Fig. 1. Phonon-photon interaction in monolayer WSe₂. (a) Optical image of the monolayer WSe₂ FET device. (b) Schematic of phonon-photon entanglement. The circularly polarized states (σ–/σ+) with angular momentum of l = –1/+1 are degenerate in WSe ₂. The σ–(σ+) photon state can only couple with l = +1 (–1) phonon and scatter to σ+(σ–) state due to conservation of angular momentum. The indistinguishability of the two paths leads to phonon-photon entanglement. (c, d) Polarization of QDs and their phonon replicas. D3a doublets are linearly polarized and orthogonal to each other, as expected from a localized neutral exciton. D3b doublets, the phonon replica of D3a, do not show any dependence on collection polarization, indicating that D3b are unpolarized. The lost of polarization information from parent peaks to phonon replicas is a result of phonon–photon entanglement.