Composite Vortices Research Articles

Interference of high-order perfect optical vortex beams

We investigate the interference of high-order perfect optical vortex (POV) beams with different topological charges. Through numerical simulations, we reveal a remarkable phenomenon: keeping the beam width, and beam radius fixed while changing the topological charge, the splitting of the composite POV beam into two distinct individual perfect vortices occurs exactly at the same inter-axial separation. The observed interference pattern exhibits pronounced sensitivity to factors such as axial separation, phase shift, beam radius, and topological charges of the constituent beams. Notably, our findings are contrasted with the interference of high-order Laguerre-Gauss (LG) beams, highlighting that the splitting of composite vortices into their individual components is more rapid in the case of LG beams. We also investigate the evolution of the interference pattern for both POV, and LG beams along the propagation direction in free-space. Our research provides significant insights into the distinct interference properties of high-order POV beams, presenting potential applications in the fields of optical manipulation and communication systems.

Dissociation of composite Abrikosov vortices in two-band superconductors in a strong rf field

In several theoretical works, it was argued that under certain conditions Abrikosov vortices in multiband superconductors can split and exist in the form of fractional vortices, formed separately in superfluid condensates of different electron bands. Such vortices possess a fractional flux quantum, and these fractional vortices attract each other, trying to join into a composite vortex with the whole flux quantum ϕ0=h/2e. In the present work, we solve numerically the nonlinear dynamic equation for the composite vortex, settled in the pinning potential well of the columnar defect within a two-band superconductor, and exerted the rf Lorentz force action. We demonstrate that at high enough rf current amplitudes such composite Abrikosov vortices will dissociate into fractional ones and escape from the pinning potential well. The sequence of these events depends on the character of the pinning potential well, e.g., the radius of the pinning potential well. The possible manifestation of such kind transitions in rf electrodynamic characteristics, such as a complex rf resistivity and harmonics generation is calculated.

Topological charge parallel measurement method for optical vortices based on computer-generated holography

The generation, propagation, and application of optical vortices have been major researched topics in recent years. In this study, a parallel measurement approach is presented to analyze the topological charge of single and composite optical vortices with the help of a spatial light modulator. The topological charges of single and composite optical vortices are measured by observing the Gaussian point position of the diffracted field, which solves the difficult problem of measuring composite optical vortices and optical vortices with large topological charges. The presented method is feasible and has strong expansibility. More composite optical vortices can be measured easily by using different computer-generated holograms. When an optical vortex is measured correctly, it can present a Gaussian point, which retains the characteristics of the optical vortex. Therefore, this point will be important in optical vortex communication.

Dynamics of fractional vortices in two-band superconductors

The entry of fractional vortices and their subsequent dynamics inside a two-band superconductor is explored based on the numerical solutions of time-dependent Ginzburg–Landau (TDGL) equations. We consider the case when superfluid electron condensates from two zones are characterized by quite different parameters, such as coherence lengths ξi, and London penetration depths λi, which in turn leads to the different critical magnetic fields Hc,iand fractional flux quanta ϕivalues for the superconducting state in these two zones. Numerical solutions of TDGL equations in increasing external magnetic field followed by mathematical modeling of magnetic flux penetration were performed for this case by finite element method. We have explored the time evolution for the fractional vortices penetration process and their subsequent dynamics inside the specimens for two geometries: the circular disk, and the circular disk with a triangular cutout. Obtained results indicate that magnetic flux penetrates inside the specimen in the form of fractional vortices when they can overcome the edge barrier, which may be different for these two vortex types. Therefore, in increasing external magnetic field first penetrate vortices with a lower barrier height (i.e., lower Hc,i) while the other type of fractional vortices start their penetration at higher external field value. Another mechanism for the formation of fractional vortices during their entrance in a two-band superconductor is related to the difference in their flux values and viscosity coefficients which determine the rate of vortex proliferation inside the sample. Within the specimen, fractional vortices move in order to arrange. Vortices of different types attract to each other and try to stick together thus forming composite vortices with the whole flux quantum value ϕ0 = h/2e.

Analytical description of sub-diffraction dark spot

Optical vortices have developed rapidly in recent times owing to their theoretical significance and attractive potential applications in extensive realms. Composite optical vortices using two or more coherently superimposed vortex beams have been widely researched. Here, we propose a novel beam pattern incoherently generated by laser beams with two distinct wavelengths. We apply this beam pattern in fluorescence super-resolution imaging based on the stimulated emission effect, and find that the size of the resulting dark spot in the focal plane lies below the diffraction limit. Crucial factors affecting the sub-diffraction dark spot, such as beam intensities, spatial displacement, pulse width, polarization, and aberration, are studied in detail. We believe that the results are beneficial for experimental studies and will serve as useful references in other circumstances where they may be utilized.

An initialisation scheme for tropical cyclones in the South China Sea

AbstractWe propose an initialisation scheme for weak tropical cyclones (TCs) in the South China Sea (SCS) by combining composite and analysis vortices to improve forecasts of weak TCs in the region. The composite vortex is obtained from good samples of analyses of TCs in the SCS, and the analysis vortex is obtained from either European Centre for Medium‐Range Weather Forecasts (ECMWF) analysis data or an operational assimilation system. The new scheme has been applied to 57 cases of weak TCs, and the effect on the forecasting of four tropical storms has been studied in detail. It can be concluded that the proposed scheme can reduce track errors and intensity errors of weak TCs, compared with the control experiment. The possible reasons for these results are investigated in a case study for Linfa. Results of batch experiments show that the new method significantly improves TC track forecasting of tropical storms, severe tropical storms and typhoons, and demonstrates significant advantages in forecasting intensity of tropical storms, compared with the control experiment. It also performs better in predicting intensity of TCs in the SCS compared with ECMWF Atmospheric Model high resolution.

Composite particle construction of the Fibonacci fractional quantum Hall state

The Fibonacci topological order is the simplest platform for a universal topological quantum computer, consisting of a single type of non-Abelian anyon, $\tau$, with fusion rule $\tau\times\tau=1+\tau$. While it has been proposed that the anyon spectrum of the $\nu=12/5$ fractional quantum Hall state includes a Fibonacci sector, a dynamical picture of how a pure Fibonacci state may emerge in a quantum Hall system has been lacking. Here we use recently proposed non-Abelian dualities to construct a Fibonacci state of bosons at filling $\nu=2$ starting from a trilayer of integer quantum Hall states. Our parent theory consists of bosonic "composite vortices" coupled to fluctuating $U(2)$ gauge fields, which is related to the standard theory of Laughlin quasiparticles by duality. The Fibonacci state is obtained by clustering the composite vortices between the layers, along with flux attachment, a procedure reminiscent of the clustering picture of the Read-Rezayi states. We further use this framework to motivate a wave function for the Fibonacci fractional quantum Hall state.

Dual-Circularly Polarized Topological Patch Antenna With Pattern Diversity

Recently, the topological properties of composite vortices, i.e., the superposition between vortex modes of a different order, have proven effective in manipulating the radiation properties of patch antennas and making them suitable for new operative scenarios. In this paper, we exploit these properties to design a multi-antenna system exhibiting both pattern- and polarization-diversity. The low mutual coupling and the possibility to steer two orthogonal polarized fields in different directions, make this radiating element an optimal candidate for antenna diversity or MIMO systems and, thus, for increasing signal quality or channel capacity of a communication system.

Manipulation of Orbital-Angular-Momentum Spectrum Using Pinhole Plates

The orbital angular momentum (OAM) spectrum of light, produced by superposition of vortex beams, is important for applications in optical metrology and classical and quantum communication. Nonetheless, manipulation of the OAM spectrum remains challenging. The authors propose a technique for control of the OAM spectrum using structured pinhole plates, which can generate both wide and narrow OAM spectra. In particular, a rather simple pinhole plate can produce an interesting series of discrete, equally spaced OAM modes: an OAM comb, akin to a frequency comb. This approach could be extended beyond photonics to work with rf, acoustic, electron, or neutron composite vortices.

Splitting of singly and doubly quantized composite vortices in two-component Bose-Einstein condensates

We study numerically the dynamical instabilities and splitting of singly and doubly quantized composite vortices in two-component Bose-Einstein condensates harmonically confined to quasi two dimensions. In this system, the vortices become pointlike composite defects that can be classified in terms of an integer pair $(\kappa_1,\kappa_2)$ of phase winding numbers. Our simulations based on zero-temperature mean-field theory reveal several vortex splitting behaviors that stem from the multicomponent nature of the system and do not have direct counterparts in single-component condensates. By calculating the Bogoliubov excitations of stationary axisymmetric composite vortices, we find nonreal excitation frequencies (dynamical instabilities) for the singly quantized $(1,1)$ and $(1,-1)$ vortices and for all variants of doubly quantized vortices, which we define by the condition $\max_{j=1,2}|\kappa_j|=2$. While the short-time predictions of the linear Bogoliubov analysis are confirmed by direct time integration of the Gross-Pitaevskii equations of motion, the time integration also reveals intricate long-time decay behavior not captured by the linearized dynamics. First, the $(1,\pm 1)$ vortex is found to be unstable against splitting into a $(1,0)$ vortex and a $(0,\pm 1)$ vortex. Second, the $(2,1)$ vortex exhibits a two-step decay process in which its initial splitting into a $(2,0)$ vortex and a $(0,1)$ vortex is followed by the off-axis splitting of the $(2,0)$ vortex into two $(1,0)$ vortices. Third, the $(2,-2)$ vortex is observed to split into a $(-1,1)$ vortex, three $(1,0)$ vortices, and three $(0,-1)$ vortices. Each of these splitting processes is the dominant decay mechanism of the respective stationary composite vortex for a wide range of intercomponent interaction strengths and relative populations of the two condensate components and should be amenable to experimental detection.

Transfer of optical vortices in coherently prepared media

We consider transfer of optical vortices between laser pulses carrying orbital angular momentum (OAM) in a cloud of cold atoms characterized by the $\Lambda$ configuration of the atom-light coupling. The atoms are initially prepared in a coherent superposition of the lower levels, creating a so-called phaseonium medium. If a single vortex beam initially acts on one transition of the $\Lambda$ scheme, an extra laser beam is subsequently generated with the same vorticity as that of the incident vortex beam. The absorption of the incident probe beam takes place mostly at the beginning of the atomic medium within the absorption length. The losses disappear as the probe beam propagates deeper into the medium where the atoms are transferred to their dark states. The method is extended to a tripod atom-light coupling scheme and a more general $n+1$-level scheme containing $n$ ground states and one excited state, allowing for creating of multiple twisted light beams. We also analyze generation of composite optical vortices in the $\Lambda$ scheme using a superposition of two initial vortex beams and study lossless propagation of such composite vortices.

Nonequilibrium interband phase textures induced by vortex splitting in two-band superconductors

We demonstrate that in a weak-coupled two-band superconducting slab the interaction between vortices penetrating the sample and its boundaries leads to the phenomenon of vortex splitting, which divides composite vortices and creates fractional ones. The interaction between vortices, attractive for different bands and repulsive for the same band, which is controlled by the electric current density flowing through the system, leads to an ordered alternating arrangement of the vortices. This arrangement creates nonequilibrium interband phase textures or domains with different signs of the Josephson energy of the interaction between the band condensates. Such phase textures have a significant effect on the dissipation caused by the vortex motion. In particular, in the phase-texture regime the onset of the dissipation is shifted to higher current densities.

Free-space optical communication based on hybrid optical mode array encoding

The generation, propagation and application of optical vortex have been hot research topics in recent years. Optical vortex carries orbital angular momentum (OAM) that potentially increases the capacity and the spectral efficiency of optical communication system as a new degree of freedom. The optical vortex can be used not only as information carrier for space-division multiplexing, but also for encoding/decoding. We present a novel free-space optical communication system based on hybrid optical mode array encoding/decoding. The array includes four modes that can easily be identified by image processing. The four modes are Gaussian beam, single optical vortex, and two different composite optical vortices. In this paper, the computer generated hologram (CGH) of the hybrid optical mode array is generated based on the object-oriented conjugate-symmetric extension Fourier holography. When the CGH is loaded onto the electronic addressing reflection-type spatial light modulator (SLM), a single light beam illuminates the SLM, and the desired hybrid optical mode array is generated. In the experiment, a m 32 pixel32 pixel Lena gray image is transferred. At the transmitter, the Lena gray image is scanned line by line. The gray value (0-255) of each pixel with 8-bit information is extracted from the image and converted into a 22 hybrid optical mode array, which is encoded into the CGH. Hence, the m 32 pixel32 pixel Lena gray image is corresponding to a sequence with 1024 CGHs. By switching the CGHs loaded onto the SLM, the Lena gray image is transmitted in the form of the hybrid optical mode array. At the receiver, each hybrid optical mode array is decoded to a pixel value. To distinguish different modes conveniently, two cross lines are set at the center of each mode. By counting the peaks of two intensity distribution lines, the modes can easily be identified. We demonstrate the image reproduction of Lena with zero bit error rate (BER). The experimental result shows the favorable performance of the free-space optical communication link based on hybrid optical mode array encoding/decoding. Compared to that of the traditional single-vortex encoding communication system, the information capacity of our system with 22 hybrid optical mode array increases by four times. In addition, the presented experimental system is feasible and has strong expansibility. The information capacity can increase by 16 times with a 44 hybrid optical mode array based on the same experimental setup. Therefore, the presented free-space optical communication system using hybrid optical mode array encoding/decoding has great significance for improving the capacity of free-space optical communication system.

Preparation of Poincaré beams with a same-path polarization/spatial-mode interferometer

We present a same-path polarization interferometer that uses two spatial light modulators to encode the most general type of Poincaré beam. We demonstrate this design by presenting new results on the encoding of symmetric C-point polarization singularities using spatial modes with high-order topological charges. We also present new results on composite C-points. These are cases where there are multiple C-points in a single beam obtained by combining two modes with composite optical vortices in orthogonal states of polarization. The measurements show good agreement with the simulations.

Dissociation Transition of a Composite Lattice of Magnetic Vortices in the Flux-Flow Regime of Two-Band Superconductors

In multiband superconductors, each superconducting condensate supports vortices with fractional quantum flux. In the ground state, vortices in different bands are spatially bounded together to form a composite vortex, carrying one quantum flux Φ(0). Here we predict dissociation of the composite vortices lattice in the flux flow state due to the disparity of the vortex viscosity and flux of the vortex in different bands. For a small driving current, composite vortices start to deform, but the constituting vortices in different bands move with the same velocity. For a large current, composite vortices dissociate and vortices in different bands move with different velocities. The dissociation transition shows up as an increase of flux flow resistivity. In the dissociated phase, Shapiro steps are developed when an ac current is superimposed with a dc current.

Composite vortices in two-component Bose-Einstein condensates

Motivated by the recent observation of composite vortices in two-gap superconductors, we investigate the occurrence and stability of composite vortices in a two-component Bose condensate. As a function of the inter-component interaction strength, the vortices in the two components of the Bose mixture can overlap and form a composite vortex object. However, when two such composite vortices approach each other, their mutual interaction may cause the composite object to dissociate in its component vortices. We derive the phase diagram for the stability of composite vortices as a function of the interaction strengths of the Bose condensates, based on a variational calculation. The effective forces between the component vortices of the composite object are also derived within this approach, and allow for an interpretation of the phase diagram.

Controlled interaction of the optical vortices generated by off-center spiral zone plates

We report a simple, cost-effective, and scalable diffractive optical element named off-center spiral zone plates (OSZPs) to generate composite optical vortices (OVs) and control their interactions. By adjusting the parameters of OSZPs, the interaction process and performance of OVs, including fluid-like rotation, annihilation of vortex anti-twins, and creation or destruction of vortex anti-twins are investigated. Besides, the rotation between the two vortices with opposite TCs is observed. Furthermore, it is revealed that the common OVs interaction is based on the process of creation and destruction of vortex anti-twins, which helps us to understand the dynamics of the underlying interactions of composite OVs.

Dynamic evolution of composite coherence vortices by superimpositions of partially coherent hyperbolic-sine-Gaussian vortex beams in non-Kolmogorov atmospheric turbulence

Some experiments show that the practical atmosphere deviates from ideal Kolmogorov model. In this paper, based on the extended Huygens-Fresnel principle and the non-Kolmogorov turbulence model proposed by Toselli et al., the analytical expression for the propagation of partially coherent hyperbolic-sine-Gaussian vortex beams through non-Kolmogorov atmospheric turbulence is derived and used to study the dynamic evolutions of composite coherence vortices formed by coherent and incoherent superpositions of two partially coherent hyperbolic-sine-Gaussian vortex beams in non-Kolmogorov atmospheric turbulence. It is shown that the evolution process of the average intensity of the superimposed beam depends on the general exponent of the non-Kolmogorov turbulence, the sign of the topological charge of the superimposed vortex beam in the source plane, and superposition scheme. The motion, the creation and the annihilation of composite coherence vortices may take place upon propagation through non-Kolmogorov turbulence, and the general exponent , sign of the topological charge and superposition scheme affect the evolution behavior. Finally, the results are compared with those of the previous work.

Composite coherence vortices in a radial beam array propagating through atmosphericturbulence along a slant path

The explicit expression for the cross-spectral density of a radial partially coherent beamarray with an initial phase distribution propagating through atmospheric turbulence alonga slant path is derived and used to study the propagation of composite coherence vorticesformed by the radial partially coherent beam array. The dependence of number,position and topological charge of composite coherence vortices on the beam arrayand atmospheric turbulence parameters is illustrated by numerical examples.

Evolution and stability of cosmic string loops with Y-junctions

We study the evolution of non-periodic cosmic string loops containing Y-junctions, such as may form during the evolution of a network of (p,q) cosmic superstrings. We set up and solve the Nambu-Goto equations of motion for a loop with junctions, focusing attention on a specific static and planar initial loop configuration. After a given time, the junctions collide and the Nambu-Goto description breaks down. We also study the same loop configuration in a U(1)xU(1) field theory model that allows composite vortices with corresponding Y-junctions. We show that the field theory and Nambu-Goto evolution are remarkably similar until the collision time. However, in the field theory evolution a new phenomenon occurs: the composite vortices can unzip, producing in the process new Y-junctions, whose separation may grow significantly, destabilizing the configuration. In particular, an initial loop with two Y-junctions may evolve to a configuration with six Y-junctions (all distant from each other). Setting up this new configuration as an initial condition for Nambu Goto strings, we solve for its evolution and establish conditions under which it is stable to the decay mode seen in the field theory case. Remarkably, the condition closely matches that seen in the field theory simulations, and is expressed in terms of simple parameters of the Nambu-Goto system. This implies that there is an easy way to understand the instability in terms of which region of parameter space leads to stable or unstable unzippings.