  We add a simple boundary term to the Polyakov action and construct a new
class of D-branes with a single null direction. On the string world-sheet the
system is described by a single quantized left-mode sector of a conformal field
theory. By a Wick rotation of spacetime, we map open strings attached to these
branes into chiral closed strings. We suggest that these so-called H-branes
describe quantum horizons - black hole, cosmological (de-Sitter), etc. We show
how one can get a space/phase space transmutation near the horizon and discuss
the new features of boundary states which become squeezed states.
