Thermal Noise Sources Research Articles

Characterizing 1550 nm optical components down to 8 K

Thermal noise sources are relevant for future gravitational wave detectors due to the foreseen increase in sensitivity, especially at frequencies below ▪. As most thermal noise sources scale with the square root of the temperature, cooling critical optical components and their suspension system is essential. This also requires a much wider range of temperature compatibility from all technology deployed in the last suspension stages, including displacement and inertial sensors. We demonstrate and characterize a setup for stable light sources and light intensity sensing for temperatures from 300 to ▪. Commercial collimators and fibers were tested to use light from stabilized laser sources in the cryogenic environment. We also investigated multiple semiconductor compositions of photodiodes and identified a solution with high and stable responsivity at ▪.

Comparing the efficacy of data-driven denoising methods for a multi-echo fMRI acquisition at 7T

In functional magnetic resonance imaging (fMRI) of the brain the measured signal is corrupted by several (e.g. physiological, motion, and thermal) noise sources and depends on the image acquisition. Imaging at ultrahigh field strength is becoming increasingly popular as it offers increased spatial accuracy. The latter is of particular benefit in brainstem neuroimaging given the small cross-sectional area of most nuclei. However, physiological noise scales with field strength in fMRI acquisitions. Although this problem is in part solved by decreasing voxel size, it is clear that adequate physiological denoising is of utmost importance in brainstem-focused fMRI experiments. Multi-echo sequences have been reported to facilitate highly effective denoising through TE-dependence of Blood Oxygen Level Dependent (BOLD) signals, in a denoising method referred to as multi-echo independent component analysis (ME-ICA). It has not been explored previously how ME-ICA compares to other data-driven denoising approaches at ultrahigh field strength. In the current study, we compared the efficacy of several denoising methods, including anatomical component based correction (aCompCor), Automatic Removal of Motion Artifacts (ICA-AROMA) aggressive and non-aggressive options, ME-ICA, and a combination of ME-ICA and aCompCor. We assessed several data quality metrics, including temporal signal-to-noise ratio (tSNR), delta variation signal (DVARS), spectral density of the global signal, functional connectivity and Shannon spectral entropy. Moreover, we looked at the ability of each method to uncouple the global signal and respiration. In line with previous reports at lower field strengths, we demonstrate that after applying ME-ICA, the data is best post-processed in order to remove spatially diffuse noise with a method such as aCompCor. Our findings indicate that ME-ICA combined with aCompCor and the aggressive option of ICA-AROMA are highly effective denoising approaches for multi-echo data acquired at 7T. ME-ICA combined with aCompCor potentially preserves more signal-of-interest as compared to the aggressive option of ICA-AROMA.

On noise-induced transient bit flips in subthreshold SRAM

We propose a rigorous SPICE simulation framework, compatible with industrial process design kits, to observe transient bit flips in CMOS SRAM due to the intrinsic transistor noise. The parameters of transient noise simulation are selected according to the noise behaviour and bandwidth of the inverter, however under CPU-time constraint. The methodology is illustrated in 28nm FD-SOI technology. We study the combined effects of the random telegraph noise, flicker and thermal noise sources, for the first time to our knowledge. The extracted mean times to failure (MTTF) are compared to those reported in the literature in extreme voltage, temperature and variability conditions. The MTTF spans from below 0.1ms to 108s, following a theoretical trend logMTTF∝VDD2.

Ultra-low-noise transimpedance amplifier in cryogenic STM for studying novel quantum states by measuring shot noise

An ultra-low-noise large-bandwidth transimpedance amplifier (TIA) for cryogenic scanning tunneling microscope (CryoSTM) is proposed. The TIA connected with the tip-sample component in CryoSTM is called as CryoSTM-TIA. Its transimpedance gain is as high as 1 GΩ, and its bandwidth is over 300 kHz, but its equivalent input noise current power spectral density is less than 4 (fA)2/Hz at 100 kHz. The low inherent noise for the CryoSTM-TIA is due to its special design: (1) its pre-amplifier is made of a pair of low-noise cryogenic high electron mobility transistors (HEMTs); (2) the noise generated by one HEMT is eliminated by a large capacitor; (3) the capacitance of the cable connected the gate of the other HEMT to the tip is minimized; (4) thermal noise sources, such as the feedback resistor, are placed in the cryogenic zone. The dc output voltage drift of the CryoSTM-TIA is very low, as 5 μV/°C. The apparatus can be used for measuring the scanning tunneling differential conductance spectra, especially the scanning tunneling shot noise spectra (STSNS) of quantum systems, even if the shot noise is very low. It provides a universal tool to study various novel quantum states by measuring STSNS, such as detecting the Majorana bound states.

Single-molecule identification of folded proteins from nanopore ionic current signatures.

Single-molecule protein sequencing would provide unprecedented insights into cellular processes and the diseases that arise from protein misfunction. Recently, nanopores have emerged as a platform for fast label-free analyte detection guided by the ionic current blockades generated from single molecules translocating under an applied electric field. The major bottleneck to nanopore protein sequencing is the need to distinguish twenty proteinogenic amino acids accurately at every single residue. Here, we demonstrate a proof-of-principle proteome characterization system that relies on ionic current signatures produced by complete translocation of natively folded proteins through an array of nanopores. Using the steric exclusion model, we computed the ionic current spectra for all structurally known proteins, initially excluding all membrane proteins, proteins containing partially-disordered domains, and multimeric protein assemblies - about 4000 proteins in total. For each protein, we computationally simulated a fluid driven tumbling through a nanopore by calculating current for 5000 randomly chosen orientations that changes the effective cross-section and thus modulates current. Ionic current signatures of proteins with varying molecular weight clearly differed by the magnitude of blockades confirming the steric exclusion origin of the current. Interestingly, proteins with similar molecular weight also showed a varied range of mean blockade currents due to changing current signatures originating from the protein shape. Using a support vector machine learning algorithm trained on our data set, we were able to theoretically distinguish the weight and shape of the 4000 chosen proteins to near perfect accuracy, in the absence of instrumentation noise. We then theoretically introduced a thermal noise source into our simulated ionic current recordings to demonstrate the minimum requirements of an experimental system that would permit accurate protein identification from a single molecule translocation.

Thermorefringent noise in crystalline optical materials

Crystalline materials are increasingly employed to construct precision optical instruments because of their reduced mechanical dissipation and consequent reduction of thermal Brownian noise. However, the anisotropy of the crystalline state implies a fundamental source of thermal noise; depolarization induced by thermal fluctuations of its birefringence. We establish the theory of this effect, which is a generalization of prior treatments of thermo-optic noises in amorphous materials. This theory---in conjunction with poorly understood anisotropic thermal stress coefficients of crystalline coatings---predict that thermo-refringent noise in crystalline mirror coatings may be lurking within an order of magnitude of Brownian noise (below 100 Hz). Thus, in order to appreciate the full promise of crystalline optical materials, a more precise understanding of their anisotropic material constants is necessary. Barring that, we elucidate measurement techniques that can affect partial coherent cancellation of thermorefringent noise. In passing, our general formalism also predicts the existence of thermal beam-pointing noise.

Supratransmission-induced traveling breathers in long Josephson junctions

The emergence of traveling sine-Gordon breathers due to the nonlinear supratransmission effect is theoretically studied in a long Josephson junction driven by suitable magnetic pulses, taking into account the presence of dissipation, a current bias, and a thermal noise source. The simulations clearly indicate that, depending on the pulse’s shape and the values of the main system parameters, such a configuration can effectively yield breather excitations only. Furthermore, a nonmonotonic behavior of the breather-only generation probability is observed as a function of the noise intensity. Finally, the dynamics of the supratransmission-induced breathers is characterized by looking at quantities such as their radiative decay lifetime and the medium’s energy.

Generation of travelling sine-Gordon breathers in noisy long Josephson junctions

The generation of travelling sine-Gordon breathers is achieved through the nonlinear supratransmission effect in a magnetically driven long Josephson junction, in the presence of losses, a current bias, and a thermal noise source. We demonstrate how to exclusively induce breather modes by means of controlled magnetic pulses. A nonmonotonic behavior of the breather-only generation probability is observed as a function of the noise intensity. An experimental protocol providing evidence of the Josephson breather's existence is proposed.

Analog Solutions of Discrete Markov Chains via Memristor Crossbars

Problems involving discrete Markov Chains are solved mathematically using matrix methods. Recently, several research groups have demonstrated that matrix-vector multiplication can be performed analytically in a single time step with an electronic circuit that incorporates an open-loop memristor crossbar that is effectively a resistive random-access memory. Ielmini and co-workers have taken this a step further by demonstrating that linear algebraic systems can also be solved in a single time step using similar hardware with feedback. These two approaches can both be applied to Markov chains, in the first case using matrix-vector multiplication to compute successive updates to a discrete Markov process and in the second directly calculating the stationary distribution by solving a constrained eigenvector problem. We present circuit models for open-loop and feedback configurations, and perform detailed analyses that include memristor programming errors, thermal noise sources and element nonidealities in realistic circuit simulations to determine both the precision and accuracy of the analog solutions. We provide mathematical tools to formally describe the trade-offs in the circuit model between power consumption and the magnitude of errors. We compare the two approaches by analyzing Markov chains that lead to two different types of matrices, essentially random and ill-conditioned, and observe that ill-conditioned matrices suffer from significantly larger errors. We compare our analog results to those from digital computations and find a significant power efficiency advantage for the crossbar approach for similar precision results.

Phase locking and noise-driven dynamics in a Josephson-junction electronic analog

We present an electronic circuit whose dynamical properties emulate those of a resistively and capacitively shunted Josephson junction (RCSJ). We show how it reproduces the switching properties of a shunted junction and its dependence on the quality factor. A thermal noise source is then used to characterize the temperature dependence of the phase dynamics. In the presence of an AC drive, phase locking is observed at integer and rational multiples of the drive frequency, and it competes with chaotic behavior when the quality factor of the junction exceeds unity. We characterize the stability of phase-locked and chaotic states in the presence of thermal noise.

Using an Atom Interferometer to Infer Gravitational Entanglement Generation

If gravitational perturbations are quantized into gravitons in analogy with the electromagnetic field and photons, the resulting graviton interactions should lead to an entangling interaction between massive objects. We suggest a test of this prediction. To do this, we introduce the concept of interactive quantum information sensing. This novel sensing protocol is tailored to provable verification of weak dynamical entanglement generation between a pair of systems. We show that this protocol is highly robust to typical thermal noise sources. The sensitivity can moreover be increased both using an initial thermal state and/or an initial phase of entangling via a non-gravitational interaction. We outline a concrete implementation testing the ability of the gravitational field to generate entanglement between an atomic interferometer and mechanical oscillator. Preliminary numerical estimates suggest that near-term devices could feasibly be used to perform the experiment.

Design Improvements on Fast, High-Order, Incremental Sigma-Delta ADCs for Low-Noise Stacked CMOS Image Sensors

Modern CMOS imaging devices are present everywhere, in the form of line, area and depth scanners. These image devices can be used in the automotive field, in industrial applications, in the consumer’s market, and in various medical and scientific areas. Particularly in industrial and scientific applications, the low-light noise performance or the high dynamic-range features are often the cases of interest, combined with low power dissipation and high frame rates. In this sense, the noise floor performance and the power consumption are the focus of this work, given that both are interlinked and play a direct role in the remaining sensor features. It is known that thermal and flicker noise sources are the main contributors to the degradation of the sensor performance, concerning the sensor output image noise. This paper presents an indirect way to reduce both the thermal and the flicker noise contributions by using thin-oxide low voltage supply column readout circuits and fast 3rd order incremental sigma-delta converters with noise shaping capabilities (to provide low noise output digital samples—74 μVrms; 0.7 e−rms; at 105 μV/e−), and thus performing correlated double sampling in a short time (19 μs), while dissipating significant low power (346 μW). Throughout the extensive parametric transistor-level simulations, the readout path produced 1.2% non-linearity, with a competitive saturation capacity (6.5 ke−) pixel. In addition, this paper addresses the readout parallelism as the main point of interest, decoupling resolution from the image noise and the frame rate, at virtually any array resolution. The design and simulations were performed with Virtuoso 6.17 tools (Cadence Design Systems, San Jose, CA, USA) using Spectre models from TS18IS Image Sensor 0.18 µm Process Development Kit (Tower Jazz Semiconductor, Migdal Haemek, Israel).

Thermal noise in electro-optic devices at cryogenic temperatures

The quantum bits (qubits) on which superconducting quantum computers are based have energy scales corresponding to photons with GHz frequencies. The energy of photons in the gigahertz domain is too low to allow transmission through the noisy room-temperature environment, where the signal would be lost in thermal noise. Optical photons, on the other hand, have much higher energies, and signals can be detected using highly efficient single-photon detectors. Transduction from microwave to optical frequencies is therefore a potential enabling technology for quantum devices. However, in such a device the optical pump can be a source of thermal noise and thus degrade the fidelity; the similarity of input microwave state to the output optical state. In order to investigate the magnitude of this effect we model the sub-Kelvin thermal behavior of an electro-optic transducer based on a lithium niobate whispering gallery mode resonator. We find that there is an optimum power level for a continuous pump, whilst pulsed operation of the pump increases the fidelity of the conversion.

Nyquist Model based Thermal Noise AnalysisFrom Passive Components to CMOS Circuits

The analysis of thermal noise in network components that have resistive properties is presented. Noise analysis, based on the Nyquist model, is calculated as the rms (voltage or current equivalent) noise generated by a transimpedance, which is the concept used by general-purpose circuit simulators like Spice. It shows how this concept is used and understood in RC circuits, and how to evaluate its effect in analog circuits, particularly in the design of CMOS integrated circuits. It is shown that the magnitude of the noise generated by a transistor is not of interest, but the net effect of all sources of thermal noise in circuits and systems, fundamentally, when the miniaturization of the transistor implies reducing the value of the supply voltages. The ultimate purpose of this contribution is to highlight the importance of noise analysis using fundamentals of circuit theory and identify the variables under the designer's control to minimize their effect on the performance of the circuits under development.

Detecting Acoustic Blackbody Radiation with an Optomechanical Antenna

Nanomechanical systems are generally embedded in a macroscopic environment where the sources of thermal noise are difficult to pinpoint. We engineer a silicon nitride membrane optomechanical resonator such that its thermal noise is acoustically driven by a spatially well-defined remote macroscopic bath. This bath acts as an acoustic blackbody emitting and absorbing acoustic radiation through the silicon substrate. Our optomechanical system acts as a sensitive detector for the blackbody temperature and for photoacoustic imaging. We demonstrate that the nanomechanical mode temperature is governed by the blackbody temperature and not by the local material temperature of the resonator. Our work presents a route to mitigate self-heating effects in optomechanical thermometry and other quantum optomechanics experiments, as well as acoustic communication in quantum information.

Thermal charge carrier driven noise in transmissive semiconductor optics

Several sources of noise limit the sensitivity of current gravitational wave detectors. Currently, dominant noise sources include quantum noise and thermal Brownian noise, but future detectors will also be limited by other thermal noise channels. In this paper, we study a thermal noise source which is caused by spatial charge carrier density variations in semiconductor materials. We provide an analytical model for the understanding of charge carrier fluctuations under the presence of screening effects and show that charge carrier noise will not be a limiting noise source for third-generation gravitational wave detectors.

Cross-Laboratory Experimental Validation of a Tunerless Technique for the Microwave Noise Parameters Extraction

In this article, a novel tunerless technique aimed at extracting the noise parameters of on-wafer transistors is experimentally validated. In detail, the effectiveness of the method has been confirmed by employing two different setups in two remotely located laboratories. The obtained noise parameters exhibit the level of accuracy typical of the standard source tuner-based Lane technique, without the well-known limitations due to the microwave tuner. The theoretical bases of the technique have been straightforwardly illustrated, and an extensive measurement campaign has been carried out on GaAs pHEMTs to confirm the suitability of the proposed approach. Furthermore, the technique can be applied to determine the contribution of additional thermal noise sources. The developed technique might represent the core of an automatic noise parameters’ extraction test bench.

One-dimensional error-correcting code for Majorana qubits

Although Majorana platforms are promising avenues toward realizing topological quantum computing, they are still susceptible to errors from thermal noise and other sources. We show that the error rate of Majorana qubits can be drastically reduced using a one-dimensional repetition code. The success of the code is due the imbalance between the phase error rate and the flip error rate. We demonstrate how a repetition code can be naturally constructed from segments of Majorana nanowires. We find the optimal lifetime may be extended from a millisecond to over one second.

Background suppressed magnetization transfer MRI.

Up to 30% of the hydrogen atoms in brain tissue are part of molecules ("semisolids") other than water. In MRI, their magnetization is typically not observed directly, but can influence the water magnetization through magnetization transfer (MT). Comparison of MRI scans differentially sensitized to MT allows estimation of the semisolid fraction and potential changes with disease. Here, we present an approach designed to improve this estimate by measuring the size of the MT effect in a single scan. A stimulated echo sequence was used to generate a spatial pattern in the longitudinal water magnetization, which was then given time to exchange with semisolids. After saturating the remaining water magnetization, reverse exchange was allowed to partly re-establish the original water magnetization pattern. The third excitation pulse then formed a stimulated echo out of this pattern. MT data were obtained on 10 human subjects at 7 T with varying exchange times. The images showed the expected time dependence of signal associated with the forward and reverse exchange processes. Excellent suppression of non-exchanging background signal was achieved. As expected, this suppression came at the price of a substantial reduction in exchange-related signal (by ~75% compared to the signal in saturation recovery MT), in part because of the reliance on a 2-step exchange process. The results demonstrate an MT signal can be observed in a single acquisition without subtraction. This may be advantageous for MT measurements when signal instabilities related to motion and physiological variations exceed thermal noise sources.

Thermorefractive noise in silicon-nitride microresonators

Thermodynamic noise places a fundamental limit on the frequency stability of dielectric optical resonators. Here, we present the characterization of thermo-refractive noise in photonic-chip-based silicon nitride microresonators and show that thermo-refractive noise is the dominant thermal noise source in the platform. We employed balanced homodyne detection to measure the thermo-refractive noise spectrum of microresonators of different diameters. The measurements are in good agreement with theoretical models and finite element method simulations. Our characterization sets quantitative bounds on the scaling and absolute magnitude of thermal noise in photonic chip-based microresonators. An improved understanding of thermo-refractive noise can prove valuable in the design considerations and performance limitations of future photonic integrated devices.