Physics Research Seminar: Guy Cohen (Tel Aviv University, Israel)

Welcome to join us for a research seminar by Prof. Guy Cohen from Tel Aviv University, Israel

Host: Jose Lado/Correlated Quantum Materials group

Title: A non-variational approach to variational quantum Monte Carlo
 

Abstract: 

Describing the ground states of continuous, real-space quantum
many-body systems, like atoms and molecules, is a significant
computational challenge with applications throughout the physical sciences. Recent progress was made by variational methods based on machine learning (ML) ansatzes. However, since these approaches are based on energy minimization, ansatzes must be twice differentiable. This (a) precludes the use of many powerful classes of ML models; and (b) makes the enforcement of bosonic, fermionic, and other symmetries
costly. Furthermore, (c) the optimization procedure is often unstable unless it is done by imaginary time propagation, which is often impractically expensive in modern ML models with many parameters. The stochastic representation of wavefunctions (SRW) is a recent approach to overcoming (c). SRW enables imaginary time propagation at scale, and makes some headway towards the solution of problem (b), but remains limited by problem (a). We argue that combining SRW with path integral
techniques leads to a new formulation that overcomes all three problems simultaneously. As a demonstration, we apply the approach to generalized "Hooke's atoms": interacting particles in harmonic wells. We benchmark our results against state-of-the-art data where possible, and use it to investigate the crossover between the Fermi liquid and the Wigner molecule within closed-shell systems. Our results shed new light on the competition between interaction-driven symmetry breaking and kinetic-energy-driven delocalization.

[1] H. Atanasova, L. Bernheimer, and G. Cohen, Stochastic Representation of Many-Body Quantum States, Nat Commun 14, 1 (2023).
[2] L. Bernheimer, H. Atanasova, and G. Cohen, Determinant and
Derivative-Free Quantum Monte Carlo Within the Stochastic Representation of Wavefunctions, arXiv:2402.06577.