Quantum Correlations of Exciton-Polaritons

n this work we study the quantum nature of a hybrid light–matter system, where we use the interactions of the matter component to introduce a sizable nonlinearity to photons. It is a longstanding goal to achieve interactions that overcome the losses in the system, resulting in the photon blockade effect that leads to nonclassical signatures measurable in photon correlation experiments. To implement such a system we combine an optical cavity with excitons in an InGaAs quantum well where the strong light–matter coupling leads to new hybridised eigenstates called polaritons. To further enhance the existing interactions between these polaritons we introduce lateral confinement of the optical mode and a second quantum well. This allows for the coupling to indirect excitons, where the spatial separation of electrons and holes introduces dipolar interactions to the system. In order to measure correlations over a wide range of polariton compositions, we use an open cavity design allowing for in situ tuning of the cavity length. This design naturally results in sizable fluctuations of the cavity length, directly translating to the energy of the optical resonance. We therefore developed a measurement procedure based on postselecting photon arrival times based on their countrate, allowing us to overcome these fluctuations and resolve the correlations of the polaritons. The interactions between purely direct exciton–polaritons allowed for the first observation of nonclassical polariton correlations by continuous wave excitation, with a value g(2)(0) = 0.90(1) at an cavity content of 28 %, marking the current record for comparable systems. Correlation measurements at lower exciton fractions show the presence of a new regime, where a small antibunching persists independent of the detuning between the excitation laser and the polariton mode. This behaviour cannot be explained by polariton–polariton interactions. We attribute them to the presence of the biexciton and propose a “dissipative blockade” mechanism, where the ...