Entanglement of single-photons and chiral phonons in atomically thin WSe2

Quantum entanglement is a fundamental phenomenon that, on the one hand, reveals deep connections between quantum mechanics, gravity and spacetime(1,2), and on the other hand, has practical applications as a key resource in quantum information processing(3). Although it is routinely achieved in photon-atom ensembles(4), entanglement involving solid-state(5-7) or macroscopic objects(8) remains challenging albeit promising for both fundamental physics and technological applications. Here, we report entanglement between collective, chiral vibrations in a two-dimensional WSe2 host-chiral phonons (CPs)-and single-photons emitted from quantum dots(9-13) (QDs) present in it. CPs that carry angular momentum were recently observed in WSe2 and are a distinguishing feature of the underlying honeycomb lattice(14,15). The entanglement results from a 'which-way' scattering process, involving an optical excitation in a QD and doubly-degenerate CPs, which takes place via two indistinguishable paths. Our unveiling of entanglement involving a macroscopic, collective excitation together with strong interactions between CPs and QDs in two-dimensional materials opens up ways for phonon-driven entanglement of QDs and engineering chiral or non-reciprocal interactions at the single-photon level.