Radio-frequency method for investigation of quantum properties of superconducting structures

We implement the impedance measurement technique (IMT) for characterization of interferometer-type superconducting qubits. In the framework of this method, the interferometer loop is inductively coupled to a high-quality tank circuit. We show that the IMT is a powerful tool for studying the response of an externally controlled two-level system to different types of excitations. Conclusive information about the qubits is obtained from a readout of the tank properties. (C) 2004 American Institute of Physics.