Stochastic resonance in periodic potentials: realization in a dissipative optical lattice

– We have observed the phenomenon of stochastic resonance on the Brillouin propagation modes of a dissipative optical lattice. Such a mode has been excited by applying a moving potential modulation with phase velocity equal to the velocity of the mode. Its amplitude has been characterized by the center-of-mass (CM) velocity of the atomic cloud. At Brillouin resonance, we studied the CM-velocity as a function of the optical pumping rate at a given depth of the potential wells. We have observed a resonant dependence of the CM velocity on the optical pumping rate, corresponding to the noise strength. This corresponds to the experimental observation of stochastic resonance in a periodic potential in the low-damping regime. A particle trapped in a potential well constitutes a model useful for the understanding of a variety of phenomena. The extension to a periodically modulated double well potential including a stochastic force leads to a complex nonlinear dynamics, and allows to modelize a variety of phenomena ranging from geophysics [1, 2] to bistable ring lasers [3], from neuronal systems [4] to the dithering effect in electronics [5] and so on. Indeed such a system exhibits the phenomenon of stochastic resonance (SR [6, 7]): the response of the system to the input signal (the modulation) shows a resonant dependence on the noise level (the amplitude of the stochastic force), so that an increase of the noise strength may lead to a better synchronization between the particle motion and the potential modulation. The phenomenon of stochastic resonance is not restricted to static double-well potentials driven by a periodic and a stochastic force, and new types of stochastic resonance have been demonstrated in various systems, as systems with a single potential well, bistable systems with periodically modulated noise, and many others [8,9,10,11,12,13,14]. In particular much attention has been devoted to the analysis of SR in periodic potentials [9, 10, 11, 12, 13, 14]. Indeed, many different physical systems are described in terms of periodic structures, and it is by now well established that the noise plays a major role in the mechanisms of transport in periodic structures. For example, the study of the underdamped motion of a particle in a periodic potential showed that it is the interplay between inertial and thermal effects which determines the peculiar mechanical properties of certain metals [15, 16]. This is precisely the