Observers following special classes of finite-lifetime trajectories have been
shown to experience an effective temperature, a generalisation of the Unruh
temperature for uniformly accelerated observers. We consider a mirror following
such a trajectory - and is hence localised to a strictly bounded causal diamond
- that perfectly reflects incoming field modes. We find that inertial observers
in the Minkowski vacuum detect particles along the half null-rays at the
beginning and end of the mirror’s lifetime. These particle distributions
exhibit multi-partite entanglement, which reveals novel structure within the
vacuum correlations. The interaction is modelled using a non-perturbative
circuit model and does not suffer from energy divergences.