Multiple Discrete Frequencies Research Articles

Shaping Quantum Noise through Cascaded Nonlinear Processes in a Dissipation-Engineered Multimode Cavity

Multimode quantum light is enticing for several applications, spanning imaging, spectroscopy, communication, and more. Parametric nonlinear processes have been vital in realizing squeezed and other quantum states of light. However, most work exploiting these processes has focused on generating multimode squeezed vacua and squeezing in mode superpositions (supermodes). Bright squeezing in multiple discrete frequency modes, if realized, could unlock novel applications in quantum-enhanced spectroscopy and optical quantum computing. Here, we show how dissipation engineering of a multimode nonlinear cavity with cascaded three-wave-mixing processes allows us to shape above-threshold frequency combs that feature strong single-mode output amplitude noise squeezing over 10 dB below the shot-noise limit, tunable across the comb. In addition, we demonstrate squeezing for multiple discrete frequency modes above threshold. This bright squeezing arises from enhancement of the (noiseless) nonlinear rate relative to decay rates in the system due to the cascaded generation of photons in a single idler “bath” mode. A natural consequence of the strong nonlinear coupling in our system is the creation of an effective cavity in the synthetic frequency dimension that sustains Bloch oscillations in the modal energy distribution. Bloch mode engineering could provide an opportunity to better control nonlinear energy flow in the synthetic frequency dimension, with exciting applications in quantum random walks and topological photonics. Lastly, we show evidence of long-range correlations in amplitude noise between discrete frequency modes, enabling long-range entanglement in a synthetic frequency dimension and providing a new resource for quantum communication. Published by the American Physical Society 2024

Study of the noise reduction performance of acoustic enclosures with ultra-thin bending labyrinth metasurfaces

This study proposes a bending labyrinth metasurface (BLM) that integrates an embedded aperture with bending channels. Adopting the thermal-viscous model and the transfer matrix method, a theoretical model for solving the absorption coefficient of the BLM unit was established. Adopting the complex frequency plane method (CFPM) and the principle of critical coupling, a 12-mm thick BLM unit was investigated and found to exhibit perfect absorption (absorption coefficient α > 0.95) specifically at a frequency of 562 Hz. Subsequently, to achieve low-frequency broadband noise reduction, the regulation principle of the sound absorption coefficient of the BLM unit was studied through multi-parameter variation. BLM units that can achieve perfect absorption at multiple discrete frequencies are proposed. Furthermore, to ensure the uniform discrete distribution of the perfect sound absorption frequency of the BLM unit, 12 BLM units were selected and coplanar connected in parallel to constitute panels with equal-height and variable-height BLMs. These panels exhibit highly efficient sound absorption within broadband ranges of 397–706 Hz and 307–706 Hz, respectively. Finally, five identical metasurface panels were bonded together to form a rectangular box-shaped acoustic enclosure, and the noise reduction performance of this enclosure was experimentally studied. The results indicate that within the frequency range of 200–1000 Hz, the average noise reduction improvements for acoustic enclosures with variable-height and equal-height BLMs are 8.3 and 8.2 dB, respectively, compared with the acoustic enclosure with a homogeneous double layer. The frequency range over which the noise reduction is improved matches the frequency range of efficient absorption of the BLM panels. This work provides both a theoretical reference and a practical guide for engineering applications for controlling low-frequency broadband noise in compact spaces.

A vibration-based method to estimate the low-wavenumber wall pressure field in a turbulent boundary layer

When an elastic structure is excited by a low-speed turbulent flow, it generates flow-induced vibration which is primarily due to the low-wavenumber components of the wall pressure field (WPF) beneath the turbulent boundary layer (TBL). Therefore, to accurately predict the vibration response of the structure, an accurate estimation of the low-wavenumber WPF is needed. While existing TBL models for WPF well predict the convective region, they exhibit significant discrepancies in predicting the low-wavenumber levels. This numerical study aims to explore the feasibility of estimation of the low-wavenumber WPF by analysing vibration data obtained from a structure excited by a TBL. An inverse method is proposed based on the relationship between the TBL forcing function and structural vibrations in the wavenumber domain. The random TBL force is simulated with deterministic loading using the uncorrelated wall plane wave technique. A model of a simply supported plate under a TBL excitation is developed to demonstrate the proposed method. The plate's acceleration data is then used to estimate the WPF in the low-wavenumber range. It is shown how using multiple discrete frequencies in the analysis can reduce the required snapshots for accurate estimation of the WPF.

The primate cortical LFP exhibits multiple spectral and temporal gradients and widespread task dependence during visual short-term memory.

Although cognitive functions are hypothesized to be mediated by synchronous neuronal interactions in multiple frequency bands among widely distributed cortical areas, we still lack a basic understanding of the distribution and task dependence of oscillatory activity across the cortical map. Here, we ask how the spectral and temporal properties of the local field potential (LFP) vary across the primate cerebral cortex, and how they are modulated during visual short-term memory. We measured the LFP from 55 cortical areas in two macaque monkeys while they performed a visual delayed match to sample task. Analysis of peak frequencies in the LFP power spectra reveals multiple discrete frequency bands between 3 and 80 Hz that differ between the two monkeys. The LFP power in each band, as well as the sample entropy, a measure of signal complexity, display distinct spatial gradients across the cortex, some of which correlate with reported spine counts in cortical pyramidal neurons. Cortical areas can be robustly decoded using a small number of spectral and temporal parameters, and significant task-dependent increases and decreases in spectral power occur in all cortical areas. These findings reveal pronounced, widespread, and spatially organized gradients in the spectral and temporal activity of cortical areas. Task-dependent changes in cortical activity are globally distributed, even for a simple cognitive task.NEW & NOTEWORTHY We recorded extracellular electrophysiological signals from roughly the breadth and depth of a cortical hemisphere in nonhuman primates (NHPs) performing a visual memory task. Analyses of the band-limited local field potential (LFP) power displayed widespread, frequency-dependent cortical gradients in spectral power. Using a machine learning classifier, these features allowed robust cortical area decoding. Further task dependence in LFP power were found to be widespread, indicating large-scale gradients of LFP activity, and task-related activity.

Determination of surface density of nonporous membranes with ultrasonic immersion measurements

ABSTRACT The surface density of nonporous membranes is estimated with a conventional ultrasonic immersion measurement system without need for a priori information about the membrane such as wave speed, density, thickness or impedance under most testing conditions. The derivation, theoretical limitations and practical restrictions of the technique are discussed. The broadband nature of the measurement allows the surface density values to be estimated at multiple discrete frequencies within the useful bandwidth of the transducer. In experimentation, the technique was used to measure surface densities in a range of 0.044–0.328 kg/m2. All calculated surface densities are within 5% or less of their nominal values with an average percent difference of 1.7%.

Signal area estimation based on deep learning

In many practical application scenarios, radio communication signals are commonly represented as a spectrogram, which represents the signal strength measured at multiple discrete time instants and frequency points within a specific time interval and frequency band, respectively. In the context of spectrum occupancy measurements, the notion of Signal Area (SA) is defined as the rectangular region in the time–frequency domain where a signal is assumed to be present. Signal Area Estimation (SAE) is an important functionality in spectrum-aware wireless systems where spectrum usage monitoring is required. However, the conventional approaches to SAE have a limited estimation accuracy, in particular at low SNR. In this work, a novel technique for SAE is proposed using Deep Learning based on Artificial Neural Network (DL-ANN) for enhanced extraction of SA information from radio spectrograms. The performance of the proposed DL-ANN method is evaluated both with software simulations and hardware experiments, and the results are compared with several conventional methods from the literature, showing significant performance improvements. A key feature of the proposed method is the improvement in the SAE accuracy compared to other existing methods (in particular in the low SNR regime) and the capability to extract the location of the detected SAs automatically. Overall, the proposed technique is a promising solution for the automatic processing of radio spectrograms in spectrum-aware wireless systems.

Coherent mode induced by supersonic molecular beam injection in EAST Ohmic plasmas

A coherent mode (CM) induced by the supersonic molecular beam injection (SMBI) was observed in Ohmic plasmas of EAST tokamak. The CM existed in the spectra of the electron temperature fluctuation and density fluctuation, but not in the spectrum of Mirnov fluctuation. The radial location of the CM was about 10 cm inside the separatrix (normalized minor radius ). In most cases, the CM has multiple discrete frequencies between with an interval of ∼1 kHz. Occasionally, there is only one dominant frequency. The poloidal scale of the CM (poloidal wavenumber , poloidal mode number ) is between that of typical ion turbulence and macroscopic magnetohydrodynamic activities. Statistical analysis results suggest that the onset of the CM requires a high temperature gradient and a relatively low density gradient. Furthermore, the transport analysis shows that the SMBI-caused perturbation propagates inward faster in plasmas with stronger CM, which implies that the CM might be correlated to a high local transport level. However, the impact of the CM on macroscopic plasma parameters including stored energy, energy confinement time, and SMBI-caused mean density fluctuation is too weak to be found in comparison with the random fluctuation and the measurement errors, which suggests that the CM does not have a clear influence on the global confinement.

Polarization-Dependent Selection Rules and Optical Spectrum Atlas of Twisted Bilayer Graphene Quantum Dots

Understanding how symmetries encode optical polarization information into selection rules in molecules and materials is important for their optoelectronic applications including spectroscopic analysis, display technology, and quantum computation. Here, we extend polarization-dependent selection rules from atoms to solid-state systems with various point groups with the help of the rotational operator for circular polarization and the twofold rotational operator (or reflection operator) for linear polarization. We use these new selection rules to study the optical properties of twisted bilayer graphene quantum dots (TBGQDs), which inherit advantages of graphene quantum dot including its ultrathin thickness, excellent biocompatibility, and shape- and size-tunable optical absorption or emission. We study how the electronic structures and optical properties of TBGQDs rely on size, shape, twist angle, and correlation effects for TBGQDs with 10 different point groups for which we obtain an optical selection rule database. We show how current operator matrix elements identify the generalized polarization-dependent selection rules. Our results show that both the electronic and optical band gaps follow power-law size scalings with a dominant role of the twist angle. We derive an atlas of optical conductivity spectra for both size and twist angle in TBGQDs. As a result of quantum confinement effects, in the atlas a new type of optical conductivity features emerges with multiple discrete absorption frequencies ranging from infrared to ultraviolet energy, allowing for applications in photovoltaic devices and photodetectors. The atlas and size scaling provide a full structure–symmetry-function interrelation and hence offer an excellent basis for the geometrical manipulation of optical properties of TBGQDs as building blocks for novel integrated carbon optoelectronics.2 MoreReceived 5 October 2021Revised 14 April 2022Accepted 3 May 2022DOI:https://doi.org/10.1103/PhysRevX.12.021055Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasElectronic structureOptical conductivityPhysical SystemsGrapheneTechniquesGroup theoryMean field theorySymmetriesTight-binding modelCondensed Matter, Materials & Applied Physics

Dynamic Harmonic Phasor Estimator Considering Frequency Deviation

The fundamental frequency of power system may deviate from the nominal value due to various reasons, such as load variation, subsynchronous resonance and fault occurrence. The maximum frequency deviation considered by the latest IEEE standard is 5 Hz. This paper proposes a dynamic harmonic synchrophasor estimator, which can accurately estimate the dynamic harmonic parameters even if the frequency deviation reaches 5 Hz. Multiple discrete frequencies are generated at a fixed frequency interval on both sides of the nominal frequency, and multiple dynamic harmonic filters are generated offline based on those frequencies. The windowed interpolation discrete Fourier transform is adopted for online monitoring of the fundamental frequency. According to the detected frequency, a harmonic filter, which is generated with the discrete frequency that is closest to the detected frequency, can be selected to analyze the dynamic harmonic synchrophasor, frequency and rate of change of frequency. The performances of the proposed estimator are verified through tests under various frequency deviation conditions, and the test results show that the proposed estimator can accurately estimate the dynamic harmonic parameters when the frequency deviation is within 5 Hz.

A 33 MHz Fast-Locking PLL with Programmable VCO and Automatic Band Selection for Clock Generator Application

This paper presents a prototype of an auto-ranging phase-locked loop (PLL) with low jitter noise over a wide operating frequency range using the multiband programmable voltage-controlled oscillator (VCO) gain stage with automatic band selection. We successfully reduce the VCO gain (Kvco) and retain the desired frequency band. The proposed PLL comprises a prescaler, phase frequency detector (PFD), charge pump (CP), programmable VCO and automatic band selection circuit. The PLL prototype with all subblocks was implemented using the TSMC 0.18 μm 1P6M process. Contrary to conventional PLL architectures, the proposed architecture incorporates a real-time check and automatic band selection circuit in the secondary loop. A high-performance dual-loop PLL wide tuning range was realized using an ASIC digital control circuit. A suitable way to maintain the Kvco low is to use multiple discrete frequency bands to accommodate the required frequency range. To maintain a low Kvco and fast locking, the automatic frequency band selection circuit also has two indigenous, most probable voltage levels. The proposed architecture provides the flexibility of not only band hopping but also band twisting to obtain an optimized Kvco for the desired output range, with the minimum jitter and spurs. The proposed programmable VCO was designed using a voltage-to-current-converter circuit and current DAC followed by a four-stage differential ring oscillator with a cross-coupled pair. The VCO frequency output range is 150–400 MHz, while the input frequency is 25 MHz. A sequential phase detection loop with a negligible dead zone was designed to adjust fine phase errors between the reference and feedback clocks. All circuit blocks of the proposed PLL were simulated using the EDA tool HSPICE and layout generation by Laker. The simulation and measured results of the proposed PLL show high linearity, with a dead zone of less than 10 pV. The differential VCO was used to improve the linearity and phase noise of the PLL. The chip measured results show rms jitter of 19.10 ps. The PLL prototype also has an additional safety feature of a power down mode. The automatic band selection PLL has good immunity for possible frequency drifting due to temperature, process and supply voltage variations. The proposed PLL is designed for −40 to +85 °C, a wide temperature range.

Low-complexity GLRT for FDA radar without training data

Conventionally adaptive detection for frequency diverse array (FDA) radar requires extra training data to estimate the range-dependent interference covariance matrix (ICM). In this paper, we propose an adaptive moving target detection approach for FDA radar without training data, where the ICM is directly estimated by applying a structured generalized likelihood ratio test (SGLRT) to the target-present samples. In order to reduce the three-dimensional (3D) search complexity of the SGLRT, we then propose an efficient unstructured GLRT (UGLRT) approach, which transforms the 3D search into a 1D Doppler-only search and a joint range-angle search. Moreover, we design a low-complexity two-stage implementation of the UGLRT for practical application. The first stage is to test multiple discrete frequency bins for target detection, while the second stage is to precisely estimate the frequency through locally optimizing the estimator function around the coarse estimate provided by the first-stage detection. As the UGLRT approach avoids the 3D search, it significantly reduces the computational complexity, compared to the SGLRT counterpart. Numerical results show that the UGLRT approach achieves almost the same detection and estimation performance as the SGLRT one.

Optoacoustic microscopy at multiple discrete frequencies

Optoacoustic (photoacoustic) sensing employs illumination of transient energy and is typically implemented in the time domain using nanosecond photon pulses. However, the generation of high-energy short photon pulses requires complex laser technology that imposes a low pulse repetition frequency (PRF) and limits the number of wavelengths that are concurrently available for spectral imaging. To avoid the limitations of working in the time domain, we have developed frequency-domain optoacoustic microscopy (FDOM), in which light intensity is modulated at multiple discrete frequencies. We integrated FDOM into a hybrid system with multiphoton microscopy, and we examine the relationship between image formation and modulation frequency, showcase high-fidelity images with increasing numbers of modulation frequencies from phantoms and in vivo, and identify a redundancy in optoacoustic measurements performed at multiple frequencies. We demonstrate that due to high repetition rates, FDOM achieves signal-to-noise ratios similar to those obtained by time-domain methods, using commonly available laser diodes. Moreover, we experimentally confirm various advantages of the frequency-domain implementation at discrete modulation frequencies, including concurrent illumination at two wavelengths that are carried out at different modulation frequencies as well as flow measurements in microfluidic chips and in vivo based on the optoacoustic Doppler effect. Furthermore, we discuss how FDOM redefines possibilities for optoacoustic imaging by capitalizing on the advantages of working in the frequency domain.

Simultaneous and continuous measurement of shear elasticity and viscosity of liquids at multiple discrete frequencies

This paper presents the extension of the classical torsional resonance viscometer towards the characterization of linear viscoelastic fluids. By simultaneously tracking multiple resonance frequencies, shear viscosity and elasticity can be monitored at multiple discrete frequencies at the same time. The proposed method is applied to the well-established sensor design of a simple rod-like structure, hence enabling a robust and versatile measurement system that can be used in different applications, such as in-line measurement or hand-held devices. In order to simultaneously control different resonance frequencies, multiple independent phase-locked loops are used, of which each subsystem is responsible for one natural vibration. An analytical description of the relationship between measurement parameters and physical fluid parameters is presented that is valid both for Newtonian and linear viscoelastic fluids. Consequently, calibration of the sensor is possible using Newtonian fluids only. To demonstrate the sensor, viscoelastic polymer and surfactant solutions are investigated at five frequencies between 2 kHz and 20 kHz. Additionally, the test fluids are characterized by means of a classical rotational rheometer (low frequency range) and diffusing-wave spectroscopy (high frequency range). The comparison of all methods shows very good agreement and validates the application of the sensor as resonant rheometer for viscoelastic fluids.

Multicolor T-Ray Imaging Using Multispectral Metamaterials.

Recent progress in ultrafast spectroscopy and semiconductor technology is enabling unique applications in screening, detection, and diagnostics in the Terahertz (T‐ray) regime. The promise of efficaciously operation in this spectral region is tempered by the lack of devices that can spectrally analyze samples at sufficient temporal and spatial resolution. Real‐time, multispectral T‐ray (Mul‐T) imaging is reported by designing and demonstrating hyperspectral metamaterial focal plane array (MM‐FPA) interfaces allowing multiband (and individually tunable) responses without compromising on the pixel size. These MM‐FPAs are fully compatible with existing microfabrication technologies and have low noise when operating in the ambient environment. When tested with a set of frequency switchable quantum cascade lasers (QCLs) for multicolor illumination, both MM‐FPAs and QCLs can be tuned to operate at multiple discrete THz frequencies to match analyte “fingerprints.” Versatile imaging capabilities are presented, including unambiguous identification of concealed substances with intrinsic and/or human‐engineered THz characteristics as well as effective diagnosis of cancerous tissues without notable spectral signatures in the THz range, underscoring the utility of applying multispectral approaches in this compelling wavelength range for sensing/identification and medical imaging.

Inversion-based interpretation of borehole sonic measurements using semianalytical spatial sensitivity functions

One of the major challenges in the interpretation of sonic logs is the presence of bed-boundary (shoulder-bed) effects, which can decrease the accuracy of the estimated elastic properties due to spatial averaging caused by the sonic receiver array across thin beds. A reliable approach to account for shoulder-bed effects in the interpretation of sonic logs is the implementation of forward modeling and inversion techniques. We have developed an efficient inversion-based interpretation method for the estimation of in situ rock formation elastic properties from sonic logs acquired in vertical wells. The method uses semianalytical spatial sensitivity functions for fast forward modeling of sonic-slowness logs and estimates formation elastic properties by iteratively matching the available logs with numerical simulations. Due to the intrinsic vertical resolution limits of sonic logs, the inversion method requires predefined bed boundaries using other high-resolution well logs. We first developed a workflow to estimate shear slowness of thin beds from flexural mode dispersions measured at multiple discrete frequencies. Then, we extended the method to estimate layer-by-layer compressional and shear slownesses by combining the slowness logs of nondispersive P- and S-waves. The method was first successfully verified using data numerically simulated for synthetic rock formations consisting of multiple thin beds and exhibiting large elastic property contrasts. Maximum relative errors and maximum uncertainty in the estimates were less than 2% and 6%, respectively. Field data acquired in wells penetrating multiple horizontal thin beds were also used to appraise the reliability and resolution improvement of the method in the estimation of formation compressional and shear slownesses. Our results indicated that our inversion-based interpretation method improved the vertical resolution of sonic logs by 70%. The new inversion-based interpretation method opens up the possibility of integrating modern borehole acoustic measurements with nuclear and resistivity logs for improved poroelastic and petrophysical interpretations.

Introducing a frequency-tunable magnetic particle spectrometer

Abstract Image quality in the new imaging modality magnetic particle imaging (MPI) heavily relies on the quality of the magnetic nanoparticles in use. Therefore, it is crucial to understand the behaviour of such particles. A common technique to analyze the behaviour of the particles is magnetic particle spectrometry (MPS). However, most spectrometers are limited to measurements at a single or multiple discrete excitation frequencies. This paper introduces a frequency-tunable spectrometer, able to perform measurements in the range of 100 Hz - 24kHz.

Nonlocal cancellation of multi-frequency-channel dispersion

We present an investigation of the temporal correlation of time-energy entangled photon pairs propagating through multi-frequency-channel dispersive media, in which photon spectra spread over multiple discrete frequency channels with dispersions. We have observed more complex coincidence structures including double coincidence envelopes and dependence on frequency detuning that are absent in the single-channel case. Our results on the correlation of the time-energy photonic entanglement in dispersive media with channel divisions would impact the fields of quantum metrology and communication.

Microfluidic Microwave Sensor for Simultaneous Dielectric and Magnetic Characterization

Herein, we demonstrate a method for simultaneously quantifying the electric and magnetic properties of liquid systems confined within a capillary. This is based upon an optimized perturbation of a microwave-frequency coaxial resonator, chosen to maximize the spatial separation of the two fields and to minimize the depolarization of the liquid. A capillary is passed through the center of the resonator so the sample occupies either maximum electric field (zero magnetic field) or maximum magnetic field (zero electric field) depending on whether an odd or even TEM mode is interrogated. This allows electric and magnetic effects to be distinguished at multiple discrete frequencies. We demonstrate this capability through the quantification of varying ionic content of saline solutions, which interact with both the electric and magnetic fields via several polarization mechanisms. The distinction of different cations and anions is also demonstrated.

Using photon mapping for multispectral modeling of scenes within THz range

A method for simulation of appearance of large, geometrically modeled environment in THz range is presented. Photon mapping technique is used with Monte Carlo photon sampling. Propagation of radiation within the scene is simulated for multiple discrete radiation frequencies, various materials are being modeled with emissivity, reflectivity and attenuation characteristics. The results are used to predict the answer of passive, multispectral terahertz detector matrix. Full Text: PDF References M. Dell?Anna, V. Antonov, D. Bagliani, M. Biasotti, J. L. Coutaz, F. Gatti, M. Kiviranta, S. Kubatkin, E. Otto and M. Sypek, "THz Spectroscopy Using Low Temperature Mesoscopic Devices", J. Low Temp. Phys. 167(3-4), 467 (2012). CrossRef H.W. Jensen, "Global Illumination using Photon Maps", Rendering Techniques ?96, 21-30 (1996) CrossRef J.T. Kajiya, The Rendering Equation, SIGGRAPH '86 Proceedings, 143-150 (1986). G. Ward, Measuring and Modeling Anisotropic Reflection, SIGGRAPH ?92 Proceedings, 265-272, (1992) The HITRAN Database, http://www.cfa.harvard.edu/hitran/ Link H. Kahn, Use of Different Monte Carlo Sampling Technique (Rand Corporation, 1955) DirectLink

Novel Coupling Structure for the Resonant Coaxial Probe

Herein we present a technique for performing complex permittivity measurements with an overmoded, evanescently perturbed coaxial resonator at microwave frequencies. The design of a noninvasive electromagnetic coupling structure, which allows transmission measurements to be taken from one end of a resonant section of coaxial cable, is discussed in detail. Quasi-spectral information was obtained through the exploitation of higher order resonances, and complex permittivity measurements of a number of common industrial solvents were taken at multiple discrete frequencies between 1 and 8 GHz. A combination of experimental and simulated results was used also to characterise the device behavior. The high stability of temporal measurements, coupled with the robustness of the design, make this device ideal for analytical chemistry and industrial process control.