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Noise Sources
Published in Antoni Rogalski, Zbigniew Bielecki, Detection of Optical Signals, 2022
Antoni Rogalski, Zbigniew Bielecki
The Johnson-Nyquist noise has a flat power spectral density up to the frequency of 1012–1014 Hz (the inverse of electrical relaxation time). This means that the noise power with frequencies contained in the 1 Hz bandwidth is the same for each frequency. Figure 3.7(a) shows the time course of a thermal noise that can be observed on the oscilloscope screen, while Figure 3.7(b) shows its power spectral density distribution. Thermal noise determines the lower limit of the noise voltage or the noise current in each detector, or the real part impedance of any element.
Fault tolerance and ultimate physical limits of nanocomputation
Published in David Crawley, Konstantin Nikolić, Michael Forshaw, 3D Nanoelectronic Computer Architecture and Implementation, 2020
A S Sadek, K Nikolić, M Forshaw
However, a much more fundamental barrier to nanoscale information systems exists as a result of the equipartition theorem of thermodynamics [47]. For a system in thermal equilibrium, every independent degree of freedom that can store energy must have average energy kT/2 due to thermal fluctuations. This gives rise to ‘white’ thermal noise, i.e. noise with a flat power spectrum. For white noise, the time correlations between fluctuations are less than the Smoluchowski time, 10−10 s [48]. In electronic circuits and devices, such thermal fluctuations give rise to Johnson–Nyquist noise. Here, voltage fluctuations arise from the thermal motion of electrons, which then relax through the resistance of the device. The noise power is simply given by ()〈Vnoise2〉=4kTRΔf
Theory of photon detectors
Published in Antoni Rogalski, Infrared and Terahertz Detectors, 2019
Johnson–Nyquist noise is associated with the finite resistance R of the device. This type of noise is due to the random thermal motion of charge carriers in the crystal and not due to fluctuations in the total number of these charge carriers. It occurs in the absence of external bias as a fluctuating voltage or current depending upon the method of measurement. Small changes in the voltage or current at the terminals of the device are due to the random arrival of charge at the terminals. The root mean square of Johnson–Nyquist noise voltage in the bandwidth ∆f is given by Equation 4.16. This type of noise has a “white” frequency distribution.
Atom chips with free-standing two-dimensional electron gases: advantages and challenges
Published in Journal of Modern Optics, 2018
G. A. Sinuco-León, P. Krüger, T. M. Fromhold
Strong coupling between neutral ultra-cold atomic matter and quantum electronic devices in an atom chip architecture requires an atom-surface separation below m, such that the atoms and material charge carriers couple via their magnetic moments or dynamical electric dipoles [34]. However, achieving such small separation requires a number of challenges to be overcome. Firstly, at sub-micron distances, an intense atom-surface attractive Casimir–Polder force dominates, making it difficult to create magnetic trapping potentials that prevent the atom cloud from collapsing onto the chip surface [10,28]. Secondly, as the atoms get closer to a surface, their coupling to the electromagnetic Johnson–Nyquist noise produced by thermal motion of conduction electrons becomes strong, leading to a reduction in the lifetime of trappable atomic states [8,10,35]. Finally, effects originating from fabrication defects of the atom chip components magnify as the atom-surface separation is reduced [13,16], making it difficult to define and control smooth atomic potential landscapes.