Scientists in Germany have observed electrons crossing an energy gap in graphene with a probability of up to 100%, revealing how intense electric fields can drive quantum transitions in real time.Researchers from the University of Regensburg, Philipps University of Marburg, and Forschungszentrum Jülich used a new imaging technique combining ultrafast lasers with electron microscopy to track the movement of electrons in the atomically thin material.The experiments captured a process known as Landau-Zener-Majorana transitions, in which electrons move between energy bands without occupying the forbidden energy states separating them.The findings could help scientists understand how electrons behave under intense electric fields and develop new ways to control electronic materials using light.Tracking electrons in real timeIn solids, electrons occupy specific ranges of energy called bands. These bands can be separated by energy gaps where electrons cannot normally exist.However, quantum mechanics allows electrons to move between bands through a process known as tunneling. The likelihood of such a transition depends on how quickly an electron approaches the energy gap.To observe the process, the researchers combined extremely short laser pulses with a photoemission momentum microscope.Unlike conventional microscopes, which produce enlarged images of physical objects, the instrument measures the energies and motion of electrons to map their distribution inside a material.The laser pulses generated strong, rapidly changing electric fields that accelerated electrons through graphene’s electronic energy structure.“If you want to know who has won a race, you have watch all participants,” said Vincent Eggers, the study’s first author.“Likewise, we must observe as many electrons as possible at one time to catch those that undergo a quantum mechanical transition while moving.”The measurements showed that electrons could cross the energy gap with a tunneling probability reaching 100% under the experimental conditions.The result demonstrates that transitions between separated energy states can become highly probable when electrons are driven rapidly enough.Light-driven quantum controlThe team used specially prepared graphene samples produced at Forschungszentrum Jülich.Graphene consists of a single layer of carbon atoms arranged in a hexagonal structure. Its electronic properties make it useful for investigating how electrons respond to external electric fields.For the experiments, the researchers used exceptionally pure samples, including rotated graphene structures that made the quantum dynamics easier to observe.“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,” said Stefan Tautz of Forschungszentrum Jülich.The technique also allowed the researchers to examine how interactions between electrons and the crystal lattice disrupt their initially coordinated motion.Understanding these effects could help identify the physical limits of controlling electrons with rapidly oscillating light fields.Such control is being investigated as a possible route toward electronics that operate faster than devices relying on conventional voltage switching.The researchers said their approach could also be applied to other quantum materials, allowing scientists to investigate electronic behavior that has previously been difficult to observe directly.“Our experiment opens a panoramic window into the quantum world. Now, we can follow in real time how electrons move through the energy landscape of a material. And this is just the beginning,” said Giacomo Inzani of the University of Regensburg.The study appears in Nature.