| Abstract: | Quantum tunnelling of electrons can be confined to the sub-cycle time scale of strong light fields, contributing
decisively to the extreme time resolution of attosecond science. Because tunnelling also enables atomic-scale spatial
resolution in scanning tunnelling microscopy (STM), integrating STM with light pulses has long been a key
objective in ultrafast microscopy, spanning the picosecond and femtosecond domains, with first signatures of
attosecond dynamics. However, while sub-cycle dynamics on the attosecond time scale are routinely controlled and
determined with high precision, controlling the direction of attosecond currents and determining their duration have
remained elusive in STM. Here, we induce STM tunnelling currents using two-colour laser pulses and dynamically
control their direction, relying solely on the sub-cycle waveform of the pulses. Projecting our measurement data
onto numerical and analytical solutions of the time-dependent Schrödinger equation reveals non-adiabatic tunnelling
as the underlying physical mechanism, yielding a current burst duration of 860 as. Despite working under ambient
conditions but free of thermal artifacts, we achieve sub-angström topographic sensitivity and a lateral spatial
resolution of 2 nm. This unprecedented capability to directionally control attosecond bursts will enable triggering
and imaging ultrafast charge dynamics in atomic, molecular and condensed systems at the spatio-temporal
.microscopy frontier of lightwave electronics |