Non-Markovian Collective Quantum Beats

Quantum beats are an interference phenomenon in the radiation from different excited levels in a multilevel atomic system. Recently it has been experimentally demonstrated that quantum beats can be cooperatively enhanced in a collection of multi-level atoms [1]. In this work, we study quantum beats emitted by two three-level V-type atoms coupled via a waveguide. We illustrate a crossover of the collective quantum beat dynamics from a Markovian to a non-Markovian regime as the atomic separation becomes sufficiently large to bring the memory effects of the electromagnetic environment into consideration. We show that quantum beats can be collectively enhanced or suppressed, akin to Dicke super- and sub-radiance, depending on the inter-atomic separation modulo the beat wavelength and the initial correlations between the atoms. Furthermore, in a non-Markovian regime, collective quantum beats can be enhanced beyond the Markovian limit as a result of retardation effects. Our results demonstrate the rich interplay between multilevel and multiatom quantum interference effects in a non-Markovian regime, which can be relevant to quantum communication between distant quantum network nodes.

[1] H. S. Han, A. Lee, K. Sinha, F. K. Fatemi, and S. L. Rolston, Phys. Rev. Lett. 127, 073604 (2021).