Strong electron-phonon coupling regime in quantum dots: Evidence for everlasting resonant polarons

Using far-infrared magnetospectroscopy in Self-assembled InAs quantum dots, we have investigated the electronic transitions from the ground s levels t o the excited p levels. The experiments consist of monitoring, by means of Zeeman tuning of the excited level, a resonant interaction between the disc rete (p, 0 LO phonon) state anti. the continuum of either (s, 1 LO phonon) or (s, 2 LO phonons). We show that the electrons and the LO phonons are alw ays in a strong coupling regime and form an everlasting mixed electron-phon on mode.