title: Flat histogram methods for quantum systems: algorithms to overcome tunneling problems and calculate the free energy.
abstract: We present a generalization of the classical Wang-Landau algorithm [Phys. Rev. Lett. 86, 2050 (2001)]] to quantum systems. The algorithm proceeds by stochastically evaluating the coefficients of a high temperature series expansion or a finite temperature perturbation expansion to arbitrary order. Similar to their classical counterpart, the algorithms are efficient at thermal and quantum phase transitions, greatly reducing the tunneling problem at first order phase transitions, and allow the direct calculation of the free energy and entropy.
authors.affiliation: Theoretische Physik, ETH Zürich, CH-8093 Zürich, Switzerland and Computation Laboratory, ETH Zürich, CH-8092 Zürich, Switzerland.
authors.forename: Matthias
authors.initials: M
authors.lastname: Troyer
authors.forename: Stefan
authors.initials: S
authors.lastname: Wessel
authors.forename: Fabien
authors.initials: F
authors.lastname: Alet