Tuning quantum corrections to the conductance in Andreev quantum dots

We study the leading quantum interference correction to the conductance of a ballistic quantum dot connected via barriers of arbitrary transparencies to both a normal-metal lead and a superconducting lead, in the absence of time-reversal symmetry. We find that the sign of the quantum correction can be tuned by the transparencies of the barriers. The validity of our final analytical result is confirmed by independent numerical simulations. We also present a simple and intuitive interpretation of the sign change in terms of an interplay between destructive and constructive interferences of pairs of Feynman paths.