An efficient nonlinear quantum gate between two single-photons is highly desirable, as it will enable processing quantum information stored in optical photons. This capability is essential for building next generation of quantum networks, and optical quantum computing. However, such a device is constrained by lack of interaction between optical photons in natural environments. Interestingly, cavity quantum electrodynamics provides several paths towards achieving nonlinear interaction between photons. This action aims at realizing a high fidelity and efficient nonlinear gate between two single-photons using a compact solid-state design. Our approach is based on using the spin-state of a hole in an InAs/GaAs quantum dot to mediate the interaction between the photons. It has recently been demonstrated that the quantum coherence of the hole state can be on the order of several hundreds of nanoseconds. Also, the hole-states have been shown to have very coherent optical transitions which makes them an ideal candidate to realize spin-photon interfaces. In order to boost the interaction between the photons and the quantum dot, a novel microcavity structure will be used. The microcavity structure has recently been developed in the host group and shows spectacular features such as a Q-factor of 1 million, and a cooperativity of 100, making the combination of the hole-state and the microcavity structure an ideal platform to realize photonic gates. The results of this action will be highly instrumental for building quantum repeaters, and may open new directions for quantum computers based on optical photons. For instance, such a nonlinear gate may be combined with a linear network of coupled waveguides to enhance the simulation capabilities of the linear network. Finally, this action is aligned very well with the goals of the Quantum Technologies flagship initiative, and will contribute to the collective effort by the European researchers towards a lead in quantum technologies.
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