Programme

O.23 -- Oral, VCTP-51

Date: Tuesday, 4 August 2026

Time: 14:40 - 15:00

Efficient two-time lesser Green’s function calculation via non-uniform pole expansions

Hoa Nghiem

Phenikaa University

Calculating the lesser Green’s function $G^<(t,t’)$ in non-equilibrium quantum impurity systems via the Keldysh formalism is linearly straightforward but computationally expensive. A real-time grid faces a critical dilemma: it must be fine enough to capture fast quantum fluctuations and long enough to resolve the long-time limit, resulting in a heavy computational bottleneck. Transforming the problem into the energy domain, $\omega$, utilizes the energy-time uncertainty relation but shifts the problem into a non-linear formulation with rapidly oscillatory $e^{i\omega t}$ kernels. This work demonstrates that these non-linear oscillations can be efficiently managed by replacing real-frequency integrals with convergent sums over Matsubara poles. Furthermore, we accelerate this convergence using the non-uniform Ozaki pole expansion, where the poles are clustered near low-energy regimes and sparsified at high-energy regimes. This approach enables accurate and long-time non-equilibrium simulations with minimized memory overhead.

Presenter: Nghiem Hoa