Large-amplitude harmonic driving of highly coherent flux qubits

ALEJANDRO FERRÓN, DANIEL DOMÍNGUEZ, AND MARÍA JOSÉ SÁNCHEZ

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

American Physical Society

Año: 2010 vol. 82 p. 134522 - 13452212

0163-1829

The device for the Josephson flux qubit can be considered as a solid-state artificial atom with multipleenergy levels. When a large-amplitude harmonic excitation is applied to the system, transitions at the energylevels avoided crossings produce visible changes in the qubit population over many driven periods that areaccompanied by a rich pattern of interference phenomena. We present a Floquet treatment of the periodicallytime-dependent Schrödinger equation of the strongly driven qubit beyond the standard two-level approach. Forlow amplitudes, the average probability of a given sign of the persistent current qubit exhibits, as a function ofthe static flux detuning and the driving amplitude, Landau-Zener-Stückelberg ͑LZS͒ interference patterns thatevolve into complex diamondlike patterns for large amplitudes. In the case of highly coherent flux qubits weshow that the higher-order diamonds can not be simply described relying on LZS transitions in each avoidedcrossing considered separately. In addition we propose a spectroscopic method based on starting the system inthe first excited state instead of in the ground state, which can give further information on the energy-levelspectrum and dynamics in the case of highly coherent flux qubits. We compare our numerical results withrecent experiments that perform amplitude spectroscopy to probe the energy spectrum of the artificial atom.