  We demonstrate quantum computation of two-point correlation functions for a
Heisenberg spin chain. Using the IBM Q 20 quantum machines, we find that for
two sites the correlation functions produce the exact results reliably. For
four sites, results from the IBM Q 20 Tokyo quantum computer are noisy due to
read out errors and decoherence. Nevertheless, the correlation functions retain
the correct spectral information. This is illustrated in the frequency domain
by accurately extracting the magnon energies from peaks in the spectral
function.
