Transport in Coherent Quantum Hall Bilayers

We develop an approach to describe transport in bilayer quantum Hall systems in which coherence is established spontaneously between layers. We use Landauer-Buttiker theory with phenomenological parameters which can be fit to experimental data to describe quasiparticle transport in bilayers with strong coherence. We use the above approach to calculate two-probe conductances for various experimental configurations. We also apply the formalism to describe high-current transport in a bilayer with a time-dependent condensate. To describe the transition from strong to weak coherence, we use a pheonomenological single ``relaxation length'' ansatz for contact-to-contact transmission coefficients. As an application, we consider longitudinal drag, and find a good agreement with experiment in the regime of well- developed Quantum Hall Effect.