Electrical and optical control of Exciton-Polariton Josephson Junctions

An exciton-polariton (EP) condensate can be considered as the charge neutral analog of a superconducting BCS state. Recent experiments show that the polariton condensate and the non-condensate polariton residues can be prepared in a quasi-equilibrium state satisfying Bose-Einstein statistics, which allows us to conceive a wide range of applications based on mesoscopic phenomena.  We propose an electrically and optically tuned EP device in analogy to a superconducting circuit. The device would be formed in a coplanar geometry parallel to the reflectors of a cavity, with lithographically defined regions hosting the 2-D exciton-polaritons serving as the left and right sides of a Josephson Junction. An in-plane electric field would control the energy difference between the two sides, while the exciton-photon coupling affects the splitting between the upper and lower EP branches. The dynamics of this interacting bosonic gas give rise to a set of Josephson-like equations, leading to oscillations in the condensate density, analogous to Josephson oscillations in a superconducting junction.

We first discuss EP tunneling as second order tunneling process of electron-hole pair. Based on the tunneling strength and other previously determined parameters, we predict the characteristic frequency of the proposed device for given geometry and material choices.  The tunneling and interaction in the exciton component introduce mixing between the upper and lower polaritons, which leads to interesting phenomena in a higher dimensional state space. We examine different physical limits for the general four-component model and point out the realistic limit and its consequences in the device application.

Such nano-fabricated devices combined with spin flip mechanisms in quantum well, will allow unprecedented local control of condensate dynamics.