  When the separation between layers in a double-quantum-well system is
sufficiently small, the ground state of the two-dimensional electron gas at
filling factor 1 has an interwell phase coherence even in the absence of
tunneling. For non-zero tunneling, this coherent state goes through a
commensurate-incommensurate transition as the sample is tilted with respect to
the quantizing magnetic field at filling factor 1. In this article, we compute
the optical (infrared) absorption spectrum of the coherent state from the
commensurate state at small tilt angle to the soliton-lattice state at larger
tilt angle and comment on the possibility of observing experimentally the
distinctive signature of the soliton lattice.

Mesoscale and Nanoscale Physics;Strongly Correlated Electrons