Topological order and thermal equilibrium in polariton condensates

We report the observation of the Berezinskii-Kosterlitz-Thouless transition for a 2D gas of exciton-polaritons, and through the joint measurement of the first-order coherence both in space and time we bring compelling evidence of a thermodynamic equilibrium phase transition in an otherwise open driven/dissipative system. This is made possible thanks to long polariton lifetimes in high-quality samples with small disorder and in a reservoir-free region far away from the excitation spot, that allow topological ordering to prevail. The observed quasi-ordered phase, characteristic for an equilibrium 2D bosonic gas, with a decay of coherence in both spatial and temporal domains with the same algebraic exponent, is reproduced with numerical solutions of stochastic dynamics, proving that the mechanism of pairing of the topological defects (vortices) is responsible for the transition to the algebraic order. Finally, measurements in the weak-coupling regime confirm that polariton condensates are fundamentally different from photon lasers and constitute genuine quantum degenerate macroscopic states

Trade agreements, regulatory institutions and services liberalization

First published: 20 August 2018Many agreements to liberalize trade in services tend to be limited in scope. This is a puzzle considering the high share of services in total employment and value added and relatively high barriers to trade in services in many countries. In this paper we argue that neglected complementarities between services trade policies and domestic regulation may help to understand the limited ambition on services observed in many trade agreements. We show that the productivity effects of services trade liberalization are conditional on regulatory quality. Our findings suggest that greater effort to design trade agreements with a view to improving regulatory quality may be a necessary condition for deepening the services coverage of trade agreements and will enhance the welfare gains from services trade liberalization