Reconstructing Nonequilibrium Regimes of Quantum Many-Body Systems from the Analytical Structure of Perturbative Expansions

We present a systematic approach to the nonequilibrium dynamics of strongly
interacting many-body quantum systems, building upon the standard perturbative
expansion in the Coulomb interaction. High-order series are derived from the
Keldysh version of the determinantal diagrammatic quantum Monte Carlo
algorithm. The reconstruction of physical quantities beyond the weak-coupling
regime is obtained using a conformal change of variable, based on the
approximate location of the singularities of these functions in the complex U
plane, and a Bayesian inference technique, that takes into account additional
non-perturbative relations, in order to control the amplification of noise
occurring at large interaction. The approach is then applied to the Anderson
quantum impurity model in the quantum dot geometry in and out of equilibrium.

C. Bertrand, S. Florens, O. Parcollet, and X. Waintal, Phys. Rev. X 9, 041008 (2019)