Polar Perturbations Research Articles

Body-wave speeds and polarizations in the presence of an initial deviatoric stress

SUMMARY Body-wave speeds and polarization directions in a homogeneous and isotropic medium can be influenced by the presence of an initial deviatoric stress, which is conventionally ignored in seismic-wave propagation theories. To the first order, the P-wave speed is sensitive to the initial deviatoric stress, and the P-wave polarization has a perturbation perpendicular to the propagation direction. In addition, the S waves travel at two distinct speeds, and the S-wave polarizations are in two orthogonal directions, which are constrained by the initial deviatoric stress and involve a perturbation parallel to the propagation direction. Using a subduction zone setting with an initial deviatoric stress on the order of tens of MPa, the P-wave speed perturbation, S-wave splitting time and polarization perturbation are estimated to be on the order of 0.01 per cent, 0.01 s and 0.01 per cent, respectively. While these effects are too small to be reliably resolved using seismic observations, the theory presented in this paper could be useful for ultrasonic stress measurements in engineering applications.

Polarization sensing of network health and seismic activity over a live terrestrial fiber-optic cable

Wide-scale sensing of natural and human-made events is critical for protecting against environmental disasters and reducing the monetary losses associated with telecommunication service downtime. However, achieving dense sensing coverage is difficult, given the high deployment overhead of modern sensor networks. Here we offer an in-depth exploration of state-of-polarization sensing over fiber-optic networks using unmodified optical transceivers to establish a strong correlation with ground truth distributed acoustic sensing. To validate our sensing methodology, we collect 85 days of polarization and distributed acoustic sensing measurements along two colocated, 50 km fiber-optic cables in Southern California. We then examine how polarization sensing can improve network reliability by accurately modeling overall network health and preemptively detecting traffic loss. Finally, we explore the feasibility of wide-scale seismic monitoring with polarization sensing, showcasing the polarization perturbations following low-intensity earthquakes and the potential to more than double seismic monitoring coverage in Southern California alone.

Black holes surrounded by generic matter distributions: Polar perturbations and energy flux

Black holes surrounded by generic matter distributions: Polar perturbations and energy flux

Pulse pattern manipulation of dichromatic soliton complexes by a twistable tapered-fiber filter

Soliton complexes highlight the particle-like dynamics of dissipative pulses. However, simple and reliable manipulation of bound solitons remains challenging, particularly for all-polarization-maintaining (PM) configurations that are free from random polarization perturbations. Here, we report controllable pulse patterns of robustly coexisting dichromatic soliton complexes in an all-PM fiber laser based on a twistable tapered-fiber filter. According to the twist angle, dichromatic pulses are switched between different patterns, and components at each wavelength can be independently manipulated, extending encodings from the time to the frequency domain. To the best of our knowledge, it is the first experimental demonstration of dual-wavelength soliton complexes that different pulse patterns coexist at separated wavebands.

Dynamical evolution of exciton-polariton Bose-Einstein condensate under coupled interaction

Abstract We studied the exciton-polariton Bose-Einstein condensation (BEC) under light field manipulation by considering the coupled interaction of the system between exciton-polariton and light. Based on the coupled Gross-Pitaevskii equation (GPE) model and with modified variational method, we analytically derived the solutions of the excitonic system under the polar angle direction perturbation and system rotation. We identified that for different rotational angular velocities and different coupled strengths, the system evolves from a meta-stable oscillation state to monotonically decaying state, with potential for the study of quantum vortex identification for such kind of coupled systems. Our theoretical results can be used to guide the study of the evolution mode of the exciton-polariton system involving coupled interaction.

Induced polar perturbations with stochastic effects in dense matter relativistic stars: A theoretical probe at intermediate sub-hydro mesoscopic scales

A linear response relation between metric and fluid perturbations driven by a background internal noise source is used as a framework for addressing stochastic effects in order to establish a mesoscopic theory for dense matter relativistic stars. In this paper, nonradial polar perturbations are worked out, which are important from the point of view of detection in future. We present qualitative first results in this paper, numerical estimates have to await further progress in theoretical modeling. These perturbations carry a new generalized stochastic nature and are obtained as solutions of the classical Einstein–Langevin equation which has been recently proposed. The significance of these stochastic nonradial polar perturbations lies at probing the intermediate sub-hydro scales inside the dense fluid. This formalism extends towards a mesoscopic scale nonequilibrium/near-equilibrium statistical mechanics study for relativistic star interiors. The generalized stochastic noise originates as the remnant of collapse mechanism and dynamical effects at intermediate scales in isolated massive stars which drives these polar perturbations. More specifically, for cold dense matter which is our focus in this paper, it is either the interplay between the degeneracy pressure and the gravitational pressure, or the multiscale phenomena like turbulences giving rise to the seeds of stochastic effects in the gravitating body. Characterizing such stochastic effects can lead to an improved understanding of the nature of dense matter and help to probe multiple scales which are yet untouched.

A Novel Continuous-Variable Quantum Key Distribution Scheme Based on Multi-Dimensional Multiplexing Technology

Dual-polarization division multiplexing (DPDM) is considered to be a potential method to boost the secure key rate (SKR) of the continuous-variable quantum key distribution (CV-QKD) system. In this article, we propose a pilot alternately assisted local local oscillator (LLO) CV-QKD scheme based on multi-dimensional multiplexing, where time division multiplexing and frequency division multiplexing are combined with dual-polarization multiplexing techniques to dramatically isolate the quantum signal from the pilot tone. We establish a general excess noise model for the LLO CV-QKD system to analyze the influence mechanism of various disturbances (e.g., time-domain diffusion, frequency-domain modulation residual, and polarization perturbation) on the key parameters, such as the channel transmittance and excess noise. Specifically, the photon leakage noise from the reference path to the quantum path and that between quantum signals with two different polarization paths are simultaneously analyzed in the dual-polarization LLO CV-QKD scheme for the first time. Furthermore, a series of simulations are established to verify the performance of the proposed scheme. The results show that the maximal isolation degree achieves 84.0 dB~90.4 dB, and the crosstalk between pilot tones and quantum signals can be suppressed to a very small range. By optimizing the system parameters (e.g., modulation variance and repetition frequency), the SKR with 12.801 Mbps@25 km is achieved under the infinite polarization extinction ratio (PER) and 30 dB residual ratio of the frequency modulation in the nanosecond-level pulse width. Moreover, the performance of the proposed DPDM CV-QKD scheme under relatively harsh conditions is simulated; the results show that the SKR with 1.02 Mbps@25 km is achieved under a relatively low PER of 17 dB with the nanosecond-level pulse width and 20 dB residual ratio of the frequency modulation. Our work lays an important theoretical foundation for the practical DPDM LLO CV-QKD system.

Quasinormal modes and isospectrality of Bardeen (Anti-) de Sitter black holes* *Supported by the the Natural Science Foundation of Hunan Province, China (2022JJ40262), and the National Natural Science Foundation of China (12375046, 12205254)

Black holes (BHs) exhibiting coordinate singularities but lacking essential singularities throughout the spacetime are referred to as regular black holes (RBHs). The initial formulation of RBHs was presented by Bardeen, who considered the Einstein equation coupled with a nonlinear electromagnetic field. In this study, we investigate the gravitational perturbations, including the axial and polar sectors, of the Bardeen (Anti-) de Sitter black holes. We derive the master equations with source terms for both axial and polar perturbations and subsequently compute the quasinormal modes (QNMs) through numerical methods. For the Bardeen de Sitter black hole, we employ the 6th-order WKB approach. The numerical results reveal that the isospectrality is broken in this case. Conversely, the QNM frequencies are calculated using the HH method for the Bardeen Anti-de Sitter black hole.

A preliminary study on linear perturbation for a non-minimal derivative coupling scalar-tensor theory

The Cisterna-Delsate-Rinaldi (CDR) model is a variant of scalar-tensor theory that modify gravity by including a term of non-minimal derivative coupling. This model gives interesting aspects in the properties of compact objects, specifically neutron stars. By adjusting one of its parameters, the maximum possible mass of neutron stars can be increased. The authors of the model had also did a perturbation analysis using odd-parity perturbation and following that they also did analysis on the slowly-rotating neutron stars. In this paper, we report our ongoing research on the linear perturbation for the Cisterna model to see its dynamical properties. More precisely, we work on the polar perturbation that affected both the metric and the scalar field, which is different from the axial perturbation used in the slow rotation case. We use higher-dimensional spacetimes to see if the obtained equations will be dimensionally dependent. To simplify calculations for this metric form, we use tetrad method. Currently, we have not succeeded in obtaining the equations of motions in the form of Regge-Wheeler-Zerilli wave equation. The reason is the metric functions cannot be easily decoupled and we find no second derivatives with respect to both time t and radius r in the equations of motion. Only the scalar field can give a wave equation. Further investigation is undergoing.

Polarization Method-Based Research on Magnetic Field Data Associated with Earthquakes in Northeast Asia Recorded by the China Seismo-Electromagnetic Satellite

Previous earthquake polarization (as the ratio of vertical and horizontal components) studies using geomagnetic data were all performed with ground data. The advantage of satellite data is that it is not limited by geography. Therefore, in this work, we tried to select 12 typical earthquakes in Northeast Asia with Ms > 5.0 and an epicenter depth ≤ 40 km within the longitude 105° E–145° E and latitude 38° N–58° N ranges from December 2018 to January 2023 for analysis by using the satellite data of the high-precision magnetometer (HPM) payload onboard the China Seismo-Electromagnetic Satellite (CSES) for the first time in a quiet magnetic environment. The geomagnetic three-component vector data were investigated, and the minimum study period was divided into 10 s intervals. Fourier transform was performed to obtain 0.01–0.2 Hz geomagnetic three-component dynamic spectra, and the time series of the polarization (as the ratio of vertical and horizontal components) data was then obtained. The average value of the polarization data over four years was used to obtain the time series of the polarization perturbation amplitude, after which joint research was conducted. The results showed that (1) earthquakes with larger magnitudes are more likely to exhibit anomaly perturbations recorded by satellites; (2) among all earthquakes with anomalies, the horizontal east–west component perturbation is the largest, the vertical component perturbation is the smallest, and the east–west component may be the dominant component in seismic anomaly observations; (3) the applicability of the polarization method to space-based earthquake-related data is limited; (4) the perturbation amplitude of polarization data can be used as a reference for extracting seismic anomalies; and (5) ion velocity Vx data from the plasma analyzer package (PAP) can be considered to approximately verify the physical mechanism of the anomaly perturbation of the horizontal component in the ionospheric magnetic field, and the two kinds of data (PAP and HPM) can be combined in seismic prediction research.

Simple and Fast Polarization Tracking Algorithm for Continuous-Variable Quantum Key Distribution System Using Orthogonal Pilot Tone

To reduce the influence of random channel polarization variation, especially fast polarization perturbation, for continuous-variable quantum key distribution (CV-QKD) systems, a simple and fast polarization tracking algorithm is proposed and experimentally demonstrated. The algorithm is implemented by an orthogonal pilot tone scheme, one of the pilot tones is used for estimating the polarization rotation angle, and the other one is used for compensating the polarization perturbation introduced phase noise. Meanwhile, residual effects are compensated precisely with the help of a real-valued FIR filter. In this case, the excess noise introduced by polarization perturbation is effectively suppressed. Experimental results show that the polarization scrambling rate ≥12.57 krad/s can be tracked by using the proposed algorithm, and a good estimated parameters performance is achieved. Compared to conventional polarization tracking algorithms such as the constant modulus algorithm (CMA), experimental results show that the polarization tracking capability of the proposed algorithm is significantly improved. Furthermore, much faster polarization tracking performance is evaluated by digital simulations, and the simulation results show that about 188.50 Mrad/s can be tracked by the proposed algorithm. Thus, our method provides effective technology for the practical application of fiber-based CV-QKD.

Physical layer encryption for coherent PDM system based on polarization perturbations using a digital optical polarization scrambler.

In this paper, a security enhanced physical layer encryption scheme is proposed for coherent optical polarization division multiplexing (PDM) systems. The concept of a digital optical polarization scrambler (DOPS) is introduced to apply high speed rotation of state of polarization (RSOP) to the transmitted signal, which enables encryption based on polarization perturbations and offers superior flexibility in polarization management. By utilizing different combinations of digital polarization device matrices and adjusting their key parameters, four encryption modes are designed. The proposed encryption scheme is successfully implemented in a PDM-QPSK system at the data rate of 32 Gbps. Experimental results demonstrate that authorized users can successfully decrypt the received signal, while the eavesdroppers cannot derive useful information with a bit error rate (BER) at approximately 0.5. To enhance system security, a 5-D chaotic system is introduced with superior properties of high sensitivity to initial values and improved uniform distribution, which guarantees the large entropy and further the system's security. This scheme can effectively prevent against brute attacks with the expanded key space of 1060.

Polar gravitational waves in f(R, T ϕ ) framework

This work analyzes the propagation of polar gravitational waves for flat FRW cosmic background and in view of f(R, T ϕ ) theory. In what follows, we opt for the Regge-Wheeler polar perturbation scheme in flat geometry of background spacetime and corresponding scalar, field source is also perturbed. The two sets of field equations for flat and perturbed geometry are constructed and furthermore used to evaluate perturbation parameters. The obtained expressions suggest that polar fluctuations affect both geometry and scalar field. The radial and temporal parts of perturbation parameters χ and σ are plotted explicitly while the behavior of ψ is observed via a numerical solution plotted as a 3D graph. The change in these fluctuations for different values of model parameter λ is noticed through these plots.

Polar Perturbations in Functional Oxide Heterostructures

AbstractGrowth and characterization of metal‐oxide thin films foster successful development of oxide‐material‐integrated thin‐film devices represented by metal‐oxide‐semiconductor field‐effect transistors (MOSFET), drawing enormous technological and scientific interest for several decades. In recent years, functional oxide heterostructures have demonstrated remarkable achievements in modern technologies and provided deeper insights into condensed‐matter physics and materials science owing to their versatile tunability and selective amplification of the functionalities. One of the most critical aspects of their physical properties is the polar perturbation stemming from the ionic framework of an oxide. By engineering and exploiting the structural, electrical, magnetic, and optical characteristics through various routes, numerous perceptive studies have clearly shown how polar perturbations advance functionalities or drive exotic physical phenomena in complex oxide heterostructures. In this review, both intrinsic (engraved by thin‐film heteroepitaxy) and extrinsic (reversibly controllable defect‐mediated disorder and polar adsorbates) elements of polar perturbations, highlighting their abilities for the development of highly tunable functional properties are summarized. Scientifically, the recent approaches of polar perturbations render one to consolidate a prospect of atomic‐level manipulation of polar order in epitaxial oxide thin films. Technologically, this review also offers useful guidelines for rational design to heterogeneously integrated oxide‐based multi‐functional devices with high performances.

Polar modes and isospectrality of Ellis-Bronnikov wormholes

We consider polar perturbations of static Ellis-Bronnikov wormholes and derive the coupled set of perturbation equations for the gravitational and the scalar field. For massless wormholes the perturbations decouple, and we obtain two identical master equations for the scalar and gravitational modes, which moreover agree with the master equation for the axial modes. Consequently there is isospectrality with threefold degenerate modes. For a finite mass of the background wormhole solutions, the equations are coupled. We then obtain two distinct branches of polar quasinormal modes for a given multipole number l, associated with the presence of the two types of fields. We calculate the quasi-normal mode frequencies and decay rates for the branches with l=2, 3 and 4. For a given l the real frequencies of the two branchesget the closer, the higher the multipole number gets.

Light-driven motion of charged domain walls in isolated ferroelectrics

Light-induced ferroelectric domain wall motion turns out to be a promising phenomenon to develop new photocontrolled devices. However, the physical origin of this light-matter coupling when material is irradiated with visible light remains unclear. Here, a phenomenological model predicting the motion of charged domain walls (CDWs) is developed. The photoinduced electronic reconstruction mechanism is proposed as the primary absorption mechanism, leading to a linear dependence for the polarization perturbation with the light intensity. Domain wall motion is then driven by the energetic difference between domains in a CDW array, such that the macroscopic polarization can be easily tuned.

Gravitational waves in f(R, T)-rainbow gravity: even modes and the Huygens principle

In the context of f(R, T)-gravity, propagation of gravitational waves (GWs) for even (or polar) modes is explored by using the Regge-Wheeler gauge in the conformally flat Friedman-Lemaitre-Robertson-Walker type rainbow (CFR) universe. Writing the perturbed field equations for the polar GWs in the CFR spacetime, we first acquire a second-order differential equation for one of the unknown perturbation factors and then get all other unknown perturbation functions. Withal, we reach a conclusion that both the four-velocity vector components except the third one and the corresponding matter distribution are affected by the polar perturbation. Furthermore, the effect of rainbow functions, which can change the geometry of space-time, on the polar GWs is also analyzed graphically. We achieve that the shape (wavelength and amplitude) of polar GWs is dramatically impressed by the alteration of rainbow functions. Lastly, we investigate whether the polar GWs satisfy the Huygens principle.

Asymmetric vortex dynamics in two-dimensional Bose–Einstein condensate with harmonic trap potential

Based on the two-dimensional Gross–Pitaevskii equation model, we investigated the asymmetric vortex evolution of two-dimensional Bose–Einstein condensates in a harmonic potential trap with polar direction perturbation. This corresponds to the generation of an asymmetric vortex evolution mode under initial vortex light manipulation together with polar direction perturbation. Unlike most of the prior work on this topic that uses a pure numerical method for the system under study, we use an exact analytical method rather than numerical simulation to investigate the key features of the system evolution dynamics in this study. Based on the variational method, and for different system parameter settings including the strength of the harmonic oscillator potential and the nonlinear interaction, we derived two evolution modes, namely, the periodic evolution oscillation mode and the monotonic decay mode, and pictorially demonstrated the evolution patterns of the system. In addition, we investigated the scenario when the system is in the rotating state, which corresponds to the action of the quadratic centrifugal potential. Notably, we also identified the damping effects for the two modes with increasing angular velocity, whose upper limit value corresponds to the constant vortex pattern of the system. Our theoretical results can be used to guide the experimental investigation of asymmetric vortex evolution in two-dimensional Bose–Einstein condensates.

Imprints of dark matter on gravitational ringing of supermassive black holes

Gravitational waves emitted from the gravitational ringing of supermassive black holes are important targets to test general relativity and probe the matter environment surrounding such black holes. The main components of the ringing waveform are black hole quasi-normal modes. In this paper, we study the effects of the dark matter halos with three different density profiles on the gravitational polar (even-parity) perturbations of a supermassive black hole. For this purpose, we first consider modified Schwarzschild spacetime with three different dark matter profiles and derive the equation of motion of the polar perturbations of the supermassive black hole. It is shown that by ignoring the dark matter perturbations, a Zerilli-like master equation with a modified potential for the polar perturbation can be obtained explicitly. Then we calculate the complex frequencies of the quasi-normal modes of the supermassive black hole in the dark matter halos. The corresponding gravitational wave spectra with the effects of the dark matter halos and their detectability have also been discussed.

Linear perturbations of Einstein-Gauss-Bonnet black holes

We study linear perturbations about non rotating black hole solutions in scalar-tensor theories, more specifically Horndeski theories. We consider two particular theories that admit known hairy black hole solutions. The first one, Einstein-scalar-Gauss-Bonnet theory, contains a Gauss-Bonnet term coupled to a scalar field, and its black hole solution is given as a perturbative expansion in a small parameter that measures the deviation from general relativity. The second one, known as 4-dimensional-Einstein-Gauss-Bonnet theory, can be seen as a compactification of higher-dimensional Lovelock theories and admits an exact black hole solution. We study both axial and polar perturbations about these solutions and write their equations of motion as a first-order (radial) system of differential equations, which enables us to study the asymptotic behaviours of the perturbations at infinity and at the horizon following an algorithm we developed recently. For the axial perturbations, we also obtain effective Schrödinger-like equations with explicit expressions for the potentials and the propagation speeds. We see that while the Einstein-scalar-Gauss-Bonnet solution has well-behaved perturbations, the solution of the 4-dimensional-Einstein-Gauss-Bonnet theory exhibits unusual asymptotic behaviour of its perturbations near its horizon and at infinity, which makes the definition of ingoing and outgoing modes impossible. This indicates that the dynamics of these perturbations strongly differs from the general relativity case and seems pathological.