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][2][3][4][5][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 pJ-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.Present-day high-frequency devices operate in the microwave range, but direct control of electron flow by the electric-field profile of few-cycle optical pulses has recently been demonstrated 12,15 . These experiments were based on strong perturbation of the electronic system in a dielectric material, resulting in a large incoherent background current. Nanoscale confinement of the region biased by the optical transient might avoid a significant influence of nonlinear conductivity in an insulating substrate and result in purely coherent tunnelling currents 16 that may be controlled by the precise shape of the electric field cycles. Our approach to reaching this goal is illustrated in the upper part of Fig. 1a. A single-cycle near-infrared pulse (left) is focused to a nanoscale junction of an electronic circuit (centre) with nonlinear and antisymmetric current-voltage (I-V) characteristics (right). An effective bias then arises when the exciting electric field is cosine-shaped (blue transient and blue dot in the I-V scheme) because its extremum occurs only for one polarity. Consequently, the symmetry of electronic transport is broken, even when integrating over the entire transient, and a net tunnelling current of electrons results through the potential barrier represented by the free-space gap (Fig. 1b,c). Our experiment favours tunnelling over other phenomena such as multiphoton ionization 4 by operating with ultrashort pulses and extreme nanoconfinement of the electric field. No background current exists when the control field is sineshaped (red transient and dot in the I-V characteristics, respectively), because positive and negative polarities now have precisely opposite effects. Consequently, the total current amplitude and direction may be set by varying the carrier-envelope phase (CEP), Δφ CEP , of the pulse. Owing to the single-cycle pulse duration, nanoscale constriction and fi...

We employ near-infrared single-cycle pulse pairs to drive interferometric autocorrelations of the ultrafast current produced by optical field emission at the nanogap of a single plasmonic nanocircuit. This highly nonlinear process depends fully on the precise temporal field profile of the optical driving pulse. Current autocorrelations are acquired with sub-femtosecond temporal resolution as a function of both pulse delay and absolute carrierenvelope phase. In this way, we study the ultrafast dynamics of electronic nanotransport. Quantitative Additional information

Optical phase noise of femtosecond lasers is analyzed over various steps of broadband nonlinear frequency conversion. The intrinsic phase jitter of our system originates from quantum statistics in the mode-locked oscillator. Supercontinuum generation by four-wave-mixing processes preserves a noise minimum at the optical carrier frequency. From there, a quadratic increase of the comb linewidth results with mutually anticorrelated phase fluctuations of both spectral wings. Passive phase locking by difference frequency generation strongly enhances the optical phase noise to a level equaling the carrier-envelope phase jitter of the fundamental comb. The same value results from quadratic extrapolation of the optical phase noise to radio frequencies. Our findings are consistent with a fully deterministic transformation of phase noise according to the elastic tape model.

Femtosecond optical pulses tunable in the near infrared are exploited to drive third harmonic generation (THG) and incoherent multiphoton photoluminescence (MPPL) in gold plasmonic nanoantennas. By comparing the yield of the two processes concurrently occurring on the same nanostructure, we extract the coherent third-order response of the antenna. Its contribution is enhanced at shorter excitation wavelengths allowing the observation of dispersion in the nonlinear susceptibility of gold.

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