Collective Radiation of Multi-Atom in Cavity Under the External Driving Field

There were several works concerning the collective radiation of two atoms in a cavity. According to their respective criteria, they all claim to have reached superradiation in a cavity (See paragraph 3 of the introduction for details). Here, we reexamine this topic and give a new but more reasonable criterion to test the collective radiation of multi atoms in the cavity. We tend to use the witness parameter Wn as the criterion of superradiance. With such new criterion, we find it is impossible to get the superradiance in good cavity. On the contrary, superradiance is much easier to be reached in a bad cavity. We take the cases of one atom, two atoms, three atoms and four atoms for example. These theoretical results can be realized by using the existing technology, which can make people understand the theory of multi-atom superradiance more clearly and stimulate future experiments.