The constructive role of noise
UC3M/DICYT Noise can induce spatial and temporal order in non-linear systems, which helps to detect and amplify weak external signals that are difficult to detect by conventional amplifiers, according to an international team composed of researchers from Germany, China and Spain in which the Universidad Carlos III de Madrid (UC3M) is a participant. The work, published in two articles of the Physical Review Letters magazine, explains that this effect can be used in the decoding and in the creation of extremely weak signals, without the need for a reference signal and in a much shorter time than with a conventional amplifier.
Until now, all methods for detecting very weak signals (with high frequencies) were based on the synchronization of that weak signal with a reference signal, that is why a signal of unknown frequency (such as, for example, an encrypted message or a barely audible fragment of information) could go unnoticed if it were "hidden" in a background of loud noise. Scientists have found a steady-state electronic system that produces consistent and stable oscillations of the current by applying a noise, which is called "coherent resonance". The frequency of these oscillations varies continuously in a wide range from zero to one hundred megahertz. If a weak frequency signal is also superimposed on that range, the system synchronizes with the weak signal, which is called stochastic resonance. This can be used to detect, process and interpret the weak signal, in a shorter period of time and without the need for a reference signal as with conventional methods.
These findings could be used to identify signals that are hidden in a large amount of noise or, reciprocally, to encrypt signals by wrapping them in background noise and recovering them later. For example, we could extract information from a conversation that had been recorded in a noisy room, astronomical observations masked by a large background noise could be analysed more efficiently, and it would even be possible to process image signals.
"Noise is usually a nuisance that we want to avoid and minimize in practical applications. However, there are times when noise plays a constructive role that can be used to produce useful results", says Luis L. Bonilla, researcher at the Department of Science and Materials Engineering and Chemical Engineering at the Instituto Gregorio Millán Barbany of the UC3M.
To demonstrate the existence of these resonances produced by noise and usable for the decoding of weak signals, the research team experimented with a super grid of semiconductors that periodically alternates layers of gallium arsenide with others of a gallium arsenide alloy with 45 percent aluminium. The numerical simulations based on electron transport models were carried out at the Instituto Gregorio Millán and the Materials Department of the UC3M, and the laboratory experiments took place at the SINANO Institute in Suzhou and at the National University of Defence Technology (China) with samples created at the Paul Drude Institute in Berlin (Germany).
Emanuel Mompo, Miguel Ruiz-Garcia, Manuel Carretero, Holger T. Grahn, Yaohui Zhang, Luis L. Bonilla, Coherence resonance and stochastic resonance in an excitable semiconductor superlattice (Resonancia coherente y resonancia estocástica en una superred semiconductora excitable). Physical Review Letters.
Zhengzheng Shao, Zhizhen Yin, Helun Song, Wei Liu, Xiujian Li, Jubo Zhu, Klaus Biermann, Luis L. Bonilla, Holger T. Grahn, Yaohui Zhang, Fast Detection of a Weak Signal by a Stochastic Resonance Induced by a Coherence Resonance in an Excitable GaAs / Al 0.45 Ga 0.55 As Superlattice (Detección rápida de una señal débil por una resonancia estocástica inducida por una resonancia coherente en una superred excitable de GaAs / Al 0.45 Ga 0.55 As). Physical Review Letters.