Numerical simulation of fermi systems

Bharath Hebbe Madhusudhana, Sebastian Scherg, Thomas Kohlert +2 more

Quantum simulators have made a remarkable progress towards exploring the dynamics of many-body systems, many of which offer a formidable challenge to both theoretical and numerical methods.While state-of-the-art quantum simulators are, in principle, able to simulate quantum dynamics well outside the domain of classical computers, they are noisy and limited in the variability of the initial state of the dynamics and the observables that can be measured.Despite these limitations, here we show that such a quantum simulator can be used to in effect solve for the dynamics of a many-body system.We develop an efficient numerical technique that facilitates classical simulations in regimes not accessible to exact calculations or other established numerical techniques.The method is based on approximations that are well suited to describe localized one-dimensional Fermi-Hubbard systems.Since this new method does not have an error estimate and the approximations do not hold in general, we use a neutral-atom Fermi-Hubbard quantum simulator with L exp 290 lattice sites to benchmark its performance in terms of accuracy and convergence for evolution times up to 700 tunneling times.We then use these approximations in order to derive a simple prediction of the behavior of interacting Bloch oscillations for spin-imbalanced Fermi-Hubbard systems, which we show to be in quantitative agreement with experimental results.Finally, we demonstrate that the convergence of our method is the slowest when the entanglement depth developed in the many-body system we consider is neither too small nor too large.This represents a promising regime for near-term applications of quantum simulators.

Yasuhiro Hatsugai, Masatoshi Imada

Hongjuan Meng, Gou Xue-Qiang, Wen-Yuan Wang +4 more

We investigate the relationships between the nonlinear Ramsey interference pattern of the angular frequency and system parameters of fermi superfluid gase in unitarity regime in three limited cases. We find that the interaction between fermions and the difference in energy between double-well potentials have a significant influence on the angular frequency of the interference pattern. Through numerical simulation and theoretical analysis, the relationship between angular frequency of the interference pattern and the system parameters is given, and the numerical simulations and theoretical analyses are in good agreement.

Robert L. Sugar

Yunuo Xiong, Hongwei Xiong

Fictitious identical particle thermodynamics has emerged as a powerful tool to overcome the fermion sign problem, enabling highly accurate simulations of one thousand fermions in warm dense matter (T. Dornheim et al., J. Phys. Chem. Lett. 15, 1305 (2024)). However, inferring the thermodynamic properties of Fermi systems from a large number of exact numerical simulations of the bosonic sector still poses subtle challenges, especially in the regime of high quantum degeneracy and in the presence of phase transitions. In this work, we demonstrate that physics-informed neural networks (PINNs), trained on data from extensive and sign-problem-free numerical simulations of the bosonic sector, offer a valuable means to infer the thermodynamic properties of Fermi systems. PINNs can play a particularly crucial role in capturing phase transitions. To illustrate the methodology of fictitious identical particles combined with PINNs for simulating the thermodynamics of Fermi systems, we explore its application in realistic scenarios, including ultracold Fermi gases in periodic potentials, and phase transitions of pair condensation formed in the unitary limit in a three-dimensional harmonic trap. For the spatially continuous Fermi-Hubbard model, we efficiently and reliably simulated hundreds of fermions here. For the Fermi gas in the unitary limit, based on the fictitious identical particle combined with PINNs, our approach confirms the universal result of the critical temperature with the increasing of the number of fermions, and is consistent with the experimental observations.