Dual-branch electron waveguide couplers

A quantum directional coupler which consists of two electron waveguides interconnected by a dual branch line scheme is analysed. With respect to a structure with a single interaction window, the crucial advantage is that the phase in the output leads can be strongly modulated through the distinct coupling paths. As a consequence, the proposed structure is highly directive in a four-terminal configuration. In order to address the above idea, a theoretical analysis is conducted by solving the two-dimensional Schrِdinger equation using a mode matching technique. Transmission spectra and conductance variations are calculated and various modes of operation are pointed out, notably a 3 dB coupling situation, a real space transfer with over 90% of transferred electrons and a coupling by evanescent modes. Finally the time response of mechanisms is briefly discussed by viewing the transfer of an electron as a resonance process.