Transient dynamics of Ohmic dissipative two-level systems driven by dc-ac fields

Theodoulos Costi, V. Meden, C. Klöckner +2 more

W. Zwerger

Hao Wang, V. N. Freire, Xian-Geng Zhao

The time-dependent average population in a two-level system interacting with an Ohmic boson bath and driven by a dc-ac field is obtained. The study is performed within the noninteracting-blip approximation and for the high-frequency driving case. The integro-differential master equation and the exact formal solution for the average transition probability are obtained. The dissipative quantum decay and the transition temperature from the coherent to the incoherent motion are investigated. The effect of the external electric field on the the dissipative two-level system is found to destroy its coherence.

W. Zwerger

Alejandro Ferrón, Daniel Domı́nguez, María José Sánchez

We study Landau-Zener-St\"uckelberg (LZS) interferometry in multilevel systems coupled to an Ohmic quantum bath. We consider the case of superconducting flux qubits driven by a dc+ac magnetic fields, but our results can apply to other similar systems. We find a dynamic transition manifested by a symmetry change in the structure of the LZS interference pattern, plotted as a function of ac amplitude and dc detuning. The dynamic transition is from an LZS pattern with nearly symmetric multiphoton resonances to antisymmetric multiphoton resonances at long times (above the relaxation time). We also show that the presence of a resonant mode in the quantum bath can impede the dynamic transition when the resonant frequency is of the order of the qubit gap. Our results are obtained by a numerical calculation of the finite time and the asymptotic stationary population of the qubit states, using the Floquet-Markov approach to solve a realistic model of the flux qubit considering up to ten energy levels.

Hao Wang, Xian-Geng Zhao

The quantum behaviour of electrons in a two-level system under the influence of an AC-DC field is investigated. The closed-form solution of quasienergy is obtained, from which the exact level crossing is found to appear at a fan structure in the section (E, E 0 ) through the parameter space (E, E 0 , omega ), where E is the magnitude of the AC field, E 0 is the magnitude of the DC field, and omega is the frequency of the AC field. It is demonstrated that the emergence of the exact crossing of quasienergies is coincident with the onset of coherent destruction of tunnelling.