 
Summary: NEST Scientific Report 2007200931
Intersubband polaritonics
T
he interaction of light with material excitations has long attracted intense experimental
and theoretical investigations. Thanks to the development of epitaxial growth
techniques, it is now possible to realize monolithic microcavity structures in which
both electrons and photons can be simultaneously confined and their interaction can
be manipulated. In a microcavity, the photonic confinement deeply modifies lightmatter
interaction, and if the coupling strength is sufficiently large compared to the damping
rates, new elementary excitations are formed which are mixed electronic and photonic
states. The socalled "cavity polaritons" were first observed in solidstate systems employing
excitonic states in semiconductors. Recently we demonstrated the strong coupling of the
confined electromagnetic radiation with the transitions between the subbands in the
conduction band of a GaAsAlGaAs heterostructure, with the corresponding formation
of "intersubband cavity polaritons" [1]. This system is very promising for the achievement
of an unprecedented "ultrastrong coupling regime" of lightmatter interaction, which is
particularly interesting for the peculiar quantum nature of its eigenstates. Furthermore,
theoretical predictions show that the ultrafast modulation of polariton coupling can result
in the release of correlated photon pairs from the polariton ground state [2], in a process
analogous to the dynamic Casimir effect and to Hawking blackhole radiation. Here we
