Environment-independent decoherence rate in classically chaotic systems

We study the decoherence of a one-particle system, whose classical correpondent is chaotic, when it evolves coupled to a weak quenched environment. This is done by analytical evaluation of the Loschmidt Echo, (i.e. the revival of a localized density excitation upon reversal of its time evolution), in presence of the perturbation. We predict an exponential decay for the Loschmidt Echo with a (decoherence) rate which is asymptotically given by the mean Lyapunov exponent of the classical system, and therefore independent of the perturbation strength, within a given range of strengths. Our results are consistent with recent experiments of Polarization Echoes in nuclear magnetic resonance and preliminary numerical simulations.