High Frequency Properties of Josephson Junctions
Kapitel i bok, 2019
In this chapter we will discuss the high frequency properties of Josephson junctions. In the first part we review the effect of a large ac perturbation on the current voltage characteristic (IVC) of a Josephson junction. Here we follow closely the original treatment by Barone and Paterno . For large ac perturbations the externally applied microwave frequency (and integer multiples of it) lock to the Josephson oscillation causing distinct current steps at fixed voltage values in the IVC. In the second part we give a short overview on the response of an underdamped Josephson junction to small microwave perturbations. In this case, when the applied microwave frequency is in resonance with the electromagnetic plasma frequency higher levels of this plasma mode get excited. This mechanism, also called resonant activation, leads for instance to a premature switching from the zero voltage state to the finite voltage state of a current biased Josephson junction. This procedure can be exploited to detect the quantized nature, i.e. the quantized energy levels, of the plasma modes. In fact the lowest two quantized energy levels of the plasma resonance mode are the key ingredient of superconducting qubits, such as the phase qubit and the transmon qubit.