Low-frequency noise in multiple-quantum-point-contact systems

Electrical-transport measurements were performed on a system consisting of two quantum point contacts (QPCs) in series, where one of the point contacts exhibited low-frequency telegraph noise due to single-impurity effects. We show this system to be ideal for the study of equilibration between the edge states that form at high magnetic fields. We investigate both the adiabatic and nonadiabatic regimes and show that in the transitional magnetic-field range the conductance is compatible with a complete equilibration but between a limited number of edge states only. We also discuss the equivalent experiment at zero field, where one can study the effect of the potential fluctuations on the collimation of the ballistic electrons. In addition, we confirm the observation of 4e2/h quantization in the conductance of a wide QPC.