Polariton-based single-photon sources

Single photons with tailored properties are fundamental resources in quantum optics, communication, computing, and metrology. However, creating these photon states is not entirely straightforward, and while there is a variety of methods that achieve this, they all suffer from either the complexity of the setup required or the fact that the system is hardly scalable. A practically viable implementation is thus still missing. In this proposal, we would like to address this problem by experimentally studying the system of microcavity polaritons, which are the coherent superposition of a photon confined to a short cavity, and a quantum well exciton. A flying photon is generated, when the polariton decays. A number of theoretical works have discussed the potential of polaritons for creating quantum-correlated photons, and there are already a couple of experimental demonstrations of quantum effects, such as, first-order correlations, and squeezing. The big advantage of the polariton system over schemes relying on the implementation of individual quantum emitters is its inherent scalability, robustness, and the possibility of tailoring specific properties, such as the wavelength, polarisation, or the temporal attributes of the generated light. In order to achieve the stated goals, we intend to utilise the latest developments in photonic engineering and theoretical semiconductor quantum optics. We propose to study three possible approaches, all based on III-V semiconductor systems. Firstly, we will fabricate submicrometer-sized pillars with integrated quantum well excitons to provide the photonic non-linearity, i.e., the strong photon-photon interaction required for generating the quantum correlations. Secondly, we will exploit the intricate quantum interference between coupled pillars. And third, we will apply a flexible, hybrid approach, where the cavity is tunable even after fabrication. This will allow us to explore a large segment of the parameter space in a time- and cost-efficient manner. Achieving polariton blockade and single photon emission from the proposed quantum well microcavity systems would certainly be a major breakthrough with impacts far beyond the community of polaritonic research. The scheme based on the coupled cavities is especially interesting, since that phenomenon has not experimentally been demonstrated in any physical system. The possibility to create single photons on demand without individual quantum emitters could lead to entirely novel schemes of highly integrated quantum optics on chip, and creating polariton number states could pave the way towards the implementation of quantum emulation schemes based on bosonic quantum fluids in semiconductors.

Single photons with tailored properties are fundamental resources in quantum optics, communication, computing, and metrology. However, creating these photon states is not entirely straightforward, and while there is a variety of methods that achieve this, they all suffer from either the complexity of the setup required or the fact that the system is hardly scalable. A practically viable implementation is thus still missing. In our project, we tried to address this problem by experimentally studying the system of microcavity polaritons, which are the coherent superposition of a photon confined to a short cavity, and a quantum well exciton. A flying photon is generated, when the polariton decays. A number of theoretical works have discussed the potential of polaritons for creating quantum-correlated photons, and there are already a couple of experimental demonstrations of quantum effects. The big advantage of the polariton system over schemes relying on the implementation of individual quantum emitters is its inherent scalability, robustness, and the possibility of tailoring specific properties, such as the wavelength, polarization, or the temporal attributes of the generated light. In order to achieve our goals, we utilized the latest developments in photonic engineering and theoretical semiconductor quantum optics. We studied three possible approaches, all based on semiconductors. Firstly, we fabricated and characterized submicrometer-sized pillars with integrated quantum well excitons of extremely high quality to provide the photonic non-linearity, i.e., the strong photon-photon interaction required for generating the quantum correlations. Secondly, we investigated the intricate quantum interference between coupled pillars. And third, we were able to show a weak but significant suppression of higher photon numbers in a flexible, hybrid approach, where the cavity is tunable even after fabrication. Even though we were able to demonstrate the effect in one of the three approaches, more research will be needed to bring it to the point where it could be useful for new technology.