Mitigating boundary effects in finite temperature simulations of false vacuum decay

The physics of false vacuum decay during first-order phase transitions in the early universe may be studied in the laboratory via cold-atom analogue simulators. However, a key difference between analogue experiments and the early universe is the trap potential confining the atoms. Rapid seeded bubble nucleation has been shown to occur at the boundary of typical trap potentials, obscuring the bulk bubble nucleation rate. This difficulty must be overcome in order to reliably probe the bulk bubble nucleation rate in an analogue simulator experiment. In this paper we show that, at finite temperature, this deleterious boundary nucleation can be mitigated by adding a 'trench' to the potential, effectively screening the boundary with a region of higher atomic density. We show that this technique is effective in two different cold-atom analogue systems, but is not needed in ferromagnetic analogue simulators.