Schmidt, RichardSadeghpour, H. R.Demler, E.2019-09-262016Schmidt, Richard, H. R. Sadeghpour, and E. Demler. 2016. “Mesoscopic Rydberg Impurity in an Atomic Quantum Gas.” Physical Review Letters 116 (10). https://doi.org/10.1103/physrevlett.116.105302.0031-90071079-71141092-0145http://nrs.harvard.edu/urn-3:HUL.InstRepos:41412127Giant impurity excitations are powerful probes for exploring new regimes of far out of equilibrium dynamics in few-and many-body quantum systems, and in situ observations of correlations. Motivated by recent experimental progress in spectroscopic studies of Rydberg excitations in ultracold atoms, we develop a new theoretical approach for describing multiscale dynamics of Rydberg excitations in quantum Bose gases. We find that the crossover from few-to many-body dynamics manifests in a dramatic change in spectral profile from resolved molecular lines to broad Gaussian distributions representing a superpolaronic state in which many atoms bind to the Rydberg impurity. We discuss signatures of this crossover in the temperature and density dependence of the spectra.en-USJournal Article2019-09-2610.1103/PhysRevLett.116.105302