We report on the first direct observation of the additivity of the quantized conductance for multiple parallel quantum point contacts. We have studied from 1 to 4 parallel quantum point contacts and find that the total conductance can be written in the form (2e
2
N
L
N
QPC/h) as a function of the applied gate voltage, where N
QPC is the number of parallel quantum point contacts. The processing of multiple parallel quantum point structures is also described.
This paper reviews our work on the experimental and theoretical analyses of the angular distribution of electrons injected through a single quantum point contact. We observed double peaks in the distribution with the point contact quantized in two modes. Our calculation of the distribution using a Fraunhofer diffraction approximation through a quantized single slit agreed well with results. In this calculation we use a Green's function in weak magnetic fields and constructed mirror images there. We also investigated the possibility of observing interference in the angular distribution between the first and second modes, and found that the interference terms of the angular distribution were cancelled due io system symmetry. Another possible way to observe interference is due to electron waves through double point contacts. To measure this interference, we developed submicron air bridges to make double point contacts with independently controlled widths. We measured the controlled additivity of the conductance for four point contacts.
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