Abstract

Two-Photon Absorption (TPA) is widely utilized nowadays for investigation of solid-state quantum-confined structures, revealing various “dark” states of matter inaccessible to conventional spectroscopy but important for quantum information processing. Recently, a condensate of strongly-coupled light-matter exciton-polaritons [1] was proposed to stimulate highly efficient THz emission, in a transition from a two-photon excited 2p “dark” exciton state [2]. This scheme could enable doubly-stimulated THz emission far more efficient than existing sources [3], and introduces new possibilities for nonlinear optics with polariton condensates, so far relying on underlying inter-particle interactions [4]. It further provides a testbed for “dark” state-condensate interactions and can implement coherent control of collective quantum states with individual qubits. So far, several groups have demonstrated TPA-based excitation of non-condensed polaritons [5,6], yet condensation via TPA was not achieved.

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