On the measurement of superpositions of chiral amplitudes by polarized light scattering

We show that no experiment involving parity can measure the left–right coherence of a state ‖ψ〉=aL‖L〉+eiφaR‖R〉 if sin φ is zero and ‖L〉 and ‖R〉 are real mirror images of one another. We then exhibit a number of experiments in elastic linear light scattering which provide all-or-none measurements of left–right coherence.