Linear microwave response of a superconducting charge qubit

Wolfram Krech, Detlef Born, Th. Wagner +1 more

Using Bloch-type equations with phenomenological energy relaxation and dephasing terms, we investigate analytically the linear response of a superconducting charge qubit (single-Cooper-pair box) to a microwave field within a two-band model. Coherence of the macroscopic quantum states of the autonomous device is due to the competition of irradiation and dephasing. An extra qubit impedance arises from this quantum effect which can be expressed in terms of quantum resistance unit, quality and detuning. The theoretical results may support the design of microwave experiments with charge-type qubits. Especially, we present a proposal for determining the dephasing time by means of reflection measurements, anticipating a high quality of the extra (quantum) impedance.

Damon S. Russell, Jean-Philip Paquette, Mehrnoosh Vahidpour +2 more

Guang-Yin Chen, Meng-Han Liu, Yueh-Nan Chen

We investigate coherent single-microwave-photon transport in the coupled superconducting transmission lines coupled to superconducting quantum interference device based charge qubits. The Fano resonance can be observed in the scattering spectra in both the linear and nonlinear regimes of the dispersion relation of the microwave photon. We further find that the degree of the two-qubit entanglement can vary from unity to zero when the Fano resonance occurs. There exists a correspondence between the entanglement and the Fano resonance.

Margareta Wallquist, J. Lantz, Vitaly S. Shumeiko +1 more

Xiao-Ling He, Yu-xi Liu, J. Q. You +1 more

To implement quantum-information processing, microwave fields are often used to manipulate superconducting qubits. We study how the coupling between superconducting charge qubits can be controlled by variable-frequency magnetic fields. We also study the effects of the microwave fields on the readout of the charge-qubit states. The measurement of the charge-qubit states can be used to demonstrate the statistical properties of photons.

Eddy Collin, Grégoire Ithier, P. Joyez +2 more