Abstract

Quantum interferences (especially destructive interferences) have been a subject of active study over the last decade Some of examples using these interferences include electromagnetically induced transparency (EIT), lasers without inversion (LWI), and highly efficient schemes for nonlinear optics In a practical point of view, the implementation of such interferences in semiconductor devices is very interesting since we cannot control critical parameters in atomic systems A few schemes of such implementation in an asymmetric coupled quantum well (QW) structure using intersubband transitions have been already proposed [1] However, they are all such structures that it is geometrically (such as by tunneling direction of electrons) determined (i e fixed) whether constructive interference or destructive interference occurs Thus, tunability was not implemented by external variables (eg external electric field) since the phase difference between the two intersubband transitions was determined in the device fabrication stages In this report, we suggest a structure in which we can change the phase difference between two intersubband transition matrix elements from 0° to 180° by the external pertuibation or variables We use the interferences between |0>-|2> and |0>-|3> transitions, where |2> and |3> states are broadened by tunneling into the same energy continuum through a thin potential barrier By controlling the parallel kinetic energy of electrons, we can change the phase difference between them via parallel-perpendicular kinetic energy coupling effects which modify the effective potential profiles of the structure (which was previously shown in other devices by many authors including the present authors [2]) In Fig 1, when E_t=0 meV ((a)), the phase difference between |0>-|2> and |0>-|3> transitions matrix elements is 180° (destructive interference) and leads to suppression of absorption at a certain energy value between two resonance (|0>-|2> and |0>-|3>) energies (see the arrow), while when E_t=300 meV ((b)), the phase difference is 0° (constructive interference) and leads to enhancement of absorption This means we can modulate optical absorption by controlling the sign of quantum interference via the parallel kinetic energy of electrons

© 2000 IEEE