Two level fluctuators in Josephson qubits

Spectroscopic analysis of superconducting qubits often shows clear signatures of avoided level crossings, indicating the presence of microscopic two-level fluctuators (TLFs) coupling to the qubit. Within ''direct coherent control'' method it was possible for the first time to investigate coherence times and temperatures properties of single TLFs. Measurements of relaxation time shows unusual behaviour of temperature dependence. Within Bloch Redfield formalism we analyse the influence of higher qubit levels on the resonance shape of relaxation time.