  We develop an extension of the variational quantum eigensolver (VQE)
algorithm - multistate, contracted VQE (MC-VQE) - that allows for the efficient
computation of the transition energies between the ground state and several
low-lying excited states of a molecule, as well as the oscillator strengths
associated with these transitions. We numerically simulate MC-VQE by computing
the absorption spectrum of an ab initio exciton model of an 18-chromophore
light-harvesting complex from purple photosynthetic bacteria.
