Manipulation Of Vortices Research Articles

Multitarget manipulation of off-axis acoustic vortices based on a focused sector-vortex transducer array

Multitarget manipulation of off-axis acoustic vortices based on a focused sector-vortex transducer array

Numerical Modeling of Vortex-Based Superconducting Memory Cells: Dynamics and Geometrical Optimization.

The lack of dense random-access memory is one of the main obstacles to the development of digital superconducting computers. It has been suggested that AVRAM cells, based on the storage of a single Abrikosov vortex-the smallest quantized object in superconductors-can enable drastic miniaturization to the nanometer scale. In this work, we present the numerical modeling of such cells using time-dependent Ginzburg-Landau equations. The cell represents a fluxonic quantum dot containing a small superconducting island, an asymmetric notch for the vortex entrance, a guiding track, and a vortex trap. We determine the optimal geometrical parameters for operation at zero magnetic field and the conditions for controllable vortex manipulation by short current pulses. We report ultrafast vortex motion with velocities more than an order of magnitude faster than those expected for macroscopic superconductors. This phenomenon is attributed to strong interactions with the edges of a mesoscopic island, combined with the nonlinear reduction of flux-flow viscosity due to the nonequilibrium effects in the track. Our results show that such cells can be scaled down to sizes comparable to the London penetration depth, ∼100 nm, and can enable ultrafast switching on the picosecond scale with ultralow energy per operation, ∼10-19 J.

Switchable dual-functional optical vortex manipulation via cylindrical phase-change metagratings

Subwavelength artificial engineering microstructures, such as metasurfaces and metagratings, can realize superior optical properties that many natural materials cannot finish. However, most functionalities achieved are mostly single and fixed. The appearance of phase-change materials makes it possible to extend the functions of metagratings. Here, we propose and demonstrate a structural design of cylindrical phase-change metagratings based on VO2, which can achieve switchable dual-functional optical vortex manipulation in the terahertz range. Specifically, by excitation of the temperature-sensitive metallic and insulating states of VO2, the simple two-dimensional cylindrical gear-like structure can achieve dual-functionality for vortex waves with orbital angular momentum, namely efficient retroreflection and near-perfect absorption. In addition, we also discussed the influence of the gear-like structure dimensions on the transmissivity and absorptivity of dual-function vortex wave manipulation. This work provides a simple and effective approach for the tunable and multifunctional control of vortex waves in subwavelength artificial devices, with potential applications in automated device design and terahertz (THz) communications.

Dynamic Acoustic Beamshaping with Coupling-Immune Moiré Metasurfaces.

Moiré effects arising from mutually twisted metasurfaces have showcased remarkable wave manipulation capabilities, unveiling tantalizing emerging phenomena such as acoustic moiré flat bands and topological phase transitions. However, the pursuit of strong near-field coupling in layers has necessitated acoustic moiré metasurfaces to be tightly stacked at narrow distances in the subwavelength range. Here, moiré effects beyond near-field interlayer coupling in acoustics are reported and the concept of coupling-immune moiré metasurfaces is proposed. Remote acoustic moiré effects decoupled from the interlayer distance are theoretically, numerically, and experimentally demonstrated. Tunable out-of-plane acoustic beam scanning is successfully achieved by dynamically controlling twist angles. The engineered coupling-immune properties are further extended to multilayered acoustic moiré metasurfaces and manipulation of acoustic vortices. Good robustness against external disturbances is also observed for the fabricated coupling-immune acoustic moiré metasurfaces. The presented work unlocks the potential of twisted moiré devices for out-of-plane acoustic beam shaping, enabling practical applications in remote dynamic detection, and multiplexed underwater acoustic communication.

Temporally deuterogenic plasmonic vortices

Abstract Over the past decade, orbital angular momentum has garnered considerable interest in the field of plasmonics owing to the emergence of surface-confined vortices, known as plasmonic vortices. Significant progress has been made in the generation and manipulation of plasmonic vortices, which broadly unveil the natures of plasmonic spin–orbit coupling and provide accessible means for light–matter interactions. However, traditional characterizations in the frequency domain miss some detailed information on the plasmonic vortex evolution process. Herein, an exotic spin–orbit coupling phenomenon is demonstrated. More specifically, we theoretically investigated and experimentally verified a temporally deuterogenic vortex mode, which can be observed only in the time domain and interferes destructively in the intensity field. The spatiotemporal evolution of this concomitant vortex can be tailored with different designs and incident beams. This work extends the fundamental understanding of plasmonic spin–orbit coupling and provides a unique optical force manipulation strategy, which may fuel plasmonic research and applications in the near future.

Introducing the Rankine vortex method for drag reduction in wall-bounded turbulent flows at low Reynolds number through streamwise vortex manipulation

It is well known that the near-wall streamwise vortices, together with the streaks, are the most important turbulent structures closely associated with drag reduction. Weakening or modifying the streamwise vortices are, thus, general approaches in near-wall turbulent control studies. In this study, a novel approach to manipulate the flow is introduced and applied to a turbulent channel flow in order to achieve drag reduction. The idea behind the “Rankine vortex method” is to generate a force based on the statistical and geometrical information of streamwise vortices. Direct numerical simulations of a turbulent channel flow at a frictional Reynolds number, Reτ, of 180 (based on the driving pressure gradient and channel half-width) are performed. The force is applied in the vicinity of the lower wall of the channel, and the results are comparatively analyzed for the cases with and without force implemented. A drag reduction of 10% is achieved. The theoretical flow control approach presented, along with the associated analysis, has the potential to enhance our current understanding of flow control mechanisms through the manipulation of near-wall turbulence.

Ultrafast Time Dynamics of Plasmonic Fractional Orbital Angular Momentum.

The creation and manipulation of optical vortices, both in free space and in two-dimensional systems such as surface plasmon polaritons (SPPs), has attracted widespread attention in nano-optics due to their robust topological structure. Coupled with strong spatial confinement in the case of SPPs, these plasmonic vortices and their underlying orbital angular momentum (OAM) have promise in novel light-matter interactions on the nanoscale with applications ranging from on-chip particle manipulation to tailored control of plasmonic quasiparticles. Until now, predominantly integer OAM values have been investigated. Here, we measure and analyze the time evolution of fractional OAM SPPs using time-resolved two-photon photoemission electron microscopy and near-field optical microscopy. We experimentally show the field's complex rotational dynamics and observe the beating of integer OAM eigenmodes at fractional OAM excitations. With our ability to access the ultrafast time dynamics of the electric field, we can follow the buildup of the plasmonic fractional OAM during the interference of the converging surface plasmons. By adiabatically increasing the phase discontinuity at the excitation boundary, we track the total OAM, leading to plateaus around integer OAM values that arise from the interplay between intrinsic and extrinsic OAM.

Composite Vortex Manipulation as a Design Tool for Reflective Intelligent Surfaces

Composite Vortex Manipulation as a Design Tool for Reflective Intelligent Surfaces

High-resolution optical imaging of single magnetic flux quanta with a solid immersion lens.

Magneto-optical imaging of quantized magnetic flux tubes in superconductors - Abrikosov vortices - is based on Faraday rotation of light polarization within a magneto-optical indicator placed on top of the superconductor. Due to severe aberrations induced by the thick indicator substrate, the spatial resolution of vortices is usually well beyond the optical diffraction limit. Using a high refractive index solid immersion lens placed onto the indicator garnet substrate, we demonstrate wide field optical imaging of single flux quanta in a Niobium film with a resolution better than 600 nm and sub-second acquisition periods, paving the way to high-precision and fast vortex manipulation. Vectorial field simulations are also performed to reproduce and optimize the experimental features of vortex images.

Reconstruction of the high-fidelity vortex wavefront via double dark resonances in a four-level atomic medium

Recent years have seen vast progress in the generation and detection of vortex light, with potential applications in classical and quantum optics. However, it is still a challenge to efficiently generate high-fidelity vortex wavefronts in practical applications. Here, we propose a scheme to reconstruct the high-fidelity vortex wavefront via double dark resonances in a four-level atomic system. It is shown that, owing to a microwave field which interacts with magnetic or electric dipole moments of relevant atomic transitions, thereby generating spatially varying double dark resonances which in turn lead to the reconstruction of the incident probe field. In addition, to gauge the quality of the reconstructed probe field in comparison to the incident probe field, we study the fidelity of the reconstructed probe field and find that the reconstructed mode has a fidelity of more than 90% under the double-dark resonant condition. This study would be helpful to demonstrate optical vortex manipulation in atomic media.

Nanoscale Manipulation of Wrinkle-Pinned Vortices in Iron-Based Superconductors

The controlled manipulation of Abrikosov vortices is essential for both fundamental science and logical applications. However, achieving nanoscale manipulation of vortices while simultaneously measuring the local density of states within them remains challenging. Here, we demonstrate the manipulation of Abrikosov vortices by moving the pinning center, namely one-dimensional wrinkles, on the terminal layers of Fe(Te,Se) and LiFeAs, by utilizing low-temperature scanning tunneling microscopy/spectroscopy (STM/S). The wrinkles trap the Abrikosov vortices induced by the external magnetic field. In some of the wrinkle-pinned vortices, robust zero-bias conductance peaks are observed. We tailor the wrinkle into short pieces and manipulate the wrinkles by using an STM tip. Strikingly, we demonstrate that the pinned vortices move together with these wrinkles even at high magnetic field up to 6 T. Our results provide a universal and effective routine for manipulating wrinkle-pinned vortices and simultaneously measuring the local density of states on the iron-based superconductor surfaces.

Guided-Wave Inspired Metasurfaces for Multifunctional Vortex Beam Generation and Manipulation

Vortex beam, manifesting the characteristic helical phase front and amplitude singularity, carries inherent orbital angular momentum (OAM) and has received intensive research from its generation, detection to various promising applications. To flexibly impart OAM to the electromagnetic (EM) waves and further control the topological charge, propagation, polarization, bandwidth and efficiency of the vortex beams, various approaches have been proposed by the science community. In this review, we briefly introduce the established methods for the generation and manipulation of vortex beams, with the focus on the fast-growing guided-wave metasurface based approach. Guided-wave metasurface contains sub-wavelength guided-wave subsystems that are capable of versatile control of the EM wave and we review some recent advances that enabled multifunctional vortex beam generation and manipulation, with an outlook towards the future development in this field. OAM topological charges switching, polarization control, divergence control, full-space vortex beam generation, broadband vortex beam generation and vortex multibeam are covered in this paper aiming to accommodate the ever-increasing demands from the vortex beam applications.

Chip-Integrated Vortex Manipulation.

The positions of Abrikosov vortices have long been considered as means to encode classical information. Although it is possible to move individual vortices using local probes, the challenge of scalable on-chip vortex-control remains outstanding, especially when considering the demands of controlling multiple vortices. Realization of vortex logic requires means to shuttle vortices reliably between engineered pinning potentials, while concomitantly keeping all other vortices fixed. We demonstrate such capabilities using Nb loops patterned below a NbSe2 layer. SQUID-on-Tip (SOT) microscopy reveals that the loops localize vortices in designated sites to a precision better than 100 nm; they realize "push" and "pull" operations of vortices as far as 3 μm. Successive application of such operations shuttles a vortex between adjacent loops. Our results may be used as means to integrate vortices in future quantum circuitry. Strikingly, we demonstrate a winding operation, paving the way for future topological quantum computing and simulations.

Anisotropic Vortex Squeezing in Synthetic Rashba Superconductors: A Manifestation of Lifshitz Invariants

Most of 2D superconductors are of type II, i.e., they are penetrated by quantized vortices when exposed to out-of-plane magnetic fields. In presence of a supercurrent, a Lorentz-like force acts on the vortices, leading to drift and dissipation. The current-induced vortex motion is impeded by pinning at defects, enabling the use of superconductors to generate high magnetic fields without dissipation. Usually, the pinning strength decreases upon any type of pair-breaking. Here we show that in Rashba superconductors the application of an in-plane field leads, instead, to an unexpected enhancement of pinning. When rotating the in-plane component of the field with respect to the current direction, the vortex inductance turns out to be highly anisotropic. We explain this phenomenon as a manifestation of Lifshitz invariant terms in the Ginzburg-Landau free energy, which are enabled by inversion and time-reversal symmetry breaking and lead to an elliptic squeezing of vortex cores. Our experiment provides access to a fundamental property of Rashba superconductors and offers an entirely new approach to vortex manipulation.

Spontaneous generation and active manipulation of real-space optical vortices.

Optical vortices are beams of light that carry orbital angularmomentum1, which represents an extra degree of freedom that can be generated and manipulated for photonic applications2-8. Unlike vortices in other physical entities, the generation of optical vortices requires structural singularities9-12, but this affects their quasiparticle nature and hampers the possibility of altering their dynamics or making them interacting13-17. Here we report a platform that allows the spontaneous generation and active manipulation of an optical vortex-antivortex pair using an external field. An aluminium/silicon dioxide/nickel/silicon dioxide multilayer structure realizes a gradient-thickness optical cavity, where the magneto-optic effects of the nickel layer affect the transition between a trivial and anon-trivialtopological phase. Rather than a structural singularity, the vortex-antivortex pairs present in the light reflected by our device are generated through mathematical singularities in the generalized parameter space of the top and bottom silicon dioxide layers, which can be mapped onto real space and exhibit polarization-dependent and topology-dependent dynamics driven by external magnetic fields. We expect that the field-induced engineering of optical vortices that we report will facilitate the study of topological photonic interactions and inspire further efforts to bestow quasiparticle-like properties to various topological photonic textures such as toroidal vortices, polarization and vortex knots, and optical skyrmions.

Suppression of vortex shedding and vortex-induced vibration of a circular cylinder using screen shrouds

Experiments were conducted in wind tunnels to investigate the one degree of freedom (1DOF) vortex-induced vibration (VIV) and vortex shedding of a circular cylinder controlled with various screen shrouds in the sub-critical Reynolds number regime. The screen shrouds, made of stainless steel screen meshes with porosities β = 37%, 48%, 61%, and 67%, were fitted concentrically outside the bare circular cylinder. The diameter ratio between the outer screen shrouds and the inner bare cylinder was fixed at 2. The VIV responses and force coefficients of the screen shrouded cylinders were first examined in a wind tunnel to quantify the effectiveness of the screen shrouds on VIV suppression. It was found that the screen shrouds significantly suppressed the maximum VIV amplitude, delayed the onset of the VIV and narrowed the lock-on region. The maximum VIV amplitude was suppressed by 90% using the β = 67% screen shroud. To further understand the effect of the shrouds on vortex manipulation, the wake characteristics of the screen shrouded cylinders with β = 37% and 67% were then examined in a wind tunnel using hot-wire anemometers over a streamwise range x* = 5−40. Phase-averaging analysis revealed that the large-scale vortices were not formed until x* = 10 or 20, before which only small-scale vortical structures were identified in the shear layers of the shrouded cylinders, indicating that the screen shrouds successfully delayed the formation of the large-scale vortices. This result was entirely different from the formation of the large-scale structures found in the bare cylinder wake. In addition, the strength of the vortical structures in the former two wakes was much weaker than that in the latter, indicating attenuated large-scale vortices in the screen shrouded cylinder wakes. After the formation of the large-scale structures, the vortices decayed slower in the screen shrouded cylinder wakes than that in the bare cylinder wake.

Broadband angular momentum cascade via a multifocal graphene vortex generator

Light beams carrying orbital angular momentum (OAM) have inspired various advanced applications, and such abundant practical applications in turn demand complex generation and manipulation of optical vortices. Here, we propose a multifocal graphene vortex generator, which can produce broadband angular momentum cascade containing continuous integer non-diffracting vortex modes. Our device naturally embodies a continuous spiral slit vortex generator and a zone plate, which enables the generation of high-quality continuous vortex modes with deep depths of foci. Meanwhile, the generated vortex modes can be simultaneously tuned through incident wavelength and position of the focal plane. The elegant structure of the device largely improves the design efficiency and can be fabricated by laser nanofabrication in a single step. Moreover, the outstanding property of graphene may enable new possibilities in enormous practical applications, even in some harsh environments, such as aerospace.

Dynamical evolution study of exciton–polariton Bose–Einstein condensate with vortex manipulation

For the exciton–polariton BEC system modulated by vortex light, we study its evolution based on the driven-dissipative Gross–Pitaevskii equation model. Via modified variational method, we first derive the two-dimensional system’s evolution pattern from the initially coherent state prepared by vortex light modulation for non-rotating states and rotating states with various angular velocities. We identify close qualitatively matched patterns by comparing our theoretically derived evolution patterns with that from pure numerical simulation, demonstrating the applicability of our theoretical treatment presented. The derived exciton–polariton evolution pattern formulation can then be used to guide experimental observations of vortex manipulation effects for the exciton–polariton BEC system, with the possible identification of quantum gyroscopic effects.

Optical vortex manipulation for topological quantum computation

Proposed approaches to topological quantum computation based on Majorana bound states may enable new paths to fault-tolerant quantum computing. Several recent experiments have suggested that the vortex cores of topological superconductors, such as iron-based superconductors, may host Majorana bound states at zero energy. To facilitate quantum computation with these zero-energy vortex bound states, a precise and fast manipulation of individual vortices is crucial. However, handling individual vortices remains a challenge, and a theoretical framework for describing individually controlled vortex motion is still critically needed. We propose a scheme for the use of local heating based on scanning optical microscopy to manipulate Majorana bound states emergent in the vortex cores of topological superconductors. Specifically, we derive the conditions required for transporting a single vortex between two stationary defects in the superconducting material by trapping it with a "hot spot" generated by local optical heating. Using these critical conditions for the vortex motion, we then establish the ideal material properties for the implementation of our manipulation scheme, which paves the way toward the controllable handling of zero-energy vortex bound states.

Reconfigurable Josephson Phase Shifter.

Phase shifter is one of the key elements of quantum electronics. In order to facilitate operation and avoid decoherence, it has to be reconfigurable, persistent, and nondissipative. In this work, we demonstrate prototypes of such devices in which a Josephson phase shift is generated by coreless superconducting vortices. The smallness of the vortex allows a broad-range tunability by nanoscale manipulation of vortices in a micron-size array of vortex traps. We show that a phase shift in a device containing just a few vortex traps can be reconfigured between a large number of quantized states in a broad [−3π, +3π] range.