We study the conductance of a quantum T-junction coupled to two electron
reservoirs and a quantum dot. In the absence of electron-electron interactions,
the conductance g is sensitive to interference between trajectories which
enter the dot and those which bypass it. We show that including an intra-dot
charging interaction has a marked influence-- it can enforce a coherent
response from the dot at temperatures much larger than the single particle
level spacing Δ. The result is large oscillations of g as a function
of the voltage applied to a gate capacitively coupled to the dot. Without
interactions, the conductance has only a weak interference signature when
T>Δ.Comment: 4 pages, 2 figures. Typos corrected, minor changes for clarity.
Accepted for publication in Phys. Rev. Let