A research team from China, Spain, and Germany has demonstrated that noise can induce spatial and temporal order in nonlinear systems, Forschungsverbund Berlin e.V. announced on its website. This effect may be used in the future to identify hidden signals in noisy environments. Signals may also be embedded in a noisy background and ciphered for later recovery, according to the research institutes’ announcement.

The results were published in two back-to-back manuscripts in Physical Review Letters, with one focusing on the experimental investigation [121, 086806 (2018)], and the second presenting a theoretical investigation based on numerical simulations [121, 086805 (2018)].

Applying noise in combination with small amplitude periodic oscillations to a nonlinear system can result in very intricate effects, according to researchers. Noise is said to be able to drive a stationary system into an oscillatory state with coherent current self-oscillations that have tunable frequencies between 0 and about 100 MHz, called a coherence resonance. By adding small-amplitude periodic oscillations to the noise with a frequency close to that of the current self-oscillations, the nonlinear system can be phase- locked to the coherence resonance, referred to as a stochastic resonance. This stochastic resonance can be used as a passive lock-in amplifier, without a reference signal and with a much shorter integration time than available for conventional lock-in amplifiers.

Until now, all methods detecting weak signals were actively based on the correlation with a known reference signal. Typical lock-in amplifiers need a reference signal in the tens of Hz to MHz range, and integration times of the order of milliseconds. The wide frequency range of the coherence resonance allows for the operation without any reference signal to reduce the integration time necessary to process the signal.

The research team has experimentally demonstrated the occurrence of coherence and stochastic resonances at room temperature in a doped, weakly coupled GaAs/(Al,Ga) As superlattice with 45% Al. Numerical simulations of the electron transport based on a discrete sequential tunneling model carried out simultaneously reproduce these results qualitatively as well. In addition, the theoretical model can be used to determine the device-dependent critical current for the coherence resonance directly from the experimental results.

Original Papers: Mompo E, Ruiz-Garcia M, Carretero M, Grahn HT, Zhang Y, Bonilla LL. Coherence resonance and stochastic resonance in an excitable semiconductor superlattice. Physical Review Letters. 2018;121(8):086805.

Shao Z, Yin Z, Song H, et al. Fast detection of a weak signal by a stochastic resonance induced by a coherence resonance in an excitable GaAs/Al0.45Ga0.55  As superlattice. Physical Review Letters. 2018;121(8):086806.

Source: Forschungsverbund Berlin e.V., Physical Review Letters