Coherent Wave Research Articles

Noise within: Signal-to-noise enhancement via coherent wave amplification in the mammalian cochlea.

The extraordinary sensitivity of the mammalian inner ear has captivated scientists for decades, largely due to the crucial role played by the outer hair cells (OHCs) and their unique electromotile properties. Typically arranged in three rows along the sensory epithelium, the OHCs work in concert via mechanisms collectively referred to as the "cochlear amplifier" to boost the cochlear response to faint sounds. While simplistic views attribute this enhancement solely to the OHC-based increase in cochlear gain, the inevitable presence of internal noise requires a more rigorous analysis. Achieving a genuine boost in sensitivity through amplification requires that signals be amplified more than internal noise, and this requirement presents the cochlea with an intriguing challenge. Here we analyze the effects of spatially distributed cochlear-like amplification on both signals and internal noise. By combining a straightforward mathematical analysis with a simplified model of cochlear mechanics designed to capture the essential physics, we generalize previous results about the impact of spatially coherent amplification on signal degradation in active gain media. We identify and describe the strategy employed by the cochlea to amplify signals more than internal noise and thereby enhance the sensitivity of hearing. For narrow-band signals, this effective, wave-based strategy consists of spatially amplifying the signal within a localized cochlear region, followed by rapid attenuation. Location-dependent wave amplification and attenuation meet the necessary conditions for amplifying near-characteristic frequency (CF) signals more than internal noise components of the same frequency. Our analysis reveals that the sharp wave cutoff past the CF location greatly reduces noise contamination. The distinctive asymmetric shape of the "cochlear filters" thus underlies a crucial but previously unrecognized mechanism of cochlear noise reduction.

Continuous Injector Geometry Variation to Augment Rotating Detonation Combustor Operation and Performance

Sensitivity of rotating detonation combustor operation and performance to oxidizer injector pressure drop was characterized using continuous variation of the injector area during combustor operation. As the oxidizer injector area was both increased and decreased, the sensitivity of the combustion process to varying injector pressure drop was characterized using high-frequency measurements of pressure and chemiluminescence intensity. Detonation wave strength and coherence were characterized using peak-to-peak intensity and power fraction calculated from point-chemiluminescence measurements. Propulsive performance of the combustor was evaluated using thrust and equivalent available pressure, relating them back to reactant supply pressures for assessment of combustor pressure gain. Pressure gain increased during a test as the oxidizer injector area was increased and the corresponding manifold pressure was decreased. At larger injector areas, pressure gain decreased as the operating mode of the combustor transitioned from detonation to deflagration, concomitant with a reduction of gross thrust. Modeling of injector recovery time revealed that the injector operated in both choked and unchoked regimes, which was used to explain detonation wave number transitions in the experiment. A broadened range of detonative operability enabled by active variation of combustor geometry resulted in higher performance with a lower injector pressure drop.

Fresnel coefficients, coherent optical scattering, and planar waveguiding

The Fresnel formalism of transmission and reflection of coherent waves on the abrupt interface between two different optical media is revisited and extended to study optical phenomena concerning guided waves. Using the Fresnel formalism, the propagation of light through different sequences of parallel layers of constant refractive index is analysed, revealing that, in all cases, the solutions corresponding to waveguiding share major features. In the analysis, aiming to connect waveguiding with coherent optical scattering, the possibility of the system having a resonance is examined, and it is shown that guided modes always emerge as singular solutions of the associated coherent scattering configuration. Invariably, the resonance condition that must be satisfied to obtain waveguiding corresponds to the pole of the associated total reflection and transmission coefficients. Even more, the fulfilment of the requirements to meet the resonance condition is a clear indication of the possibility of waveguiding.

Ultrafast X-ray Diffraction Probe of Coherent Spin-State Dynamics in Molecules.

We propose an approach to probe coherent spin-state dynamics of molecules using circularly polarized hard X-ray pulses. For the dynamically aligned nitric oxide molecules in a coherent superposition spin-orbit coupled electronic state that can be prepared through stimulated Raman scattering, we demonstrate the capability of ultrafast X-ray diffraction to not only reveal the quantum beating of the coherent spin-state wave packet but also image the spatial spin density of the molecule. With a circularly polarized ultrafast X-ray diffraction signal, we show that the electronic density matrix can be retrieved. The spatiotemporal resolving power of ultrafast X-ray diffraction paves the way for tracking transient spatial wave function in molecular dynamics involving the spin degree of freedom.

Topological atom optics and beyond with knotted quantum wavefunctions

Atom optics demonstrates optical phenomena with coherent matter waves, providing a foundational connection between light and matter. Significant advances in optics have followed the realization of structured light fields hosting complex singularities and topologically non-trivial characteristics. However, analogous studies are still in their infancy in the field of atom optics. Here, we investigate and experimentally create knotted quantum wavefunctions in spinor Bose–Einstein condensates which display non-trivial topologies. In our work we construct coordinated orbital and spin rotations of the atomic wavefunction, engineering a variety of discrete symmetries in the combined spin and orbital degrees of freedom. The structured wavefunctions that we create map to the surface of a torus to form torus knots, Möbius strips, and a twice-linked Solomon’s knot. In this paper we demonstrate close connections between the symmetries and underlying topologies of multicomponent atomic systems and of vector optical fields—a realization of topological atom-optics.

Coherent THz spin dynamics in antiferromagnets beyond the approximation of the Néel vector

Controlled generation of coherent spin waves with highest possible frequencies and shortest possible wavelengths is a cornerstone of spintronics and magnonics. Here, using Heisenberg antiferromagnet RbMnF3, we demonstrate that laser-induced THz spin dynamics corresponding to pairs of mutually coherent counter-propagating spin waves with the wavevectors up to the edge of the Brillouin zone cannot be understood in terms of magnetization and antiferromagnetic (Néel) vectors, conventionally used to describe spin waves. Instead, we propose to model such spin dynamics using the spin correlation function. We derive a quantum-mechanical equation of motion for the latter and emphasize that unlike the magnetization and antiferromagnetic vectors the spin correlations in antiferromagnets do not exhibit inertia.

Measurement of Beta and Theta Brain Wave Coherence with Cardiac Wave Rhythm in Managers with Rational Decision-Making Style Based on Emotional Intelligence through ERT Cognitive Task

Objective: Since human life and society depend on brain functions, our understanding of the brain and mind can significantly impact all dimensions of human life. Therefore, the main objective of this study was to assess the coherence of brain waves (EEG) and cardiac wave rhythms (HRV) based on neuroscientific and neurocardiology principles. Methods and Materials: This research utilized an experimental design, specifically a quasi-experimental approach without a control group, and was applied in nature. The statistical population consisted of managers (90 individuals) from both public and private sectors in Gilan Province in 2022. From this population, 30 individuals were randomly selected. Their brain waves and cardiac rhythms were simultaneously recorded in both resting and decision-making states from the CZ region of the brain and triangular regions around the heart using the ProComp 2 neurofeedback tool while performing the emotional intelligence assessment test. The research instrument included the ERT cognitive test (Emotional Recognition Task) designed by Cambridge University in 1980 and administered through the Cantab software and BioGraph Infiniti version 0.6 software. For the purposes of this study, the cognitive task was provided to participants via software. The data were analysed using analysis of variance and mean comparison test via SPSS-26. Findings: The correlation test of brain waves and cardiac waves in resting and cognitive task states showed significant differences. No coherence between EEG and ECG was observed in the resting state compared to the cognitive task state. Conclusion: The results indicate that changes in brain waves and cardiac waves, and the coherence between these waves, vary among managers with similar decision-making styles. These variations depend on the environmental, mental, and emotional conditions of the individuals.

Numerical direct scattering transform for breathers

We consider the model of the focusing one-dimensional nonlinear Schrödinger equation (fNLSE) in the presence of an unstable constant background, which exhibits coherent solitary wave structures—breathers. Within the inverse scattering transform (IST) method, we study the problem of the scattering data numerical computation for a broad class of breathers localized in space. Such a direct scattering transform (DST) procedure requires a numerical solution of the auxiliary Zakharov–Shabat system with boundary conditions corresponding to the background. To find the solution, we compute the transfer matrix using the second-order Boffetta–Osborne approach and recently developed high-order numerical schemes based on the Magnus expansion. To recover the scattering data of breathers, we derive analytical relations between the scattering coefficients and the transfer matrix elements. Then we construct localized single- and multi-breather solutions and verify the developed numerical approach by recovering the complete set of scattering data with the built-in accuracy providing the information about the amplitude, velocity, phase and position of each breather. To combine the conventional IST approach with the efficient dressing method for multi-breather solutions, we derive the exact relation between the parameters of breathers in these two frameworks.

A multiple cancer cell optical biosensing metastructure realized by CPA.

A one-dimensional optical biosensing metastructure (OBM) with graphene layers is presented in this paper. It is realized by coherent perfect absorption (CPA) and operates in the transverse electric mode. It shows a strong linear fitting relationship between the refractive index (RI) of the analysis layer and the frequency corresponding to the absorption peak, and the R-square is up to 1. Additionally, based on the principle of CPA, the OBM can realize the function of multiple cancer cell detection by adjusting the detection range by controlling the phase difference of coherent electromagnetic waves. Its detection ranges are 1.34-1.355 and 1.658-1.662. Thanks to its high-quality factor, great figure of merit, and low detection limit, whose best values are, respectively, 6.9 × 104, 1.2 × 104 RIU-1, and 3.6 × 10-6 RIU, the detection of weak changes in the RI of a cancer cell is possible. Additionally, its sensitivity can reach 26.57 THz RIU-1. This OBM based on CPA has major implications for advancing the study and investigation into the application of CPA. It also provides a simple and efficient approach to distinguish cancer cells and may be widely used in the biomedical field.

Functionality multiplexing in high-efficiency metasurfaces based on coherent wave interferences

Functionality multiplexing in high-efficiency metasurfaces based on coherent wave interferences

Remote transport of high-dimensional orbital angular momentum states and ghost images via spatial-mode-engineered frequency conversion

The efficient transport and engineering of photonic orbital angular momentum (OAM) lie at the heart of various related classical and quantum applications. Here, by leveraging the spatial-mode-engineered frequency conversion, we realize the remote transport of high-dimensional orbital angular momentum (OAM) states between two distant parties without direct transmission of information carriers. We exploit perfect vortices for preparing high-dimensional yet maximal O AM entanglement. Based on nonlinear sum-frequency generation working with a strong coherent wave packet and a single photon, we conduct the Bell-like state measurements for high-dimensional perfect vortices. We experimentally achieve an average transport fidelity 0.879 ± 0.048 and 0.796 ± 0.066 for a complete set of 3-dimensional and 5-dimensional OAM mutually unbiased bases, respectively. Furthermore, by exploring the full transverse entanglement, we construct another strategy of quantum imaging with interaction-free light. It is expected that, with the future advances in nonlinear frequency conversion, our scheme will pave the way for realizing truly secure high-dimensional quantum teleportation in the upcoming quantum network.

Exploring the vibrational series of pure trilobite Rydberg molecules

In trilobite Rydberg molecules, an atom in the ground state is bound by electron-atom scattering to a Rydberg electron that is in a superposition of high angular momentum states. This results in a homonuclear molecule with a permanent electric dipole moment in the kilo-debye range. Trilobite molecules have previously been observed only with admixtures of low-l states. Here we report on the observation of two vibrational series of pure trilobite Rubidium-Rydberg molecules that are nearly equidistant. They are produced by three-photon photoassociation and lie energetically more than 15 GHz below the atomic 22F state of rubidium. We show that these states can be used to measure the electron-atom scattering length at low energies in order to benchmark current theoretical calculations. In addition to measuring their kilo-Debye dipole moments, we also show that the molecular lifetime is increased compared to the 22F state due to the high-l character. The observation of an equidistant series of vibrational states opens the way to observe coherent molecular wave packet dynamics.

Quantum wavefront shaping with a 48-element programmable phase plate for electrons

We present a 48-element programmable phase plate for coherent electron waves produced by a combination of photolithography and focused ion beam. This brings the highly successful concept of wavefront shaping from light optics into the realm of electron optics and provides an important new degree of freedom to prepare electron quantum states. The phase plate chip is mounted on an aperture rod placed in the C2 plane of a transmission electron microscope operating in the 100-300 kV range. The phase plate’s behavior is characterized by a Gerchberg-Saxton algorithm, showing a phase sensitivity of 0.075 rad/mV at 300 kV, with a phase resolution of approximately 3$1010^{-3} $. In addition, we provide a brief overview of possible use cases and support it with both simulated and experimental results.

On the Role of Coherent Plane Wave Compounding in Shear Wave Elasticity Imaging: The Convolution Effect and Its Implications

Objective: The clinical applicability of shear wave elasticity imaging (SWEI) has been confounded by its appreciable inter-system variability and unsatisfactory sensitivity. While SWEI relies on plane wave imaging (PWI) to achieve real-time rendering, it has been rarely noticed that PWI can affect SWEI’s performance. This work is aimed at demonstrating that the use of coherent plane wave compounding (CPWC) can be a factor causing SWEI’s underperformance. Methods: We presented a model to formally describe the slow-time behavior of CPWC in motion tracking. This model reveals that CPWC introduces temporal convolution on the observed motion, making the motion sampling process a low-pass filter (LPF). For validation, shear waves were produced in a phantom in the same way but sampled via PWI using different compounding numbers (CN) and pulse repetition frequencies (PRF), with the obtained signals compared with the inferences drawn from our model. Similar experiments were performed to reconstruct two small targets in the phantom in order to appraise the impact of CPWC on SWEI’s sensitivity. Discussion: The validation experiment shows that the measurements match well with the model inferences, which verifies the LPF nature of CPWC. The phantom study also shows that either increasing CN or decreasing PRF can cause the loss of high-frequency motion information, leading to blurred target delineation by SWEI. Conclusion: The convolution effect can help understand the variability of SWEI. Researchers should beware this effect when working on SWEI standardization. Clinicians using SWEI should also be cautious because this effect makes it harder to identify small lesions.

A two-dimensional angular interpolation based on radial basis functions for high frame rate ultrafast imaging.

To solve the problem of reduced image quality in plane wave imaging (PWI), coherent plane wave compounding (CPWC) has been introduced, based on a combination of plane wave images from several directions (i.e., with different angles). However, the number of angles needed to reach a reasonable image quality affects the maximum achievable frame rate in CPWC. In this study, we suggest reducing the tradeoff between the image quality and the frame rate in CPWC by employing two-dimensional (2D) interpolation based on radial basis functions. More specifically, we propose constructing a three-dimensional spatio-angular structure to integrate both spatial and angular information into the reconstruction prior to 2D interpolation. The rationale behind our proposal is to reduce the number of transmissions and then apply the 2D interpolation along the angle dimension to reconstruct the missing information corresponding to the angles not selected for CPWC imaging. To evaluate the proposed technique, we applied it to the PWI challenges in the medical ultrasound database. Results show that we can achieve 3× to 4× improvement in frame rate while maintaining acceptable image quality compared to the case of using all the angles.

Arithmetic logic unit based on the metastructure with coherent absorption.

An arithmetic logic unit (ALU) based on the metastructure (MS) with coherent absorption (CA) is proposed in this Letter. The ALU can perform AND and exclusive OR logical operations at the same frequency point. So it can be regarded as an optical half-adder. By controlling the chemical potential of graphene and the phase difference of coherent electromagnetic waves (EWs), two different binary numbers are input into the ALU. The dynamic absorption peaks, which are generated based on the CA, output the outcomes of the carry-digit bit and non-carry sum bit. This ALU can be used in the field of optical processing and encryption, such as processing hamming code. This given ALU based on the MS with CA has major implications for advancing the study and investigation into the application of CA. Furthermore, it also provides a new, to the best of our knowledge, idea for the study of MS with logical operation.

On coherently processing multiple arrays in underwater environments with spatial coherence losses from random medium effects and sensor position uncertainties

Under ideal circumstances coherently beamforming multiple distributed arrays should provide improvements over the standard approach of processing the arrays individually and combining them incoherently. These include improved directivity and higher gain. However, two major challenges when coherently processing spatially separated arrays in a real ocean are dealing with coherence losses or wave front distortions caused by random medium effects like internal waves and uncertainties in sensor locations. Some of the consequences are degraded beampatterns and poorer array directivity. In this paper, we perform a simulation-based study utilizing numerical propagation models along with theory examining the effects of wave front distortions induced by random medium effects like internal waves and sensor position uncertainties on coherently beamforming distributed arrays in representative ocean waveguides. Realistic realizations of wave front distortions are generated from actual internal wave measurements and models. The sensitivities of coherent processing to these effects are characterized by resultant beampatterns and losses in array directivity along with a quantification of the tolerances.

Spatial and temporal distributions of atmospheric refractive-index structure parameter measured by moiré deflectometry

Random fluctuation of refractive index distorts the wavefront of light propagation in the atmosphere, which destroys the coherence of the light waves, as well as has an impact on optical detection and communication, etc. In this paper, a phase-based measurement method for synchronously temporal and spatial distributions of atmospheric refractive-index structure parameter is applied. First of all, the depended relation between phase and refractive-index structure parameter is established, based on which an experiment is adopted. In experiment, 3600 frames of moiré fringes were obtained within an hour. And then, the phase and deflection angles distributions of moiré fringes are obtained by Fourier analysis and multi-grid method. Finally, the temporal and spatial distributions of refractive-index structure parameter are yielded according to the deduced theoretical relationship. The results show that both the temporal and spatial distributions refractive-index structure parameter could be measured by moiré deflectometry, and they are in good agreement with the existing methods. In a word, the related results could provide some references for studying the refractive-index structure parameter and the influence of atmosphere on optical detection and communication.

A gauge field theory of coherent matter waves

A gauge field treatment of a current oscillating at frequency ν of interacting neutral atoms leads to a set of matter-wave duals to Maxwell's equations for the electromagnetic field. In contrast to electromagnetics, the velocity of propagation has a lower limit rather than upper limit, and the wave impedance of otherwise free space is negative real-valued rather than 377 Ω. Quantization of the field leads to the matteron, the gauge boson dual to the photon. Unlike the photon, the matteron is bound to an atom and carries negative rather than positive energy, causing the source of the current to undergo cooling. Eigenstates of the combined matter and gauge field annihilation operator define the coherent state of the matter-wave field, which exhibits classical coherence in the limit of large excitation.

Disruption of EEG resting state functional connectivity in patients with focal epilepsy

BackgroundEpilepsy is a network disease and EEG could be used to evaluate dynamic inter-regional connectivity. The aim of the current study is to explore disruption of resting state EEG functional connectivity in focal epilepsy using coherence and phase lag degree. This cross-sectional study included 30 patients with focal epilepsy and 30 matched healthy controls. One to two minutes of EEG segmented into 2-s epochs during awake eye-closed state were analyzed using fast Fourier transform to yield four frequency bands: delta, theta, alpha and beta. Coherence and phase lag degree were computed between each pair of 19 EEG electrodes and were assessed at the intra-hemispheric (frontal–parietal and frontal–temporal) and inter-hemispheric (frontal, temporal and parietal) levels. The frequency of interictal epileptiform discharges (IEDs) was calculated from a 60-min EEG recording session.ResultsCompared to healthy controls, patients had lower theta coherence at left frontal–parietal (P = 0.017), lower delta coherence at inter-frontal (P = 0.045), higher theta phase lag at right frontal–parietal (P = 0.01) and lower delta phase lag at inter-temporal (P = 0.046) levels. Patients with left-sided epilepsy had lower theta coherence at left frontal–parietal (P = 0.026), higher theta phase lag at right frontal–parietal (P < 0.001), higher delta phase lag at right frontal–temporal (P = 0.036) and higher theta phase lag at inter-parietal (P = 0.028) levels. The frequency of IEDs correlated with phase lag of delta (P = 0.036, r = 0.406) and theta (P = 0.005, r = 0.513).ConclusionsPatients with focal epilepsy had significant interictal functional connectivity disruption detected by coherence and phase lag degree of delta and theta waves and correlated with frequency of IEDs.