Symmetric and Non-Symmetric Bases of Quantum Integrable Particle Systems with Long-Range Interactions

We study in an algebraic manner the symmetric basis of the Calogero model and the non-symmetric basis of the corresponding Calogero model with distinguishable particles. The Rodrigues formulas are presented for the polynomial parts of both bases. The square norm of the non-symmetric basis is evaluated. Symmetrization of the non-symmetric basis reproduces the symmetric basis and enables us to calculate its square norm.     

Long-Range Order in Nonequilibrium Systems of Interacting Brownian Linear Oscillators

Long-range order (lro) is established with the help of a generalized Peierls argument for non-equilibrium lattice systems of one-dimensional (linear) interacting oscillators whose equation of motion (for a finite number of them) is the Smolouchowski equation for the density of a probability distribution. Interaction is mediated through the pair nearest-neighbor quadratic translation invariant potential. The initial density is Gibbsian with a potential energy satisfying the Ruelle superstability and regularity conditions.     

Entropy-Driven Phase Transitions in Multitype Lattice Gas Models

In multitype lattice gas models with hard-core interaction of Widom–Rowlinson type, there is a competition between the entropy due to the large number of types, and the positional energy and geometry resulting from the exclusion rule and the activity of particles. We investigate this phenomenon in four different models on the square lattice: the multitype Widom–Rowlinson model with diamond-shaped resp. square-shaped exclusion between unlike particles, a Widom–Rowlinson model with additional molecular exclusion, and a continuous-spin Widom–Rowlinson model. In each case we show that this competition leads to a first-order phase transition at some critical value of the activity, but the number and character of phases depend on the geometry of the model. We also analyze the typical geometry of phases, combining percolation techniques with reflection positivity and chessboard estimates.     

原子与弱相干腔场相互作用系统中的量子特性

考虑腔场处于弱相干态的情况,研究了两个全同的二能级原子与耦合腔相互作用系统中原子的偶极压缩和原子间的纠缠特性。研究结果表明,随耦合腔耦合系数增大,原子的偶极压缩减弱。另一方面,随耦合腔耦合系数增大,原子间的纠缠也减弱,这一结果与耦合腔处于真空态的情况相反。     

耦合原子与腔场多光子相互作用过程中的量子信息传递

建立了"多耦合原子--腔"系统的多光子相互作用模型. 利用腔量子电动力学理论, 研究了原子与腔场相互作用过程中量子信息传递的特性, 分析了原子间耦合作用对量子信息传递的影响. 结果表明: 在一定的相互作用时间内, 量子信息可以在腔场与原子间可逆传递或保持, 原子间的偶极作用导致量子纠缠信息非完全传递和非完全保持.     

On the Spectroscopic Structure of Two Interacting Electrons in a Quantum Dot

The shifted 1/N expansion technique used by El-Said [Phys. Rev. B 61 (2000) 13026], to study the relative Hamiltonian of two interacting electrons confined in a quantum dot, is investigated. El-Said's results from shifted large-N (or 1/N) expansion technique are revised and results from an alternative method are also reported. The distinctive role of the central spike term, (m ²-1/4)/q ², in determining spectral properties of the above problem is shown, moreover.     

Mean-Field Driven First-Order Phase Transitions in Systems with Long-Range Interactions

We consider a class of spin systems on ℤ ^d with vector valued spins (S _x ) that interact via the pair-potentials J _x,y S _x ⋅S _y . The interactions are generally spread-out in the sense that the J _x,y 's exhibit either exponential or power-law fall-off. Under the technical condition of reflection positivity and for sufficiently spread out interactions, we prove that the model exhibits a first-order phase transition whenever the associated mean-field theory signals such a transition. As a consequence, e.g., in dimensions d≥3, we can finally provide examples of the 3-state Potts model with spread-out, exponentially decaying interactions, which undergoes a first-order phase transition as the temperature varies. Similar transitions are established in dimensions d = 1,2 for power-law decaying interactions and in high dimensions for next-nearest neighbor couplings. In addition, we also investigate the limit of infinitely spread-out interactions. Specifically, we show that once the mean-field theory is in a unique “state,” then in any sequence of translation-invariant Gibbs states various observables converge to their mean-field values and the states themselves converge to a product measure.     

Stability of Semiclassical Gravity Solutions with Respect to Quantum Metric Fluctuations

We discuss the stability of semiclassical gravity solutions with respect to small quantum corrections by considering the quantum fluctuations of the metric perturbations around the semiclassical solution. We call the attention to the role played by the symmetrized 2-point quantum correlation function for the metric perturbations, which can be naturally decomposed into two separate contributions: intrinsic and induced fluctuations. We show that traditional criteria on the stability of semiclassical gravity are incomplete because these criteria based on the linearized semiclassical Einstein equation can only provide information on the expectation value and the intrinsic fluctuations of the metric perturbations. By contrast, the framework of stochastic semiclassical gravity provides a more complete and accurate criterion because it contains information on the induced fluctuations as well. The Einstein–Langevin equation therein contains a stochastic source characterized by the noise kernel (the symmetrized 2-point quantum correlation function of the stress tensor operator) and yields stochastic correlation functions for the metric perturbations which agree, to leading order in the large N limit, with the quantum correlation functions of the theory of gravity interacting with N matter fields. These points are illustrated with the example of Minkowski space-time as a solution to the semiclassical Einstein equation, which is found to be stable under both intrinsic and induced fluctuations.     

Quantum Mechanics of Two-Field Parametric Frequency Converter Interacting with a Single Atom

In this communication we deal with a new model Hamiltonian representing the interaction between a two-level atom and two electromagnetic field modes in a cavity. The interaction between the modes has been taken into account and considered to be of a parametric frequency converter type. The model can be regarded as a generalization of two different systems: the Jaynes–Cummings model (atom–field interaction) and the two-mode frequency converter model (field–field interaction). Under a certain condition an exact solution for the equations of motion in the Heisenberg picture is given. The wavefunction in the Schrödinger picture is also constructed and used to discuss some statistical properties related to the model. We assume that the fields are initially in coherent states. We discuss atomic inversion, photon number distribution, squeezing and other phenomena. We show in all cases that the system is very sensitive to any variation in the mean photon numbers.     

The Effects of an Impurity in an Ising‐XXZ Diamond Chain on Thermal Entanglement,on Quantum Coherence,and on Quantum Teleportation

The effects of an impurity plaquette on the thermal quantum correlations measurement by the concurrence, on quantum coherence quantified by the recently proposed l₁‐norm of coherence and on quantum teleportation in a Ising‐ $XXZ$ diamond chain are discussed. Such an impurity is formed by the $XXZ$ interaction between the interstitial Heisenberg dimers and the nearest‐neighbor Ising coupling between the nodal and interstitial spins. All the interaction parameters are different from those of the rest of the chain. By tailoring them, quantum entanglement and quantum coherence can be controlled and tuned. Therefore, the quantum resources—thermal entanglement and quantum coherence—of the model exhibit a clear performance improvement in comparison to the original model without impurities. It is demonstrated that quantum teleportation can be tuned by its inclusion. Thermal teleportation is modified in a significant way as well, and a strong increase in the average fidelity is observed. The exact solution is furnished by the use of the transfer‐matrix method.     

Form Factors of Branch-Point Twist Fields in Quantum Integrable Models and Entanglement Entropy

In this paper we compute the leading correction to the bipartite entanglement entropy at large sub-system size, in integrable quantum field theories with diagonal scattering matrices. We find a remarkably universal result, depending only on the particle spectrum of the theory and not on the details of the scattering matrix. We employ the “replica trick” whereby the entropy is obtained as the derivative with respect to n of the trace of the nth power of the reduced density matrix of the sub-system, evaluated at n=1. The main novelty of our work is the introduction of a particular type of twist fields in quantum field theory that are naturally related to branch points in an n-sheeted Riemann surface. Their two-point function directly gives the scaling limit of the trace of the nth power of the reduced density matrix. Taking advantage of integrability, we use the expansion of this two-point function in terms of form factors of the twist fields, in order to evaluate it at large distances in the two-particle approximation. Although this is a well-known technique, the new geometry of the problem implies a modification of the form factor equations satisfied by standard local fields of integrable quantum field theory. We derive the new form factor equations and provide solutions, which we specialize both to the Ising and sinh-Gordon models.     

Troubles with Quantum Anisotropic Cosmological Models: Loss of Unitarity

The anisotropic Bianchi I cosmological model coupled with perfect fluid is quantized in the minisuperspace. The perfect fluid is described by using the Schutz formalism which allows to attribute dynamical degrees of freedom to matter. A Schrödinger-type equation is obtained where the matter variables play the role of time. However, the signature of the kinetic term is hyperbolic. This Schrödinger-like equation is solved and a wave packet is constructed. The norm of the resulting wave function comes out to be time dependent, indicating the loss of unitarity in this model. The loss of unitarity is due to the fact that the effective Hamiltonian is hermitian but not self-adjoint. The expectation value and the bohmian trajectories are evaluated leading to different cosmological scenarios, what is a consequence of the absence of a unitary quantum structure. The consistency of this quantum model is discussed as well as the generality of the absence of unitarity in anisotropic quantum models.     

Quantum Entropy of Spin Fields in the Schwarzschild-Anti-de Sitter Black Hole with a Global Monopole

The quantum entropies of gravitational, electromagnetic, neutrino and scalar fields in the static Schwarzschild-anti-de Sitter black hole with a global monopole are investigated by using the brick-wall model. The quantum entropy contain two parts: One is quadratically divergent term which takes a geometric character; the other is spin-dependent, logarithmically divergent terms. The whole expression of the entropy of a spin field does not take the form of the scalar field. PACS: 04.70. Dy, 97.60.Lf     

Spectral Gaps of Quantum Hall Systems with Interactions

A two-dimensional quantum Hall system without disorder for a wide class of interactions including any two-body interaction with finite range is studied by using the Lieb–Schultz–Mattis method [Ann. Phys. (N.Y.) 16:407 (1961)]. The model is defined on an infinitely long strip with a fixed, large width, and the Hilbert space is restricted to the lowest (n _max+1) Landau levels with a large integer n _max. We prove that, for a noninteger filling of the Landau levels, either (i) there is a symmetry breaking at zero temperature or (ii) there is only one infinite-volume ground state with a gapless excitation. We also prove the following two theorems: (a) If a pure infinite-volume ground state has a nonzero excitation gap for a noninteger filling , then a translational symmetry breaking occurs at zero temperature. (b) Suppose that there is no non-translationally invariant infinite-volume ground state. Then, if a pure infinite-volume ground state has a nonzero excitation gap, the filling factor must be equal to a rational number. Here the ground state is allowed to have a periodic structure which is a consequence of the translational symmetry breaking. We also discuss the relation between our results and the quantized Hall conductance, and phenomenologically explain why odd denominators of filling fractions giving the quantized Hall conductance are favored exclusively.     

克尔介质中纠缠光与三能级原子作用的光子统计

采用求解薛定谔方程和数值计算方法,研究了克尔介质中双模纠缠相干光场与三能级原子相互作用系统的光子统计性质,分析了双模纠缠相干光场的纠缠程度、克尔介质与光场的耦合强度、双模光的平均光子数和原子基态概率幅对光子统计性质的影响。结果表明：双模纠缠相干光场的纠缠程度对光子统计性质没有明显的影响;克尔效应增强使光子统计性质的时闻演化曲线的振荡频率变大、振荡幅度变小;当保持场模1的平均光子数不变而场模2的平均光子数变小时,光子统计性质的时间演化曲线的振荡幅度变大。     

Existence of a Phase Transition in a Continuous Quantum System

We prove the existence of a phase transition in the quantum Widom–Rowlison model in two dimension. The case of Boltzmann and Bose statistics are explicitly discussed.     

Algebraic Geometry in Discrete Quantum Integrable Model and Baxter's T–Q Relation

We study the diagonalization problem of certain discrete quantum integrable models by the method of Baxter's T–Q relation from the algebraic geometry aspect. Among those the Hofstadter type model (with the rational magnetic flux), discrete quantum pendulum and discrete sine-Gordon model are our main concern in this report. By the quantum inverse scattering method, the Baxter's T–Q relation is formulated on the associated spectral curve, a high genus Riemann surface in general, arisen from the study of spectrum problem of the system. In the case of degenerated spectral curve where the spectral variables lie on rational curves, we obtain the complete and explicit solution of the T–Q polynomial equation associated to the model, and the intimate relation between the Baxter's T–Q relation and algebraic Bethe Ansatz is clearly revealed. The algebraic geometry of a general spectral curve attached to the model and certain qualitative properties of solutions of the Baxter's T–Q relation are discussed incorporating the physical consideration.     

Interaction of Three Electromagnetic Fields with a Resonance Medium in the EPR Region

A system of Bloch equations that were modified with allowance for the presence of a dipole–dipole reservoir is suggested. This system was used to solve the problem of interaction of three fields in the EPR region, from which one field is saturating, another is a probing one, and the third is a combination one resulting from the interaction of the first two fields in a resonance medium. The imaginary and real parts of the system susceptibility at a frequency of the probing field have been studied in detail, at both different frequencies of interacting waves and coinciding ones (degenerate case). For the degenerate case, the frequency dependence of the coefficient of the parametric coupling of waves is also considered. The results of the present work are compared with similar results obtained from the Provotorov and Bloch equations (density matrices) in an optical range, and also with experimental data. The passage of weak waves through a layer of the medium is considered, and the possibility of their amplification in an absorbing medium is shown.