Single polariton nonlinearities
Exciton polaritons are composite quasiparticles resulting from the strong coupling of cavity photons and quantum well (QW) excitons embedded within a microcavity (MC) . Polaritons interact nonlinearly due to their excitonic component and can form macroscopically coherent condensates . They are scalable to form arrays by either etching  or optical patterning  of the microcavity. However, in the presently studied systems, polariton-polariton interaction energy is smaller as compared to their line-broadening.
The goal of this project is to achieve nonlinear quantum regime in photonics where the single-site effective photon interaction energy is larger than the losses. This will open a plethora of interesting phenomena such as photon blockade, photon crystallisation and opportunities to realize quantum simulators for the study of condensed matter problems such as Mott-insulator to superfluid phase transitions in arrays of optical cavities. So far, the lack of scalable devices with sufficient nonlinearities and low-enough losses has been the main obstacle for the experimental realization of these phenomena. There are two approaches towards overcoming this problem: manufacturing higher quality microcavities or enhancing the polariton nonlinearities. Here, we employ electrically driven MC and exploit quantum confined Stark effect (QCSE) to form dipolar polaritons and tune exciton-exciton interaction. Furthermore, we implement spatial lateral confinement in sub-μm pillars to squeeze and enhance further polariton-polariton interactions to achieve single polariton nonlinearities.
 C. Weisbuch,M.Nishioka, A. Ishikawa, and Y., Arakawa, Phys. Rev. Lett, 69, 3314 (1992).
 J. Kasprzak et al., Nature, 443, 409 (2006).
 T. Gao et al., , Phys. Rev. B 85, 235102 (2012).
 G. Tosi et al., Nat. Phys. 8, 190 (2012).
 S.I. Tsintzos et al., Phys. Rev. Lett. 121, 037401 (2018)