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 Ω R was observed both at liquid helium temperatures ( 2 Ω R = 33 meV ) as well as at 300 K ( 2 Ω R = 32 meV ), for a transition energy ω 12 = 123 meV . The observed ratio Ω r ω 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.