The influences of dipole-dipole interaction and detuning on the sudden death of entanglement between two atoms in the Tavis-Cummings model

The influences of dipole-dipole interaction and detuning on the entanglement between two atoms with different initial tripartite entangled W-like states in the Tavis Cummings model have been investigated by means of Wootters＇ concurrence, respectively. The results show that the entanglement between the two atoms can be enhanced via appropriately tuning the strength of dipole-dipole interaction of two atoms or the detunings between atom and cavity, and the so-called sudden death effect can he weakened simultaneously.

Position-dependent property of resonant dipole-dipole interaction mediated by localized surface plasmon of an Ag nanosphere

We use the photon Green-function method to study the quantum resonant dipole-dipole interaction（RDDI） induced by an Ag nanosphere（ANP）.As the distance between the two dipoles increases,the RDDI becomes weaker,which is accompanied by the influence of the higher-order mode of the ANP on RDDI declining more quickly than that of the dipole mode.Across a broad frequency range（above 0.05 eV）,the transfer rate of the RDDI is nearly constant since the two dipoles are fixed at the proper position.In addition,this phenomenon still exists for slightly different radius of the ANPs.We find that the frequency corresponding to the maximum transfer rate of RDDI exhibits a monotonic decrease by moving away one dipole as the other dipole and the ANP are kept fixed.In addition,the radius of ANP has little effect on this.When the two dipoles are far from the ANP,the maximum transfer rate of the RDDI takes place at the frequency of the dipole mode.In contrast,when the two dipoles are close to the ANP,the higher-order modes come into effect and they will play a leading role in the RDDI if they match the transition frequency of the dipole.Our results may be used in a biological detector and have a certain guiding significance for further application.

Effects of dipole-dipole interaction on entanglement transfer

A system consisting of two different atoms interacting with a two-mode vacuum, where each atom is resonant only with one cavity mode, is considered. The effects of dipole-dipole （dd） interaction between two atoms on the atom-atom entanglement and mode--mode entanglement are investigated. For a weak dd interaction, when the atoms are initially separable, the entanglement between them can be induced by the dd interaction, and the entanglement transfer between the atoms and the modes occurs efficiently; when the atoms are initially entangled, the entanglement transfer is almost not influenced by the dd interaction. However, for a strong dd interaction, it is difficult to transfer the entanglement from the atoms to the modes, but the atom-atom entanglement can be maintained when the atoms are initially entangled.

The entanglement of two dipole-dipole coupled atoms interacting with a thermal field via a two-photon process

This paper studies entanglement between two dipole-dipole coupled atoms interacting with a thermal field via a two-photon process. It shows that the entanglement is dependent on the mean photon number of the thermal field and the dipole-dipole interaction. The results also show that the atom-atom entanglement through the two-photon process is larger than that through the one-photon process and a remarkable amount of entanglement between the atoms still remains at certain times even for a very highly noisy thermal field.

Excitation Dependence of Dipole-Dipole Broadening in Selective Reflection Spectroscopy

We investigate the dipole-dipole broadened selective reflection spectrum with the Cs atomic aensity of 10^14- 10^15 cm^-3. The dipole-dipole broadening is reduced and the hyperfine splitting is well resolved when the ground state atoms are excited by a detuned pump beam. The dependences of dipoleMipole broadening of Cs atoms in the 6S1/2（F= 3） → 6P3/2（F＇= 4） hyperfine transition line on atomic density and the excitation factor are studied. It is found that the reduction of the dipole-dipole broadening is dependent on the pump beam power and is independent of the atomic density in this density range. These results are useful for understanding of the dynamical process in this range of atomic density.

Critical Property of the Geometric Phase in the Dicke Model with the Dipole-dipole Interactions

We obtained the ground-state energy level and associated geometric phase in the Dicke model with the dipoledipole interactions analytically by the Holstein-Primakoff transformation and the boson expansion approach in the thermodynamic limit. The nonadiabatic geometric phase induced by the photon field was derived with the time-dependent unitary transformation. It is shown that dipole-dipole interactions have a deep influence on scaled behavior of the geometric phase at the critical point.

Dynamic Dipole-Dipole Magnetic Interaction and Damped Nonlinear Oscillations

Static dipole-dipole magnetic interaction is a classic topic discussed in electricity and magnetism text books. Its dynamic version, however, has not been reported in scientific literature. In this article, the author presents a comprehensive analysis of the latter. We consider two identical permanent cylindrical magnets. In a practical setting, we place one of the magnets at the bottom of a vertical glass tube and then drop the second magnet in the tube. For a pair of suitable permanent magnets characterized with their mass and magnetic moment we seek oscillations of the mobile magnet resulting from the unbalanced forces of the anti-parallel magnetic dipole orientation of the pair. To quantify the observed oscillations we form an equation describing the motion of the bouncing magnet. The strength of the magnet-magnet interaction is in proportion to the inverse fourth order separation distance of the magnets. Consequently, the corresponding equation of motion is a highly nonlinear differential equation. We deploy Mathematica and solve the equation numerically resulting in a family of kinematic information. We show our theoretical model with great success matches the measured data.

Numerical Experiment for Dipole-Dipole Interaction in Electro-Magnetism with Help of a Regular Tetrahedron

Aim of this work is to try to explain, on a Rational basis, some equations of Electro-Magnetism, which are based on Experimental data. Any Electric Field can produce a Field of many small Electric Dipoles, continuously distributed in space. In a region, where the Electric Field is constant, in direction and magnitude, all the small Dipoles are parallel to the Electric Field, and are represented by a single, long, parallel to them, fixed in space, Electric Dipole, which is here called Compass. An Alternating current, in a straight Conductor, is studied, by a simple, short computer program, for step-by-step nonlinear dynamic analysis. It is found that, only an Alternating current, not a direct current, can produce an Electric Dipole, in a straight Conductor. The two above Dipoles (Compass-Conductor) are assumed with equal lengths ℓ, lying on two skew lines, perpendicular to each other, at a distance ℓ√2, thus forming, by their four ends, a Regular Tetrahedron, with side length ℓ. Repulsion, between Like Charges, obeys the simple Coulomb Electro-Static law. Whereas Interaction (Attraction or Repulsion), between Unlike Charges, obeys a more accurate Lennard-Jones law. The analysis of Dipole-Dipole (Compass-Conductor) Interaction is performed by hand calculator. The only out-of-balance forces, in the regular Tetrahedron, acting on the Rigid Conductor, are the so-called magnetic forces. Their direction is found, in a simple Rational way, with help of Regular Tetrahedron, without recoursing to a “right-hand-rule”. The proposed model is applied to 1) The force acting on an Electric Charge moving in a magnetic field. 2) The force acting on a Current carrying straight Conductor, due to a magnetic field. 3) The magnetic fields created around a Current carrying straight Conductor. In these applications, proposed model gives reasonable results. Particularly, in third application, results, obtained by proposed model, are found in satisfactory approximation with corresponding ones, obtained by an empirical formula, based on relevant Experimental observations of H.-C. Oersted and A.-M. Ampère. So, the reliability of proposed model is checked. Position and direction of magnetic field vector coincide with those of a corresponding fixed Compass of a constant Electric Field. Main point of present work is that, without introducing the concept of a magnetic field vector, by combining field of dipoles, produced by an electric field, with dipole of an alternating current carrying conductor, the magnetic forces can be determined.

Designing Fano-Like Quantum Routing via Atomic Dipole-Dipole Interactions

Fano-like quantum routing of single photons in a system with two waveguides coupled to two collocated atoms is investigated theoretically. Using a full quantum theory in real space, photonic scattering amplitudes along four ports of the waveguide network are analytically obtained. It is shown that, by adjusting the atomic dipole-dipole interaction, an evident Fano-line shape emerges in the scattering spectra of the single-dot configuration system. Moreover, Fano resonance can also be achieved by varying the atom-waveguide coupling strength and atomic detuning, in the presence of the atomic dipole-dipole interaction. Therefore, the atomic dipole-dipole interaction may be utilized as a possible way to control spectral Fano-like resonance. The feasibility with the experimental waveguide channels is also discussed.

Higher-Order Corrections to Algebraic Derivation of Electric Dipole-Dipole Interaction

Nucleons are fermions with intrinsic spins exhibiting dipole character. Dipole-dipole interaction via their dipole moments is the key feature quantifying the short-range nucleonics interaction in two-body physics. For a pair of interacting dipoles, the energy of a pair is the quantity of interest. The same is true for chemical polar molecules. For both cases, derivation of energy almost exclusively is carried out vectorially [1]. Although uncommon the interacting energy can be derived algebraically too. For the latter Taylor, expansion is applied [2]. The given expression although appears to be correct it is incomplete. In our report, by applying Taylor’s expansion up to the 4th order and utilizing a Computer Algebra System we formulate the missing terms. Our report highlights the impact of correcting missing terms by giving two explicit examples.

Effect of dipole-dipole interaction among atoms on atomic dynamics and entropy evolution of the field

New developments in the high techniques associated with quantum optics have made it possible to produce a high-Q cavity with an extremely small size comparable to the wavelength of atomic emission. In such cavities with so small size, many distinctive phenomena of atomic motion interacting with cavity field appear to be quite attractive. The Jaynes-Cummings model describes the interaction of a two-level atom with a single mode field. When two atoms enter the domain of the cavity field simultaneously, and interact with each other through the dipole-dipole coupling with the exchange of

Doping Induced Tailoring in the Morphology,Band-Gap and Ferromagnetic Properties of Biocompatible ZnO Nanowires, Nanorods and Nanoparticles

The modification of nanostructured materials is of great interest due to controllable and unusual inherent properties in such materials. Single phase Fe doped Zn O nanostructures have been fabricated through simple, versatile and quick low temperature solution route with reproducible results. The amount of Fe dopant is found to play a significant role for the growth of crystal dimension. The effect of changes in the morphology can be obviously observed in the structural and micro-structural investigations, which may be due to a driving force induced by dipole-dipole interaction. The band gap of Zn O nanostructures is highly shifted towards the visible range with increase of Fe contents, while ferromagnetic properties have been significantly improved.The prepared nanostructures have been found to be nontoxic to SH-SY5 Y Cells. The present study clearly indicates that the Fe doping provides an effective way of tailoring the crystal dimension, optical band-gap and ferromagnetic properties of Zn O nanostructure-materials with nontoxic nature, which make them potential for visible light activated photocatalyst to overcome environmental pollution, fabricate spintronics devices and biosafe drug delivery agent.

Study of the Dielectric Behaviour of Cr-Doped Zinc Nano Ferrites Synthesized by Sol-Gel Method

The series of Cr-Zn nano ferrites having the general composition CrxZnFe2-xO4 (0 ≤ x ≤ 0.5) have been synthesized successfully in the nanocrystalline form using the sol-gel method. The samples were sintered at 900°C for 3 hours. The effect of chromium substitution on dielectric properties of Zn-ferrites is reported in this paper. The analysis of XRD patterns revealed the formation of single phase cubic spinel structure for all the Cr-Zn ferrite samples. The FTIR spectra show two strong absorption bands in the range of 400 - 600 cm-1, which corroborate the spinel structure of the samples. The average grain size was found to be in the nanometer range and of the order of 43 - 63 nm obtained using TEM images. The lattice parameter and crystallite size decrease with increase in Cr concentration (x). The investigation on dielectric constant (ε'), dissipation factor (D) and ac conductivity (σac) was carried out at a fixed frequency 1 kHz and in the frequency range of 100 Hz to 1 MHz at room temperature using LCR meter. The plots of dielectric constant (ε') versus frequency show the normal dielectric behavior of spinel ferrites. The value of ac conductivity (σac) increases with increase in frequency for all the compositions. The appearance of the peak for each composition in the dissipation factor versus frequency curve suggests the presence of relaxing dipoles in the Cr-Zn nano ferrite samples. It is also found that the shifting of the relaxation peak towards lower frequency side with an increase in chromium content (x) is due to the strengthening of dipole-dipole interactions. The composition and frequency dependence of the dielectric constant, dielectric loss and ac-conductivity are explained based on the Koop’s two-layer model, Maxwell-Wagner polarization process, and Debye relaxation theory.

Dipole–dipole interactions enhance non-Markovianity and protect information against dissipation

Preserving non-Markovianity and quantum entanglement from decoherence effect is of theoretical and practical significance in the quantum information processing technologies.In this context, we study a system S that is initially correlated with an ancilla A, which interacts with the environment E via an amplitude damping channel.We also consider dipole-dipole interactions(DDIs) between the system and ancilla, which are responsible for strong correlations.We investigate the impact of DDIs and detuning on the non-Markovianity and information exchange in different environments.We show that DDIs are not only better than detuning at protecting the information(without destroying the memory effect) but also induce memory by causing a transition from Markovian to non-Markovian dynamics.In contrast, although detuning also protects the information, it causes a transition from non-Markovian to the Markovian dynamics.In addition, we demonstrate that the non-Markovianity grows with increasing DDI strength and diminishes with increasing detuning.We also show that the effects of negative detuning and DDIs can cancel out each other, causing a certain loss of coherence and information.

Dynamics of two polarized nanoparticles

The intrinsic dynamics of two interacting electric polarized nanorods is theoretically investigated. The relative motion between them caused by electric dipole-dipole interaction is derived based on the generalized Lagrangian formulation. The results show that the relative translation and rotation are nonlinear and closely dependent on the initial configuration of the two nanorods. Furthermore, the general conditions of the initial configuration, which determine the two nanorods to repel or attract each other at the initial time, are obtained. The two-dimensional relative motion of the two nanorods shows that the antiparallel and head-to-tail ordering stable self-assembly are respectively formed in two planar initial configurations. For different three-dimensional initial configurations, the interesting dynamic relative attraction, repulsion, and oscillation with rotation are respectively realized. Finally, the theoretical schemes which realize the relaxing, direct head-to-tail ordering, and direct antiparallel ordering stable self-assembly are presented according to the different modes of the motion of the nanoparticles. Some of our results agree well with the results of experiments and simulations.

Ground-state phases and spin textures of spin–orbit-coupled dipolar Bose–Einstein condensates in a rotating toroidal trap

We investigate the ground-state phases and spin textures of spin-orbit-coupled dipolar pseudo-spin-1/2 Bose-Einstein condensates in a rotating two-dimensional toroidal potential.The combined effects of dipole-dipole interaction(DDI),spin-orbit coupling(SOC),rotation,and interatomic interactions on the ground-state structures and topological defects of the system are analyzed systematically.For fixed SOC strength and rotation frequency,we provide a set of phase diagrams as a function of the DDI strength and the ratio between inter-and intra-species interactions.The system can show rich quantum phases including a half-quantum vortex,symmetrical(asymmetrical)phase with quantum droplets(QDs),asymmetrical segregated phase with hidden vortices(ASH phase),annular condensates with giant vortices,triangular(square)vortex lattice with QDs,and criss-cross vortex string lattice,depending on the competition between DDI and contact interaction.For given DDI strength and rotation frequency,the increase of the SOC strength leads to a structural phase transition from an ASH phase to a tetragonal vortex lattice then to a pentagonal vortex lattice and finally to a vortex necklace,which is also demonstrated by the momentum distributions.Without rotation,the interplay of DDI and SOC may result in the formation of a unique trumpet-shaped Bloch domain wall.In addition,the rotation effect is discussed.Furthermore,the system supports exotic topological excitations,such as a half-skyrmion(meron)string,triangular skyrmion lattice,skyrmion-halfskyrmion lattice,skyrmion-meron cluster,skyrmion-meron layered necklace,skyrmion-giant-skyrmion necklace lattice,and half-skyrmion-half-antiskyrmion necklace.

Entanglement in a generalized Jaynes-Cummings model

We investigate the pairwise entanglement and global entanglement in a generalized Jaynes-Cummings model, which can be used to realize Greenberger-Horne-Zeilinger （GHZ） entangled state （Zheng S B 2001 Phys. Rev. Lett. 87 230404）. Our results show that the W-type entangled states cannot be generated based on the model. The dependences of entanglement on Rabi frequency λ and dipole-dipole coupling strength Ω are given. It is found that there exists the quantum phase transition when λ= Ω. For typical experimental data, the critical temperature for pairwise entanglement is on the order of 10^-6 K. Based on these results, two strategies that overcome decoherence are proposed.

Measurement-induced disturbance between two atoms in Tavis-Cummings model with dipole dipole interaction

Quantum correlation, measured by measurement-induced disturbance （MID）, between two two-level atoms is investi- gated in detail in Tavis-Cummings model with dipole--dipole interaction （DDI）. We find that MID can be determined only by the dipole-dipole interaction between the two atoms when the cavity and atoms are at resonance. Moreover, DDI will have different effects on MID for two different kinds of initial states.

Effect of Geodynamic Activities on an Existing Dam: A Case Study of Ojirami Dam, Southern Nigeria

Geodynamics is the study of the forces and their effects on motion and physics of the processes and the phenomena attending the steady evolution of the earth and the changes that are still going on. This study revealled the significance of electrical resistivity method on effect of geodynamic activities on an existing Dam monitoring at Ojirami Dam, Edo State, Nigeria. The electrical resistivity method involved three techniques: 2D Electrical Resistivity Tomography (ERT), Vertical Electrical Sounding (VES) and Horizontal Profiling (HP). 2D ERT using Dipole-Dipole electrode array with inter-station separation of 5 m and an expansion factor that varied from 1 to 5 with Nine (9) VES were carried out using Schlumberger array with current electrode spacing varying from 1.0 to 65.0 m and HP using Wenner array with an electrode spacing of 20 m and electrode movement at 5 meters. The 2-D imaging (Dipole-Dipole) gave information on the subsurface characteristic which section delineated five major geologic layers comprising of the topsoil, weathered basement, fractured zone, partly fractured basement and the fresh basement. The geoelectric sections identified three to four geoelectric/geologic subsurface layers along the traverse. The HP revealled the pattern of resistivity variations within the subsurface. The entire results correlate well with one another showing that all the techniques used were complemented. The combination of these techniques has proved effective and useful in geodynamic activities of the existing dam. Ojirami Dam is at a critical point of yielding to activities of geodynamic processes that may occur from the main axis, of major weak zones as observed between 75 to 95.00 m and 115 to 145.00 m. Hence, there is need to call government attention for further confirmatory test using other geophysical methods and subsequently putting in place remedial measures to prevent its future occurrence.

Landau damping in a dipolar Bose–Fermi mixture in the Bose–Einstein condensation(BEC) limit

By using a mean-field approximation which describes the coupled oscillations of condensate and noncondensate atoms in the collisionless regime, Landau damping in a dilute dipolar Bose-Fermi mixture in the BEC limit where Fermi superfluid is treated as tightly bounded molecules, is investigated. In the case of a uniform quasi-two-dimensional （2D） case, the results for the Landau damping due to the Bose-Fermi interaction are obtained at low and high temperatures. It is shown that at low temperatures, the Landau damping rate is exponentially suppressed. By increasing the strength of dipolar interaction, and the energy of boson quasiparticles, Landau damping is suppressed over a broader temperature range.