Noise Spectral Density Research Articles

Low‐Frequency Current Fluctuations in Quasi‐1D (TaSe4)2I Weyl Semimetal Nanoribbons

AbstractLow‐frequency current fluctuations, i.e., electronic noise, in quasi‐1D (TaSe4)2I Weyl semimetal nanoribbons are discussed. It is found that the noise spectral density is of the 1/f type and scales with the square of the current, SI ~ I2 (f is the frequency). The noise spectral density increases by almost an order of magnitude and develops Lorentzian features near the temperature T ≈ 225 K. These spectral changes are attributed to the charge‐density‐wave phase transition even though the temperature of the noise maximum deviates from the reported Peierls transition temperature in bulk (TaSe4)2I crystals. The noise level, normalized by the channel area, in these Weyl semimetal nanoribbons is surprisingly low, ≈10−9 µm2 Hz−1 at f = 10 Hz, when measured below and above the Peierls transition temperature. The obtained results shed light on the specifics of electron transport in quasi‐1D topological Weyl semimetals and can be important for their proposed applications as downscaled interconnects.

Human Perception Intelligent Analysis Based on EEG Signals

The research on brain cognition provides theoretical support for intelligence and cognition in computational intelligence, and it is further applied in various fields of scientific and technological innovation, production and life. Use of the 5G network and intelligent terminals has also brought diversified experiences to users. This paper studies human perception and cognition in the quality of experience (QoE) through audio noise. It proposes a novel method to study the relationship between human perception and audio noise intensity using electroencephalogram (EEG) signals. This kind of physiological signal can be used to analyze the user’s cognitive process through transformation and feature calculation, so as to overcome the deficiency of traditional subjective evaluation. Experimental and analytical results show that the EEG signals in frequency domain can be used for feature learning and calculation to measure changes in user-perceived audio noise intensity. In the experiment, the user’s noise tolerance limit for different audio scenarios varies greatly. The noise power spectral density of soothing audio is 0.001–0.005, and the noise spectral density of urgent audio is 0.03. The intensity of information flow in the corresponding brain regions increases by more than 10%. The proposed method explores the possibility of using EEG signals and computational intelligence to measure audio perception quality. In addition, the analysis of the intensity of information flow in different brain regions invoked by different tasks can also be used to study the theoretical basis of computational intelligence.

Observation of atmospheric scintillation during the 2020 total eclipse in northern Patagonia

During the December 2020 total eclipse we registered time resolved light measurements of incident solar light with VIS-NIR photodiodes in northern Patagonia. Signals compatible with the observation of shadow bands in the 200 s before and after totality were observed. A strong increase in the normalized noise spectral densities of recorded incident radiation near totality suggests the presence of shadow bands. Originally high-altitude balloon measurements and spatial correlation ground measurements were planned, but the harsh climate conditions limited the campaign’s results.

Gain and noise spectral density in a parametric amplifier with added white noise: Theory and experiment

In this paper, we discuss the behavior of a linear classical parametric amplifier in the presence of white noise and give theoretical estimates of the noise spectral density based on approximate Green’s functions obtained by using averaging techniques. To validate our theory, we compare the analytical results with experimental data from an analog circuit and with numerical simulations of the model’s stochastic differential equations. The experimental data were accurately described by our model. Moreover, we noticed spectral components in the output signal of the amplifier, which are due to noisy precursors of instability. The position, width, and magnitude of these components are in agreement with the noise spectral density obtained by the theory proposed here.

10 dB interferometer enhancement by squeezing of photon shot noise with sub-femtometer resolution and eye-safe optical power

Quantum technologies that exploit quantum-correlated resources offer advantages over quantum technologies that just exploit coherent states. Here we propose and demonstrate the exploitation of squeezed light to enhance laser interferometers being at the sensitivity limit of eye-safe optical powers into a new regime otherwise impossible without sacrificing eye-safety. We realised a homodyne Mach–Zehnder interferometer that in its arms used an eye-safe combined optical power of only 10 mW at the wavelength of 1550 nm, and nevertheless achieved a displacement noise spectral density of as low as 0.26 fm Hz−1/2. This value is more than a factor of below what is possible with 10 mW in ideal coherent states at 1550 nm and slightly lower than what is possible with 100 mW at the same wavelength. We envision a new user application for squeezed light in avoiding costs for laser safety measures.

Stabilizing and Improving Qubit Coherence by Engineering the Noise Spectrum of Two-Level Systems

Superconducting circuits are a leading platform for quantum computing. However, their coherence times are still limited and exhibit temporal fluctuations. Those phenomena are often attributed to the coupling between qubits and material defects that can be well described as an ensemble of two-level systems (TLSs). Among them, charge fluctuators inside amorphous oxide layers contribute to both low-frequency $1/f$ charge noise and high-frequency dielectric loss, causing fast qubit dephasing and relaxation. Moreover, spectral diffusion from mutual TLS interactions varies the noise amplitude over time, fluctuating the qubit lifetime. Here, we propose to mitigate those harmful effects by engineering the relevant TLS noise spectral densities. Specifically, our protocols smooth the high-frequency noise spectrum and suppress the low-frequency noise amplitude via depolarizing and dephasing the TLSs, respectively. As a result, we predict a drastic stabilization in qubit lifetime and an increase in qubit pure dephasing time. Our detailed analysis of feasible experimental implementations shows that the improvement is not compromised by spurious coupling from the applied noise to the qubit.

Seismic Signature of Rain and Wind Inferred From Seismic Data

AbstractSeismic stations are increasingly used to monitor river activity and to quantify sediment transport during flood events. In tropical regions, cyclone‐induced floods are often associated with heavy rain and strong wind episodes, generating complex seismic records involving the simultaneous signature of water, sediment, rainfall and wind. Hence, seismic characterization of rain and wind is then required to better decipher each process and improve our understanding of the river seismic signature. In this study, we investigate experimentally the seismic response of rain and wind using data recorded by geophones deployed in various soil types and at different burial depth (BD), co‐located with various meteorological instruments. Our results show that the power spectral density (PSD) of the seismic noise intensifies at a frequency between 60 and 500 Hz for rain and 5 and 500 Hz for wind, in the presence of rain precipitation as low as 0.025 mm/min and/or wind speed ≥3 m/s. PSD analysis indicates that the seismic signal associated with rain decreases with the BD with a value of ∼2–5 dB in a depth difference of 10 cm. We also observe that each soil type has its own seismic signature. The 4‐min root mean square correlation between the seismic signal amplitude and the rain precipitation suggests that they best correlate with Pearson coefficient >0.90 at BD of 30 cm. The transfer function between the precipitation rate (or kinetic energy) and the seismic signal amplitude shows that the signal recorded by the geophone can be used as a robust proxy for these parameters.

Approximate analytical methods for stationary response probability density of a SDOF system with a nonlinear spring under non-Gaussian random excitation

Approximate analytical methods for finding the stationary response probability density of a SDOF system with a wide class of nonlinear springs under non-Gaussian random excitation are proposed. The non-Gaussian excitation is a stationary stochastic process prescribed by an arbitrary probability density with finite variance and a power spectral density with a bandwidth parameter. In order to obtain the response probability distribution of the system, two approximate methods are developed by theoretically extending the Monte Carlo simulation observations on the properties of the response distribution obtained in the previous study. One of the methods is applied when the bandwidth of the excitation power spectrum is narrower than that of the primary resonance peak of the system. In this case, the system becomes quasi-static, and its equation of motion reduces to the equilibrium equation for the stiffness and excitation terms. This equilibrium equation is used to derive the approximate solution of the response distribution. The only requirement of this method is that the nonlinear spring of the system is continuous and monotonically increasing. The other method is proposed for the case of the wide excitation bandwidth compared to the system bandwidth. In this method, the exact solution of the response distribution under Gaussian white noise is utilized. The value of the white noise spectral density parameter in the solution is determined by the equivalent linearization. The second method is applicable to systems with arbitrary integrable nonlinear springs. In numerical examples, we consider three nonlinear systems whose spring characteristics are quite different. Besides, two types of non-Gaussian excitation probability densities with differences in shape are used. It is demonstrated that the proposed methods can reproduce the unique shape of the response probability density caused by the spring nonlinearity and the excitation non-Gaussianity. From the results, the range of the bandwidth ratio between the excitation and the system where the response distribution is accurately obtainable is also examined for each method.

Identifying the physical mechanisms of polycrystalline lead salt photoconductors

Polycrystalline infrared lead salt detectors exhibit exceptionally high sensitivity near room temperature and, as such, are ubiquitous in commercial instruments such as spectrometers and flame detectors. The underlying physical mechanism behind this remarkable performance has been the subject of speculation for many years. In this treatise, data from work performed at BAE Systems and St. John's Optical Systems and from the published literature are analyzed to identify common mechanisms that contribute to the photoconductivity of polycrystalline lead salt detectors from a multitude of material deposition and process technologies, and it was concluded that much of the behavior can be attributed to surface-related phenomenon. Physical models are proposed to explain the observations. Finally, there is a brief description of measurements related to noise in these complex structures, indicating the importance of ohmic contacts, but the observed low frequency spectral noise density remains a mystery.

Low frequency noise in p-InAsSbP/n-InAs/n-InAsSbP and p-InAsSbP/n-InAsSbP mid-IR light emitting diodes

The frequency and current dependences of the optical output spectral noise density, Slph, in p-InAsSbP/n-InAs infrared light emitting diodes (LEDs) has been measured for the first time. LEDs with emission centered at wavelengths λ = 2.8 and 3.5 µm have been studied. In both cases, in the frequency range 2 ≤ f ≤ 100 Hz the noise spectrum is 1/f like. At constant LED pumping current, Slph is proportional to the photocurrent squared (∼Iph2). The 1/f noise intensity Slph for the LED with emission centered at λ = 2.8 µm is ∼2 times higher. In the LED pumping current range 0.02 ≤ ILED ≤ 0.1 A (60 ≤ jLED ≤ 300 A/cm2) the optical output 1/f noise is practically independent of ILED.The intensity of the LEDs’ optical output 1/f noise is less than the intensity of the photodiode reverse bias current noise by ∼4 orders of magnitude.

±0.3V Bulk-Driven Fully Differential Buffer with High Figures of Merit

A high performance bulk-driven rail-to-rail fully differential buffer operating from ±0.3V supplies in 180 nm CMOS technology is reported. It has a differential–difference input stage and common mode feedback circuits implemented with no-tail, high CMRR bulk-driven pseudo-differential cells. It operates in subthreshold, has infinite input impedance, low output impedance (1.4 kΩ), 86.77 dB DC open-loop gain, 172.91 kHz bandwidth and 0.684 μW static power dissipation with a 50-pF load capacitance. The buffer has power efficient class AB operation, a small signal figure of merit FOMSS = 12.69 MHzpFμW−1, a large signal figure of merit FOMLS = 34.89 (V/μs) pFμW−1, CMRR = 102 dB, PSRR+ = 109 dB, PSRR− = 100 dB, 1.1 μV/√Hz input noise spectral density, 0.3 mVrms input noise and 3.5 mV input DC offset voltage.

The Impact of an Extended Gate Field Plate on the DC and RF Characteristics of a Junctionless Thin-Film Transistor

In this work, conventional and drain offset junctionless (JL) finlike thin-film transistors (FinTFTs) with and without extended gate field plate (E-GFP) are fabricated. Drain offset JL FinTFTs showed a higher breakdown voltage than that of the conventional one. By extending the GFP over the drain offset region, holes were generated on the surface of the drain offset region that reduce drain resistance. Therefore, the drain offset JL FinTFT with E-GFP exhibited better on-current, breakdown, and high-frequency characteristics than the one without E-GFP. Results also show that all the noise spectral densities of various JL FinTFTs follow a 1/f trend and were similar in the studied frequency range.

Doping Compensation Enables High-Detectivity Infrared Organic Photodiodes for Image Sensing.

Infrared organic photodiodes have gained increasing attention due to their great application potentials in night vision, optical communication, and all-weather imaging. However, the commonly occurring high dark current and low detectivity impede infrared photodetectors from portable applications at room temperature. Herein, an efficient and generic doping compensation strategy is developed to improve the detectivity of infrared organic photodiodes. A series of n-type organic semiconductors is investigated, and it is found that doping compensation strategy not only reduces the trap density of states and dark currents, but also restrains the nonradiative recombination with improved charge transport and collection. As a result, an ultralow noise spectral density of 8× 10-15 A Hz-1/2 as well as a high specific detectivity over 1013 Jones in 780-1070nm is achieved at room temperature. More importantly, the high-performance infrared organic photodiodes can be successfully applied in high-pixel-density image arrays without patterning sensing layers. These findings provide important compensation design insights that will be crucial to further improve the performance of infrared organic photodiodes in the future.

Fingerprints of Qubit Noise in Transient Cavity Transmission.

Noise affects the coherence of qubits and thereby places a bound on the performance of quantum computers. We theoretically study a generic two-level system with fluctuating control parameters in a photonic cavity and find that basic features of the noise spectral density are imprinted in the transient transmission through the cavity. We obtain analytical expressions for generic noise and proceed to study the cases of quasistatic, white and 1/f^{α} noise in more detail. Additionally, we propose a way of extracting the noise power spectral density in a frequency band only bounded by the range of the qubit-cavity detuning and with an exponentially decaying error due to finite measurement times. Our results suggest that measurements of the time-dependent transmission probability represent a novel way of extracting noise characteristics.

Analog Circuits Using Double-Gate Multilayer MoS2 Field-Effect Transistor for Sensor Applications

The advantages of novel double-gate (DG) multilayer MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> transistors for analog circuit applications are presented. Such components are shown to be especially useful in signal-conditioning circuits in sensor instrumentation systems. The nearly symmetric DG device architecture can be exploited in the design of analog front-end circuits to mitigate the effect of flicker (1/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}$ </tex-math></inline-formula> ) noise. Quantum mechanical calculations validated by comparisons with experimental data indicate that with active semiconductor layer thickness >2 monolayers (MLs), the sheet carrier density per gate is increased relative to single gate field-effect transistors (FETs) resulting in a lower noise figure. Calculated normalized noise spectral power densities for the single and DG thin-film transistors (TFTs) at the same gate bias clearly show that the DG devices have lower noise than the single gate devices. In sensors for low-frequency signals such as bio-signals, DG transistors allow convenient direct coupling of the signal through one gate, with the other gate available for mixing with a high-frequency signal and/or applying bias voltages without requiring large capacitors. Such circuits are well-suited for use with silicon CMOS technology using back-end-of-the-line (BEOL) fabrication methods.

Thermal Fluctuations and Electromagnetic Noise Spectra in Quantum Statistical Mechanics

We derive the thermal noise spectrum of the longitudinal and transverse electric field operator of a given wave vector starting from the quantum-statistical definitions and relate it to the frequency and wave vector dependent complex conductivity in a homogeneous, isotropic system of electromagnetic interacting charged particles in the frame of the non-relativistic QED. No additional assumptions except the validity of linear response are used in the proof. The Nyquist formula for vanishing frequency, as well as the noise spectral density of Callen-Welton follow as byproduct. Furthermore we discuss also the noise of the photon occupation numbers.

Effect of noise components on L-shaped and T-shaped heterojunction tunnel field effect transistors

This paper reports on a comparative study of the analysis of electrical noise of heterojunction tunnelling-field-effect-transistors with an L-shaped gate (LTFET) and with a T-shaped gate (TTFET) using numerical simulations. The effect of different noise components on both structures were investigated at low frequency and high frequency to check the viability of the proposed devices. The two source regions are used in TTFET to increase the tunnelling area that enhances the ON-current. Also, we studied the effect of introducing Gaussian traps onto the interface of the source-gate oxide and channel-gate oxide on different noise components and net noise. TTFET outperforms LTFET in terms of electrical parameters and noise spectral densities, thereby offering a solution to the trade-off between high tunnelling rates and noise spectral densities in TFETs. The proposed LTFET and TTFETs are free from ambipolarity issues and can further be deployed in low power applications.

Three-dimensional stacked filter: A non-linear filter for series images obtained using a transmission electron microscope

De-noising is an important issue in quantitative high-resolution transmission electron microscopy (HRTEM), and its roles become even more important in applications such as beam-sensitive materials and dynamic characterisations, where the attainable signal-to-noise ratio (SNR) of HRTEM images is frequently limited. In this study, we introduce a three-dimensional stacked filter (3DSF), a novel non-linear filter in which a series of HRTEM images is stacked into a 3D data cube and then treated with the Wiener filter in the 3D domain. In comparison to the traditional Wiener filter, which is widely used for individual images, this filter can accurately estimate the power spectral density of noise and filter images with a higher SNR, fewer artefacts and greater computation efficiency, which works particularly well for HRTEM images containing periodic information and feature similarities in successive micrographs, as demonstrated by simulated and experimental images of graphene and metal–organic framework (MOF). When applied to an ultra-low dose (∼8 e/Å2) HRTEM image stack of MOF MIL-101, the 3DSF could distinguish 40 consecutive frames, revealing the trajectory of subtle lattice shrinkage during the exposure.

Line shape of a delayed self-heterodyne varied with noise types and delays.

The delayed self-heterodyne and self-homodyne (DSH) method is widely used for measuring the line shapes of high coherent lasers. This method results in an autocorrelation of a laser line under the condition of a delay that is much larger than its coherent time. In practice, the delay is often not so long, especially for very narrow linewidth lasers, resulting in errors in rebuilding the laser's line shape from the DSH line. Many papers were devoted to the topic, but most of them are based on the formula for white noise. Analytical formulas of phase variance for 1/f noises are presented in this paper; the DSH line shapes for different noise types and different delay lengths are simulated based on the formulas. Some experimental data of the DSH line, combined with the power spectral density of frequency noise, are processed, showing good agreement with the theoretical analysis. It is indicated that the DSH line shape shows complicated behaviors varied with the delay, with noise types, and with the measurement duration. Such effects are to be compensated for in retrieving the laser's linewidth from the DSH data.

Waveforms and fluxes: Towards a self-consistent effective one body waveform model for nonprecessing, coalescing black-hole binaries for third generation detectors

We present a comprehensive comparison between numerical relativity (NR) angular momentum fluxes at infinity and the corresponding quantity entering the radiation reaction in TEOBResumS, an Effective-One-Body (EOB) waveform model for nonprecessing coalescing black hole binaries on quasi-circular orbits. This comparison prompted us to implement two changes in the model: (i) including Next-to-Quasi-Circular corrections in the $\ell=m$, $\ell\leq 5$ multipoles entering the radiation reaction and (ii) consequently updating the NR-informed spin-orbital sector of the model. This yields a new waveform model that presents a higher self-consistency between waveform and dynamics and an improved agreement with NR simulations. We test the model computing the EOB/NR unfaithfulness $\bar{F}_{\rm EOB/NR}$ over all 534 spin-aligned configurations available through the Simulating eXtreme Spacetime catalog, notably using the noise spectral density of Advanced LIGO, Einstein Telescope and Cosmic Explorer, for total mass up to $500M_\odot$. We find that the maximum unfaithfulness $\bar{F}^{\rm max}_{\rm EOB/NR}$ is mostly between $10^{-4}$ and $10^{-3}$, and the performance progressively worsens up to $\sim 5\times 10^{-3}$ as the effective spin of the system is increased. We perform similar analyses on the \SEOB{} model, that delivers $\bar{F}^{\rm max}_{\rm EOB/NR}$ values uniformly distributed versus effective spin and mostly between $10^{-3}$ and $10^{-2}$. We conclude that the improved TEOBResumS model already represents a reliable and robust first step towards the development of highly accurate waveform templates for third generation detectors.