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How to make a bilayer exciton condensate flow

Bose condensation is responsible for many of the most spectacular effects in physics because it can promote quantum behavior from the microscopic to the macroscopic world. Bose condensates can be distinguished by the condensing object; electron-electron Cooper-pairs are responsible for superconductivity, Helium atoms for superfluidity, and ultracold alkali atoms in vapors for coherent matter waves. Electron-hole pair (exciton) condensation has maintained special interest because it has been difficult to realize experimentally, and because exciton phase coherence is never perfectly spontaneous. Although ideal condensates can support an exciton supercurrent, it has not been clear how such a current could be induced or detected, or how its experimental manifestation would be altered by the phase-fixing exciton creation and annhilation processes which are inevitably present. In this article we explain how to induce an exciton supercurrent in separately contacted bilayer condensates, and predict electrical effects which enable unambiguous detection.