  When ensembles of atoms interact with coherent light fields a great many
interesting and useful effects can be observed. In particular, the group
velocity of the coherent fields can be modified dramatically.
Electromagnetically induced transparency is perhaps the best known example,
giving rise to very slow light. Careful tuning of the optical fields can also
produce stored light where a light field is mapped completely into a coherence
of the atomic ensemble. In contrast to stored light, in which the optical field
is extinguished, stationary light is a bright field of light with a group
velocity of zero. Stationary light has applications in situations where it is
important to maintain an optical field, such as attempts to engineer large
nonlinear interactions. In this paper we review the stationary light
demonstrations published to date and provide a unified theoretical framework
that describes the experimental observations. We also discuss possible
applications of stationary light with a particular focus on all-optical phase
gates for quantum information technology.
