Light-matter strong coupling in extreme nanophotonic cavities

#light

Photonic cavities can be high-finesse, confining photons for very long times, but due to the diffraction limit usually have large mode volumes. On other hands, nanoplasmonic cavities achieve extremely sub-wavelength mode volumes that allowed us to bring strong-coupling at room temperature, but are very lossy (both radiative and material losses). In this talk I will present our work on two very different nanophotonic cavities(i) a nanoplasmonic cavities formed by tightly-coupling two nanometallic structures and (ii) a high-finesse photonic crystal cavity that also achieves sub-wavelength mode volumes. Plasmonic nanocavities have the ability to significantly confine and enhance light, while at the same time efficiently radiate energy to the far-field. Due to these properties, unprecedented light-matter interactions have been realised at room temperature, such as light-matter strong-coupling. In this talk, I will first explain how the strong-coupling regime is achieved in these systems. I will also present the complex set of plasmonic modes supported by extreme plasmonic nanoantennas, their impact on the excitation and radiative properties of the antenna and how geometrical symmetries dominate their behaviour. Furthermore, when multiple quantum emitters are placed within plasmonic nanocavities sub-radiant entangled states emerge that are long-lived. However, Rabi oscillations do not survive for long periods of time in plasmonic nanocavities, due to their high losses. A high-finesse cavity on the other hand, retains photons within the cavity for long times. I will present photonic crystal waveguide designs that are both high-finesse (Q=10^7) and achieve sub-wavelength mode volumes (V~0.6\lamba^3). Our new designs operate at 780nm to couple with cold atoms, and easily reach deep within the strong coupling regime to form an ideal environment to realise quantum entanglement. Through the entropy dynamics of two emitters we demonstrate local multi-partite entanglement, which is very robust to atomic displacements. Such photonic cavity designs are easily scaled-up to construct large quantum networks with both local and global entanglement.