Adding Photonic Entanglement to Superradiance by Using Multilevel Atoms

Abstract: We show here that the photonic states emitted by ensembles of multilevel atoms via a superradiance process exhibit entanglement in the modal (frequency) degree of freedom, making this collective emission process a favorable candidate for a fast, bright and deterministic source of entangled photons. This entanglement is driven by two mechanisms: (i) selective excitation of the atomic ensemble to a superposition state and (ii) degeneracies of the optical transitions due to internal structure of the emitting atoms. The latter induces intricate non-radiative virtual transitions in the ensemble, which create interatomic correlations that are imprinted onto the emitted photons. One of the important outcomes of this complexity is the generation of mode-independent entangled multiphoton states. In addition, we study the dynamics of the correlations of the superradiating multilevel atom ensembles, and demonstrate a case where they exhibit beating in steady-state due to the aforementioned virtual transitions.