An RF Circuit Model of a Quantum Point Contact

We develop a realistic, physics based, practical RF circuit model for the AC impedance of a quantum point contact that includes the ohmic contacts, the on-chip ``lead{''} resistance and kinetic inductance, and the quantum point contact impedance itself. The kinetic inductance of the electrons in the ``leads{''} in series with the quantum point contact capacitance form a resonant tank circuit whose resonant frequency depends on the width of the quantum point contact channel. These measurements probe devices in the following qualitative regime: They are in the ballistic limit, and the measurement frequency is higher than the electron scattering frequency.