Polarization Correlation Research Articles

Hydrodynamic helicity polarization in relativistic heavy ion collisions

We study helicity polarization through the $(3+1)$-dimensional relativistic viscous hydrodynamic models at $\sqrt{{s}_{NN}}=200$ GeV $\text{Au}+\text{Au}$ collisions. Similar to the local spin polarization, we consider the helicity polarization beyond global equilibrium and investigate the contributions induced by thermal vorticity, shear viscous tensor, and the fluid acceleration. We find that the local helicity polarization induced by thermal vorticity dominates over other contributions. It also implies that, in low-energy collisions, the fluid vorticity as part of thermal vorticity may play the crucial role in the total helicity polarization. Such a finding could be useful for probing the local strength of vorticity in rotational quark gluon plasmas by measuring helicity polarization. Our simulation confirms the strict space reversal symmetry, whereas we also compare our numerical results with approximated relations derived from ideal Bjorken flow. Our studies also provide a baseline for the future investigation on local parity violation through the correlations of helicity polarization.

Quantum entanglement and axion physics

The axion particle is the outcome of the proposed Peccei–Quinn mechanism for solving the strong CP problem. Axion is also a popular dark matter candidate. Thus, there is an increased interest in establishing its existence. Axions couple to two photons and most experiments search for the transition of an axion into a photon, in the presence of a magnetic field. In our study, we examine the coupling of the axion into a pair of entangled photons. The presence of a magnetic field changes the polarization correlations of the entangled photons, thus offering an unambiguous signature for axion existence.

Gain-dependent Purcell enhancement, breakdown of Einstein's relations, and superradiance in nanolasers

Light emitters in a single-mode nanolaser interact with the same cavity field, that gives rise to polarization correlations which transform the cavity mode. Usually these correlations are ignored, however, collective phenomena can lead to the distinct sub- and superradiance, whose fully quantum description is challenging. Here, we develop a simple yet rigorous picture of radiative transitions in single-mode nanolasers that accounts for polarization correlations. We show that the collective behavior of emitters modifies the photonic density of states leading to gain-dependent Purcell enhancement of spontaneous emission. Moreover, the stimulated emission rate is dependent on both the photon number and the laser lineshape. As the laser line narrows, stimulated emission becomes stronger than predicted by Einstein's relations and the nanolaser reaches the threshold earlier. Finally, we provide concise, ready-to-use expressions for spontaneous and stimulated emission rates seamlessly describing both conventional and superradiant nanolasers.

Multi-polarization fusion generative adversarial networks for clear underwater imaging

Polarization imaging has become a promising way for clear underwater vision, which depends on the difference of polarization characteristics between backscattered light and target signal. In this paper, to achieve clear underwater color polarization imaging, we propose a learning-based method that uses multi-polarization fusion adversarial generative networks to learn the relationship between polarization information and object radiance. The proposed method is especially designed for multiple polarimetric images, which can effectively extract the polarization correlations of images with different polarization states. Moreover, to train the proposed network, we build, for the first time to our knowledge, a color polarization image dataset from natural underwater environments through passive polarization imaging. The experimental results in laboratory and natural underwater environments show that it is feasible to introduce polarization information into learning-based image recovery, and deep learning technology is conducive to the extraction of polarization information. Comparing with other methods, the proposed method can effectively remove the backscattered light and recover the object radiance.

Giant strain with ultra-low hysteresis by tailoring relaxor temperature and PNRs dynamic in BNT-based lead-free piezoelectric ceramics

State-of-the-art ferroelectric materials with large field-induced strain together with low hysteresis are required in high precision or positioning devices. However, the high electro-strain is always suffered from a large strain hysteresis, severely restricting its practical application. In this study, the relaxor temperature (Tf) of BNT-6BT near the morphotropic phase boundary with initially high polarization was adjusted to near room temperature by adding Sr0.7La0.2TiO3. The room temperature relaxation properties feature with the high dynamic polar nanoregions with moderate polar spatial correlations, which paired the high strain (0.325%) and ultra-low hysteresis (8.02%). This actuation strain is superior to those of previously reported lead-free piezoelectric materials. Meanwhile, the strain responses also displayed outstanding temperature and frequency stability from 30°C to 150 °C and 1 Hz–25 Hz, respectively, indicating its practical application potential. The results will provide new insight into the design of high-performance BNT-based ceramics for use in actuators.

Imaging myocardial perfusion with [99mTc] Tc-HMPAO: Fiction or reality? – Preliminary results

Introduction and objectives: [ 99mTc] Tc-HMPAO, developed for brain imaging, is taken up by the heart, but never used to study it. We aimed to compare cardiac images with [99mTc] Tc-HMPAO and [ 99mTc] Tc-Tetrofosmin, using imaging techniques. Materials and methods: Cardiac gated SPECTs with [99mTc] Tc-HMPAO were compared with myocardial perfusion scintigraphies (MPS) with [99mTc] Tc-Tetrofosmin in three inpatients, from the vascular surgery ward. We developed algorithms in MATLAB R2016 to compare the [99mTc] Tc-Tetrofosmin/ [99mTc] Tc-HMPAO images. Pixel-wise correlations for slices, reversibility, and polar maps were obtained. Results: Correlations of both radiotracers’ myocardial images were as high as 0.93. Polar maps correlations were 0.93-0.95 (for both stress and rest) and 0.62-0.90 (reversibility). One of the patients (smoker) had significant lung [99mTc] Tc-HMPAO uptake. Conclusions: Cardiac SPECT with [99mTc] Tc-HMPAO might be a screening method for myocardial ischemia in non-smoking patients with epilepsy suspected of having heart changes, and who need to perform a brain perfusion SPECT. Keywords: myocardial perfusion scintigraphy; epilepsy; HMPAO; myocardial SPECT.

Analysis and experimental demonstration of propagation features of radially polarized specific non-uniformly correlated beams.

With the development of the unified theory of coherence and polarization, the novel physical properties generated by different correlation structures of vector partially coherent beams (PCBs) have attracted much attention. Recently, a new class of structured beams have been proposed [Opt. Lett.45, 3824 (2020)10.1364/OL.397316], called vector specific non-uniformly correlated beams. These beams combine non-uniform polarization and non-uniform correlation, and they exhibit propagation features not seen in conventional vector PCBs. In this Letter, we continue the analysis of the previous work, taking radially polarized Hermite non-uniformly correlated (RPHNUC) beams as an example, and focus on the physical interpretation of the peculiar propagation features of such beams. We verify the predicted behavior of RPHNUC beams through experiment.

Steady-state cooperative effects in a continuously generating superradiant Raman laser

A generalized model of the continuously generating superradiant Raman laser is considered. The model includes competing individual and cooperative atomic processes arising from the interaction of atoms with external light fields. We show that proper selection of the model parameters leads to cooperative effects in the atomic active laser medium. We calculate the steady state values of the atomic polarization and two-atom correlations. Using the quantum regression theorem, we determine the spectral characteristics of the collectively emitted light. We use cumulant expansion to estimate the higher-order correlations between atoms. Keywords: superradiant laser, correlated states of atoms, cooperative effects, cumulant expansion.

Кооперативные эффекты при стационарной генерации сверхизлучательного рамановского лазера

A generalized model of the continuously generating superradiant Raman laser is considered. The model includes competing individual and cooperative atomic processes arising from the interaction of atoms with external light fields. We show that proper selection of the model parameters leads to cooperative effects in the atomic active laser medium. We calculate the steady state values ​​of the atomic polarization and two-atoms correlations. Using the quantum regression theorem, we determine the spectral characteristics of the collectively emitted light. We use cumulant expansion to estimate the higher-order correlations between atoms.

Vacuum Dependent Bell Local Hidden Variable Models and Generalized C.H.S.H. Inequalities

We extend a previous model of the author which generalizes Bell local hidden variable models to the case of entangled photon pairs assuming that the standard Bell correlation functions depend on a hidden vacuum index. We deduce a generalization of Bell theorem assuming that classical observables are not dichotomic and that photon pair emission and detection is not a stationary stochastic process. We derive a photon imperfect polarization correlation functions due to rotational invariance breaking induced by hidden vacuum spin currents. We implement formally this approach deducing a generalization of C.H.S.H. inequalities which asymptotically converges to the standard one and which might be competitive with standard quantum mechanics predictions. We suggest to test this inequalities conceiving new E.P.R.-Bell like tests with time dependent detector efficiency and photon flux. Finally, we suggest to apply these generalized inequalities to the correlation functions of entangled classical spinning waves realized recently with metamaterials.

Broadband-laser-diode pumped periodically poled potassium titanyl phosphate-Sagnac polarization-entangled photon source

We experimentally demonstrate a polarization-entangled photon source at 810 nm using a type-II phase-matched periodically poled potassium titanyl phosphate (PPKTP) crystal pumped by a low-cost, broadband laser diode with a central wavelength of 405 nm and a typical bandwidth of 0.53 nm. The PPKTP crystal is placed in a Sagnac loop to realize the compact size and high stability. The downconverted biphotons, the signal and the idler, have typical bandwidths of 5.57 and 7.32 nm. We prepare two Bell states | Ψ + ⟩ and | Ψ − ⟩ with the fidelities of 0.948 ± 0.004 and 0.963 ± 0.002 . In the polarization correlation measurement, the visibilities are all higher than 96.2%, and in the Bell inequality test, the S value can achieve 2.78 ± 0.01 . This high-quality and low-cost entangled photon source may have many practical applications in quantum information processing.

Digital toolbox for vector field characterization

Abstract Vectorial structured light fields have displayed properties advantageous in many disciplines ranging from communications, microscopy and metrology to laser cutting and characterizing quantum channels. The generation of these fields has been made convenient through the implementation of nanophotonic metasurfaces amongst other static and digital techniques. Consequently, the detection and characterisation of these fields is of equal importance. Most existing techniques involve using separate polarization optics and correlation filters to perform the projective measurements – or are only able to perform such measurements on a subset of possible vector states. We present a compact, fully automated measurement technique based on a digital micro-mirror device (DMD), which facilitates the complete, local and global, characterisation of the spatial mode and polarization degrees-of-freedom (DOFs) for arbitrary vectorial fields. We demonstrate our approach through the identification of relevant hybrid-order Poincaré spheres, the reconstruction of state vectors on these spheres, as well as the recovery of the non-separability and states-of-polarization for a variety of vector beams.

FPGA Utilized to Control the Coincidence Logic of Quantum Entangled Pairs (QEP)

Control of quantum signals is very robust design technique and very important in quantum signal processing (QSP). It is not easy in experimentation platforms. Field Programmable Gate Array (FPGA) is using to control very various range of devices in quantum fields through PCs. FPGA needs to run modules of components to communicate and interfacing with the PC, through decode perform commands to direct control of digital hardware’s. If programmer has a real-time control of the FPGA via USB, it can be possible to evaluate design parameters changes in real-time, without reprogramming the FPGA. That makes the proposed design platforms easier for researchers. This paper discusses experiment of control quantum signals by FPGA to control coincidence logic for Quantum Entangled Pair (QEP), that able to measure polarization correlations relationships between photons of the QEP. This FPGA helps to determine detection events at different detectors which can be attributed to a single photon pair. Also to determine the correlation time between two different beams frequencies is extremely accurate according to the delay between the beams, which is very short.

Origin of Relaxor Behavior in Barium‐Titanate‐Based Lead‐Free Perovskites

AbstractIt is well known that disordered relaxor ferroelectrics exhibit local polar correlations. The origin of localized fields that disrupt long‐range polar order for different substitution types, however, is unclear. Currently, it is known that substituents of the same valence as Ti4+ at the B‐site of barium titanate lattice produce random disruption of TiOTi chains that induces relaxor behavior. On the other hand, investigating lattice disruption and relaxor behavior resulting from substituents of different valence at the B‐site is more complex due to the simultaneous occurrence of charge imbalances and displacements of the substituent cation. The existence of an effective charge mediated mechanism for relaxor behavior appearing at low (<10%) substituent contents in heterovalent modified barium titanate ceramics is presented in this work. These results will add credits to the current understanding of relaxor behavior in chemically modified ferroelectric materials and also acknowledge the critical role of defects (such as cation vacancies) in lattice disruption, paving the way for chemistry‐based materials design in the field of dielectric and energy storage applications.

Helicity polarization in relativistic heavy ion collisions

We discuss the helicity polarization which can be locally induced from both vorticity and helicity charge in non-central heavy ion collisions. Helicity charge redistribution can be generated in viscous fluid and contributes to azimuthal asymmetry of the polarization along global angular momentum or beam momentum. We also discuss on detecting the initial net helicity charge from topological charge fluctuation or initial color longitudinal field by the helicity polarization correlation of two hyperons and the helicity alignment of vector mesons in central heavy ion collisions.

Polarization correlation in the superfluorescent decay process.

We investigated the polarization properties of superfluorescence (SF) emitted from dense cesium atomic vapor in a cell. The atoms were excited from the 6S ground to the 8P state using a femtosecond laser pulse. The SF fields generated on the cascaded decay, 8P→8S→7P, mediated the nonlinear optical process. We observed 4.2-µm and 456-nm forward directional emissions generated on the 8S→7P and 7P→6S transitions, respectively. The polarizations of the two fields were correlated in each laser shot, and their directions fluctuated from shot to shot, reflecting the noise that initiated the 4.2-µm emission.

A note on the parity of Iπ = 5− state in 126,128Xe

Excited states in [Formula: see text]Xe were populated via [Formula: see text]Sn(9Be, 5n[Formula: see text]) and [Formula: see text]Sn(9Be, 3n[Formula: see text]) fusion-evaporation reactions, respectively, at a beam energy of 48[Formula: see text]MeV. The electromagnetic (electric or magnetic) nature and multipolarity of some inter-band [Formula: see text] rays are determined from linear polarization and angular correlation measurements. Re-measured/newly measured linear polarization asymmetry helps to assign the parity of 2302-keV ([Formula: see text]Xe)/2228-keV ([Formula: see text]Xe) [Formula: see text] state unequivocally.

Modern problems and prospects for the development of magnetotelluric monitoring on the territory of the Bishkek geodynamic test site

The high sensitivity of the electromagnetic parameters of the geological environment to the influence of geodynamic processes for the territory of the Bishkek geodynamic test site is shown. An assessment of the characteristics of the stress-strain state of the geological environment and the behavior of variations in electromagnetic parameters has been carried out in order to identify patterns in their relationship for seismically active regions of the Tien Shan. The promising objects for monitoring observations are identified and the results obtained are presented. The experimental results obtained indicate that the position of the regions of stable correlation (clusters) on the polar correlation diagrams is associated with the geoelectric structure of the observation point and corresponds to the orientation of the main tectonic elements in the vicinity of this point. A detailed geological and geophysical interpretation of geoelectric sections was carried out in order to separate modern active faults and weakened zones of the Earth’s crust, for example, the Kochkor basin. The relationship between the manifestation of geoelectric inhomogeneities and the spatial distribution of the epicenters of seismic events is revealed; it is shown that a significant part of earthquake epicenters is confined to structural inhomogeneities of the Earth’s crust; the depths of the geoelectric section, most sensitive to the influence of geodynamic processes, have been determined. The behavior of variations in the electrical conductivity of the earth‘s crust in a wide range of periods has been investigated according to the data of profile magnetotelluric soundings (MTS) at the Kentor geophysical monitoring minipolygon. Field experiments confirm the concept of the relationship between the stress-strain state of the medium and the change in apparent resistivity through the redistribution of saline solutions between fracture systems. The problems and trends in the development of magnetotelluric monitoring of modern geodynamic processes in the Northern Tien Shan are shown. To solve the tasks set, a methodology for conducting monitoring studies is proposed, which most fully takes into account the specific features of the deep structure and distribution of seismicity of the Bishkek geodynamic test site.

Symmetric Excitons in an (001)-Based InAs/GaAs Quantum Dot Near Si Dopant for Photon-Pair Entanglement

The sacrificed-QD-layer method can well control the indium deposition amount to grow InAs quantum dots (QDs) with isotropic geometry. Individual Si dopant above an (001)-based InAs QD proves a new method to build a local electric field to reduce fine structure splitting (FSS = X1−X2) and show D3h symmetric excitons. The lowest FSS obtained is 3.9 μeV with the lowest energy X state (LX) anticlockwise rotate from [1–10] (i.e., zero FSS will be crossed in a proper field). The lateral field projection induces a large eh separation and various FSS, LX, and emission intensity polarization. The lateral field along [1–10] breaks the X1–X2 wavefunction degeneracy for independent HH and VV cascade emissions with robust polarization correlation. With FSS ~4 μeV and T1 ~0.3 ns fastened in a distributed Bragg reflector cavity, polarization-resolved XX–X cross-correlations show fidelity ~0.55 to a maximal entangled state |HH> + |VV>. A higher fidelity and zero FSS will be obtained in the hybrid QD structure with a junction field integrated to tune the FSS and a sub-bandgap excitation to avoid influences from electrons in the barrier.

Two-point polarization correlations of random paraxial and nonparaxial electromagnetic fields

We investigate the two-point polarization correlation properties of random, statistically stationary, two-dimensional (2D) and three-dimensional (3D) electromagnetic fields. To this end two specific mutual polarization correlation functions are introduced, one based on a geometric approach using the Poincar\'e vectors and the other on the energy distribution employing the Jones vectors. Both approaches provide equivalent information about the space-time polarization correlations and enable one to associate with the field a polarization length over which the equal-time polarization states remain essentially unchanged. For fields obeying Gaussian statistics, the polarization correlation functions take on simple forms in terms of measurable quantities representing electromagnetic coherence. The formalism is demonstrated with two examples: blackbody radiation inside a cavity and in the far zone of a cavity wall aperture.