Impedance measurement technique for quantum systems

W. P. Kirk

Anatoly Yu. Smirnov

We study dissipative dynamics and a magnetic response of two coupled flux qubits interacting with a high quality tank in the framework of the impedance measurement technique (IMT). It is shown that the observation of the difference between a sum of IMT signals from separated qubits and the signal from the system when both qubits are in the degeneracy point (IMT deficit) implies immediately a formation of the entangled two-qubit eigenstates.

Evgeni V. Il’ichev, Nikolai Oukhanski, Th. Wagner +7 more

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.

Yashika Aneja, Monika Thakran, Monika Yashika +3 more

A. Izmalkov, M. Grajcar, E. V. Il’ichev +6 more

We have studied the low-frequency magnetic susceptibility of two inductively coupled flux qubits using the impedance measurement technique (IMT), through their influence on the resonant properties of a weakly coupled high-quality tank circuit. In a single qubit, an IMT dip in the tank's current-voltage phase angle at the level anticrossing yields the amplitude of coherent flux tunneling. For two qubits, the difference (IMT deficit) between the sum of single-qubit dips and the dip amplitude when both qubits are at degeneracy shows that the system is in a mixture of entangled states (a necessary condition for entanglement). The dependence on temperature and relative bias between the qubits allows one to determine all the parameters of the effective Hamiltonian and equilibrium density matrix, and confirms the formation of entangled eigenstates.

Yashika Aneja, Monika Thakran, Asheesh Kumar Sharma +2 more