  Nonperturbative coupling between cavity photons and excitons leads to
formation of hybrid light-matter excitations termed polaritons. In structures
where photon absorption leads to creation of excitons with aligned permanent
dipoles, the elementary excitations, termed dipolar polaritons, are expected to
exhibit enhanced interactions. Here, we report a substantial increase in
interaction strength between dipolar polaritons as the size of the dipole is
increased by tuning the applied gate voltage. To this end, we use coupled
quantum well structures embedded inside a microcavity where coherent electron
tunneling between the wells controls the size of the excitonic dipole.
Modifications of the interaction strength are characterized by measuring the
changes in the reflected intensity of light when polaritons are driven with a
resonant laser. Factor of 6.5 increase in the interaction strength to linewidth
ratio that we obtain indicates that dipolar polaritons could be used to
demonstrate a polariton blockade effect and thereby form the building blocks of
many-body states of light.
