Powell, StephenSachdev, Subir2019-09-272007Powell, Stephen, and Subir Sachdev. 2007. “Excited-State Spectra at the Superfluid-Insulator Transition out of Paired Condensates.” Physical Review A 75 (3). https://doi.org/10.1103/physreva.75.031601.1050-29471094-1622http://nrs.harvard.edu/urn-3:HUL.InstRepos:41417417We describe gapped single-particle and collective excitations across a superfluid to insulator quantum phase transition of particles (bosons or fermions) in a periodic potential, with an even number of particles per unit cell. We demonstrate that the dynamics are controlled by a quantum impurity problem of a localized particle interacting with the bulk critical modes. Critical exponents are determined by a renormalization group analysis. We discuss applications to spin oscillations of ultracold atoms in optical lattices and to the electronic phases in the cuprate and related compounds.en-USJournal Article2019-09-2710.1103/PhysRevA.75.031601