  Although quantum computers are predicted to have many commercial
applications, less attention has been given to their potential for resolving
foundational issues in quantum mechanics. Here we focus on quantum computers'
utility for the Consistent Histories formalism, which has previously been
employed to study quantum cosmology, quantum paradoxes, and the
quantum-to-classical transition. We present a variational hybrid
quantum-classical algorithm for finding consistent histories, which should
revitalize interest in this formalism by allowing classically impossible
calculations to be performed. In our algorithm, the quantum computer evaluates
the decoherence functional (with exponential speedup in both the number of
qubits and the number of times in the history), and a classical optimizer
adjusts the history parameters to improve consistency. We implement our
algorithm on a cloud quantum computer to find consistent histories for a spin
in a magnetic field, and on a simulator to observe the emergence of
classicality for a chiral molecule.
