Dicke-enhanced single-emitter strong coupling at ambient conditions as a quantum resource

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Strong coupling of light and matter at the single emitter level is a fundamental quantum resource since it offers (i) deterministic energy exchange between single photons and a two-level system, and (ii) the possibility to achieve single-photon nonlinearities via the anharmonicity of the Jaynes-Cummings ladder. We recently demonstrated strong coupling of a quantum dot and a broadband plasmonic nanoresonator at room temperature and ambient conditions and, to explain these results, postulated broadband multilevel coupling leading to a Dicke-type enhancement of the single-emitter coupling strength as well as enhanced coupling of the quantum emitter to the plasmonic nanoresonator. In the present project, both conjectures will be put under scrutiny and carried forward towards a quantum resource. To do so, we will develop a platform to integrate strongly coupled quantum emitter - plasmonic nanoresonator systems on a surface. Dielectrophoresis will be used to integrate quantum dots at desired positions, such as plasmonic hotspots, using electrically connected plasmonic nanostructures - a technological advance that was pioneered by one of us. An additional advantage of such nanostructures is the possibility to apply very large DC electric fields to quantum emitters which will be used to introduce tunability via the quantum confined Stark-effect. To experimentally achieve a Dicke-type enhancement of the coupling strength we will use PbS or PbSe quantum dots that offer up to 64 nearly degenerate levels close to the conduction band edge of a quantum dot. This should increase the coupling strength by nearly one order of magnitude thereby relaxing fabrication tolerances. Core-shell colloidal quantum dots will be prepared at the highest possible quality with controlled surface chemistry such that single-emitter experiments can be performed. On the theoretical side, we will develop a new approach to the quantum optics of light matter coupling at the nanoscale that takes into account the quasinormal mode structure of plasmonic nanoresonators and considers their role in broadband light matter interactions. Our results will lead to a methodology that will establish strong and possibly ultrastrong light-matter interaction at the single emitter basis as a novel quantum resource. Accessibility will be strongly enhanced by the largely reduced fabrication tolerances that should become affordable because of the increased coupling. The quantum multi-quasi-normal mode theory will provide a complete theoretical framework to accurately predict quantum light-matter dynamics at these extreme conditions and will aid the experimental implementation of devices for quantum information processing and quantum sensing. Specifically, as a final goal, we propose the implementation and characterization of a nanoscale single-photon transistor based on a scalable architecture.