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Light-matter interactions in condensed media at room-temperature are fundamentally limited by electron-phonon coupling. For instance, while the excitation cross-section of an isolated atom, or of a single quantum emitter at cryogenic temperatures, can reach one half of the wavelength of light squared (meaning that ~50% of incoming photons will interact for a diffraction-limited excitation); this value is reduced by 6-7 orders of magnitude for a fluorescent molecule or for a colloidal quantum dot at room temperature because of homogeneous phonon broadening. In order to render the exceptional optical properties of single quantum systems (such as single-photon emission and nonlinearities) efficiently accessible at room temperature and in condensed media, it is essential to enhance and optimize these interaction cross-sections.
In this presentation, I will detail some of our recent work towards this goal. In particular, I will describe how DNA-based self-assembly can be used to introduce, in a deterministic way, a controlled number of quantum emitters in the nanoscale hot-spot of a plasmonic resonator. Using this approach, we can enhance single-photon emission from fluorescent molecules by more than two orders of magnitude in a weak-coupling regime (ACS Nano 10, 4806 (2016)). Using five organic molecules, it is also possible to reach a strong-coupling regime with a single dimer of gold nanoparticles (ACS Nano 15, 14732 (2021)).
An alternative platform to plasmonics, in order to enhance light-matter interactions at room temperature, is the use of nanoscale optical resonators made of high-index dielectric materials such as silicon or gallium phosphide. I will discuss some of our recent work on the use of silicon resonators to enhance or inhibit spontaneous emission from electric or magnetic optical emitters (Phys. Rev. Applied 6, 064016 (2016) & Nano Lett. 18, 3481 (2018)); as well as the development of colloidal dielectric resonators to enhance quadratic or cubic nonlinear optical properties.
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