Mesoscopic fluctuations in biharmonically driven flux qubits

摘要

We investigate flux qubits driven by a biharmonicmagnetic signal, with a phase lag that acts as an effective timereversal broken parameter. The driving induced transition rate between the ground and the excited state of the fluxqubit can be thought of as an effective transmittance, profiting from a direct analogy between interference effectsat avoided level crossings and scattering events in disordered electronic systems. For time scales prior to fullrelaxation, but large compared to the decoherence time, this characteristic rate has been accessed experimentallyby Gustavsson et al. [Phys. Rev. Lett. 110, 016603 (2013)] and its sensitivity with both the phase lag and thedc flux detuning explored. In this way, signatures of universal conductance fluctuationslike effects have beenanalyzed and compared with predictions from a phenomenological model that only accounts for decoherence, asa classical noise. Here we go beyond the classical noise model and solve the full dynamics of the driven flux qubitin contact with a quantum bath employing the Floquet-Born-Markov master equation.Within this formalism, thecomputed relaxation and decoherence rates turn out to be strongly dependent on both the phase lag and the dcflux detuning. Consequently, the associated pattern of fluctuations in the characteristic rates display importantdifferences with those obtained within the mentioned phenomenological model. In particular, we demonstratethe weak localizationlike effect in the average values of the relaxation rate. Our predictions can be tested foraccessible but longer time scales than the current experimental times.