  Quantum resonances, i.e., metastable states with a finite lifetime, play an
important role in nuclear physics and other domains. Describing this phenomenon
theoretically is generally a challenging task. In this work, we combine two
established techniques to address this challenge. Complex scaling makes it
possible to calculate resonances with bound-state-like methods. Finite-volume
simulations exploit the fact that the infinite-volume properties of quantum
systems are encoded in how discrete energy levels change as one varies the size
of the volume. We apply complex scaling to systems in finite periodic boxes and
derive the volume dependence of states in this scenario, demonstrating with
explicit examples how one can use these relations to infer infinite-volume
resonance energies and lifetimes.
