Universal scattering with general dispersion relations

TitleUniversal scattering with general dispersion relations
Publication TypeJournal Article
Year of Publication2022
AuthorsWang, Y, Gullans, M, Na, X, Whitsitt, S, Gorshkov, AV
JournalPhys. Rev. Research
Start Page023014
Date Published4/6/2022
KeywordsFOS: Physical sciences, Mathematical Physics (math-ph), Quantum Physics (quant-ph)

Many synthetic quantum systems allow particles to have dispersion relations that are neither linear nor quadratic functions. Here, we explore single-particle scattering in general spatial dimension D≥1 when the density of states diverges at a specific energy. To illustrate the underlying principles in an experimentally relevant setting, we focus on waveguide quantum electrodynamics (QED) problems (i.e. D=1) with dispersion relation ϵ(k)=±|d|km, where m≥2 is an integer. For a large class of these problems for any positive integer m, we rigorously prove that when there are no bright zero-energy eigenstates, the S-matrix evaluated at an energy E→0 converges to a universal limit that is only dependent on m. We also give a generalization of a key index theorem in quantum scattering theory known as Levinson's theorem -- which relates the scattering phases to the number of bound states -- to waveguide QED scattering for these more general dispersion relations. We then extend these results to general integer dimensions D≥1, dispersion relations ϵ(k)=|k|a for a D-dimensional momentum vector k with any real positive a, and separable potential scattering.