Tunnel Noise Research Articles

Extracting the scaling dimension of quantum Hall quasiparticles from current correlations

Fractional quantum Hall quasiparticles are generally characterized by two quantum numbers: electric charge $Q$ and scaling dimension $\mathrm{\ensuremath{\Delta}}$. For the simplest states (such as the Laughlin series), the scaling dimension determines the anyonic statistics of the quasiparticle (the statistical phase $\ensuremath{\theta}=2\ensuremath{\pi}\mathrm{\ensuremath{\Delta}}$). For more complicated states (featuring counterpropagating modes or non-Abelian statistics), knowing the scaling dimension is not enough to extract the quasiparticle statistics. Nevertheless, even in those cases, knowing the scaling dimension facilitates distinguishing different candidate theories for describing the quantum Hall state at a particular filling (such as PH-Pfaffian and anti-Pfaffian at $\ensuremath{\nu}=\frac{5}{2}$). Here, we propose a scheme for extracting the scaling dimension of quantum Hall quasiparticles from thermal tunneling noise produced at a quantum point contact. Our scheme makes only minimal assumptions about the edge structure and features the level of robustness, simplicity, and model independence comparable with extracting the quasiparticle charge from tunneling shot noise.

Aerodynamic noise separation of helicopter main and tail rotors using a cascade filter with Vold-Kalman filter and cyclic Wiener filter

The noise issue has become an important factor limiting the massive application of helicopters as the requirements for helicopter reliability and comfort continue to increase. As the primary noise source of helicopters, the main and tail rotor aerodynamic noise should be separated for individual noise reduction investigations. According to the frequency domain characteristics, the rotor aerodynamic noise can be divided into tonal noise and broadband noise. A cascade filtering method with Vold-Kalman filter and cyclic Wiener filter is proposed in this paper to separate the tonal and modulated broadband noise of the main and tail rotors, respectively. The classical method only considers the periodic characteristics of the main and tail rotor aerodynamic noise for harmonic separation. The broadband noise is not considered within the separation of interest due to its randomness, which leads to the inaccuracy of the conventional method for the aerodynamic noise separation of the main and tail rotors. The broadband noise exhibits a second-order cyclostationarity due to the periodic modulation of the rotational motion of the rotor. According to its cyclostationarity, while considering the periodicity of tonal noise for harmonic separation, the proposed cascade filtering method also performs the separation of broadband noise. More precise separations of the main and tail rotor can be obtained by this method. The efficacy of the proposed cascade filtering method is demonstrated in both the simulation and wind tunnel noise measurement.

Low-noise large-bandwidth transimpedance amplifier for measuring scanning tunneling shot noise spectra in cryogenic STM and its applications

Shot noise is a powerful tool to study quantum systems. In this work, a design of transimpedance amplifier (TIA) for a cryogenic scanning tunneling microscope (CryoSTM) is proposed to meet the requirements of the shot noise measurements for quantum systems. In the TIA, the preamplifier is made of the low-noise low-power cryogenic high electron mobility transistors. With the high transimpedance gain of 1 GΩ, the bandwidth of the proposed TIA is larger than 300 kHz. In the CryoSTM, the TIA with the tip-sample component is called as CryoSTM-TIA. The bandwidth of the proposed CryoSTM-TIA is still larger than 300 kHz. Its equivalent input noise current power spectral density is less than 30(fA)2/Hz at 100 kHz. It is detailed, for quantum systems, by using the CryoSTM-TIA, how to measure scanning tunneling current spectra, scanning tunneling differential conductance spectra, and scanning tunneling noise current power spectra, in atomic scale, and then extract their scanning tunneling shot noise spectra. Thus, it is possible to study novel quantum phenomena in various quantum systems by measuring shot noise with the CryoSTM-TIA, such as the Andreev reflection in atomic scale, the Kondo effect in a single molecular magnet, and the existence of Majorana bound states, etc.

The separation and identification of distributed noise sources with local coherence by a subspace equivalent-source method

Identification of distributed and locally coherent aerodynamic noise sources, such as airfoil noise and blade noise, attracts considerable attention these years. When using beamforming techniques, errors in source positions may be caused by the assumption of incoherent sources. A subspace equivalent-source method is proposed to decompose and identify different components of sources. Sound pressure radiated from each component is represented by coherent structures of the overall sound field, which are calculated by using the Proper Orthogonal Decomposition. The equivalent-source model is modified for the influence of the flow field and the shear layer by using a geometry method. Truncated Singular Value Decomposition is applied to avoid singularities generated by the inverse problem and reduce errors of source identification. The proposed algorithm is verified by numerical simulations and a benchmark experiment of airfoil noise in the wind tunnel. Leading edge noise, trailing edge noise and tip noise are successfully separated and located. The distribution of each source is estimated more accurately than Conventional Beamforming and deconvolution methods. Source decomposition and intrinsic coherence among equivalent sources both account for better performance.

Direct evidence for Cooper pairing without a spectral gap in a disordered superconductor above Tc.

The idea that preformed Cooper pairs could exist in a superconductor at temperatures higher than its zero-resistance critical temperature (Tc) has been explored for unconventional, interfacial, and disordered superconductors, but direct experimental evidence is lacking. We used scanning tunneling noise spectroscopy to show that preformed Cooper pairs exist up to temperatures much higher than Tc in the disordered superconductor titanium nitride by observing an enhancement in the shot noise that is equivalent to a change of the effective charge from one to two electron charges. We further show that the spectroscopic gap fills up rather than closes with increasing temperature. Our results demonstrate the existence of a state above Tc that, much like an ordinary metal, has no (pseudo)gap but carries charge through paired electrons.

An experimental investigation of hydrodynamic performance, cavitation, and noise of a normal skew B-series marine propeller in the cavitation tunnel

In this paper, the hydrodynamic performance, cavitation inception, and acoustic performance of a 5-bladed B-series propeller are experimentally investigated in the Sharif University of Technology cavitation tunnel. For hydrodynamic performance, thrust, torque, and efficiency of the propeller model were measured in open water tests. In the cavitation study, in addition to blade cavitation, tip vortex cavitation was also observed, and the cavitation bucket diagram was extracted in different advance coefficients. Finally, for the acoustic analysis of the propeller, the emitted noise in the cavitation tunnel was recorded using two hydrophones according to the recommended procedures of the International Towed Tank Conference (ITTC). Accordingly, the effects of the propeller ambient pressure and cavitation number on the sound pressure level of the B-series propeller are determined. The results can be used to determine the effects of flow parameters on the hydrodynamic and acoustic characteristics of the propeller. Moreover, points of cavitation inception are obtained in all advance coefficients, and it will be possible to extract the proper operating depth without cavitation or lower cavitation.

Nanoelectromechanical rotary current rectifier

Nanoelectromechanical systems (NEMS) are devices integrating electrical and mechanical functionality on the nanoscale. Because of individual electron tunneling, such systems can show rich self-induced, highly non-linear dynamics. We show theoretically that rotor shuttles, fundamental NEMS without intrinsic frequencies, are able to rectify an oscillatory bias voltage over a wide range of external parameters in a highly controlled manner, even if subject to the stochastic nature of electron tunneling and thermal noise. Supplemented by a simple analytic model, we identify different operational modes of charge rectification. Intriguingly, the direction of the current depends sensitively on the external parameters.

Implementation of Geometric Quantum Gates on Microwave‐Driven Semiconductor Charge Qubits

AbstractA semiconductor‐based charge qubit, confined in double quantum dots, can be a platform to implement quantum computing. However, it suffers severely from charge noises. Here, a theoretical framework to implement universal geometric quantum gates in this system is provided. It is found that, while the detuning noise can be suppressed by operating near its corresponding sweet spot, the tunneling noise, on the other hand, is amplified and becomes the dominant source of error for single‐qubit gates, a fact previously insufficiently appreciated. It is demonstrated, through numerical simulation, that the geometric gates outperform the dynamical gates across a wide range of tunneling noise levels, making them particularly suitable to be implemented in conjunction with microwave driving. To obtain a nontrivial two‐qubit gate, a hybrid system is introduced with charge qubits coupled by a superconducting resonator. When each charge qubit is in resonance with the resonator, it is possible to construct an entangling geometric gate with fidelity higher than that of the dynamical gate for experimentally relevant noise levels. Therefore, the results suggest that geometric quantum gates are powerful tools to achieve high‐fidelity manipulation for the charge qubit.

Tunnel Noise Effects on Hypersonic Cylinder-Induced Transitional Shock-Wave/Boundary-Layer Interactions

Experiments were conducted on a cylinder-induced shock-wave/boundary-layer interaction (SBLI) at Mach 6. The state of the interaction was brought through transition using a combination of boundary-layer trips and Reynolds number sweeps. The unit Reynolds number was varied over a range of 2 to 8 million per meter (M/m). The Actively Controlled Expansion wind-tunnel nozzle boundary layers transitioned near , which resulted in a threefold increase in the freestream disturbances. Trends related to SBLI properties (including the size of the separation region, peak surface heating, and surface pressure fluctuation spectra) correlated with the freestream disturbance signature. Separation distances on the centerline were bounded by laminar and turbulent conditions at and , respectively. The shape and extent of the separation region exhibited sensitivity to the transition process over a unit Reynolds number range of 3 to . Heat transfer from the reattachment shock was monitored for untripped and tripped configurations. The former demonstrated a near-linear relationship between heat transfer coefficient and unit Reynolds number, whereas the transitional SBLI configuration revealed a sudden rise in heat transfer coefficient that mirrored that of the freestream disturbances near . PCB® and Kulite® pressure transducers measured increased surface pressure fluctuations near for all model configurations, with the cylinder exciting a 40 kHz instability that led to SBLI transition for the tripped configuration.

Study on the Influence of Tunnel Environmental Noise on Driving Fatigue

Almost all tunnel traffic accident investigation point out that fatigue driving is one of the important causes of accidents. In the long tunnel driving process, due to the acoustic characteristics of the tunnel, drivers are in a high noise environment for a long time. By recording the electroencephalogram (EEG) of drivers under tunnel noise conditions, the EEG characteristics of driving fatigue are described by using specific EEG power spectrum, moreover, attention level is measured by spectrum of SMR. The correlation model between different noise and driver’s attention and fatigue degree is obtained, and the influence of tunnel noise on driving safety is analysed. The analysis results have great practical significance to improve the driving safety of drivers.

Experimental research on crossflow instability for a hypersonic 4∶1 elliptic cone

In this work, the cross-flow instability on the surface of a blunt elliptical cone with a long-short-axis ratio of 4∶1 is studied experimentally in the Mach 6 hypersonic quiet wind tunnel. Comprehensive use of temperature sensitive paint (TSP) technology, nano-tracer-based planar laser scattering (NPLS) technology and Kulite sensor pressure test to measure the temperature distribution in the cross-flow area on the surface of the model, boundary layer flow structure and model surface pressure are tested. The mechanism of boundary layer transition in the cross-flow control area on the surface of the elliptical cone is studied, and the influence law of incoming flow unit Reynolds number and angle of attack on boundary layer transition is obtained, and some conclusions are obtained below. In the wind tunnel noise mode, the transition of the boundary layer in the cross-flow area between the surface center line and the leading edge of the elliptical cone model with a length-to-short-axis ratio of 4∶1 is controlled by the traveling waves, and no footprint of the steady vortex is found. The characteristic frequency of the traveling wave is about 20 kHz. When the unit Reynolds number of the incoming flow increases, the transition position will be advanced, and the frequency and amplitude of the traveling wave will increase. Within a certain angle of attack, the transition position of the upwind boundary layer is delayed, and the characteristic frequency of the traveling wave does not change much but the energy is weakened. When the angle of attack continues to increase, the transition phenomenon disappears.

Vehicle Detection Using Deep Learning Technique in Tunnel Road Environments

This paper proposes a real-time detection method for a car driving ahead in real time on a tunnel road. Unlike the general road environment, the tunnel environment is irregular and has significantly lower illumination, including tunnel lighting and light reflected from driving vehicles. The environmental restrictions are large owing to pollution by vehicle exhaust gas. In the proposed method, a real-time detection method is used for vehicles in tunnel images learned in advance using deep learning techniques. To detect the vehicle region in the tunnel environment, brightness smoothing and noise removal processes are carried out. The vehicle region is learned after generating a learning image using the ground-truth method. The YOLO v2 model, with an optimal performance compared to the performances of deep learning algorithms, is applied. The training parameters are refined through experiments. The vehicle detection rate is approximately 87%, while the detection accuracy is approximately 94% for the proposed method applied to various tunnel road environments.

Perfect modulation between fully spin-polarized spin-singlet and -triplet Andreev entanglements in a narrow quantum spin Hall system

We consider a quantum spin Hall (QSH) insulator strip touching on one s-wave superconductor sandwiched between two ferromagnetic insulators and study its scattering processes, tunneling conductance, and noise power by using an extended Bogoliubov-de Gennes scattering formalism. It is demonstrated that interedge coupling and noncollinear magnetizations allow for producing the usual and novel crossed Andreev reflections (ARs), respectively, and thus the corresponding spin-singlet and -triplet pairing entanglements. Moreover, by proper tuning of the band structures of the ferromagnetic layers, under the resonance bias voltage, not only perfect but also fully spin-polarized crossed AR at any magnetic orientational angle α is exhibited, which can be experimentally confirmed by the tunneling conductance and noise power. Particularly, the perfect and fully spin-polarized modulation between the spin-singlet and -triplet Andreev entanglements could be performed by α at certain energy values, which suggest that the setup can act as a topological superconducting spintronic device with such a manipulation function.

Effects of surface texture on tire-pavement noise and skid resistance in long freeway tunnels: From field investigation to technical practice

In order to effectively control tire-pavement noise in long freeway tunnels, this study aims to determine suitable low-noise pavement texture. The main indicators evaluated include texture parameters, A-weighted sound pressure level, octave, sideway force coefficient and the actual unit cost of building single texture. Sound signals at the tire-pavement interface are detected by the OBSI system without the influence of other nearby sources, then acquired by Dewesoft system and sent to a laptop computer for post-processing on Coinv DESPET software platform. The continuous friction tester is used to measure sideway force coefficient on each pavement surface at same vehicle speed. All testing efforts are based on previous investigation sections and two specially constructed long freeway tunnel sections with various specific textures. Afterwards, the technique for order preference by similarity to ideal solution, is adopted for the final comprehensive evaluation. The study found that the freeway tunnel is a hostile acoustic environment. The tire-pavement noise inside the tunnel is about 20 dB(A) higher than the external normal sections, whether it is asphalt pavement or cement concrete pavement. In addition, the longitudinal equidistant groove with large center spacing of 25 cm, not only help eliminates the pumping noise but prevents the side sliding of vehicles, is considered to be an effective technique on the premise considering economic cost. Also note that, the section near the tunnel entrance belongs to the transition zone of tire-pavement noise and a bottom area of skid resistance. The transverse unequal spacing groove can yet be regarded as a suitable choice for this section and wet section inside the tunnel. What is more, an interesting finding is that there is no direct correlation between tire-pavement noise and sideway force coefficient, regardless of groove textures. This means that a quieter pavement texture can be obtained without hindering the skid resistance. In this sense, the findings of this study may provide a little practical reference to create a “quiet, safe,” surface texture suitable for the long freeway tunnels.

Inclined slow acoustic waves incident to stagnation point probes in supersonic flow

Tunnel noise in supersonic testing facilities is known to be a decisive factor in boundary layer transition experiments. It defines initial conditions for the growth of modal instabilities by the receptivity mechanism. That is, to interpret experimental results, the determination of tunnel noise is of crucial importance. It is common to use stagnation point probes equipped with pressure transducers in supersonic flows, but since tunnel noise undergoes modulation during the measurement, the probes must be calibrated. The predominant component of tunnel noise is caused by the nozzle boundary layer which radiates highly inclined slow acoustic waves. Therefore, the calibration of stagnation point probes for these disturbances is essential. For quasi-steady deviations from the free stream, an analytic reduced-order method holds. A corresponding conflicting model derived by Stainback & Wagner (1972, AIAA Paper 72-1003) is revised and corrected. Inclined slow acoustic waves generate higher pressure perturbations at the probe than non-inclined waves. In general, costly three-dimensional direct numerical simulations can be used for calibration. In this study, however, new axisymmetric boundary conditions are proposed to reduce the problem to two dimensions to efficiently investigate the detection of incident inclined slow acoustic waves by stagnation point probes. A cylindrical probe with a rounded edge is investigated in supersonic flow at a Mach number $Ma=5.9$. For the inclination angle of radiated slow acoustic waves, stagnation point pressure fluctuations abruptly decay with increasing Strouhal number and a similar behaviour can be seen at constant Strouhal number with increasing inclination angle. Two simple criteria for the onset of decay based on the radial wavenumber are deduced. Furthermore, stagnation point pressure fluctuations were decomposed into an initial pulse impact and resonant amplification to separately investigate the effects. The initial pulse determines the overall pressure signal. At high inclination angles, a new mechanism for resonance caused by a surface pressure wave travelling at the phase speed of the incident wave was found to supersede resonance caused by oscillating acoustic waves prevailing at low inclination angles.

Characterization of Freestream Disturbances in Conventional Hypersonic Wind Tunnels

Although low-disturbance (“quiet”) hypersonic wind tunnels are believed to provide more reliable extrapolation of boundary-layer transition behavior from ground to flight, the presently available quiet facilities are limited to Mach 6, moderate Reynolds numbers, low freestream enthalpy, and subscale models. As a result, only conventional (“noisy”) wind tunnels can reproduce both Reynolds numbers and enthalpies of hypersonic flight configurations and must therefore be used for flight vehicle test and evaluation involving high Mach number, high enthalpy, and larger models. This paper outlines the recent progress and achievements in the characterization of tunnel noise that have resulted from the coordinated effort within the AVT-240 specialists group on hypersonic boundary-layer transition prediction. The new experimental measurements cover a range of conventional wind tunnels with different sizes and Mach numbers from 6 to 14 and extend the database of freestream fluctuations within the spectral range of boundary-layer instability waves over commonly tested models. New direct numerical simulation datasets elucidate the physics of noise generation inside the turbulent nozzle wall boundary layer, characterize the spatiotemporal structure of the freestream noise, and account for the propagation and transfer of the freestream disturbances to a Pitot-mounted sensor.

Spin decoherence in a two-qubit CPHASE gate: the critical role of tunneling noise

Rapid progress in semiconductor spin qubits has enabled experimental demonstrations of a two-qubit logic gate. Understanding spin decoherence in a two-qubit logic gate is necessary for optimal qubit operation. We study spin decoherence due to 1/f charge noise for two electrons in a double quantum dot used for a two-qubit controlled-phase gate. In contrast to the usual belief, spin decoherence can be dominated by the tunneling noise from 1/f charge noise instead of the detuning noise. Tunneling noise can dominate because the effect of tunneling noise on the spin qubit is first order in the charge admixture; while the effect of the detuning noise is only second order. The different orders of contributions result in different detuning dependence of the decoherence, which provides a way to identify the noise source. We find that decoherence in a recent two-qubit experiment was dominated by the tunneling noise from 1/f charge noise. The results illustrate the importance of considering tunneling noise to design optimal operation of spin qubits.

High-Performance Back-Illuminated Three-Dimensional Stacked Single-Photon Avalanche Diode Implemented in 45-nm CMOS Technology

We present a high-performance back-illuminated three-dimensional stacked single-photon avalanche diode (SPAD), which is implemented in 45-nm CMOS technology for the first time. The SPAD is based on a P+/Deep N-well junction with a circular shape, for which N-well is intentionally excluded to achieve a wide depletion region, thus enabling lower tunneling noise and better timing jitter as well as a higher photon detection efficiency and a wider spectrum. In order to prevent premature edge breakdown, a P-type guard ring is formed at the edge of the junction, and it is optimized to achieve a wider photon-sensitive area. In addition, metal-1 is used as a light reflector to improve the detection efficiency further in backside illumination. With the optimized 3-D stacked 45-nm CMOS technology for back-illuminated image sensors, the proposed SPAD achieves a dark count rate of 55.4 cps/μm2 and a photon detection probability of 31.8% at 600 nm and over 5% in the 420–920 nm wavelength range. The jitter is 107.7 ps full width at half-maximum with negligible exponential diffusion tail at 2.5 V excess bias voltage at room temperature. To the best of our knowledge, these are the best results ever reported for any back-illuminated 3-D stacked SPAD technologies.

Experimental investigation of wavy leading edges on rod-aerofoil interaction noise

Experimental studies are performed to investigate the effect of wavy leading edges on rod-aerofoil interaction noise in an open-jet anechoic wind tunnel. NACA 0012 aerofoils with straight and wavy leading edges (denoted by SLE and WLE, respectively) are embedded in the wake of a circular rod. The WLEs are in the form of sinusoidal profiles of amplitude, A, and wavelength, W. Parametric studies of the amplitude and wavelength characteristics are conducted to understand the effect of WLEs on noise reduction. It is observed that the sound power reduction level is sensitive to both the amplitude and wavelength of the WLEs. The WLE with the largest amplitude and smallest wavelength can achieve the most considerable noise reduction effect of up to 4 dB. The influences of rod diameter, d, and free-stream velocity, U0, on the noise reduction effect of the WLEs are also investigated. In addition, a parametric study of the influence of separating rod-aerofoil distance on the acoustic radiation of the SLE case and on the sound power reduction level of the WLE cases is performed. It is found that a critical spacing exists where the acoustic radiation and noise reduction can be divided into two different “modes”.

Combined free-stream disturbance measurements and receptivity studies in hypersonic wind tunnels by means of a slender wedge probe and direct numerical simulation

Combined free-stream disturbance measurements and receptivity studies in hypersonic wind tunnels were conducted by means of a slender wedge probe and direct numerical simulation. The study comprises comparative tunnel noise measurements at Mach 3, 6 and 7.4 in two Ludwieg tube facilities and a shock tunnel. Surface pressure fluctuations were measured over a wide range of frequencies and test conditions including harsh test environments not accessible to measurement techniques such as Pitot probes and hot-wire anemometry. A good agreement was found between normalized Pitot pressure fluctuations converted into normalized static pressure fluctuations and the wedge probe readings. Quantitative results of the tunnel noise are provided in frequency ranges relevant for hypersonic boundary-layer transition. Complementary numerical simulations of the leading-edge receptivity to fast and slow acoustic waves were performed for the applied wedge probe at conditions corresponding to the experimental free-stream conditions. The receptivity to fast acoustic waves was found to be characterized by an early amplification of the induced fast mode. For slow acoustic waves an initial decay was found close to the leading edge. At all Mach numbers, and for all considered frequencies, the leading-edge receptivity to fast acoustic waves was found to be higher than the receptivity to slow acoustic waves. Further, the effect of inclination angles of the acoustic wave with respect to the flow direction was investigated. An inclination angle was found to increase the response on the wave-facing surface of the probe and decrease the response on the opposite surface for fast acoustic waves. A frequency-dependent response was found for slow acoustic waves. The combined numerical and experimental approach in the present study confirmed the previous suggestion that the slow acoustic wave is the dominant acoustic mode in noisy hypersonic wind tunnels.