Nanosecond Time-Resolved Population Measurements of Collective Emission in Nearly Fully Inverted Ultracold Atomic Ensembles. 

Understanding and controlling the behaviours of an ensemble of emitters sharing an electromagnetic field environment is one of the current research frontiers, with applications ranging from quantum optics and quantum information science. One intriguing situation is that a system with fully inverted emitters could spontaneously form macroscopic coherence and even

many-body correlations in photons and matter. Fully unveiling such nonequilibrium dynamics require not only detecting radiated photons but also the access to the internal states of emitters. However, full population inversion as well as direct state measurements have remained exclusive due to technical difficulties in fast manipulation of atoms in a timescale much shorter

than the excited-state lifetime.

Here, we adapt our ultrafast manipulation technologies, developed for Rydberg quantum simulation [1-3] and computation [4], to the study of many-body decay using ⁸⁷Rb Bose–Einstein condensate or Mott insulator lattice. Atoms are almost fully excited to the 5P3/2 state in one nanosecond shorter than the lifetime 26 ns, and subsequently are ionized with variable delay. By detecting either ions or remaining ground state atoms we demonstrate state-resolved measurement of collective decay with nanosecond resolution. This method provides not only the complemental study of collective decay with conventional photon measurement but also enabled access of interatomic correlation combined with the site resolved imaging in optical tweezers or lattice.