Nonlinear electron-wave directional coupler

We propose a class of quantum interference device that is an electronic counterpart of the nonlinear optical directional coupler. Nonlinear coupled wave equations including Coulomb charging effects in coupled electron waveguides predict coupling lengths depending on the amplitude of the input electron waves, and also predict that for the initial condition, the electron wave function is equally distributed to two electron waveguides; a small initial fluctuation of the wave function causes the localization of the electron wave in one of the two waveguides by symmetry-breaking instability. These operating characteristics would be useful for constructing ultrafast self-switching devices and logic gates.