New Degree Of Freedom Research Articles

Simulations of spin/polarization-resolved laser–plasma interactions in the nonlinear QED regime

Strong-field quantum electrodynamics (SF-QED) plays a crucial role in ultraintense laser–matter interactions and demands sophisticated techniques to understand the related physics with new degrees of freedom, including spin angular momentum. To investigate the impact of SF-QED processes, we have introduced spin/polarization-resolved nonlinear Compton scattering, nonlinear Breit–Wheeler, and vacuum birefringence processes into our particle-in-cell (PIC) code. In this article, we provide details of the implementation of these SF-QED modules and share known results that demonstrate exact agreement with existing single-particle codes. By coupling normal PIC simulations with spin/polarization-resolved SF-QED processes, we create a new theoretical platform to study strong-field physics in currently running or planned petawatt or multi-petawatt laser facilities.

MD simulation of primary radiation damage in fcc multi-principal element alloys: Effect of compositional undulation

Fcc single phase alloys with highly concentrated solid solution are competitive candidates for the next-generate radiation-tolerant materials. The present study uses molecular dynamics simulations to study the displacement cascades of NiCoFeCr fcc single-phase concentrated solid-solution alloys (SP-CSAs). The effects of compositional undulation on the generation and evolution of the defects, produced by primary knock-on atoms, are quantitatively analysed. Our simulation results show that the undulation renders considerable compositionally graded interfaces (CGIs) with high threshold energy for displacement, and these CGIs can act as pre-existing defect sinks and confine interstitial defects motion. This increases the recombination rate of residual defects, thus leading to the suppression of Frenkel pairs and large-sized interstitial clusters. In addition, such effect of compositional undulation is correlated with the specific chemical elements, i.e., the Ni-Fe and Co-Fe undulated SP-CSA yield slower radiation damage accumulation. Our findings suggest a new degree of freedom to tailor radiation-tolerance for concentrated solid-solution alloys.

Dual-mode dual-band circular polarization device based on three-layer plasmonic metasurface

In this work, we proposed a three-layer metasurface with rotated gold split-rings as a polarization device that has two adjacent operating bands in two different modes. The proposed metasurface can be used as a circular polarization selector in transmission mode as well as a circular polarization converter in reflection mode. In transmission mode, it can transmit right- and left-handed circularly polarized light at the corresponding wavelengths of 2130 and 3040 nm with transmission efficiencies of 85.3% and 83.8%, respectively. In reflection mode, it can convert two types of circularly polarized light into those of the orthogonal state with conversion efficiencies of 70.3% and 77.3% in the opposite bands, respectively. The results of the theoretical calculation by transfer matrix method are consistent with these simulation results, and the current distribution results illustrate the coupling mechanism under the proposed chiral structure. In addition, the influence of parameters on circular dichroism was investigated, demonstrating the strong robustness of the structure. The proposed metasurface provides a new degree of freedom for multifunctional photonic integrated devices, which can be used for applications in optical communication and imaging.

Quantum curves from refined topological recursion: The genus 0 case

We formulate geometrically (without reference to physical models) a refined topological recursion applicable to genus zero curves of degree two, inspired by Chekhov-Eynard and Marchal, introducing new degrees of freedom in the process. For such curves, we prove the fundamental properties of the recursion analogous to the unrefined case. We show the quantization of spectral curves due to Iwaki-Koike-Takei can be generalized to this setting and give the explicit formula, which turns out to be related to the unrefined case by a simple transformation. For an important collection of examples, we write down the quantum curves and find that in the Nekrasov-Shatashvili limit, they take an especially simple form.

Dielectric diatomic metasurface-assisted versatile bifunctional polarization conversions and incidence-polarization-secured meta-image.

Dielectric metasurface empowering efficient light polarization control at the nanoscale, has recently garnered tremendous research interests in the field of high-resolution image encryption and display, particularly at low-loss wavelengths in the visible band. Nevertheless, due to the single fixed polarization conversion function, the image (either positive or negative image) can always be decrypted in a host-uncontrollable manner as long as the user applies an analyzer to select the polarization component of the output light. Here, we resort to half-waveplate- and quarter-waveplate-like silicon nanopillars to form a metamolecule of a dielectric diatomic metasurface, which can yield versatile linearly polarized (LP) and circularly polarized (CP) light upon orthogonally linear-polarized incidences, providing new degrees of freedom for image display and encryption. We show both theoretically and numerically that versatile different paired LP and CP combinations could be achieved by simply adjusting the orientation angles of the two nanopillars. The bifunctional polarization conversion functions make possible that a meta-image can only be seen when incident light is linearly polarized at a specific polarization angle, whereas no image can be discerned for the orthogonal polarization incidence case, indicating the realization of incidence-polarization secured meta-image. This salient feature holds for all individual metamolecules, reaching a remarkable image resolution of 52,916 dots per inch. By fully exploiting all polarization conversions of four designed metamolecules, three-level incidence polarization-secured meta-image can also be expected.

Wet Chemical and Plasma Etching of Photosensitive Glass

Photosensitive glasses for radiation-induced 3D microstructuring, due to their optical transparency and thermal, mechanical, and chemical resistance, enable the use of new strategies for numerous microscale applications, ranging from optics to biomedical systems. In this context, we investigated the plasma etching of photosensitive glasses after their exposure and compared it to the established wet chemical etching method, which offers new degrees of freedom in microstructuring control and microsystem fabrication. A CF4/H2 etching gas mixture with a constant volumetric flow of 30 sccm and a variable H2 concentration from 0% to 40% was utilized for plasma-based etching, while for wet chemical etching, diluted hydrofluoric acid (1% ≤ cHF ≤ 20%) was used. Therefore, both etching processes are based on a chemical etching attack involving fluorine ions. A key result is the observed reversion of the etch selectivity between the initial glassy and partially crystallized parts that evolve after UV exposure and thermal treatment. The crystallized parts were found to be 27 times more soluble than the unexposed glass parts during wet chemical etching. During the plasma etching process, the glassy components dissolve approximately 2.5 times faster than the partially crystalline components. Unlike wet chemical etching, the surfaces of plasma etched photostructured samples showed cone- and truncated-cone-shaped topographies, which supposedly resulted from self-masking effects during plasma etching, as well as a distinct physical contribution from the plasma etching process. The influences of various water species on the etching behaviors of the homogeneous glass and partially crystallized material are discussed based on FTIR-ATR and in relation to the respective etch rates and SNMS measurements.

Exciton Superposition across Moiré States in a Semiconducting Moiré Superlattice

Moiré superlattices of semiconducting transition metal dichalcogenides enable unprecedented spatial control of electron wavefunctions, leading to emerging quantum states. The breaking of translational symmetry further introduces a new degree of freedom: high symmetry moiré sites of energy minima behaving as spatially separated quantum dots. We demonstrate the superposition between two moiré sites by constructing a trilayer WSe2/monolayer WS2 moiré heterojunction. The two moiré sites in the first layer WSe2 interfacing WS2 allow the formation of two different interlayer excitons, with the hole residing in either moiré site of the first layer WSe2 and the electron in the third layer WSe2. An electric field can drive the hybridization of either of the interlayer excitons with the intralayer excitons in the third WSe2 layer, realizing the continuous tuning of interlayer exciton hopping between two moiré sites and a superposition of the two interlayer excitons, distinctively different from the natural trilayer WSe2.

Molecular dynamics study on the thermal conductivity and ballistic resistance of twisted graphene

The twist as a new degree of freedom induces several angle dependent properties in twisted graphene, such as electronic and optical properties. However, the ballistic resistance and thermal conductivity of twisted graphene remain not well understood and experimentally challenging. Therefore, the effect of interlayer twist angle on the thermal conductivity and ballistic resistance of bilayer graphene (BLG) has been explored using molecular dynamics simulation herein. Results show that the thermal conductivity of graphene is very sensitive to the twist angle of the interlayer plane. As the twist angle increases from 0° to 60°, the in-plane thermal conductivity of twisted bilayer graphene (t-BLG) first decreases and then increases with a periodic interval of 30°, exhibiting an asymmetric double V-shaped curve. And the cross-plane thermal conductivity of t-BLG gradually first decreases from 0° to 30° and then increases from 30° to 60°, also showing an asymmetric V-shaped curve. In contrast, the interlayer twist angle has a limited influence on the ballistic resistance of t-BLG. With the change of the twist angle, the ballistic limit velocity does not change much, and the fluctuation range is less than 1.56%; the relative kinetic energy also changes little with the fluctuation less than 4%. Such a slight difference is insufficient to make a significant change in its ballistic resistance and its impact resistance is mainly affected by the number of membrane layers. Each additional layer increases its ballistic limit speed by about 8%. This study will provide some theoretical guidance for the study of heat dissipation in the anti-ballistic process of twisted graphene and the design of advanced protective materials.

Pacemod: parametric contour-based modifications for glyph generation

Metaphoric glyphs are intuitively related to the underlying problem domain and enhance the readability and learnability of the resulting visualization. Their construction, however, implies an appropriate modification of the base icon, which is a predominantly manual process. In this paper, we introduce the parametric contour-based modification (PACEMOD) approach that lays the foundations of automated, controllable icon manipulations. Technically, the PACEMOD parametric representation utilizes diffusion curves, enriched with new degrees of freedom in arc-length parameterization, which allows for manipulation of the icon contours’ geometry and the related color attributes. Moreover, we propose an implementation of our generic approach for a specific, automated design of metaphoric glyphs, based on periodic, wave-like contour modifications. Finally, the practicality of such periodic contour modifications is demonstrated by two visualization examples, which comprise uncertainty visualization of a rain forecast and gradient glyphs applied to COVID-19 data. In summary, with the PACEMOD approach we introduce an instrument that facilitates a user-centered design of metaphoric glyphs and provides a generic basis for potential further implementations according to specific applications.

Slot driven dielectric electromagnetically induced transparency metasurface.

The control of resonant metasurface for electromagnetically induced transparency (EIT) offers unprecedented opportunities to tailor lightwave coupling at the nanoscale leading to many important applications including slow light devices, optical filters, chemical and biosensors. However, the realization of EIT relies on the high degree of structural asymmetry by positional displacement of optically resonant structures, which usually lead to low quality factor (Q-factor) responses due to the light leakage from structural discontinuity from asymmetric displacements. In this work, we demonstrate a new pathway to create high quality EIT metasurface without any displacement of constituent resonator elements. The mechanism is based on the detuning of the resonator modes which generate dark-bright mode interference by simply introducing a slot in metasurface unit cells (meta-atoms). More importantly, the slot diameter and position on the meta-atom can be modulated to tune the transmittance and quality factor (Q-factor) of the metasurface, leading to a Q-factor of 1190 and near unity transmission at the same time. Our work provides a new degree of freedom in designing optically resonant elements for metamaterials and metasurfaces with tailored wave propagation and properties.

A Wearable Glove with Electrothermal‐Controlled Ionogels for Adhesive Gripping

In this article, a lightweight, untethered wearable adhesive glove (total weight 72 g) is developed to empower the human hand with adhesive gripping. A textile glove comprises ionogels with embedded flexible heaters and a wireless electronic control module. The thermoresponsive ionogel with switchable adhesion achieves a switching ratio of 4.9 after heating 4.4 s under 4 V voltage, enabling on‐demand object pickup and release. As demonstration examples, the wearable adhesive glove is shown to grasp multiple objects with single‐finger adhesion and manipulate card with two‐finger adhesion. It is shown in the experiments that the wearable adhesive glove can expand the gripping modes and enhance the gripping ability of the human hand by giving it a new degree of freedom of adhesion.

An Integrated Magnetometer Module With MFCs Based on Diamond NV Centers

In recent years, nitrogen vacancy (NV) centers in diamond have become a promising solid-state magnetic sensor for applications due to their high sensitivity to magnetic field and excellent spatial resolution at room temperature. However, diamond magnetometer has complex and large optical system and microwave system, it is necessary to address the requirements of the measured environment for the small space and high sensitivity of the magnetometer in practical applications. In this paper, we propose an integrated magnetometer module with magnetic flux concentrators (MFCs) shaped like the wings of an airplane. The fiber coupler, diamond, microwave antenna, filters, photodetector and a weak signal processing circuit are integrated in the integrated module. MFCs are also integrated to collect flux from a larger area and concentrate it into the center of diamond magnetometer, which are used to improve the sensitivity of the diamond magnetometer. The volume of the integrated module is limited to 3.81 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and achieve the actual magnetic sensitivity of sub-0.34 nT/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> . In the designed magnetometer module, the devices are assembled more easily and tightly, which provides a new degree of freedom for the production of diamond magnetometer.

Pre/Post-Merger Consistency Test for Gravitational Signals from Binary Neutron Star Mergers

Gravitational waves from binary neutron star (BNS) mergers can constrain nuclear models, predicting their equation of state (EOS). Matter effects on the inspiral-merger signal are encoded in the multipolar tidal polarizability parameters, whose leading order combination is sufficient to capture, with high accuracy, the key features of the merger waveform. Similar EOS-insensitive relations exist for the post-merger signal and can be used to model the emissions from the remnant. Several works suggested that the appearance of new degrees of freedom in high-density post-merger matter can be inferred by observing a violation of these EOS-insensitive relations. Here, we demonstrate a Bayesian method to test such an EOS-insensitive relation between the tidal polarizability parameters (or any other equivalent parameter) and the dominant post-merger frequency using information from the pre-and-post-merger signal. Technically, the method is similar to the inspiral-merger-ringdown consistency tests of General Relativity with binary black holes. However, differently from the latter, BNS pre/post-merger consistency tests are conceptually less informative and they only address the consistency of the assumed EOS-insensitive relation. Specifically, we discuss how such tests cannot conclusively discriminate between an EOS without respecting such a relation and the appearance of new degrees of freedom (or phase transitions) in high-density matter.

Tunable Interband Transitions in Twisted h-BN/Graphene Heterostructures.

In twisted h-BN/graphene heterostructures, the complex electronic properties of the fast-traveling electron gas in graphene are usually considered to be fully revealed. However, the randomly twisted heterostructures may also have unexpected transition behaviors, which may influence the device performance. Here, we study the twist-angle-dependent coupling effects of h-BN/graphene heterostructures using monochromatic electron energy loss spectroscopy. We find that the moiré potentials alter the band structure of graphene, resulting in a redshift of the intralayer transition at the M point, which becomes more pronounced up to 0.22eV with increasing twist angle. Furthermore, the twisting of the Brillouin zone of h-BN relative to the graphene M point leads to tunable vertical transition energies in the range of 5.1-5.6eV. Our findings indicate that twist-coupling effects of van der Waals heterostructures should be carefully considered in device fabrications, and the continuously tunable interband transitions through the twist angle can serve as a new degree of freedom to design optoelectrical devices.

Tunable Sensitivity in Long Period Fiber Gratings During Mode Transition With Low Refractive Index Intermediate Layer

Double-clad fibers where the second cladding has a lower refractive index than the first cladding, prove to be ideal structures for potentiating and tuning the sensitivity in long-period fiber gratings (LPFGs) operating in mode transition. When a thin film is deposited on the optical fiber, the second cladding performs acts as a barrier that initially prevents the transition to guidance in the thin film of one of the modes guided in the first cladding. Finally, the transition to guidance occurs with a sensitivity increase, in analogy to the tunnel effect observed in semiconductors. This improvement has been demonstrated both as a function of the thin film thickness and the surrounding medium refractive index, with enhancement factors of 4 and 2, respectively. This idea reinforces the performance of LPFGs, adding a new degree of freedom to the mode transition and the dispersion turning point phenomena. Moreover, the control of the variation of the effective index of cladding modes could be applied in other structures, such as tilted-fiber gratings or evanescent wave sensors.

Active Power Oscillation Suppression Based on Decentralized Transient Damping Control for Parallel Virtual Synchronous Generators

Similar to the traditional synchronous generator (SG), a drawback of the virtual synchronous generator (VSG) is the active power oscillation, especially in the system with parallel VSGs. In this paper, a decentralized transient damping (DTD) control strategy is proposed to suppress active power oscillation during load fluctuations in the parallel VSGs system, which is based on embedding the transient electromagnetic power compensation and transient damping power compensation (TDPCP) control into the original VSG active power controller, providing two new degrees of freedom for the flexible regulation of the system damping ratio without frequency measurement. In this way, the damping ratio of the parallel VSGs system can be adjusted more freely without affecting the steady-state characteristics of the system. Therefore, this flexible transient damping characteristic can facilitate the suppression of active power oscillation under load fluctuations. Moreover, the proposed method is immune to the parameter mismatch of the parallel VSGs. The design of key parameters and stability analysis are presented. Finally, the feasibility of the proposed control strategy is verified through the simulation and experimental results.

Joint Transceiver Beamforming and Reflecting Design for Active RIS-Aided ISAC Systems

Integrated sensing and communication (ISAC) is recognized as a promising technology with great potential in saving hardware and spectrum resources, since it simultaneously realizes radar detection and user communication functions in the fully-shared platform. Employing reconfigurable intelligent surface (RIS) in ISAC systems is able to provide a virtual line-of-sight (LoS) path to conquer blockage problem as well as introduce new degrees of freedom (DoFs) to further enhance system performance. Nevertheless, the multiplicative fading effect of passive RIS limits its applications in the absence of direct links, which promotes the development of active RIS. In this paper, we consider an active RIS-assisted ISAC system and aim to jointly design the transmit beamformer, the active RIS reflection and the radar receive filter to maximize the radar output signal-to-noise ratio (SNR) while guaranteeing pre-defined signal-to-interference-plus-noise ratios (SINRs) for communication users. To solve for this non-convex problem, an efficient algorithm is developed by leveraging the techniques of block coordinate descent (BCD), Dinkelbach's transform and majorization-minimization (MM). Simulation results verify the significant advancement of deploying active RIS in ISAC systems, which can achieve up to 32 dB radar SNR enhancement compared with the passive RIS-assisted ISAC systems.

Why Is White Noise Not Enough? Using Radio Front-End Models While Designing 6G PHY

Each subsequent generation of wireless standards imposes stricter spectral and energy efficiency demands. So far, layered wireless transceiver architectures have been used, allowing for instance to separate channel decoding algorithms from the front-end design. Such an approach may need to be reconsidered in the upcoming 6G era. Especially hardware-originated distortions have to be taken into account while designing other layer algorithms, as high throughput and energy efficiency requirements will push these devices to their limits, revealing their non-linear characteristics. In such a context, this paper will shed some light on the new degrees of freedom enjoyed while cross-layer designing as well as controlling multicarrier and multiantenna transceivers in 6G systems.

Aberration of gravitational waveforms by peculiar velocity

ABSTRACT One key prediction of General Relativity is that gravitational waves are emitted with two independent polarizations. Any observation of extra polarization mode, spin-1 or spin-0, is consequently considered a smoking gun for deviations from General Relativity. In this paper, we show that the velocity of merging binaries with respect to the observer gives rise to spin-1 polarization in the observer frame even in the context of General Relativity. These are pure projection effects, proportional to the plus and cross polarizations in the source frame, hence they do not correspond to new degrees of freedom. We demonstrate that the spin-1 modes can always be rewritten as pure spin-2 modes coming from an aberrated direction. Since gravitational waves are not isotropically emitted around binary systems, this aberration modifies the apparent orientation of the binary system with respect to the observer: the system appears slightly rotated due to the source velocity. Fortunately, this bias does not propagate to other parameters of the system (and therefore does not spoil tests of General Relativity), since the impact of the velocity can be fully reabsorbed into new orientation angles.

One-centre corrected two-electron integrals in inner projection-based integral evaluations

Cholesky decomposition (CD) of the two-electron integrals and the resolution-of-identity (RI) techniques are established inner projection methods to efficiently evaluate two-electron integrals. Both approaches share the notion of an auxiliary basis set as a mean to reduce the scaling. In the past years, the close relationship between the two approaches has fostered developments on how to systematically derive unbiased auxiliary basis sets – atomic CD (aCD) and atomic compact CD (acCD) auxiliary basis sets, different to the precomputed auxiliary basis sets. The accuracy of these approximations in the RI approach can be further improved via an explicit correction of the one-centred two-electron integrals, which is the main object of this research. Correcting the one-centred two-electron integrals directly, which scales linear with system size, is expected to provide a new degree of freedom to the design of auxiliary basis sets. This can either be used to gain faster convergence towards the conventional treatment of the two-electron integrals or as a mean to design lighter auxiliary basis sets while maintaining the same accuracy as of the uncorrected approach. The benchmarks of the one-centre corrections applied to several auxiliary basis set types were investigated in this paper.