  Bipolaron formation in a two-dimensional lattice with harmonic confinement,
representing a simplified model for a quantum dot, is investigated by means of
quantum Monte Carlo simulations. This method treats all interactions exactly
and takes into account quantum lattice fluctuations. Calculations of the
bipolaron binding energy reveal that confinement opposes bipolaron formation
for weak electron-phonon coupling, but abets a bound state at intermediate to
strong coupling. Tuning the system from weak to strong confinement gives rise
to a small reduction of the minimum Frohlich coupling parameter for the
existence of a bound state.
