Quantum Polaritonics: from molecules to noble metals

When: Friday, 6th March (2015), 12:00h
Place: Departamento de Física de la Materia Condensada, Facultad Ciencias, Module 3, Seminar Room (5th Floor).
Speaker: Stephane Kena-Cohen, Department of Engineering Physics, Polytechnique Montreal, Canada.

Polaritons are the normal modes of systems where the interaction between light and matter must be treated explicitly. In this seminar, I will discuss experiments that exploit two distinct types of polaritons: cavity exciton-polaritons (a mixture of molecular excitons with a Fabry-Pérot cavity mode) and surface plasmon-polaritons (a mixture of the electromagnetic field with the plasma oscillations of a metal’s conduction electrons).

In the first case, we show that by hybridizing the excitonic transition of an organic semiconductor with a long-lived cavity mode, quasiparticles with an effective mass 10-10 times that of a rubidium atom can be formed. As a result of their light mass, these quasiparticles can be made to spontaneously condense into their lowest energy state in a manner analogous to that of Bose-Einstein condensation (BEC), but at room temperature. Although our system is intrinsically out of equilibrium, we show that much of the BEC phenomenology is preserved. Furthermore, we find that the energy of these polariton condensates exhibits an intensity-dependent blueshift due to nonlinear interactions between polaritons. This nonlinearity, which is inherited by the cavity mode allows for the realization of a number of fascinating effects such as superfluidity, the formation of dark or bright solitons and all-optical switching.
In the second case, we will describe how plasmonic waveguides and resonators can be used to confine the electromagnetic field to sub-wavelength dimensions and thus lead to high field intensities. These intensities can be exploited to increase optical nonlinearities and this has interesting consequences for integrated quantum optics. I will discuss recent experiments where we exploit the bosonic character of surface plasmons to demonstrate on-chip quantum interference using the plasmonic Hong-Ou-Mandel effect. Such quantum interference is the fundamental building block of quantum information schemes based on linear optics.