Unpolarized State Research Articles

Broadband Depolarization via Plasmonic Metasurfaces: Conversion from Purely Polarized to Absolute Unpolarized States

Broadband Depolarization via Plasmonic Metasurfaces: Conversion from Purely Polarized to Absolute Unpolarized States

Computer homogenization of porous piezoceramics of different ferrohardness with random porous structure and inhomogeneous polarization field

The article is concerned with the homogenization problems, in which the effective moduli of porous piezoceramic composites are determined taking into account the inhomogeneity of the polarization field. The homogenization problems are solved by the finite element method in the framework of the theory of effective moduli and the Hill energy principle using the ANSYS package. To this end, in static problems of electroelasticity, the displacements and electric potential, which are linear in spatial variables, are specified on the boundary of a representative volume to provide constant stress and electric induction fields for a homogeneous reference medium. After solving a set of boundary value problems under different boundary conditions and determining the volume-averaged stress components and the electric induction vector, a complete set of effective moduli for the piezoelectric composite is calculated. A representative volume of the piezocomposite is created in the form of a regular finite element mesh consisting of cubic elements. Pores in the representative volume are assumed to be filled with a piezoelectric material with extremely small moduli. Finite elements with pore properties are selected according to a simple random algorithm. The inhomogeneous polarization field is found by solving an electrostatic problem, in which the polarization process in the representative volume is modeled based on a simplified linear formulation. The local coordinate systems for individual finite elements of the composite matrix are specified by the directions of the polarization vectors. In the following, when solving the problems of electroelasticity, these local coordinate systems associated with the elements of the piezoelectric matrix allow recalculating the material properties according to the formulas of transformation of the tensor components as the coordinate systems rotate. In addition, consideration is given to different models describing the change in the moduli of the material from an unpolarized state to a polarized one as a function of the polarization vector. Computational experiments were carried out for three types of piezoceramics: soft ferroelectric piezoceramics PZT-5H, piezoceramics PZT-4 of medium ferrohardness, and piezoceramics PZT-8 with higher degree of ferrohardness. The dependences of the effective moduli on porosity are compared for different laws of polarization inhomogeneity and different kinds of piezoceramic material of the composite matrix.

Discriminating States of Polarization

Equiprobable incoherent mixtures of two totally polarized states of light whose associated three-dimensional Jones vectors are mutually orthogonal are called discriminating states and constitute a peculiar type of state that plays a key role in the characteristic decomposition of a generic state into a totally polarized state, a totally unpolarized state, and a discriminating state. In general, discriminating states are three-dimensional, in the sense that the strengths of the three components of the electric field are nonzero for any Cartesian reference frame considered. In the limiting case that the electric field evolves in a fixed plane, the discriminating state is said to be regular and corresponds to a two-dimensional unpolarized state. The special features of discriminating states cover, e.g., their possible synthesis from infinite pairs of mutually orthogonal states as well as their transverse spin. The nature and properties of discriminating states are comprehensively analyzed based on their associated intrinsic Stokes parameters, which leads to meaningful interpretations in terms of the associated polarization ellipsoids and spin vectors.

Mirroring and reversible fine-tuning of the transport spin-polarization in PC3 nanoribbons based on an electrical method

The electrical approach is favored over the conventional magnetic approach for its low energy consumption and continuously variable control of spin polarization. Inspired by the recently reported PC3 monolayer, we investigate its spin-dependent electron transmission characteristics through the first-principles calculations. The results show that the transmission peaks with opposite spin directions at the Fermi level have precisely opposite responses to the gate voltage, which leads to the system being able to alter between spin-polarized and unpolarized states, and as well as achieving any ratio between − 100 % and 100 % for spin-up and spin-down electrons. Notably, this regulation is also reversible and mirror-symmetric. Further research demonstrates that the crux lies in the particular transmission peak contributed by the edge sp2-hybridized C atoms. This study sheds new light on the potential of PC3 as a novel nanoelectronic material for spintronics applications, suggesting that it can be used to create bipolar spin filters with tunable filtering effects.

Number-phase uncertainty relations and bipartite entanglement detection in spin ensembles

We present a method to detect bipartite entanglement based on number-phase-like uncertainty relations in split spin ensembles. First, we derive an uncertainty relation that plays the role of a number-phase uncertainty for spin systems. It is important that the relation is given with well-defined and easily measurable quantities, and that it does not need assuming infinite dimensional systems. Based on this uncertainty relation, we show how to detect bipartite entanglement in an unpolarized Dicke state of many spin-1/2 particles. The particles are split into two subensembles, then collective angular momentum measurements are carried out locally on the two parts. First, we present a bipartite Einstein-Podolsky-Rosen (EPR) steering criterion. Then, we present an entanglement condition that can detect bipartite entanglement in such systems. We demonstrate the utility of the criteria by applying them to a recent experiment given in K. Lange et al. [Science 360, 416 (2018)] realizing a Dicke state in a Bose-Einstein condensate of cold atoms, in which the two subensembles were spatially separated from each other. Our methods also work well if split spin-squeezed states are considered. We show in a comprehensive way how to handle experimental imperfections, such as the nonzero particle number variance including the partition noise, and the fact that, while ideally BECs occupy a single spatial mode, in practice the population of other spatial modes cannot be fully suppressed.

Three-dimensional polarization state and spin structure of a tightly focused radially polarized Gaussian Schell-model beam

In this work, we revisit the tight focusing of a radially polarized partially coherent Gaussian Schell-model beam and examine the effect of spatial coherence of the incident beam on the focal-plane three-dimensional (3D) polarization characters, including the 3D degree of polarization, polarimetric dimensionality, and polarimetric structure. The polarimetric structure and the associated structure for the spin density vector of the tightly focused field are obtained via the 3D characteristic decomposition of the $3\ifmmode\times\else\texttimes\fi{}3$ polarization matrix. We demonstrate that the generated focused field shows the genuine 3D polarization state and a sophisticated spin structure due to the reduced spatial coherence in the incident beam. We find the contributions to whole 3D polarization state of the focused field from the pure state, middle-term state, and 3D unpolarized state in the characteristic decomposition, as well as the contributions to the total spin density vector from the spins of pure state and middle-term state can be controlled by the transverse spatial coherence width of the incident Gaussian Schell-model beam. In addition, the genuine 3D polarization and the spin structure are analyzed in the connection of the recently introduced concept of polarimetric nonregularity.

Size dependence- and induced transformations- of fractional quantum Hall effects under tilted magnetic fields

Two-dimensional electron systems subjected to high transverse magnetic fields can exhibit Fractional Quantum Hall Effects (FQHE). In the GaAs/AlGaAs 2D electron system, a double degeneracy of Landau levels due to electron-spin, is removed by a small Zeeman spin splitting, g mu _B B, comparable to the correlation energy. Then, a change of the Zeeman splitting relative to the correlation energy can lead to a re-ordering between spin polarized, partially polarized, and unpolarized many body ground states at a constant filling factor. We show here that tuning the spin energy can produce fractionally quantized Hall effect transitions that include both a change in nu for the R_{xx} minimum, e.g., from nu = 11/7 to nu = 8/5, and a corresponding change in the R_{xy}, e.g., from R_{xy}/R_{K} = (11/7)^{-1} to R_{xy}/R_{K} = (8/5)^{-1}, with increasing tilt angle. Further, we exhibit a striking size dependence in the tilt angle interval for the vanishing of the nu = 4/3 and nu = 7/5 resistance minima, including “avoided crossing” type lineshape characteristics, and observable shifts of R_{xy} at the R_{xx} minima- the latter occurring for nu = 4/3, 7/5 and the 10/7. The results demonstrate both size dependence and the possibility, not just of competition between different spin polarized states at the same nu and R_{xy}, but also the tilt- or Zeeman-energy-dependent- crossover between distinct FQHE associated with different Hall resistances.

Nonlinear dynamics of tunable spin-orbit coupled Bose-Einstein condensates in deep optical lattices

We discuss the localization and spin dynamics of tunable spin-orbit coupled Bose-Einstein condensates in deep optical lattices. Rich localized phenomena (breather, soliton, self-trapping, and diffusion) are observed. The critical conditions for occurring different localized states are obtained analytically and confirmed numerically. Under the critical conditions, we observe localized states with fixed initial spin polarization. When the critical condition is not satisfied, because of spin-momentum locking, quenching of Raman coupling from soliton state excites spin dynamics. If initially the soliton is in a nearly unpolarized (polarized) state, persistent (damped) spin dynamics is excited. The system finally transforms to a new polarized state in the damped spin dynamics. The localization and spin dynamics can be well controlled by periodic modulation of Raman coupling.

Two-component parton fractional quantum Hall state in graphene

We study the $\nu={\pm}1/2$ fractional quantum Hall states in graphene observed by Zibrov et al. [Nat. Phys. 14, 930 (2018)]. The parton construction is employed to provide a valley unpolarized trial wave function for these states. The lattice scale valley anisotropic terms in the Hamiltonian soften the repulsion between electrons in different valleys to favor the valley unpolarized state. The validity of our proposal is corroborated by numerical calculations.

Conformational change-modulated spin transport at single-molecule level in carbon systems

Controlling the spin transport at the single-molecule level, especially without the use of ferromagnetic contacts, becomes a focus of research in spintronics. Inspired by the progress on atomic-level molecular synthesis, through first-principles calculations, we investigate the spin-dependent electronic transport of graphene nanoflakes with side-bonded functional groups, contacted by atomic carbon chain electrodes. It is found that, by rotating the functional group, the spin polarization of the transmission at the Fermi level could be switched between completely polarized and unpolarized states. Moreover, the transition between spin-up and spin-down polarized states can also be achieved, operating as a dual-spin filter. Further analysis shows that, it is the spin-dependent shift of density of states, caused by the rotation, that triggers the shift of transmission peaks, and then results in the variation of spin polarization. Such a feature is found to be robust to the length of the nanoflake and the electrode material, showing great application potential. Those findings may throw light on the development of spintronic devices.

A Model-based Technique for Ad Hoc Correction of Instrumental Polarization in Solar Spectropolarimetry

We present a new approach for correcting instrumental polarization by modeling the nondepolarizing effects of a complex series of optical elements to determine physically realizable Mueller matrices. Provided that the Mueller matrix of the optical system can be decomposed into a general elliptical diattenuator and general elliptical retarder, it is possible to model the crosstalk between both the polarized and unpolarized states of the Stokes vector and then use the acquired science observations to determine the best-fit free parameters. Here we implement a minimization for solar spectropolarimetric measurements containing photospheric spectral lines sensitive to the Zeeman effect using physical constraints provided by polarized line and continuum formation. This model-based approach is able to provide an accurate correction even in the presence of large amounts of polarization crosstalk and conserves the physically meaningful magnitude of the Stokes vector, a significant improvement over previous ad hoc techniques.

Cooling classical many-spin systems using feedback control

We propose a technique for polarizing and cooling finite many-body classical systems using feedback control. The technique requires the system to have one collective degree of freedom conserved by the internal dynamics. The fluctuations of other degrees of freedom are then converted into the growth of the conserved one. The proposal is validated using numerical simulations of classical spin systems in a setting representative of nuclear magnetic resonance experiments. In particular, we were able to achieve 90% polarization for a lattice of 1000 classical spins starting from an unpolarized infinite temperature state.

Entanglement and work extraction in the central-spin quantum battery

We consider a central-spin battery where $N_b$ central spins serve as battery cells and $N_c$ bath spins serve as charging units. It is shown that the energy stored in the battery that can be extractable is quantified by the ergotropy, and that battery-charger entanglement is quantified via the Von Neumann entropy. By using an exact approach to a one-cell and two-cell battery, our analytical results suggest that, during the charging process, the extractable work slowly increases before the battery-charger entanglement reaches its maximum and then it will rapidly increase when the entanglement begins to decrease. In particular, we rigorously show that there is an inverse relationship between the extractable work and the entanglement at the end of the charging process. Moreover, we investigate different approaches to realize optimal work extraction without wasted energy. Among them a central-spin battery with an unpolarized Dicke state as the charger possesses a universal charging time $\propto 1/N_c$, large extractable work, and $\sqrt{N_c}$-improvement of charging power compared with the battery in the Tavis-Cummings limit. The above-mentioned results have also been numerically verified in multi-cell batteries. Our results pave the way to improve extractable work storage in the central-spin battery and highlight a competitive relation between the extractable work and the battery-charger entanglement.

Tailoring spatially unpolarized light on the Poincaré sphere: From equator states via meridian states to generalized great-circle states

In this paper we investigate the generation, manipulation and invariance properties of spatially unpolarized light in the context of classical optics. We generate spatially randomly polarized light by exploiting the optical activity of a so-called Cornu depolarizer and demonstrate tailored, spatial polarization distributions on the Poincar\'e sphere. We begin with the generation of equator states of spatially unpolarized light, i.e., the manifold of the superposition of all linearly polarized light states in the spatial domain. A quarter-wave plate is utilized to transform these equator polarization states into meridian states and finally a second, subsequent quarter-wave plate results in tilted meridian states or generalized great-circle states on the Poincar\'e sphere. These results of all realized unpolarized states are visually confirmed by tomographic reconstruction of the spatially distributed polarization states on the Poincar\'e sphere by extracting the data from the spatially resolved Stokes parameter measurements. Furthermore, all these experimental results are in excellent agreement with classical Mueller formalism calculations based on the Mueller matrices for the Cornu depolarizer and the wave plates, yielding the tailored manifold of polarization states on the Poincar\'e sphere's surface, confirming the naming of the unpolarized light states in accordance with geodesy. Therefore, we have realized a scheme for the tailored generation of spatially depolarized light based on the Cornu depolarizer and quarter-wave plates with interesting application perspectives and giving further insight into polarization.

Rashba-split surface state and spin-dependent photon emission from Re(0001) at Γ¯

The unoccupied electronic structure of the Re(0001) surface is investigated by spin- and angle-resolved inverse photoemission, experimentally and theoretically. The work is focused on the states around the center of the surface Brillouin zone $\overline{\mathrm{\ensuremath{\Gamma}}}$, where a hole pocket of a surface state with Rashba-type spin splitting is detected. Furthermore, we observe spin-dependent photon emission from unpolarized surface and bulk states at $\overline{\mathrm{\ensuremath{\Gamma}}}$. The size and sign of the spin asymmetry depends on experimental parameters such as the direction of the electron spin polarization and the photon detection angle. Maximum (zero) spin asymmetry is detected if the electron spin polarization and the plane of photon emission are perpendicular (parallel). The effect is traced back to spin-orbit-induced hybridization of the involved states.

Bistability in the polarity circuit of yeast.

Cells polarize their growth or movement in many different physiological contexts. A key driver of polarity is the Rho GTPase Cdc42, which when activated becomes clustered or concentrated at polar sites. Multiple models for polarity establishment have been proposed. All of them rely on positive feedback to reinforce regions of high Cdc42 activity. Positive feedback can lead to bistability, a scenario in which cells can exist in either a polarized or unpolarized state under identical external conditions. Determining if the signaling circuit that drives Cdc42 polarity is bistable would provide important information about the mechanism that underlies polarity establishment and insights into the design features required for proper cellular function. We studied polarity establishment during the mating response of yeast. Using microfluidics to precisely control the temporal profile of mating pheromone and live-cell imaging to monitor the polarity process in single living cells, we found that the polarity circuit of yeast shows hysteresis, a characteristic feature of bistable systems. Our analysis also revealed that cells exposed to high pheromone concentrations rapidly lose polarity following a precipitous removal of pheromone. We used a reaction-diffusion model for polarity establishment to demonstrate that delayed negative regulation is sufficient to explain our experimental results. [Media: see text] [Media: see text] [Media: see text] [Media: see text].

A two-dimensional electron gas suspended above a neutralizing background

We consider a two-dimensional electron gas system consisting of a layer of electrons suspended above its jellium neutralizing background counterpart. We investigate the energy of the system in the Hartree–Fock approximation as a function of separation distance between the layer of electrons and the background. We find that the energy of the system is influenced by the separation distance in such a way that the new energy contribution originating from such a separation behaves as an effective kinetic energy term. The increase of the overall energy with increase of the separation distance adversely affects the stability of electron liquid states at high density. The results are derived for a fully spin-polarized (spinless) system of electrons in the thermodynamic limit, but can easily be generalized to a spin unpolarized state.

Quark-sector Lorentz violation in Z-boson production

Quark-sector Lorentz violation is studied in the context of Drell-Yan dilepton production including effects from Z-boson exchange. We show the chiral nature of the weak interactions enables parity-violating and spin-dependent effects to be studied using unpolarized initial states. Constraints are placed on dimensionless and CPT-even coefficients for Lorentz violation for the first two generations of quarks using measurements from the Large Hadron Collider.

Feasible and economical scheme to entangle a polarized coherent state and a polarized photon

We design a scheme to generate a new type of hybrid entanglement between a macroscopic polarized coherent state and a single polarized photon. Concretely, a polarized Schrodinger cat state, an entangled polarized photon pair, and a polarized coherent state, which have been prepared off-line, are supplied as inputs to our scheme. Then, using conventional optical devices such as beam splitters, polarizing beam splitters, half-wave plates, and photon-number-resolving detectors, all the necessary operations can be effectively performed in-line. Conditioned on photon detection results, creation of the desired hybrid entanglement is heralded. The total success probability of our scheme is twice as high as that in existing schemes for unpolarized coherent states. Our scheme is not only feasible but also economical with regard to resource consumption because no active displacement operations must be utilized in-line. We also consider practical factors affecting the scheme performance, including decoherence of the input states, realistic resources, and device imperfections. Detailed analyses show that our scheme is robust against small imperfection effects and could be implemented with current technology. The proposed hybrid entanglement would serve as a vital resource for processing information encoded in superpositions of differently polarized coherent states which represent a new format of qubit.

A Simple Method for Including Polarization Effects in Solvation Free Energy Calculations When Using Fixed-Charge Force Fields: Alchemically Polarized Charges.

The incorporation of polarizability in classical force-field molecular simulations is an ongoing area of research. We focus here on its application to hydration free energy simulations of organic molecules. In contrast to computationally complex approaches involving the development of explicitly polarizable force fields, we present herein a simple methodology for incorporating polarization into such simulations using standard fixed-charge force fields, which we call the alchemically polarized charges (APolQ) method. APolQ employs a standard classical alchemical free energy change simulation to calculate the free energy difference between a fully polarized solute particle in a condensed phase and its unpolarized state in a vacuum. APolQ can in principle be applied to any microscopically homogeneous system (e.g., pure or mixed solvents). We applied APolQ to hydration free energy data for a test set of 45 neutral solute molecules in the FreeSolv database and compared results obtained using three different water models (SPC/E, TIP3P, and OPC3) and using minimal basis iterative Stockholder (MBIS) and restrained electrostatic potential (RESP) partial charge methodologies. In comparison with AM1-BCC, we found that APolQ outperforms it for the test set. Despite our method using default GAFF parameters, the MBIS partial charges yield absolute average deviations 1.5–1.9 kJ mol–1 lower than using AM1 bond charge correction (AM1-BCC). We conjecture that this method can be further improved by fitting the Lennard-Jones and torsional parameters to partial charges derived using MBIS or RESP methodologies.