, observing Landau-Zener-Majorana transitions in which electrons move between bands without occupying the forbidden states.

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Under the experimental conditions, electrons crossed the energy gap with a tunneling probability reaching 100 %. The researchers used exceptionally pure, rotated graphene samples to minimise impurity-induced disturbances, allowing the delicate quantum dynamics to be resolved. The technique also revealed how electron-lattice interactions disrupt initially coordinated motion, providing a direct view of scattering processes that limit ultrafast electronic control.

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The ability to drive and monitor electrons with light-induced fields suggests a pathway toward electronic devices that operate faster than conventional voltage-switching technologies. The authors note that the approach could be extended to other quantum materials, potentially uncovering electronic behaviours that have previously been inaccessible to direct observation.

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Vincent Eggers, the study’s first author, emphasized the need to monitor many electrons simultaneously to capture fleeting quantum transitions. Stefan Tautz of Forschungszentrum Jülich highlighted that the experiments require near-perfect atomic-level material quality to prevent impurities from obscuring the observed dynamics. Both researchers indicated that their method may help define the physical limits of light-driven electron control.

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• “If you want to know who has won a race, you have watch all participants,” — Vincent Eggers, the study’s first author

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• “These precision experiments require material that is nearly perfect at the atomic level. This ensures that impurities do not obscure the delicate quantum dynamics of the electrons,” — Stefan Tautz, of Forschungszentrum Jülich

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