Sub-cycle optical phase control of nanotunnelling in the single-electron regime

The high peak electric fields provided by single-cycle light pulses can be harnessed to manipulate and control charge motion in solid-state systems, resulting in electron emission out of metals and semiconductors(1-6) or high harmonics generation in dielectrics(7,8). These processes are of a non-perturbative character and require precise reproducibility of the electric-field profile(9-14). Here, we vary the carrier-envelope phase of 6-fs-long near-infrared pulses with pi-level energy to control electronic transport in a laterally confined nanoantenna with an 8 nm gap. Peak current densities of 50 MA cm(-2) are achieved, corresponding to the transfer of individual electrons in a half-cycle period of 2 fs. The observed behaviours are made possible by the strong distortion of the effective tunnelling barrier due to the extreme electric fields that the nanostructure provides and sustains under sub-cycle optical biasing. Operating at room temperature and in a standard atmosphere, the performed experiments demonstrate a robust class of nanoelectronic switches gated by phase-locked optical transients of minute energy content.