  The recently developed density matrix quantum Monte Carlo (DMQMC) algorithm
stochastically samples the N -body thermal density matrix and hence provides
access to exact properties of many-particle quantum systems at arbitrary
temperatures. We demonstrate that moving to the interaction picture provides
substantial benefits when applying DMQMC to interacting fermions. In this first
study, we focus on a system of much recent interest: the uniform electron gas
in the warm dense regime. The basis set incompleteness error at finite
temperature is investigated and extrapolated via a simple Monte Carlo sampling
procedure. Finally, we provide benchmark calculations for a four-electron
system, comparing our results to previous work where possible.
