An international research collaboration has identified a previously unknown constraint in quantum mechanics that operates at the intersection of space and time. The team, comprising scientists from the Regensburg Center for Ultrafast Nanoscopy and the Max Planck Institute in Hamburg, built specialized laser systems to observe electron behavior at unprecedented scales. Their work reveals that as researchers gain greater precision in measuring when an electron moves, the electron’s spatial distribution becomes less defined, and vice versa.
The experiments employed ultrafast scanning tunneling microscopy to track individual electrons moving across atomic distances in attoseconds—billionths of a billionth of a second. Researchers used precisely timed laser pulses to drive electrons from a metal tip toward a silver surface, measuring the resulting electrical current to detect movement. By adjusting the time interval between paired laser pulses, scientists directly observed how electrons respond and confirmed that motion occurs on attosecond timescales. Notably, the electrons exhibited quantum tunneling behavior, passing through energy barriers as quantum waves rather than moving like classical particles.
Computational models developed by collaborators reproduced the experimental findings and revealed an additional detail: electron motion lagged approximately 500 attoseconds behind the laser field. The simulations showed that light behavior near the space-time limit displayed characteristics of both waves and particles simultaneously, revealing fundamental quantum phenomena that occur only at these extreme scales.
The research uncovered a tradeoff wherein increased temporal precision requires additional energy, causing electron wave packets to spread more broadly through space. Conversely, constraining electrons to smaller spatial regions reduces the ability to pinpoint when their motion occurs. This space-time limitation represents a newly demonstrated boundary condition in quantum mechanics with potential applications for developing faster electronic and quantum computing technologies.
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