Presence Of Low-frequency Noise Research Articles

Flux Noise Reduction of HTS-SQUIDs via Introduction of Antidots

High- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> superconducting quantum interference devices (HTS-SQUID), which can be used at near liquid nitrogen temperature, allow for reduction of the SQUID equipment both size and operating costs. However, the noise of HTS-SQUID, which consists of white and 1/f noise is higher than that of low- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> SQUID. The 1/f noise, particularly prominent in HTS devices, is generated by fluctuations of the critical current in the Josephson junction and by the motion of the magnetic flux trapped in the superconducting thin film. Presence of low-frequency noise is a problem especially in HTS-SQUID applications such as bioinstrumentation, environmental measurement, and magnetic contamination inspection. Nanoscale holes (antidots) in HTS films are known to attract and pin magnetic flux. In this study, we investigate the effect of artificially introduced nanoscale antidots near the junction boundaries on the noise characteristics of bicrystal SQUIDs. We used focused ion beam irradiation to create in YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-</sub> <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">_δ</i> (YBCO) thin film holes of about 90 nm in diameter. As a result of the antidots introduction, the 1/f noise of the bicrystal SQUID in a magnetic field of 66 μT at 77 K was significantly reduced.

Fast high-fidelity single-qubit gates for flip-flop qubits in silicon

The flip-flop qubit, encoded in the states with antiparallel donor-bound electron and donor nuclear spins in silicon, showcases long coherence times, good controllability, and, in contrast to other donor-spin-based schemes, long-distance coupling. Electron spin control near the interface, however, is likely to shorten the relaxation time by many orders of magnitude, reducing the overall qubit quality factor. Here, we theoretically study the multilevel system that is formed by the interacting electron and nuclear spins and derive analytical effective two-level Hamiltonians with and without periodic driving. We then propose an optimal control scheme that produces fast and robust single-qubit gates in the presence of low-frequency noise without relying on parametrically restrictive sweet spots. This scheme increases considerably both the relaxation time and the qubit quality factor.

Characteristics of cabin noise of light rail systems

Light rail or light rail transit (LRT) is a form of urban rail transit system with rolling stock similar to a tram but operating at a higher capacity on exclusive surface or elevated tracks. They are typically run on rubber wheels with quieter cabins compared to that of higher capacity mass rapid transit systems. We recorded and analyzed cabin noise of 4 light rail lines: Danhai light rail line in Taipei New City (Taiwan) and Bukit Panjang, Punggol, and Sengkang LRT lines in Singapore based on a smartphone app with the accuracy of the microphone calibrated against a typical type 1 sound level meter. All 4 light rail lines are relatively quiet where each of their overall equivalent noise level is under 75 dBA. The more than 10 dB difference between the overall equivalent dBA and dBC for each line has indicated a significant presence of low frequency noise in the light rail lines. The difference between the overall maximum dBA and dBC is however not as large as the difference between the overall equivalent dBA and dBC for each line. More study would need to be conducted on the reduction of lower frequency noise for improving the aural comfort of the light rail systems.

Fast high-fidelity entangling gates for spin qubits in Si double quantum dots

Implementing high-fidelity two-qubit gates in single-electron spin qubits in silicon double quantum dots is still a major challenge. In this work, we employ analytical methods to design control pulses that generate high-fidelity entangling gates for quantum computers based on this platform. Using realistic parameters and initially assuming a noise-free environment, we present simple control pulses that generate CNOT, CPHASE, and CZ gates with average fidelities greater than 99.99\% and gate times as short as 45 ns. Moreover, using the local invariants of the system's evolution operator, we show that a simple square pulse generates a CNOT gate in less than 27 ns and with a fidelity greater than 99.99\%. Last, we use the same analytical methods to generate two-qubit gates locally equivalent to $\sqrt{\mathrm{CNOT}}$ and $\sqrt{\mathrm{CZ}}$ that are used to implement simple two-piece pulse sequences that produce high-fidelity CNOT and CZ gates in the presence of low-frequency noise.

Transient and steady-state readout of nanowire gas sensors in the presence of low-frequency noise

Nanowire sensors show great promise in a variety of sensing applications due to their potential for high sensitivities. Practical nanowire sensor systems, however, are often limited by low-frequency, 1/f noise. This work presents theoretical and experimental results comparing the performance metrics of sensing schemes using transient and steady-state parameters in the presence of 1/f noise. Criteria are derived for when the considered transient or steady-state sensing schemes will have a better signal-to-noise ratio (SNR). The theoretical results for the SNR of these sensing schemes are applied to experimental data from carbon nanotube NO2 sensors. These data and theoretical results demonstrate that due to the Langmuir binding behavior of the sensor-analyte system, sensing using the considered transient parameters increases linearity and decreases response time relative to steady-state sensing. Noise analysis further shows that with current devices, transient sensing has a lower SNR relative to steady-state sensing, however this may change if functionalization is considered. The use of transient parameters also has the potential to reduce sensor drift due to 1/f noise, improving system stability. In addition to providing useful considerations towards the design of carbon nanotube gas sensors, these results are relevant towards understanding the SNR of other chemical and biological sensors limited by 1/f noise.

A game-theoretical perspective for decentralized active noise control

Active noise control (ANC) is a methodology that aims to attenuate acoustic noise creating a silent zone around the target. ANC techniques are particularly useful in the presence of low frequency noise, where passive control is ineffective and impractical. However, the computational cost of ANC applications involving a high number of sensors and actuators, such as active shielding, appears to be an important limitation. One possible approach to deal with this problem is to resort to decentralized control. This is a technique that decomposes a complex control problem into smaller ones that are addressed independently using different controllers. This article studies a decentralized scheme for ANC from a game-theoretical perspective. This formalizes the Nash equilibrium (i.e., the simultaneous best strategy) in the interaction between the controllers. Indeed, in the Nash Equilibrium, the control signals achieve stable conditions. In this framework, it is straightforward to analytically compare the decentralized control scheme to the standard centralized one.

Separation of closely located IR Fourier absorption bands using the genetic algorithm

The genetic algorithm was used for analyzing experimental closely located analytical conformation-sensitive IR Fourier absorption bands of low-molecular compounds incorporated into a polymeric matrix. Model experiments demonstrated the efficiency of spectrum reconstruction using the genetic algorithm as compared to the least squares method in the case of closely located components and in the presence of low-frequency noise in the spectrum.

Low-frequency noise and urban space

Investigation of the sonic environment of the contemporary city suggests that there is a profound dissonance between the profile of contemporary popular music and the physical character of the urban built environment itself, resulting in living conditions that are in significant respects rebarbative. Central to this problem is the increasing presence of low-frequency noise (LFN) in the urban landscape in general and in popular music in particular. Concerns about noise pollution have grown rapidly since the late twentieth century, manifesting themselves in the actions of private lobby groups as well as in government environmental policies. LFN pollution, however, has been largely camouflaged under questions of volume. In fact, the usual systems of measurement of noise pollution are largely ineffective for LFN, which also has its own distinctive aetiology which produces serious trauma and even death. The proliferation of LFN trauma appears to be the fastest growing component of noise pollution. This paper explores LFN, why it is so distinctively threatening to wellbeing, why it has only recently become so pervasive as to have generated its own proliferating research literature, and why it is such a prominent problem in the convergence of the modern city and contemporary popular music.

Macroscopic Resonant Tunneling in the Presence of Low Frequency Noise

We develop a theory of macroscopic resonant tunneling of flux in a double-well potential in the presence of realistic flux noise with a significant low-frequency component. The rate of incoherent flux tunneling between the wells exhibits resonant peaks, the shape and position of which reflect qualitative features of the noise, and can thus serve as a diagnostic tool for studying the low-frequency flux noise in SQUID qubits. We show, in particular, that the noise-induced renormalization of the first resonant peak provides direct information on the temperature of the noise source and the strength of its quantum component.

Spatiotemporal mapping of cortical activity accompanying voluntary movements using an event-related beamforming approach.

We describe a novel spatial filtering approach to the localization of cortical activity accompanying voluntary movements. The synthetic aperture magnetometry (SAM) minimum-variance beamformer algorithm was used to compute spatial filters three-dimensionally over the entire brain from single trial neuromagnetic recordings of subjects performing self-paced index finger movements. Images of instantaneous source power ("event-related SAM") computed at selected latencies revealed activation of multiple cortical motor areas prior to and following left and right index finger movements in individual subjects, even in the presence of low-frequency noise (e.g., eye movements). A slow premovement motor field (MF) reaching maximal amplitude approximately 50 ms prior to movement onset was localized to the hand area of contralateral precentral gyrus, followed by activity in the contralateral postcentral gyrus at 40 ms, corresponding to the first movement-evoked field (MEFI). A novel finding was a second activation of the precentral gyrus at a latency of approximately 150 ms, corresponding to the second movement-evoked field (MEFII). Group averaging of spatially normalized images indicated additional premovement activity in the ipsilateral precentral gyrus and the left inferior parietal cortex for both left and right finger movements. Weaker activations were also observed in bilateral premotor areas and the supplementary motor area. These results show that event-related beamforming provides a robust method for studying complex patterns of time-locked cortical activity accompanying voluntary movements, and offers a new approach for the localization of multiple cortical sources derived from neuromagnetic recordings in single subject and group data.

Measurement uncertainty in the presence of low-frequency noise

We discuss the measurement uncertainty in the presence of different types of fundamental noise processes, especially 1/f noise. The treatment is based on the Allan variance of an n-sample average with two deadtime parameters relevant in metrology. Some results applicable to situations that are common in metrology, e.g., international comparisons, are derived. Experimentally, the output of Zener voltage standards in the frequency range from 10/sup -6/ Hz to 10/sup 3/ Hz is studied and behavior closely resembling that of 1/f noise is found at all time scales of practical interest. The noise floor of a 10 V Zener standard was found to be 60 nV and the 1/f corner frequency 3.5 Hz. Environmental variations cause the long-term (>100 s) deviations of the Zener voltage to slightly increase from the limiting 1/f noise level.

Destriping of polarized data in a CMB mission with a circular scanning strategy

A major problem in Cosmic Microwave Background (CMB) anisotropy mapping, especially in a total-power mode, is the presence of low-frequency noise in the data streams. If unproperly processed, such low-frequency noise leads to striping in the maps. To deal with this problem, solutions have already been found for mapping the CMB temperature fluctuations but no solution has yet been proposed for the measurement of CMB polarization. Complications arise due to the scan-dependent orientation of the measured polarization. In this paper, we investigate a method for building temperature and polarization maps with minimal striping effects in the case of a circular scanning strategy mission such as the Planck mission.

Binary Pulsar Tests of General Relativity in the Presence of Low-Frequency Noise

AbstractThe influence of the low-frequency timing noise on the precision of measurements of the Keplerian and post-Keplerian orbital parameters in binary pulsars is studied. Fundamental limits on the accuracy of tests of alternative theories of gravity in the strong-field regime are established. The gravitational low-frequency timing noise formed by an ensemble of binary stars is briefly discussed.

Analysis of the accuracy of a destriping method for future cosmic microwave background mapping with the PLANCK SURVEYOR satellite

A major problem in cosmic microwave back- ground radiation (CMBR) anisotropy measurements is the presence of low-frequency noise in the data streams. This noise arises from thermal instabilities of optical elements or of the thermal bath, gain instabilities and 1=f noise in the electronics, and other poorly understood processes. If improperly monitored or processed, this excess low- frequency noise might lead to striping in the maps, com- promising the success of the experiment. In this paper, we show that a simple destriping method will clean the maps obtained with the High Frequency Instrument of the PLANCK SURVEYOR mission of any signicant ad- ditional noise from low-frequency drifts, provided that the knee frequency of the low frequency noise is less than the spinning frequency of the satellite, i.e. fknee 0:017 Hz. For the High Frequency Instrument of PLANCK, the nom- inal knee frequency of the noise is fknee' 0:01 Hz or less, and thus no signicant striping nor increase of the noise rms is expected due to low-frequency drifts. In addition, we show that even if the knee frequency of the low fre- quency noise were somewhat higher than the spinning fre- quency of the satellite one could estimate and remove the striping with a excellent accuracy.

Form and Function Relationships in Lateral Line Systems: Comparative Data from Six Species of Antarctic Notothenioid Fish

The structure and physiology of the anterior lateral line canal systems were studied in six species of fish belonging to two different families within the suborder of antarctic fish Notothenioidei. Many of the canals within the species belonging to the genus Trematomus are relatively straight sided tubes with diameters around 0.4 mm. Some of the canals in Trematomus, and most of the canals in the icefishes (family Channichthyidae) are more complex. Relatively small pores lead into large tubules, the walls of which appear partially membranous, and the canals not much more than constrictions between adjacent tubules. Dissostichus mawsoni, a large species, has canals with distinctive wide and narrow sections, 1.8 mm and 0.48 mm, respectively. Despite these morphological differences the frequency response characteristics of anterior lateral line units are remarkably similar in all six species. In the case of D. mawsoni, this functional similarity results from narrow sections of the canals, which provide the viscous resistance to flow that preserves the mechanical filtering properties of the canal despite the huge size difference between D. mawsoni and the other species. It is argued that the most appropriate way to view canals is as high pass filters which attenuate lower frequencies, and that this effect is best illustrated by comparing the frequency response characteristics of superficial and canal neuromasts using a sinusoidal stimulus that has a constant peak-to-peak velocity. The functional contribution of canals is to attenuate low frequencies and improve the signal-to-noise ratio for biologically important signals in the presence of low frequency noise produced, for example, by the animal's own movements.

Effects of noise frequency on performance and annoyance for women and men.

Effects of noise frequencies on both performance on a complex psychomotor task and annoyance were investigated for men (n = 30) and women (n = 30). Each subject performed a complex psychomotor task for 50 min. in the presence of low frequency noise, high frequency noise, or ambient noise. Women and men learned the task at different rates. Little effect of noise was shown. Annoyance ratings were subsequently obtained from each subject for noise of various frequencies by the method of magnitude estimation. High frequency noises were more annoying than low frequency noises regardless of sex and immediate prior exposure to noise. Sex differences in annoyance did not occur. Not direct relationship between learning to perform a complex task while exposed to noise and annoyance by that noise was demonstrated.