Search

The bunching of light resulting from the spontaneous emission of an atomic ensemble is a well known effect, shared with various sources of thermal fields. It is, on the other hand, also an integral part of recently developed quantum memories for various applications. Here we theoretically and experimentally investigate the statistical correlations in light spontaneously scattered from a cold ensemble of two level atoms. We demonstrate that the bunching of light in this situation is both long-lived and robust to various parameters of the excitation process. This memory comes from constructive interference of the emitted light for particular distributions of positions of the atoms, being washed out by their movement. We offer both a first-principles quantum theory for the process and a corresponding classical theory. We also introduce various methods to treat long-term fluctuations of the experimental data in order to be able to compare it to our simple theories. As a result, we obtain a detailed picture of such spontaneous scattering processes in cold atomic ensembles, which may result in better control of quantum memories heralded by these processes.

Superradiance in an ensemble of atoms leads to the collective enhancement of radiation in a particular mode shared by the atoms in their spontaneous decay from an excited state. The quantum aspects of this phenomenon are highlighted when such collective enhancement is observed in the emission of a single quantum of light. Here we report a further step in exploring experimentally the nonclassical features of superradiance by implementing the process not only with single excitations, but also in a two-excitations state. Particularly we measure and theoretically model the wave-packets corresponding to superradiance in both the single-photon and two-photons regimes. Such progress opens the way to the study and future control of the interaction of nonclassical light modes with collective quantum memories at higher photon numbers., 5 pages, 4 figures. V2: substantial changes on the introductory part of the paper