Transition from Ohmic to adiabatic transport in quantum point contacts in series

Ballistic electron transport has been studied in a device consisting of two quantum point contacts (QPC's) in a series, connected by a 1.5-{μ}m-wide cavity. In the absence of a magnetic field the measured device resistance is approximately the sum of the (quantized) resistances of the individual QPC's. In a magnetic field a gradual transition to the adiabatic transport regime is observed, which is reached at B{}1.0 T. In this regime the device conductance is completely determined by the QPC with the lowest conductance. An explanation is given for the observed transition from Ohmic to adiabatic transport.