# Easing the Monte Carlo sign problem

Quantum physicists at the Freien Universität and the Helmholtz-Zentrum (HZB) developed a method to calculate quantum materials more quickly. The mathematical tool is a feasible and promising means to reduce the sign problem of the quantum Monte Carlo method.

News from Aug 17, 2020

Physics researchers work worldwide on simulating quantum materials on the computer in order to calculate their magnetic and thermal properties as well as phase transitions. They aim to enable the development of future materials for energy-efficient IT technology.

However, computer simulations are very time and capacity consuming. This is due to the wave-particle dualism and the sign problem of the quantum Monte Carlo method, which makes the calculations extremely complex.

The team of Prof. Dr. Jens Eisert, who heads the joint research group at Freie Universität Berlin and HZB, developed a mathematical procedure that greatly reduces the computational cost of the sign problem. The research results were recently published in Science Advances.

The authors argued that solid-state systems can be viewed from very different angles and that the sign problem can play a different role depending on the perspective. "It is then a matter of dealing with the solid-state system in such a way that the sign problem is minimised," explained Dominik Hangleiter, first author of the study.

The researchers demonstrated that the methodology works well for simple solid-state systems with spins. Moreover, the mathematical tool can be applied to more complex spin systems and promises faster calculation of their properties.

### Keywords

- Dominik Hangleiter
- Helmholtz-Zentrum Berlin
- HZB
- Jens Eisert
- Monte Carlo method
- quantum materials
- quantum physics
- sign problem