Spin Rings Research Articles

Tripartite correlations in a Heisenberg [formula omitted] spin ring in thermal equilibrium

Tripartite correlations are investigated at length by various witnesses such as tripartite negativity, genuine tripartite entanglement, total tripartite correlations and genuine tripartite correlations. Their behaviors following various tunable system parameters as well as their connections with quantum phase transitions (QPTs) in a three-qubit Heisenberg XXZ spin ring with three-spin interaction in thermal equilibrium are discussed. The results show that these tripartite correlation witnesses can faithfully detect the critical points associated with QPTs at zero temperature limit in this model. In addition, total tripartite correlations and genuine tripartite correlations can even signal critical points with respect to anisotropy Δ at finite low temperatures.

A Review of Ring Staple Yarn Spinning Method Development and Its Trend Prediction

In this article, ring staple single yarn spinning method development has been reviewed after an introductory background about ring spinning principle and ring staple yarn defect problems. The review concludes that previous novel ring staple spinning methods have been developed mainly on a basis of staple spinning strand control enhancements by means of separating single strands into two or several subones, concentrating triangular ring spinning strand, rewrapping protruding fiber ends, and improving online twisting density distribution. Reputed novel ring spinning technologies are included in this review such as siro-spinning, solo-spinning, compact spinning, air-jet spinning, air-suction spinning, and Nu-torque yarn spinning. The inadequacy of some reviewed novel spinning methods is considered as a motility of ring spinning method further development. It is predicted that ring staple spinning can be further developed via increasing spinning efficiency and improving online spinning strand properties.

Thermal entanglement in a {Cu3} single molecular magnet in the magnetic field

We have investigated the properties of thermal entanglement in a triangular spin ring of the single molecular magnet (SMM) Na9[Cu3Na3(H2O)9 (α-AsW9O33)2]·26H2O in a magnetic field, and the pairwise concurrences of arbitrary two Cu2+ ion qubits are calculated numerically, hereafter abbreviated as C12, C23 and C13, respectively. Results show that the magnitude and direction of magnetic field as well as temperature have important effects on the pairwise thermal entanglement. Moreover, C12, C23 and C13 have difference variations with the change of the parameters. We also plot the changes of the critical temperatures Tc of C12, C23 and C13 with the magnetic fields along three different directions, and from the critical temperature-magnetic field phase diagrams one can obtain the ranges of parameters in which the pairwise thermal entanglement in a triangular spin ring of the SMM exists. Therefore, the pairwise entanglement can be controlled and enhanced in the SMM by choosing appropriate magnitude and direction of magnetic field and temperature.

Towards the chemical tuning of entanglement in molecular nanomagnets

Antiferromagnetic spin rings represent prototypical realizations of highly correlated, low-dimensional systems. Here we theoretically show how the introduction of magnetic defects by controlled chemical substitutions results in a strong spatial modulation of spin-pair entanglement within each ring. Entanglement between local degrees of freedom (individual spins) and collective ones (total ring spins) are shown to coexist in exchange-coupled ring dimers, as can be deduced from general symmetry arguments. We verify the persistence of these features at finite temperatures, and discuss them in terms of experimentally accessible observables.

Lord of the rings

Magnets built of molecular rings of magnetic ions are fundamental model systems for studying the complex correlations and dynamics of quantum spins at the atomic scale. A new generation of neutron spectrometers can reveal complete four-dimensional maps of the spin correlations in spin rings.

Zero Temperature Magnetic Frustration in Nona-Membered s=3/2 Spin Rings with Bond Defect

Zero Temperature Magnetic Frustration in Nona-Membered s=3/2 Spin Rings with Bond Defect

Anisotropy, Geometric Structure and Frustration Effects in Molecule-Based Nanomagnets

In this paper we review our results of comprehensive study of molecular nanomagnets recently synthesized in the form of the chromium-based molecules and bimetallic copper-containing chains as well as we present some new findings. We focus on effects of anisotropy, geometry and frustration appearing in various thermodynamic properties of the nanoscale magnets which are described by Heisenberg-like spin models and simulated by accurate numerical methods. We show that bond-dependent exchange anisotropy is needed to model magnetic torque in the Cd-doped chromium ring. We argue that only in the limit of infinite rings (n -> infinity) frustration can be considered as the opposite to bipartiteness in the odd numbered (3 <= n <= 9) s = 3/2 quantum spin rings. We analyse the influence of exchange interactions and anisotropy on magnetic susceptibility of bimetallic (S = 3/2, s = 1/2) chains composed of Cu ions linked to different 3d ions by fitting experimental data. We reach the remarkable consistency of the density functional theory estimates of the magnetic couplings in Crs molecule and provide strong support to the spin models exploited in the literature.

Bistability and nonequilibrium transitions in the system of cavity polaritons under nanosecond-long resonant excitation

The polarization dependence of nonequilibrium transitions in a multistable cavity-polariton system is studied under a nanosecond long resonant optical excitation at the normal and magic angle incidences with various polarizations of the pump beam. The temporal correlations between the frequency, intensity, and optical polarization of the intra-cavity field, which all undergo sharp threshold-like changes due to the spin dependent interaction of cavity polaritons, are visualized. The observed dynamics cannot be reproduced within the conventional semi-classical model based on the Gross-Pitaevskii equations. To explain the observed phenomena, it is necessary to take into account the unpolarized exciton reservoir which brings on additional blueshift of bright excitons, equal in the $\sigma^+$ and $\sigma^-$ polarization components. This model explains the effect of polarization instability under both pulsed and continuous wave resonant excitation conditions, consistently with the spin ring pattern formation that has recently been observed under Gaussian shaped excitation.

Determination of exchange energies in the sawtooth spin ring {Mo75V20} by ESR

The magnetism of the polyoxometalate cluster {Mo75V20}, containing a sawtooth ring of 10 corner-sharing triangles located on the equator of the barrel-shaped molecule, has remained debatable since it is masked by contributions from impurities as well as temperature-independent paramagnetism. In this article we demonstrate the usefulness of ESR measurements since the temperature dependence of the ESR intensity can discriminate between impurity and molecular contributions. We determine the exchange parameters and therefore also the low-lying spectrum of {Mo75V20}, especially the low-lying singlet states which so far have been probed solely by specific heat measurements.

A novel method to reduce hairiness level of ring spun yarn

The quality of ring spun yarns is largely determined by its level of hairiness. The existence of hairiness inevitably affects the quality of ring spun yarns. This paper presents an innovative method on lowering the level of hairiness of ring spun yarns. This can be achieved by shooting compressed air to the yarn, through a swirl nozzle comprising a yarn duct and an airjet nozzle attached to a traditional ring spin frame. When compressed air is applied from the air-jet nozzle to the yarn duct, the swirling air flow tucks surface fibers of the ring spun yarns into its body. Four controllable variable parameters for the process, supplied pressure, nozzle position, twist factor and spindle speed, and their effects on the lowering of yarn hairiness will be clarified. Their impact on the quality of the yarn is statistically analyzed, and the optimum outcome of the combination of parameters for the process, will thus be determined.

Heisenberg spin bus as a robust transmission line for quantum-state transfer

We study the protocol known as quantum state transfer for a strongly coupled antiferromagnetic spin chain or ring (acting as a spin bus), with weakly coupled external qubits. By treating the weak coupling as a perturbation, we find that perfect state transfer (PST) is possible when second order terms are included in the expansion. We also show that PST is robust against variations in the couplings along the spin bus and between the bus and the qubits. As evidence of the quantum interference which mediates PST, we show that the optimal time for PST can be smaller with larger qubit separations, for an even-size chain or ring.

Algebraic classification of five-dimensional spacetimes using scalar invariants

There are a number of algebraic classifications of spacetimes in higher dimensions utilizing alignment theory, bivectors and discriminants. Previous work gave a set of necessary conditions in terms of discriminants for a spacetime to be of a particular algebraic type. We demonstrate the discriminant approach by applying the techniques to the Sorkin–Gross–Perry soliton, the supersymmetric and doubly spinning black rings and some other higher dimensional spacetimes. We show that even in the case of some very complicated metrics, it is possible to compute the relevant discriminants and extract useful information from them.

Frustration signatures in the anisotropic model of a nine-spin s = 3/2 ring with bond defect

Effects of magnetic frustration in the model of nine-membered antiferromagnetic s = 3/2 molecular spin ring are investigated. We use a Heisenberg spin model with nearest-neighbor interactions, single-ion anisotropy and with tunable bond defect leading to continuously varying topology: from closed to open ring. In order to identify a frustrated phase we calculate the full energy spectrum of the model and a number of thermodynamic quantities at low temperature. The calculations are performed by means of numerically exact methods: quantum transfer matrix and exact diagonalization. It is shown that total and local magnetizations, nearest-neighbor spin correlations and spin fluctuations can serve as consistent frustration signatures. Magnetizations and spin-spin correlations are reduced in the frustrated phase whereas fluctuations and correlations of fluctuations increase. The ground state in a frustrated phase is a m = 1/2 doublet and in the non-frustrated phase a m = 3/2 doublet. In the system studied bipartiteness is not opposite to frustration as there are regions in the parameter space for which the system is neither bipartite nor frustrated.

Entanglement in finite spin rings with noncollinear Ising interaction

We investigate the entanglement properties of finite spin rings, with noncollinear Ising interaction between nearest neighbours. The orientations of the Ising axes are determined either by the spin position within the ring (model A) or by the direction of the bond (model B). In both cases, the considered spin Hamiltonians have a point group symmetry, rather than a translation invariance, as in spin rings with collinear Ising interaction. The ground state of these models exhibit remarkable entanglement properties, resembling GHZ-like states in the absence of an applied magnetic field (model B). Besides, the application of an homogeneous magnetic field allows to modify qualitatively the character of the ground state entanglement, switching from multipartite to pairwise quantum correlations (both models A and B).

A low complexity scheme for entanglement distributor buses

For technological purposes and theoretical curiosity, it is very interesting to have a building block that produces a considerable amount of entanglement between on-demand sites through a simple control of a few sites. Here, we consider permanently-coupled spin networks and study entanglement generation between qubit pairs to find low-complexity structures capable of generating considerable entanglement between various qubit pairs. We find that in axially symmetric networks the generated entanglement between some qubit pairs is rather larger than generic networks. We show that in uniformly-coupled spin rings each pair can be considerably entangled through controlling suitable vertices. To set the location of controlling-vertices, we observe that the symmetry has to be broken for a definite time. To achieve this, a magnetic flux can be applied to break symmetry via Aharonov-Bohm effect. Such a set up can serve as an efficient entanglement distributor bus in which each vertex-pair can be efficiently entangled through exciting only one fixed vertex and controlling the evolution time. The low-complexity of this scheme makes it attractive for use in nanoscale quantum information processors.

Polarization Bistability and Resultant Spin Rings in Semiconductor Microcavities

The transmission of a pump laser resonant with the lower polariton branch of a semiconductor microcavity is shown to be highly dependent on the degree of circular polarization of the pump. Spin dependent anisotropy of polariton-polariton interactions allows the internal polarization to be controlled by varying the pump power. The formation of spatial patterns, spin rings with a high degree of circular polarization, arising as a result of polarization bistability, is observed. A phenomenological model based on effective semiclassical equations of motion provides a good description of the experimental results. Inclusion of interactions with the incoherent exciton reservoir, which provides spin-independent blueshifts of the polariton modes, is found to be essential.

Spin Rings in Bistable Planar Semiconductor Microcavities

A remarkable feature of exciton-polaritons is the strongly spin-dependent polariton-polariton interaction, which has been predicted to result in the formation of spin rings in real space [Shelykh, Phys. Rev. Lett. 100, 116401 (2008)]. Here we experimentally demonstrate the spin bistability of exciton polaritons in an InGaAs-based semiconductor microcavity under resonant optical pumping. We observe the formation of spin rings whose size can be finely controlled in a spatial scale down to the micrometer range, much smaller than the spot size. Demonstration of optically controlled spin patterns in semiconductors opens way to the realization of spin logic devices and spin memories.

Thermal entanglement in molecular spin rings

The thermal entanglement in the triangular molecular spin ring with Dzyaloshinskii—Moriya interaction is studied. The concurrences of arbitrary two spins of the triangular molecular spin ring for various cases are evaluated. The tendency of the concurrence with Dzyaloshinskii—Moriya interaction and temperature is analysed and discussed. We note that the concurrence arrives at its maximum in the regime with the large Dzyaloshinskii—Moriya interaction and low temperature, and gradually decreases to zero with the increase of temperature. The concurrence has different features for the ferromagnetic and antiferromagnetic cases. For completeness, we also numerically calculate the concurrence of spin rings with N > 3 spins and analyse their behaviours.

Thermodynamic instability of doubly spinning black objects

We investigate the thermodynamic stability of neutral black objects with (at least) two angular momenta. We use the quasilocal formalism to compute the grand canonical potential and show that the doubly spinning black ring is thermodynamically unstable. We consider the thermodynamic instabilities of ultra-spinning black objects and point out a subtle relation between the microcanonical and grand canonical ensembles. We also find the location of the black string/ membrane phases of doubly spinning black objects.

Synthesis, crystal structure and magnetism of a new mixed germanium–polyoxovanadate cluster

A new germanium–polyoxovanadate, (H 3aep) 4[V 14Ge 8O 50]·2(aep)·13H 2O ( 1), has been synthesized under solvothermal conditions applying GeO 2, NH 4VO 3, Cu(NO 3) 2·3H 2O and an aqueous solution of 1-(2-aminoethyl)-piperazine (aep, C 6H 18N 3) in the temperature range from 110 to 150 °C. The compound crystallizes in the non-centrosymmetric tetragonal space group P-42 1 c with a = 17.193(1) Å, c = 16.501(1) Å, V = 4877.9(5) Å 3 and Z = 2. The structure consists of isolated spherical [V IV 14Ge IV 8O 50] 12− cluster anions and protonated amine molecules as counterions. The cluster anion can be viewed as a derivative of the [V 18O 42] archetype by replacing four VO 5 pyramids by four Ge 2O 7 units. The latter are formed by corner-sharing of two [GeO 4] 4− tetrahedra. At temperatures above 150 °C the compound (H 2pip) 4(Hpip) 4[V IV 14Ge IV 8O 50(H 2O)] ( 2) (pip = piperazine, C 4N 2H 10) is formed and during the reaction Cu 2+ is reduced to elemental copper. This redox reaction is essential for the formation of 2. The crystal water molecules in the structure of 1 are emitted at low temperatures. The magnetic properties are dominated by strong intra-cluster antiferromagnetic coupling and the strongest exchange between edge- and corner-sharing VO 5 square pyramids results in an eight-membered spin ring to which two three-membered spin bridges are joined. The magnetic susceptibility data suggest that even at the low temperature of 2 K several multiplet states are still significantly populated.