The resistance of two quantum point contacts in series

Abstract
The resistance of two quantum point contacts (QPCs) in series is investigated experimentally. The voltage is measured both across and in between the series pair. The normalised transmission coefficient, T, for ballistic transport is determined from the data using simple theory. T varies between 0.5 and 1.0 depending on the number of conducting 1D channels through each point contact. T is always found to be a minimum value when the number of 1D channels in each QPC is the same.