Giant intersubband polariton splitting in InAs/AlSb microcavities

The optical response of the intersubband excitation of multiple InAs/AlSb quantum wells embedded in a planar semiconductor microcavity has been studied through angle-dependent reflectance measurements. Using a resonator based on total internal reflection, a strong coupling is demonstrated between the intersubband optical transition and the cavity photon, with the attendant formation of intersubband polaritons. A giant vacuum-Rabi splitting 2 Omega(R) was observed both at liquid helium temperatures (2 Omega(R) = 33 meV) as well as at 300 K (2 Omega(R) = 32 meV), for a transition energy (omega(12) = 123 meV. The observed ratio Omega(r)/omega(12) is a record high value (14%) for any strongly-coupled systems, and demonstrates the huge potential of this material for the achievement of the ultra-strong coupling regime predicted theoretically. ((c)) 2007 Elsevier Ltd. All rights reserved.