Quantum coherent manipulation of two-level systems in superconducting circuits

Two level systems (TLS) appear in the insulating layers of microfabricated superconducting circuits and are known to be a source of superconducting qubit decoherence. Here we theoretically analyze the quantum evolution of a two-level system bath which is related to a recent experiment performed with a superconducting resonator. During the application of simultaneous time-varying bias and continuous microwave fields TLSs pass through resonance with the latter field such that Landau- Zener crossings cause the TLS to remain in the ground (Floquet) state or become inverted. The TLS are analyzed for insulating films, which convey a distribution of tunneling parameters and associated TLS inversion regimes. Under certain conditions we indeed find that the TLS population should be inverted over a wide range of frequencies. Discussion is included on how new TLS environments could aff ect theoperation of resonators and qubits.