Researchers Observe Electron Motion at Space-Time Limit

An international collaboration has successfully observed the intrinsic quantum motion of individual electrons at the space-time limit while tunneling through an energy barrier. This was achieved using atomic-scale lightwave-driven scanning tunneling microscopy with attosecond time resolution, as reported in the journal Nature Photonics. The researchers modulated the tunneling barrier with two time-delayed near-infrared pulses, identifying isolated electron tunneling transients shorter than 1 fs.

Quantum Motion and Tunneling

The spatial extension of the measured tunneling wave packet depends on the interplay of multi-photon and field-driven dynamics, confirmed by full quantum simulations. The team localized the attosecond-confined tunneling wave packet on the angstrom scale, enabling the mapping of a single copper adatom on a silver surface. This integration of attosecond science with atomic-scale scanning tunneling microscopy allows for the study of wavefunction dynamics within atoms, molecules, and solids.

Space-Time Limit Implications

The findings reveal a fundamental limitation in determining an electron's location and its behavior over time, known as the "space-time limit." The researchers found that the electrons did not respond instantaneously to the light field, with a delay of approximately 500 attoseconds. This discovery highlights a trade-off: the more precisely an electron's position in time is defined, the more its wave packet spreads spatially. This relationship provides experimental insight into a fundamental constraint that could influence future quantum technologies and ultrafast electronics.