Abstract
We utilize Leggett-Garge inequality to study the quantum phenomenon in an atomic ensemble of Rubidium atoms. The interaction between the ensemble and single photons is treated by cavity quantum electrodynamics (cavity QED). Ensembles of different optical depths, corresponding to cavity QED systems with different coupling strengths and cavity loss rates, are considered. In particular, we consider two cases where the coupling strengths are either comparable or much larger than the cavity loss rate. Violation of Leggett-Garge inequality are found in both cases, which demonstrates the presence of quantumness in an atomic ensemble. In future works, effect of temperature of atomic ensembles will be included to study the violation of Leggett-Garge inequality.