We perform the numerical equivalent of a phase sensitive experiment on doped
t−J ladders. We apply proximity effect fields with different complex phases
at both ends of an open system and we study the transport of Cooper pairs.
Measuring the response of the system and the induced Josephson current, Density
Matrix Renormalization Group calculations show how, depending on the doping
fraction, the rung-leg parity of the pair field changes from minus to plus as
the density of holes is increased. We also study the pair charge stiffness, and
we observe a supression of the superconductivity in the region where static
stripes appear. We compare our results with predictions from bosonization and
renormalization group analysis.Comment: 4 pages, 5 figure
