Gigantic photon-photon coupling in biased semiconductor microcavities: A step toward single-photon blockade

We discuss optical nonlinearities in biased semiconductor microcavities. Op tical nonlinearities arise from field screening by spatially separated elec tron-hole pairs in biased quantum wells (QWs). However, in wide QWs where t he spatial separation is large, biasing is accompanied by a drastic decreas e of oscillator strength, and has a negative impact on the optical nonlinea rity. We show here that in an exciton polariton microcavity in the strong c oupling regime, a decrease in oscillator strength only weakly affects the o ptical nonlinearity. Gigantic enhancement of photon-photon interaction is t hen realized by biasing, and the single-photon blockade limit can be reache d.