A laboratory analogue of the event horizon using slow light in an atomic medium

Singularities underlie many optical phenomena(1). The rainbow, for example, involves a particular type of singularity-a ray catastrophe-in which light rays become infinitely intense. In practice, the wave nature of light resolves these infinities, producing interference patterns. At the event horizon of a black hole(2), time stands still and waves oscillate with infinitely small wavelengths. However, the quantum nature of light results in evasion of the catastrophe and the emission of Hawking radiation(3). Here I report a theoretical laboratory analogue of an event horizon: a parabolic profile of the group velocity(7) of light brought to a standstill in an atomic medium(4-6) can cause a wave singularity similar to that associated with black holes. In turn, the quantum vacuum is forced to create photon pairs with a characteristic spectrum, a phenomenon related to Hawking radiation(3). The idea may initiate a theory of 'quantum' catastrophes, extending classical catastrophe theory(8,9).