Strongly-coupled organic-based microcavities for polariton condensation and quantum batteries

This thesis concerns the study of organic-based microcavities in both the strong and weak coupling regimes. The first three experimental chapters (Chapters 4-6) concern strongly-coupled microcavities for polariton condensation, whereas Chapter 7 studies a mix of weakly- and strongly coupled cavities for use as quantum batteries.

A new cavity structure utilising a hybrid metal-dielectric mirror containing a boron dipyrromethene derivative was studied and found to give higher quality factors and Rabi splittings than the traditional double-distributed Bragg reflector (DBR) structure. It was then demonstrated that a hybrid-mirror cavity, whose bottom mirror consisted of only three layers, could support polariton condensation with only a slightly increased threshold compared to the double-DBR control.

A new dye, which has been used in weakly-coupled lasers, was investigated and shown to undergo polariton condensation despite a seemingly-broad absorption linewidth. Notably, polariton condensation was maintained for more than 37,000 pulses in air, showing remarkably enhanced photostability compared to previously studied small molecules.

A new technique for confining polariton condensates was studied in which two organic dyes were incorporated into a single microcavity such that one was strongly-coupled to the cavity mode and the other was weakly-coupled. The weakly-coupled dye was saturated optically to generate an ultrafast refractive index change, resulting in a blueshift of the polariton mode. This blueshift created an 'energy barrier' that could potentially be used to confine a polariton condensate that would be generated by pumping the strongly-coupled dye.

Microcavities containing a fluorescent dye at varying concentrations were used to demonstrate superabsorption in a prototype Dicke quantum battery. Here, each molecule was considered as a "battery" interacting with a common cavity mode. Fast spectroscopy was used to demonstrate superextensive charging power and energy storage density, giving the first evidence of superabsorption with a macroscopic number of molecules.