N ov 1 99 4 LA – UR 94 – 3817 Decoherence , re - coherence , and the black hole information

We analyze a system consisting of an oscillator coupled to a field. With the field traced out as an environment , the oscillator loses coherence on a very short decoherence timescale; but, on a much longer relaxation timescale, predictably evolves into a unique, pure (ground) state. This example of re-coherence has interesting implications both for the interpretation of quantum theory and for the loss of information during black hole evaporation. We examine these implications by investigating the intermediate and final states of the quantum field, treated as an open system coupled to an unobserved oscillator.