  We show that interference experiments can be used to identify the
spin-incoherent regime of strongly interacting one-dimensional conductors. Two
qualitative signatures of spin-incoherence are found: a strong magnetic field
dependence of the interference contrast and an anomalous scaling of the
interference contrast with the applied voltage, with a temperature and magnetic
field dependent scaling exponent. The experiments distinguish the
spin-incoherent from the spin-polarized regime, and so may be useful in
deciding between alternative explanations proposed for the anomalous
conductance quantization observed in quantum point contacts and quantum wires
at low density.
