title: Quantum stochastic resonance in symmetric systems.
abstract: We investigate the low-temperature quantum stochastic resonance (QSR) phenomenon in a two-level system (TLS) which is coupled to an Ohmic heat bath. In contrast to common belief we find that QSR occurs also for symmetric (i.e., unbiased) TLS's if the viscous friction parameter alpha exceeds a critical value: We demonstrate that with respect to the spectral power amplification measure QSR always occurs for alpha>1; in contrast, the output signal-to-noise ratio exhibits an amplification only for alpha>3/2.
authors.affiliation: Institute of Physics, University of Augsburg, Universitätsstrasse 1, 86135 Augsburg, Germany.
authors.forename: I
authors.initials: I
authors.lastname: Goychuk
authors.forename: P
authors.initials: P
authors.lastname: Hänggi