Nonlinear optics with coupled polariton modes

S.R.K. Rodriguez, A. Amo, I. Sagnes, E. Galopin, A. Lemaitre and J. Bloch

Laboratoire de Photonique et de Nanostructures, LPN/CNRS, Route de Nozay, 91460 Marcoussis, France

Extreme optical nonlinearities emerge when photons are spatially confined and rendered mutually interacting. Semiconductor optical microcavities are promising solid-state systems wherein these two conditions can be simultaneously fulfilled. Photons in a microcavity can couple strongly to excitons in semiconductor quantum wells, giving rise to composite light-matter quasi-particles known as polaritons. The excitonic constituent confers polaritons giant interaction strengths, while the photonic constituent enables micron-scale confinement of polaritons followed by photon emission. Hence, polaritons constitute an excellent system for studying light-matter interactions under the infuence of tunable coupling, driving, nonlinearity, and dissipation. In addition to single-mode nonlinearities, coupled polariton modes exhibit rich nonlinear dynamics and steady-states due to the interplay between nonlinear interactions and linear coupling. Here, we will present recent experimental results on coupled semiconductor micropillars exhibiting such strongly nonlinear optical dynamics and steady-states.
Our group has demonstrated several hallmark features of nonlinear Josephson oscillations in a photonic system. The system studied consists of two tunnel-coupled semiconductor micropillars. The dynamics was characterized by measuring the population imbalance and phase difference between polaritons in adjacent pillars under pulsed excitation. In the linear regime (low pump power), polaritons oscillate between the two pillars - Rabi oscillations. For increased pumping, the oscillations become nonlinear. For even higher pumping, polaritons are trapped by the intensity-induced nonlinearity in the pumped pillar. This fascinating phenomenon, known as macroscopic self-trapping, was observed for the first time in a photonic system in Ref. [1]. Recently, we have studied the steady-states of coupled polariton modes under resonant excitation [2]. In particular, we have observed how the symmetries of the hybrid modes formed by the tunnel coupling between the two cavities can be broken, and restored, as the pump power increases. Distinct nonlinear thresholds enable us to abruptly increase the emitted intensity by one of the two coupled cavities or both. As we will show, these effects are associated with optical multistability and a pronounced hysteresis spanning several orders of magnitude in pump power. These results illustrate new ways to achieve all-optical nonlinear switching, and offer intriguing prospects for accessing the quantum regime with polaritons. In particular, non-classical states of light seem within reach with state-of-the-art polariton systems. Such extremely nonlinear optical cavities hold great promise for the realization of polariton blockade, photon fermionization, and quantum phase transitions beyond the Bose-Hubbard model.

References
1. Abbarchi, M. et al., Macroscopic quantum self-trapping and Josephson oscillations of exciton polaritons, Nature Phys., 9, 275, (2013)
2. Rodriguez, S. R. K. et al., "manuscript under preparation", (2015)