Molecular Structure in Electronic Strong Coupling

Xin Feng, Chen Wang, Hongjing Ma +4 more

Strong coupling-like phenomenon between plasmonic cavities and emitters provides a new way to realize the quantum-like effect controlling at microscale/nanoscale. We investigate the strong coupling-like phenomenon in the structure of single metallic nanoparticle embedded in molecular J-aggregates by the classical simulation method and show that the size of the metallic nanoparticle and the oscillator strength of molecular J-aggregates impact the strong coupling-like phenomenon. The strong coupling-like phenomenon is induced by the interactions between two dipoles formed by the metallic nanoparticle and molecular J-aggregates or the interactions between the dipole generated from molecular J-aggregates and the quadrupole generated from the metallic nanoparticle. The strong coupling-like phenomenon appears evidently with the increase in oscillator strength of molecular J-aggregates. The detuning energy linearly decreases with the increase in radius of the metallic nanoparticle. Our structure has potential applications in quantum networks, quantum key distributions and so on.

Robin Findlay Hendry

Artem Strashko

This dissertation studies the effects of strong matter-light coupling on properties of organic molecules and inorganic semiconductors. The interplay of complex intramolecular dynamics and strong coupling of a photon to molecular transitions results in new physics having no counterparts in other systems. In contrast, low-energy optically active excitations of semiconductors (excitons) usually do not feature such complexity. However, the combination of strong electronic correlations and strong matter-light coupling leads to new physics. Firstly, the effect of strong coupling between molecular vibrations and infrared photons on Raman scattering (RS) is considered. This is motivated by the experiment of Ref. [1] showing up to 10³ enhancement of RS signal under strong coupling. While the exact analytical results of this dissertation predict around 100% enhancement of total RS signal, they cannot explain orders of magnitude enhancement, leaving the question open for further studies. Next, the effects of strong coupling of an optical photon and a molecular electronic transition on molecular lasing properties are discussed. Starting from a microscopic description of a driven-dissipative system, an exact (in the thermodynamic limit) mean-field solution is developed. It allows to uncover the mechanism of molecular lasing in the weak and strong coupling regime and to obtain a non-equilibrium lasing phase diagram. Finally, a semiconductor with different densities of electrons and holes, strongly coupled to a microcavity photon, is studied. While finite electron-hole density imbalance is detrimental for excitonic condensation, it may still lead to a condensed state of excitons with finite centre of mass momentum coexisting with unpaired electrons. On the other hand, due to its low mass, a photon favours zero center of mass momentum condensation. The variational mean-field calculations reveal that the interplay of these effects leads to a variety of novel states with coexisting polariton condensate and unpaired electrons.

Jochen Vogt

Athul S. Rema, Adrián E. Rubio López, Felipe Herrera

Quantum emitters near the surface of silver nanoparticles undergo Rabi oscillations in electronic population dynamics due to strong coupling with near-field multipole modes that are not radiative. Low-frequency nanoparticle dipole modes are radiative but do not couple strong enough to quantum emitters. These features limit the observation of strong coupling. Using macroscopic quantum electrodynamics theory within a Lorentzian pseudo-mode approximation for the non-Markovian interaction kernel, we demonstrate that by coating spherical silver nanoparticles with a thin molecular J-aggregate layer, the resulting core-shell plexciton resonance restructures the local electromagnetic vacuum at dipole-mode frequencies to enable Rabi oscillations for quantum emitters that otherwise would only undergo exponential population decay. Specifically, we show for quantum dot emitters in the near field of silver nanospheres of 20 nm radius, that weak-to-strong coupling crossovers can be induced using 2 nm J-aggregate shells. Our work demonstrates the potential of molecular aggregates to enable deep sub-wavelength structuring of the vacuum field for the observation of coherent quantum dynamics in optical nanocavities.

R. Guy Woolley