Distributed manipulation of two-qubit entanglement with coupled   continuous variables
  We study the dynamics of two qubits separately sent through two coupled resonators, each initially containing a coherent state field. We present analytical arguments and numerical calculations for the qubit-field system under different two-qubit initial states, photon hopping strengths, and detunings. In far off-resonant regime, the maximal entanglement of two qubits can be generated with the initial qubit state in which one qubit is in the excited state and the other is in the ground state, and the initially maximal two-qubit entanglement can be frozen and fully revived even for large mean photon number. When the qubits are both initially in their excited states or ground states, the qubit-qubit entanglement birth and death apparently appear in the regime where the photon hopping strength is close to qubit-field detuning, and its peaks do not decrease monotonically as the interaction time increases. It is interesting to observe that when there is photon hopping strength between two fields, the field-field entanglement can be larger than one and increases as the initial amplitude of the coherent state grows. By postselecting the fields both in their coherent states, the entanglement of two initially unentangled qubits can be largely improved. Our present setup is fundamental for the distributed quantum information processing and applicable to different physical qubit-resonator systems. 
Li-Tuo Shen, Rong-Xin Chen, Huai-Zhi Wu, Zhen-Biao Yang
quant-ph