  We propose a feasible experimental test of a 1-D version of the Fermi problem
using superconducting qubits. We give an explicit non-perturbative proof of
strict causality in this model, showing that the probability of excitation of a
two-level artificial atom with a dipolar coupling to a quantum field is
completely independent of the other qubit until signals from it may arrive. We
explain why this is in perfect agreement with the existence of nonlocal
correlations and previous results which were used to claim apparent causality
problems for Fermi's two-atom system.
