Vacuum-Induced Quantum Decoherence and the Entropy Puzzle
  Or: ``How to generate an ensemble in a single event?'' Following recent work on entropy in strong interactions, I explain the concept of environment-induced quantum decoherence in elementary quantum mechanics. The classically chaotic inverted oscillator becomes partially decoherent already in the environment of a single other oscillator performing only vacuum fluctuations. One finds exponential entropy growth in the subsystem with a Lyapunov exponent, which approaches the classical one for weak coupling.   Presented at the Workshops on ``Quantum Infrared Physics'', Paris,   6 - 10.6.94, and ``QCD 94'', Montpellier, 7 - 13.7.94.   Invited talk at the NATO Adv. Res. Workshop on ``Hot Hadronic Matter'',   Divonne, 27.6. - 1.7.94. To appear in the Proceedings. 
Hans-Thomas Elze