Physicists in Germany have filmed electrons doing something quantum mechanics says should be essentially impossible: leaping cleanly across an energy gap that would normally take them through 17 intermediate levels, without passing through any of them.
The team, based at the University of Regensburg, Philipps-Universität Marburg and the Forschungszentrum Jülich research center, used an ultrafast imaging technique — built around a photoemission momentum microscope paired with attosecond laser pulses — to track individual electrons in graphene as a strong light field pushed them from one energy band into a much higher one. The results, published this week in Nature, mark the first direct observation of what's known as a Landau-Zener-Majorana transition: a long-predicted but never-before-filmed process in which a particle "tunnels" across a forbidden energy gap instead of climbing through it step by step.
Vincent Eggers, the study's first author, likened the challenge to timing a race: "If you want to know who has won a race, you have to watch all participants," he said of the need to track electrons across the material's entire energy landscape at once, rather than at a single point. Under the right conditions, the team found, electrons crossed the gap with a tunneling probability approaching 100 percent — effectively skipping from a low energy level to the 20th rung on the ladder, bypassing everything in between.
A clearer window into the quantum world
The researchers credit much of their success to the purity of their graphene samples, which were specially grown and "rotated" to minimize the defects and impurities that normally blur this kind of measurement. "Now we can track electrons moving across the entire energy landscape of a solid in real time," said Rupert Huber, one of the study's senior authors, whose lab led the imaging work. His co-author Giacomo Inzani described the technique more broadly as opening "a panoramic window into the quantum world," applicable beyond graphene to other two-dimensional quantum materials.
The work builds on a growing body of research into "lightwave electronics," the idea that the oscillations of a laser pulse — rather than the voltage in a conventional transistor — could someday be used to switch and control electrons directly, at speeds far beyond what today's chips can manage. The team says the same imaging approach could help identify how fast such light-driven switching could realistically go, including the physical bottlenecks, such as collisions between electrons and vibrating atoms in the crystal lattice, that limit how cleanly the process can be controlled.
No commercial application exists yet, and the researchers frame the result as a measurement breakthrough rather than a working device — it gives physicists, for the first time, a way to actually watch this kind of transition happen rather than infer it indirectly. Follow-up work is expected to test the technique on other quantum materials beyond graphene.
