Macroscopic quantum self-trapping and Josephson oscillations of exciton-polaritons

TL;DR

This paper demonstrates the observation of non-linear Josephson oscillations and macroscopic self-trapping in coupled exciton-polariton condensates within a photonic molecule, revealing new non-linear quantum phenomena in photonic systems.

Contribution

First experimental observation of non-linear Josephson effects and self-trapping in exciton-polariton condensates in a photonic molecule, enabling studies of complex non-linear quantum regimes.

Findings

Coherent tunneling oscillations at low densities.

Self-trapping of condensates at high densities.

Transition from self-trapping to oscillations with pi phase due to polariton lifetime.

Abstract

A textbook example of quantum mechanical effects is the coupling of two states through a tunnel barrier. In the case of macroscopic quantum states subject to interactions, the tunnel coupling gives rise to Josephson phenomena including Rabi oscillations, the a.c. and d.c. effects, or macroscopic self-trapping depending on whether tunnelling or interactions dominate. Non-linear Josephson physics, observed in superfluid helium and atomic condensates, has remained inaccessible in photonic systems due to the required effective photon-photon interactions. We report on the observation of non-linear Josephson oscillations of two coupled polariton condensates confined in a photonic molecule etched in a semiconductor microcavity. By varying both the distance between the micropillars forming the molecule and the condensate density in each micropillar, we control the ratio of coupling to interaction energy. At low densities we observe coherent oscillations of particles tunnelling between the two micropillars. At high densities, interactions quench the transfer of particles inducing the macroscopic self-trapping of the condensate in one of the micropillars. The finite lifetime of polaritons results in a dynamical transition from self-trapping to oscillations with pi phase. Our results open the way to the experimental study of highly non-linear regimes in photonic systems, such as chaos or symmetry-breaking bifurcations.