Fano interference and resonances in open systems

Abstract

A scenario of quantum interference in which decaying (quasibound) states interfere with the continuum or with other quasibound states is investigated. The model we adopt as the basis of our analysis consists of two or three antidots in an electronic waveguide. In a perfect waveguide, electron states belong to different subbands and antidots give a transfer between them. For a waveguide with two antidots we have observed interesting phenomena: interference between one subband of the quasibound state and a background second subband, and interference of resonant group states of different subbands. In this case, the zero of the Fano resonance is shifted to the complex plane and the coupling parameter becomes complex. In a waveguide with three antidots, degeneracy of two quasibound states takes place and interference of these states occurs. The Fano interference of two nearly degenerate resonances may bring a full suppression of pair resonances in the transmission. We explain that this is due to the parities of the quasibound states. Our results show that the zero of the Fano resonance due to interference between the quasibound states and the continuum is generally placed in the complex plane. This gives an additional possibility for manipulating conductance resonances in a waveguide by changing the antidot parameters.