  Quantum systems with geometrical frustration remain an outstanding challenge
for numerical simulations due to the infamous numerical sign problem. Here, we
overcome this obstruction via complex path integration in a geometrically
frustrated ladder of interacting bosons at finite density. This enables studies
of the many-body ground state properties, otherwise inaccessible with standard
quantum Monte Carlo methods. Specifically, we study a chemical potential tuned
quantum phase transition, along which we track the emergence of
quasi-long-range order and critical softening of the single particle gap. We
chart future methodological improvements and applications in generalized
geometrically frustrated lattice models.
