Preempting Fermion Sign Problem: Unveiling Quantum Criticality through Nonequilibrium Dynamics

Abstract: The notorious fermion sign problem, arising from fermion statistics, constitutes one of the main obstacles of deciphering quantum many-body systems by numerical approach. The progress in overcoming sign problem will definitely lead to a great leap in various areas of modern physics. Here, by deviating from the conventional cognition that nonequilibrium studies should be more complicated than equilibrium cases, we propose an innovative framework based on nonequilibrium critical dynamics to preempt sign problem and investigate quantum critical point in fermionic model through numerically exact quantum Monte Carlo (QMC) simulation. By virtue of universal scaling theory of imaginary-time relaxation dynamics, we demonstrate that accurate critical point and critical exponents can be obtained in the short-time stage, in which the sign problem is not severe such that the QMC is accessible. After confirming the effectiveness of the method in two typical interacting fermionic models featuring Dirac quantum critical point (QCP), we for the first time reveal the quantum phase diagram in the Hubbard model hosting $\rm SU(3)$-symmetric Dirac fermions, and find that the QCP between Dirac semi-metal and a $\lambda_8$-antiferromagnetic phase belongs to a new universality class different from the previously known Gross-Neveu transitions.