  Correlated fermions are of high interest in condensed matter (Fermi liquids,
Wigner molecules), cold atomic gases and dense plasmas. Here we propose a novel
approach to path integral Monte Carlo (PIMC) simulations of strongly degenerate
non-ideal fermions at finite temperature by combining a fourth-order
factorization of the density matrix with antisymmetric propagators, i.e.,
determinants, between all imaginary time slices. To efficiently run through the
modified configuration space, we introduce a modification of the widely used
continuous space worm algorithm, which allows for an efficient sampling at
arbitrary system parameters. We demonstrate how the application of determinants
achieves an effective blocking of permutations with opposite signs, leading to
a significant relieve of the fermion sign problem. To benchmark the capability
of our method regarding the simulation of degenerate fermions, we consider
multiple electrons in a quantum dot and compare our results with other ab
initio techniques, where they are available. The present permutation blocking
path integral Monte Carlo approach allows us to obtain accurate results even
for $N=20$ electrons at low temperature and arbitrary coupling, where no other
ab initio results have been reported, so far.
