TRANSMISSION RESONANCES AND ZEROS IN QUANTUM WAVE-GUIDE SYSTEM WITH ATTACHED RESONATORS

Transmission phenomena in quantum waveguide structures are studied by examining the transmission amplitude in the complex-energy plane. We f ind that, similar to double-barrier resonant tunneling, there are tran smission poles in the complex-energy plane for quantum waveguide struc tures which contain quasibound states in attached t-stub resonators. I n contrast to double-barrier resonant tunneling, however, we find that the quantum-wire networks also possess transmission zeros (antiresona nces), which always occur on the real-energy axis. The existence of tr ansmission zeros is a characteristic feature of a quantum waveguide sy stem with attached resonators, but is absent for double-barrier resona nt tunneling, which contains the resonant cavity as part of the transm ission channel. We demonstrate that each quasibound state of the reson antly coupled quantum waveguide system leads to a zero-pole pair of th e transmission amplitude in the complex-energy plane. The previously n oted resonance-antiresonance behavior of the transmission probability, which leads to its sharp variation as a function of energy, can be un derstood in terms of these zero-pole pairs.