Area resonances in excitation and ionization of quantum wells by ultrashort sub-cycle electric field pulses

Summary form only given. Interaction of quantum systems with sub-cycle electric field pulses whose duration is much shorter than the system´s evolution time is a new area in ultrafast quantum electronics with a great potential for novel effects. In particular, it may seem meaningless to ask whether an ultra-broad-band sub-cycle (non-oscillating) pulse can resonantly excite a particular quantum transition. As we show, for a limiting case of a pulse that may be modeled by a /spl delta/-function of time, conventional frequency resonances are replaced for sub-cycle pulses by area resonances, which occur when the pulse area assumes specific values related to the electron eigenenergies. In a finite QW, pulses area-resonant to the even-number levels, remove all the population from the ground (initial) state. Moreover, a new surprising effect occurs in the ionization of this system: at the dipole-allowed area resonances, the spectrum of ionized electrons sharply concentrates near the bottom of the continuum, while at the area resonances to the odd-number bound levels, the photoelectron spectra are maximally broad. Area resonances may be observable with available sub-cycle pulses (half-cycle pulses). By the same token, due to this effect, sub-cycle pulses may become an efficient way to control population in QW.