  We report active tuning of the polariton resonance of quantum well excitons
in a semiconductor microcavity using applied stress. Starting with the quantum
well exciton energy higher than the cavity photon mode, we use stress to reduce
the exciton energy and bring it into resonance with the photon mode. At the
point of zero detuning, line narrowing and strong increase of the
photoluminescence are seen. By the same means, we create an in-plane harmonic
potential for the polaritons, which allows trapping, potentially making
Bose-Einstein condensation of polaritons analogous to trapped atoms possible.
We demonstrate drift of the polaritons into this trap.
