Decoherence of two qubits coupled with one-mode cavity without   rotating-wave approximation
  The decoherence of two qubits, coupled with one-mode cavity separately, has been investigated exactly. The results show that, for the resonant case, the decoherence behavior of system is similar to Markovian case when the coupling strength is weak, while the concurrence vanishes in finite time and might recover fractional initial entanglement before it permanently vanishes when the coupling strength is strong. And for detuning case, the entanglement could periodically recover after a period of time from its disappearance. These results are quite different from that of system subjected to Jaynes-Cummings model. 
Fa-Qiang Wang, Wei-Ci Liu and Rui-Sheng Liang