  Charge transfer in a tunnel junction is studied under dc and ac voltage bias
using quantum shot noise. Under dc voltage bias $V$, spectral density of noise
measured within a very large bandwidth enables to deduce the current-current
correlator in the time domain by Fourier transform. This correlator exhibits
regular oscillations proving that electrons try to cross the junction
regularly, every $h/eV$. Using harmonic and bi-harmonic ac voltage bias, we
then show that quasiparticles excitations can be transferred through the
junction in a controlled way. By measuring the reduction of the excess shot
noise, we are able to determine the number of electron-hole pairs surrounding
the injected electrons and demonstrate that bi-harmonic voltage pulses realize
an on-demand electron source with a very small admixture of electron-hole
pairs.
