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Exact reduced dynamics and entanglement evolution of two coupled spins in a quantum spin environment X.Z. Yuan1,2, Hsi-Sheng Goan1*, and K.D. Zhu2 1Department of Physics and Center for Theoretical Sciences, National Taiwan University, Taipei 10617, Taiwan 2Department of Physics, Shanghai Jiao Tong University, Shanghai 200240, China * Presenting author The exact quantum dynamics of the reduced density matrix of two coupled spin qubits in a quantum Heisenberg XY spin star environment in the thermodynamic limit at arbitrary temperatures is obtained using a novel operator technique. This special operator techniques is mathematically simple and physically clear, and allows us to treat systems and environments that could all be strongly coupled mutually and internally. To study their entanglement evolution, the concurrence of the reduced density matrix of the two coupled spins is also obtained exactly. It is shown that the dynamics of the entanglement depends on the initial state of the system and the coupling strength between the two coupled spins, the thermal temperature of the spin environment and the interaction between the constituents of the spin environment. We also investigate the effect of detuning which in our model can be controlled by the strength of a locally applied external magnetic field. It is found that the detuning has significant effect on the entanglement generation between the two spin qubits.