  Quantum Monte Carlo is one of the most powerful numerical tools for studying
nonpeturbative properties of quantum many-body systems. However, its
application to real-time problems is limited since the complex and
highly-oscillating path-integral weight of the real-time evolution harms the
important sampling. % , which is the notorious sign problem. In this Letter, we
show that some real-time problems in open fermion systems can be simulated
using the quantum Monte Carlo. To this end, we prescribe a mapping between a
real-time problem in open quantum systems and a statistical problem in
non-Hermitian quantum systems; for some cases, the latter can be solved without
suffering from the complex measure problem. To explain our idea and demonstrate
how it works, we compute the real-time evolution of fidelities in open fermion
systems under dissipation.

Quantum Physics;Statistical Mechanics;High Energy Physics - Lattice;High Energy Physics - Theory