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Quantum Monte Carlo simulations of quantum many body systems are plagued by the Fermion sign problem. The computational complexity of simulating Fermions scales exponentially in the projection time $\beta$ and system size. The sign problem…

Strongly Correlated Electrons · Physics 2021-06-02 Ryan Levy , Bryan K. Clark

The sign problem is a notorious problem, which occurs in Monte Carlo simulations of a system with a partition function whose integrand is not positive. One way to simulate such a system is to use the factorization method where one enforces…

High Energy Physics - Lattice · Physics 2012-11-08 Konstantinos N. Anagnostopoulos , Takehiro Azuma , Jun Nishimura

The notorious fermion sign problem, arising from fermion statistics, presents a fundamental obstacle to the numerical simulation of quantum many-body systems. Here, we introduce a framework that circumvents the sign problem in the studies…

Strongly Correlated Electrons · Physics 2026-01-07 Yin-Kai Yu , Zhi-Xuan Li , Shuai Yin , Zi-Xiang Li

The path integral formulation of quantum mechanical problems including fermions is often affected by a severe numerical sign problem. We show how such a sign problem can be alleviated by a judiciously chosen constant imaginary offset to the…

Strongly Correlated Electrons · Physics 2024-10-23 Christoph Gäntgen , Evan Berkowitz , Thomas Luu , Johann Ostmeyer , Marcel Rodekamp

Numerical simulations of numerous quantum systems suffer from the notorious sign problem. Important examples include QCD and other field theories at non-zero chemical potential, at non-zero vacuum angle, or with an odd number of flavors, as…

High Energy Physics - Lattice · Physics 2015-06-25 J. Cox , C. Gattringer , K. Holland , B. Scarlet , U. -J. Wiese

We argue the sign problem of the fermion determinant at finite density. It is unavoidable not only in Monte-Carlo simulations on the lattice but in the mean-field approximation as well. A simple model deriving from Quantum Chromodynamics…

High Energy Physics - Phenomenology · Physics 2008-11-26 Kenji Fukushima , Yoshimasa Hidaka

This paper presents a method for alleviating sign problems in lattice path integrals, including those associated with finite fermion density in relativistic systems. The method makes use of information gained from some systematic expansion…

High Energy Physics - Lattice · Physics 2020-11-11 Scott Lawrence

The fermion sign problem remains the primary obstacle in simulating the thermodynamic properties of various fermionic systems. In this work, we present a sign-blocking method to mitigate the numerical instability inherent in the sign…

Computational Physics · Physics 2026-04-14 Yunuo Xiong , Hongwei Xiong

The negative sign problem in quantum Monte Carlo (QMC) simulations of cluster impurity problems is the major bottleneck in cluster dynamical mean field calculations. In this paper we systematically investigate the dependence of the sign…

Strongly Correlated Electrons · Physics 2015-11-18 Hiroshi Shinaoka , Yusuke Nomura , Silke Biermann , Matthias Troyer , Philipp Werner

Ab initio path integral Monte Carlo (PIMC) simulations constitute the gold standard for the estimation of a broad range of equilibrium properties of a host of interacting quantum many-body systems spanning conditions from ultracold atoms to…

Chemical Physics · Physics 2025-08-27 Paul Hamann , Jan Vorberger , Tobias Dornheim

We study the distribution of the phase angle and the magnitude of the fermion determinant as well as its correlation with the chiral condensate and the baryon number for QCD at non-zero quark chemical potential. Results are derived to…

High Energy Physics - Lattice · Physics 2010-03-19 M. P. Lombardo , K. Splittorff , J. J. M. Verbaarschot

In this paper, we discover a new quantum Monte Carlo (QMC) method to solve the fermion sign problem in interacting fermion models by employing Majorana representation of complex fermions. We call it "Majorana QMC" (MQMC). Especially, MQMC…

Strongly Correlated Electrons · Physics 2015-07-22 Zi-Xiang Li , Yi-Fan Jiang , Hong Yao

We present a new Monte Carlo algorithm for simulating quantum spin systems which is able to suppress the negative sign problem. This algorithm has only a linear complexity in the lattice size used for the simulation. A general description…

High Energy Physics - Lattice · Physics 2007-05-23 A. Galli

In this work we solve the sign problem of a frustrated quantum impurity model consisting of three quantum spin-half chains interacting through an anti-ferromagnetic Heisenberg interaction at one end. We first map the model into a repulsive…

Strongly Correlated Electrons · Physics 2017-04-03 Connor T. Hann , Emilie Huffman , Shailesh Chandrasekharan

The study of lattice gauge theories with Monte Carlo simulations is hindered by the infamous sign problem that appears under certain circumstances, in particular at non-zero chemical potential. So far, there is no universal method to…

High Energy Physics - Lattice · Physics 2017-03-27 Mari Carmen Bañuls , Krzysztof Cichy , J. Ignacio Cirac , Karl Jansen , Stefan Kühn , Hana Saito

We solve the sign problem in a particle-hole symmetric spin-polarized fermion model on bipartite lattices using the idea of fermion bags. The solution can be extended to a class of models at half filling but without particle-hole symmetry.…

Strongly Correlated Electrons · Physics 2014-03-19 Emilie Fulton Huffman , Shailesh Chandrasekharan

We propose a framework based on the concept of the semigroup to understand the fermion sign problem. By using properties of contraction semigroups, we obtain sufficient conditions for quantum lattice fermion models to be sign-problem-free.…

Strongly Correlated Electrons · Physics 2024-08-28 Zhong-Chao Wei

Approaches to finite baryon density lattice QCD usually suffer from uncontrolled systematic uncertainties in addition to the well-known sign problem. We test a method - sign reweighting - that works directly at finite chemical potential and…

High Energy Physics - Lattice · Physics 2021-12-09 Attila Pasztor , Szabolcs Borsanyi , Zoltan Fodor , Kornel Kapas , Sandor D. Katz , Matteo Giordano , Daniel Nogradi , Chik Him Wong

Motivated by the important role played by the phase of the fermion determinant in the investigation of the sign problem in lattice QCD at nonzero baryon density, we derive an analytical formula for the average phase factor of the fermion…

High Energy Physics - Lattice · Physics 2009-10-16 Jacques Bloch , Tilo Wettig

We present a solution to the sign problem in a class of particle-hole symmetric Hamiltonian lattice fermion models on bipartite lattices using the idea of fermion bags. The solution remains valid when the particle-hole symmetry is broken…

High Energy Physics - Lattice · Physics 2015-12-03 Emilie Huffman , Shailesh Chandrasekharan