We study the dynamics of spontaneous generation of coherence and photon-spin-qubit entanglement in a Λ system with nondegenerate lower levels. The cases of entanglement in frequency only and frequency and polarization are compared and the reduced density matrix and entanglement entropy are analyzed. We explore in detail how which-path information manifest when the energy difference between the qubit states is larger than the linewidth of the excited state suppresses coherence. A framework is provided to describe the dynamics of spontaneous generation of coherence and (ideal) photodetection in obtaining the postmeasurement qubit density matrix. A simple model of photodetection with a quantum eraser to suppress which-path information in the detection measurement is implemented. It is found that such quantum eraser purifies the qubit density matrix after photodetection; our results are in agreement with those reported in recent experiments.
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