Quantum Hall line junction with impurities as a multi-slit 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 that 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. 
I. Yang, W. Kang, L.N. Pfeiffer, K.W. Baldwin, K.W. West, Eun-Ah Kim,   and E. Fradkin