Relaxation of Josephson qubits due to strong coupling to two-level systems

We investigate the energy relaxation (T1) process of a qubit coupled to a bath of dissipative two-level fluctuators (TLF). We consider the fluctuators strongly coupled to the qubit both in the limit of spectrally separated single TLF's as well as in the limit of spectrally dense TLF's. We conclude that the avoided level crossings, usually attributed to very strongly coupled single TLF's, could also be caused by many weakly coupled spectrally dense fluctuators.