The Gull group works on computational quantum many-body theory at the Faculty of Physics, University of Warsaw, as part of the ERC Advanced grant Quantum Algorithms. We develop and apply field-theoretic methods, quantum Monte Carlo algorithms, and analytic continuation techniques for realistic correlated electron systems.

The group maintains an affiliation with the University of Michigan.

We have open positions for postdocs and PhD students. See the Positions page for details, or contact emanuel.gull@gmail.com directly.

Research Highlights

Quantum Impurity Solvers — We develop continuous-time quantum Monte Carlo and tensor-train algorithms for the numerically exact solution of quantum impurity models across a wide range of temperatures and interaction strengths.

Compressed Representations and Analytic Continuation — We design compact representations of Green’s functions using pole expansions, Chebyshev polynomials, and the intermediate representation, and develop analytic continuation methods to extract real-frequency spectra from imaginary-time data.

Mathematical Properties of Green’s Functions — We study the analytical structure of single- and two-particle Green’s functions and develop diagrammatic frameworks and denoising algorithms that enforce known spectral constraints.

Quantum Computing — We develop hybrid classical-quantum algorithms for many-body problems, with a focus on understanding when quantum hardware offers a genuine advantage over classical methods.

Realistic Electronic Structure Methods — In collaboration with the Zgid group, we develop self-consistent many-body perturbation theory and embedding methods for the ab initio simulation of real materials.

Recent Publications and Preprints

Recent Publications

  1. Compact representation and long-time extrapolation of real-time data for quantum systems using the ESPRIT algorithm — Phys. Rev. B 113, 115129 (2026)
  2. Inchworm tensor train hybridization expansion quantum impurity solver — Phys. Rev. B 112, 085120 (2025)
  3. Minimal pole representation for spectral functions — J. Chem. Phys. 162, 214111 (2025)
  4. Pairing boost from enhanced spin-fermion coupling in the pseudogap regime — Phys. Rev. B 112, L041105 (2025)
  5. Minimal pole representation and analytic continuation of matrix-valued correlation functions — Phys. Rev. B 110, 235131 (2024)

Recent Preprints

  1. Validity and Limits of Low Order Hybridization Expansion Approaches for Multi-Orbital Systems (May 4, 2026)
  2. Evolution of the Saddle Point in Antimony Telluride Homologous Superlattices (April 22, 2026)
  3. H-NESSi: The Hierarchical Non-Equilibrium Systems Simulation package (April 7, 2026)
  4. Multi-orbital dynamical mean-field theory with a complex-time solver (December 29, 2025)
  5. Global approximations to correlation functions of strongly interacting quantum field theories (December 20, 2025)
  6. Discovering topological phases in gray-Tin (November 27, 2025)