Robust analytic continuation combining the advantages of the sparse modeling approach and the Padé approximation

Analytic continuation (AC) from the imaginary-time Green's function to spectral is a crucial process for numerical studies of dynamical properties quantum many-body systems. This process, however, an ill-posed problem; that is, obtained spectrum unstable against noise function. Though several methods have been developed, each them has its own advantages and disadvantages. The sparse modeling (SpM) AC method, example, robust but suffers unphysical oscillations in low-energy region. We propose new method combines SpM with Pad\'{e} approximation. combination, called SpM-Pad\'{e}, inherits robustness accuracy Pad\'{e}, compensating disadvantages each. demonstrate SpM- yields low-variance low-biased results almost same computational cost as method.