Double-Mode Excited Entangled Coherent States and Their Fidelity

In this paper, we introduce the definition of a new kind of continuous-variable-type entangled coherent states, called double-mode excited entangled coherent states through acting creation operators on the double-mode entangled coherent states. We briefly present how to produce them from the two mode ECSs through an interaction between laser and atoms. We further focus on studying the fidelity of the states and discussing the influence of photon excitations on fidelity.     

Entangled Finite Dimensional Pair Coherent States and Their Applications

Intermediate states of electromagnetic field are reviewed. It is a type of the correlated two-mode states (converter state). Based on the resonant ion-cavity interaction, we propose a scheme to generate these states revealing their connection with the converter state. The practical feasibility of this method is also discussed. We discuss nonclassicality of a finite dimensional pair coherent states in terms of sub-Poissonian photon statistics as well as the negativity of the Wigner function after deriving the analytic expression for the Wigner function. We explore a superposition of two finite dimensional pair coherent states. We show that such states possess inherent nonclassical properties such as sub-Poissonian distribution, anti-correlation between the two modes and violation of Cauchy-Schwarz inequalities. The s-parameterized characteristic function (CF) is considered. The phase distribution in the framework of Pegg and Barnett formalism, W-function and Q-function are discussed. Furthermore, a two-level atom in interaction with a two-mode quantized electromagnetic fields besides a frequency converter interaction initially prepared in an entangled two-mode coherent state is presented. Exact solution of the wave function in the Schrödinger picture is obtained. Some statistical aspects of this model are presented. The results are employed to perform a careful investigation of the temporal evolution of the atomic inversion, entropy squeezing and variance squeezing. General conclusions reached are illustrated by numerical results.     

An Alternative Model of the Damped Harmonic Oscillator Under the Influence of External Force

In this paper we introduce the modified time-dependent damped harmonic oscillator. An exact solution of the wave function for both Schrödinger picture and coherent state representation are given. The linear and quadratic invariants are also discussed and the corresponding eigenvalues and eigenfunctions are calculated. The Hamiltonian is transformed to SU(1,1) Lie algebra and an application to the generalized coherent state is discussed. It has been shown that when the system is under critical damping case the maximum squeezing is observed in the first quadrature F _x . However, for the overcritical damping case the maximum squeezing occurs in the second quadrature F _y . Also it has been shown that the system for both cases is sensitive to the variation in the coherent state phase.     

Single-atom laser: Coherent and nonclassical effects in the regime of a strong atom-field correlation

Based on the approximation of strong correlations between an atom and an intracavity field, which implies the equal probabilities of finding the atom in the ground state and n photons in the field and of finding the atom in an excited state and n?1 photons in the field, it is shown that the conditional states of a field generated by a single-atom laser are described by the diagonal part of the generalized coherent Mittag-Leffler state. The quasi-distributions P and Q of the intracavity-field probability amplitude are found, and the boundedness of the Glauber function on a segment is shown. The possibility of inversionless lasing is demonstrated, and the absence of a lasing threshold is found for some region of parameters. The regimes of generation of the amplitude-squeezed states of the field are studied and the parameters of the system providing the maximum squeezing are determined. It is shown that the atom-field states are entangled at weak pump intensities.     

Tripartite Entanglement in an Atom-Cavity-Optomechanical System

We investigate tripartite entanglement in an atom-cavity-optomechanical system consisting of a two-level atom coupled to a cavity with an oscillating mirror at one end. The maximally entangled state between the atom, the field and the oscillating mirror can be prepared in the ideal case. It is shown that the atomic coherent angle that is relatively small makes tripartite entanglement much stronger against dissipative effects in a finite time interval. The parameter k plays a very important role in the oscillating frequency of the tripartite entanglement. More importantly, the π-tangle decays more quickly with the increasing of spontaneous emission rate γ and mean photon number n.     

The checkerboard family of entangled states of two qutrits

By modifying the method of Bruß and Peres, we construct two new families of entangled two qutrit states. For all density matrices ρ in these families we have ρ _ij = 0 for i + j odd. The first family depends on 27 independent real parameters and includes both PPT and NPT states. The second family consists of PPT entangled states. The number of independent real parameters of this family is ≥ 11     

The New Multipartite Squeezing Operator and Some of its Properties

In this paper, we introduce a pair of mutually conjugate multipartite entangled state representations for defining the squeezing operator of entangled multipartite S_n(λ) which involves an n-mode bosonic operator realization of the SU(1,1) Lie algebra. This operator squeezes the multipartite entangled state in a natural way. We discuss the transform properties of a_j and \(a_{j}^{\dagger }\) under the operation of S_n(λ) and derive the interaction Hamiltonian which can generate such an evolution. In addition, the corresponding multipartite squeezed vacuum state |λ〉 is obtained. Based on this, the variances of the n-mode quadratures in |λ〉 are evaluated and the violation of the Bell inequality for |λ〉 is examined by using the formalism of Wigner representation.     

Teleportation of aTripartite Squeezed Entangled State Via EPR Entangled State with Continuous Variables

A scheme for teleporting an arbitrary tripartite entangled state is proposed when three bipartite entangled states (|η〉) with continuous variables are used as quantum channels. Quantum teleportation can be carried out successfully if the receiver adopts an appropriate unitary transformation. The calculation is greatly simplified by virtue of the Schmidt decompositions of both tripartite entangled state |p _t ,χ ₂,χ ₃〉 and |η〉. Any tripartite state which can be expanded in terms of |p _t ,χ ₂,χ ₃〉 may be teleported in this way due to the completeness of |p _t ,χ ₂,χ ₃〉.     

Complex Wavelet Transform of the Two-mode Quantum States

By employing the bipartite entangled state representation and the technique of integration within an ordered product of operators, the classical complex wavelet transform of a complex signal function can be recast to a matrix element of the squeezing-displacing operator U ₂(μ, σ) between the mother wavelet vector 〈ψ| and the two-mode quantum state vector |f〉 to be transformed. 〈ψ|U ₂(μ, σ)|f〉 can be considered as the spectrum for analyzing the two-mode quantum state |f〉. In this way, for some typical two-mode quantum states, such as two-mode coherent state and two-mode Fock state, we derive the complex wavelet transform spectrum and carry out the numerical calculation. This kind of wavelet-transform spectrum can be used to recognize quantum states.     

Investigation of zero-frequency solutions to the pion dispersion equation

The instability of nuclear matter is considered for the case where it is generated by the vanishing of the frequencies of collective excitations belonging to specific types (specifically, excitations that have the pion quantum numbers J ^π = 0^?). The behavior of zero-frequency solutions to the pion dispersion equation is analyzed versus the strength G′ of spin—isospin particle—hole interaction. It is shown that there exists a strength value G′_tr (|G′_tr| ? 1) such that, for G′ < G′_tr, zero-frequency solutions are excitations of the ω _P type, while, for G′ ≥ G′_tr, such solutions are excitations of the ω _c type. Excitations of the ω _P type for G′ < ?1 describe the instability of nuclear matter against small density fluctuations (Pomeranchuk’s instability), while excitations of the ω _c type are responsible for the instability associated with pion condensation at G′ ≈ 2. For stable nuclear matter, the solutions ω _P(κ) and ω _c (κ) lie on unphysical sheets of the complex plane of frequency.     

2 + 1 Flavors QCD Equation of State in NJL Model with Proper Time Regularization

Totally symmetric A_1g phonons are studied for the equilibrium and coherent states of a Bi₂Te₃ lattice. Equilibrium phonons were investigated in the frequency domain by the method of spontaneous Raman scattering, whereas coherent phonons were studied by the method of active femtosecond spectroscopy in the time domain. In the latter case, femtosecond laser pulses were used both for generating and detecting coherent A_1g phonons having a well-defined phase allowing the selective optical control of the lattice dynamics. A comparison of the results obtained in the frequency and time domains suggests that diagonal and nondiagonal elements of the density matrix of lattice excitations relax with the same characteristic time to the equilibrium and zero values, respectively.     

Electric quadrupole moments of light nuclei and transition probabilities for them in the multiquantum approximation of the orthogonal scheme

A method for calculating electric quadrupole moments of light nuclei and probabilities of electric quadrupole transitions in them in the multiquantum approximation of the orthogonal scheme is proposed. Specific calculations of these quantities are performed for the ₄ ⁸ Be nucleus with allowance for all U(3(A ? 1)) states characterized by the λ = [44] Young diagram, the quantum numbers K _min and K _min + 2 of the O(3A ? 1)) group, and the number E = K + 2N (N = 0, 1, …, 9) of oscillator quanta. It is shown that an extension of the basis from the E = K _min to the E = K _min + 2 approximation leads to an increase of 15 to 45% in the electric quadrupole moments and to an increase in the transition probabilities B(E2) by a factor of 1.6 to 2.8. The inclusion of E = K + 2N (N = 0, 1, …), states involving multiquantum excitations (ρ excitations) increases additionally the results by 10 to 30%. The results of these calculations are compared with their counterparts obtained in the multiquantum approximation of the unitary scheme.     

Two-photon nutation excited in a two-level spin system by microwave and RF fields

Two-photon transient nutation is observed in a two-level spin system (E′₁ centers in crystalline quartz) using a transverse microwave field and a linearly polarized rf field oriented along a static magnetic field in the electron paramagnetic resonance. Nutation is excited when the sum of the energies of a microwave photon and a rf photon is equal to the energy difference between two spin states. The two-photon nature of nutation is confirmed by measuring its frequency as a function of the amplitude and frequency of the rf field as well as the amplitude of the microwave field. The amplitude of the effective field of two-photon transitions is measured. It is shown that the decay rate of two-photon nutation is close to the decay rate for one-photon nutation and is determined by the spin-spin interaction between E′₁ centers.     

Quantum information-holding single-photon router based on spontaneous emission

In this paper, we propose a single-photon router via the use of a four-level atom system coupled with two one-dimensional coupled-resonator waveguides. A single photon can be directed from one quantum channel into another by atomic spontaneous emission. The coherent resonance and the photonic bound states lead to the perfect reflection appearing in the incident channel. The fidelity of the atom is related to the magnitude of the coupling strength and can reach unit when the coupling strength matches g _a = g _b . This shows that the transfer of a single photon into another quantum channel has no influence on the fidelity at special points.     

Dense Coding in a Two-Spin Squeezing Model with Intrinsic Decoherence

Quantum dense coding in a two-spin squeezing model under intrinsic decoherence with different initial states (Werner state and Bell state) is investigated. It shows that dense coding capacity χ oscillates with time and finally reaches different stable values. χ can be enhanced by decreasing the magnetic field Ω and the intrinsic decoherence γ or increasing the squeezing interaction μ, moreover, one can obtain a valid dense coding capacity (χ satisfies χ > 1) by modulating these parameters. The stable value of χ reveals that the decoherence cannot entirely destroy the dense coding capacity. In addition, decreasing Ω or increasing μ can not only enhance the stable value of χ but also impair the effects of decoherence. As the initial state is the Werner state, the purity r of initial state plays a key role in adjusting the value of dense coding capacity, χ can be significantly increased by improving the purity of initial state. For the initial state is Bell state, the large spin squeezing interaction compared with the magnetic field guarantees the optimal dense coding. One cannot always achieve a valid dense coding capacity for the Werner state, while for the Bell state, the dense coding capacity χ remains stuck at the range of greater than 1.     

Spectrum generating algebra and coherent states of the <Emphasis Type="Italic">C</Emphasis><Subscript>λ</Subscript>-extended oscillator

C_λ-extended oscillator algebras, generalizing the Calogero-Vasiliev algebra, where C_λ is the cyclic group oforder λ, have recently proved very useful in the context of supersymmetric quantum mechanics and some of its variants. Here, we determine the spectrum generating algebra of the C_λ-extended oscillator. We then construct its coherent states, study their nonclassical properties, and compare the latter with those of standard λ-photon coherent states, which are obtained as a special case. Finally, we briefly review some other types of coherent states associated with the C_λ-extended oscillator.     

Entanglement Teleportation via Two-Qubit Spin Squeezing Model

Entanglement teleportation via two spins coupled to each other by one axis twisting spin squeezing interaction is investigated. We mainly concentrate on the properties of the channel entanglement, the output entanglement and the teleportation fidelity. It shows that the output entanglement increases linearly with increasing the value of the input entanglement. With the increasing of T, the teleportated entanglement increases sharply from zero to a maximum value and then decreases slowly to zero when the temperature is improved to one threshold value of T _c , and the threshold value of T _c increases with the increasing of the input entanglement. When enlarging the external magnetic, F _a firstly decreases quickly to a minimum value as the critical magnetic field Ω _c is reached, then it increases abruptly to a maximum value and finally it will be a certain value. Besides, the critical external magnetic Ω _c increases when μ is larger. For Ω<Ω _c the value of the average fidelity increases with the increasing of μ, but for Ω>Ω _c the value of it decreases from a maximum value. The influence of T on the average fidelity is similar with μ.     

<Emphasis Type="Italic">M</Emphasis>α and <Emphasis Type="Italic">M</Emphasis>β X-ray emission spectra of Au atoms upon photoionization of <Emphasis Type="Italic">L</Emphasis> subshells

The structure and relative intensity of the Mα and Mβ X-ray fluorescence spectra of Au atoms are studied experimentally at the energies of absorbed photons both below and above the ionization thresholds of L subshells (Kα_{1, 2} radiation of Cr, Cu, and Mo). The M ₅ N and M ₄ N high-energy satellites are separated from the total spectral profiles and their relative intensities are determined. A model of the M emission is proposed that allows one to take into account the main channels of vacancy transfer from L to M subshells, which are responsible for the generation of double vacancy (M _{4, 5} N and M _{4, 5} O) and triple vacancy (M _{4, 5} N ², M _{4, 5} NO, and M _{4, 5} O ²) states. Comparison of the experimental relative intensities of separated M ₅ N and M ₄ N satellites excited by the Mo Kα_{1, 2} radiation with the calculated results indicates the correctness of the model used. The partial and total M emission cross sections of Au in the absorbed photon energy range of 5–30 keV are calculated. It is found that, in the photon energy region above the ionization threshold of the L ₃ subshell, our results noticeably differ from the data calculated by other authors. Possible reasons for these discrepancies are discussed.     

Soliton dynamics in a spin nematic

One-dimensional localized waves, which can be considered as soliton elementary excitations, exist in a magnet with a unit spin and comparable bilinear and biquadratic spin-spin interactions, with which the state of spin nematic is realized. These excitations are characterized by a certain momentum P and a certain energy E. The structure of these solitons has been found, and the E = E(P) dependence, which plays the role of the dispersion law of these soliton elementary excitations, has been constructed. The energy of a soliton with a certain momentum is shown to be lower than that of the quasiparticles of a linear theory. At small momenta, these E = E(P) dependences of the soliton and quasiparticles coincide asymptotically. The dependence of the soliton energy on the soliton momentum is a periodic function with a period P ₀ = π?/a, whose value does not depend on exchange integrals and depends only on a single crystal parameter, namely, the interatomic distance a. These soliton excitations have common features with the so-called Lieb states, which are well known in many condensed matter models.