  We present a phase diagram for a double quantum well bilayer electron gas in
the quantum Hall regime at total filling factor $\nu =1$, based on exact
numerical calculations of the topological Chern number matrix and the
(inter-layer) superfluid density. We find three phases: a quantized Hall state
with pseudo-spin superfluidity, a quantized Hall state with pseudo-spin
``gauge-glass'' order, and a decoupled composite Fermi liquid. Comparison with
experiments provides a consistent explanation of the observed quantum Hall
plateau, Hall drag plateau and vanishing Hall drag resistance, as well as the
zero-bias conductance peak effect, and suggests some interesting points to
pursue experimentally.
