Ultrafast microscopy reaches the electron space-time limit

Teams at the University of Regensburg and Max Planck used two infrared laser pulses with precisely adjustable delay to drive electrons from a sharp metal tip through a barrier to a silver surface only a few atomic distances away, reconstructing the motion through current. The experiment shows that localizing an electron more precisely in time requires more energy and spreads its wave packet in space, a space-time tradeoff distinct from Heisenberg's position-momentum relation; the electron response also lagged the light field by roughly 500 attoseconds. After using a single surface atom to confine the packet, the team still achieved atomic spatial and attosecond temporal resolution. It has not produced a chip 100,000 times faster, but provides a measurement basis for observing and controlling chemical bonds, quantum tunneling and electron-speed limits.