Quantum Hall line junction with impurities as a multislit Luttinger liquid interferometer

We report on quantum interference between a pair of counterpropagating quantum Hall edge states that are separated by a high-quality tunnel barrier. Observed Aharonov-Bohm oscillations are analyzed in terms of resonant tunneling between coupled Luttinger liquids which creates bound electronic states between pairs of tunnel centers that act like interference slits. We place a lower bound in the range of 20-40 mu m for the phase coherence length and directly confirm the extended phase coherence of quantum Hall edge states.