Polariton Boxes in a Tunable Fiber Cavity

We present an approach for realizing confined quantum-well cavity polaritons that enables in situ tuning of the cavity length and thereby of the polariton energy and lifetime. Our setup is based on a versatile semiintegrated low- temperature fiber-cavity platform, which allows us to demonstrate the formation of strongly confined polaritons with unprecedented quality factors. At high pump powers, we observe signatures of polariton lasing.