Gaussian states as minimum uncertainty states

In bosonic fields, Gaussian states, which consist of a rather wide family of states including coherent states, squeezed states, thermal states, etc., have many classical-like features, and are usually defined from the mathematical perspective in terms of characteristic functions. It is well known that some special Gaussian states, such as coherent states, are minimum uncertainty states for the conventional Heisenberg uncertainty relation involving canonical pair of position and momentum observables. A natural question arises as whether all Gaussian states can be characterized as minimum uncertainty states. In this work, we show that indeed Gaussian states coincide with minimum uncertainty states for an information-theoretic refinement of the conventional uncertainty relation established in Luo (2005) [40]. This characterization puts Gaussian states on a novel basis of physical significance.     

Excited Binomial States and Excited Negative Binomial States of the Radiation Field and Some of Their Statistical Properties

We introduce excited binomial states and excited negative binomial states of theradiation field by repeated application of the photon creation operator on binomialstates and negative binomial states. They reduce to Fock states and excitedcoherent states in certain limits and can be viewed as intermediate states betweenFock states and coherent states. We find that both the excited binomial statesand excited negative binomial states can be exactly normalized in terms ofhypergeometric functions. Base on this interesting characteristic, some of thestatistical properties are discussed.     

Truncated Coherent States and Photon-Addition

A class of states of the electromagnetic field involving superpositions of all the excited states above a specified low energy eigenstate of the electromagnetic field is introduced. These states and the photon-added coherent states are shown to be the limiting cases of a generalized photon-added coherent state. This new class of states is nonclassical, non-Gaussian and has equal uncertainties in the field quadratures. For suitable choices of parameters, these uncertainties are very close to those of the coherent states. Nevertheless, these states exhibit sub-Poissonian photon number distribution, which is a nonclassical feature. Under suitable approximations, these states become the generalized Bernoulli states of the field. Nonclassicality of these states is quantified using their entanglement potential.     

Interface states on semiconductor/insulator surfaces

It is well known that impurities and defects in semiconductors are associated with energy levels in the forbidden gap. Similar states occur at the surface of a semiconductor where the crystal lattice and the symmetry are strongly disturbed. These states are called surface states. Owing to the two-dimensional nature of the surface, their density is measured per unit area, in contrast to bulk states, which are measured per unit volume. A third type of states, similar to surface states, occurs at the interface between two adjacent materials. These states are called interface states. Very often they are also simply called surface states.     

Quasi-Bound States of Two Magnons in the Spin-1/2XXZ Chain

We study two-magnon Bethe states in the spin-1/2 XXZ chain. The string hypothesis assumes that complex rapidities of the bound states take special forms. It is known, however, that there exist “non-string states,” which substantially disagrees with the string hypothesis. In order to clarify their nature, we study the large-N behavior of solutions of the Bethe-Ansatz equations to obtain explicit forms of typical Bethe states, where N is the length of the chain, and apply the scaling analysis (the multifractal analysis) to the Bethe states. It turns out that the non-string states contain “quasi-bound” states, which in some sense continuously interpolate between extended states and localized states. The “quasi-bound” states can be distinguished from known three types of states, i.e., extended, localized, and critical states. Our results indicate that there might be a need to reconsider the standard classification scheme of wavefunctions.     

Entanglement and Decoherence in Two-Dimensional Coherent State Superpositions

A detailed investigation of entanglement in the generalized two-dimensional nonorthogonal states, which are expressed in the framework of superposed coherent states, is presented. In addition to quantifying entanglement of the generalized two-dimensional coherent states superposition, necessary and sufficient conditions for maximality of entanglement of these states are found. We show that a large class of maximally entangled coherent states can be constructed, and hence, some new maximally entangled coherent states are explicitly manipulated. The investigation is extended to the mixed system states and entanglement properties of such mixed states are investigated. It is shown that in some cases maximally entangled mixed states can be detected. Furthermore, the effect of decoherence, due to both cavity losses and noisy channel process, on such entangled states are studied and its features are discussed.     

A Scheme for Generating Cluster States via Raman Interaction

A scheme for generating cluster states via Raman interaction is proposed. In the scheme, we firstly prepare cluster states of multi-cavities with information encoded in the coherent states and then generate cluster states of multiatoms, which encode the information in the ground states of A-type atoms. The advantages of our scheme are that the atomic spontaneous radiation can be efficiently reduced since the cavity frequency is largely detuned from the atomic transition frequency and the Hadamard gate operation of the coherent states is replaced by measuring the coherent states.     

一维无公度系统Aubry模型的Anderson转变

数值计算结果表明,一维无公度系统Aubry模型存在扩展态、中间态和局域态。由扩展态向局域态的转变,要经过处于势强度v=2t附近的一段过渡区。这个新的结果不同于用对偶性理论证明给出的结论,即当势强度V<2t时都是扩展态,而当V>2t时都是局域态,在V=2t存在Anderson转变。 关键词：     

Blind Quantum Signature with Controlled Four-Particle Cluster States

A novel blind quantum signature scheme based on cluster states is introduced. Cluster states are a type of multi-qubit entangled states and it is more immune to decoherence than other entangled states. The controlled four-particle cluster states are created by acting controlled-Z gate on particles of four-particle cluster states. The presented scheme utilizes the above entangled states and simplifies the measurement basis to generate and verify the signature. Security analysis demonstrates that the scheme is unconditional secure. It can be employed to E-commerce systems in quantum scenario.     

Chimera states in bipartite networks of FitzHugh–Nagumo oscillators

Chimera states consisting of spatially coherent and incoherent domains have been observed in different topologies such as rings, spheres, and complex networks. In this paper, we investigate bipartite networks of nonlocally coupled FitzHugh–Nagumo (FHN) oscillators in which the units are allocated evenly to two layers, and FHN units interact with each other only when they are in different layers. We report the existence of chimera states in bipartite networks. Owing to the interplay between chimera states in the two layers, many types of chimera states such as in-phase chimera states, antiphase chimera states, and out-of-phase chimera states are classified. Stability diagrams of several typical chimera states in the coupling strength–coupling radius plane, which show strong multistability of chimera states, are explored.     

Statistical Properties and Algebraic Characteristics of Quantum Superpositions of Negative Binomial States

We introduce new kinds of states of quantized radiation fields,which are the superpositions of megative binomial states.They exhibit remarkable nonclassical properties and reduce to Schrodinger cat states in a certain limit.The algebras involved in the even and odd negative binomial states turn out to be generally deformed oscillator algebras.It is found that the even and odd negative binomial states satisfy the same eigenvalue equation with the same eigenvalue and they can be viewed as two-photon nonlinear coherent states.Two methods of generating such the states are proposed.     

Kaluza-Klein states versus winding states: can both be above the string scale?

Closed strings in extra compactified dimensions give rise to both Kaluza-Klein states and winding states. Since the masses of these states play a reciprocal role, it is often believed that either the lightest Kaluza-Klein states or the lightest winding states must be at or below the string scale. In this Letter, we demonstrate the contrary, showing that there exist toroidal compactifications for which all Kaluza-Klein states as well as all winding states are heavier than the string scale. Within the context of low-scale string theories, this implies that it may be possible to cross the string scale without detecting any states associated with spacetime compactification.     

三粒子系统的解纠缠

给出了三粒子系统三类解纠缠的定义,研究了三粒子系统纯态解纠缠的三个基本规律,发现存在一些可以解纠缠为直积态集或“一粒子直积两粒子分离”态集或完全分离态集的三粒子纠缠态集,但一个普适的将三粒子纠缠态集解纠缠为直积态集或“一粒子直积两粒子分离”态集或完全分离态集的装置均不存在. 关键词： 解纠缠 三粒子系统     

Nonclassical properties and algebraic characteristics of negative binomial states in quantized radiation fields

We study the nonclassical properties and algebraic characteristics of the negative binomial states introduced by Barnett recently. The ladder operator formalism and displacement operator formalism of the negative binomial states are found and the algebra involved turns out to be the SU(1,1) Lie algebra via the generalized Holstein-Primarkoff realization. These states are essentially Perelomov's SU(1,1) coherent states. We reveal their connection with the geometric states and find that they are excited geometric states. As intermediate states, they interpolate between the number states and geometric states. We also point out that they can be recognized as the nonlinear coherent states. Their nonclassical properties, such as sub-Poissonian distribution and squeezing effect are discussed. The quasiprobability distributions in phase space, namely the Q and Wigner functions, are studied in detail. We also propose two methods of generation of the negative binomial states. d 32.80.Pj Optical cooling of atoms; trapping Received 8 May 1999 and Received in final form 8 November 1999     

Pairwise Quantum Correlations for Superpositions of Dicke States

Pairwise correlation is really an important property for multi-qubit states. For the two-qubit X states extracted from Dicke states and their superposition states, we obtain a compact expression of the quantum discord by numerical check. We then apply the expression to discuss the quantum correlation of the reduced two-qubit states of Dicke states and their superpositions, and the results are compared with those obtained by entanglement of formation, which is a quantum entanglement measure.     

Entangled squeezed states:Bell state measurement and teleportation

We construct orthogonal Bell states with entangled squeezed vacuum states and show that these states can be discriminated with arbitrary precision when the amplitude of the squeezed states becomes sufficiently large. A scheme of teleporting a superposition state of the squeezed vacuum states based on the Bell state measurement is presented.     

Superposed graphene coherent states

Using an annihilation operator, coherent states related to the electron of graphene layer placed in a magnetic field, can be obtained. In this paper, we define even and odd superposed graphene coherent states and then, we consider their entanglement, squeezing and statistical properties. To study the entanglement, we use concurrence. The results show that odd superposed graphene coherent states are maximally entangled states for all values of coherence parameter. However, the entanglement of graphene coherent states and also even superposed depend on the coherence parameter. In addition, examining the Mandel parameter shows sub-Poissonian statistics for graphene coherent states and their odd superposition; while, even superposed states do not show sub-Poissonian statistics at all. Also, we find that graphene coherent states and even superposition may be squeezed while the odd states do not show squeezing.     

Nonclassical properties of odd and even elliptical states

As a generalization of the optical circular states, elliptical states which are quantum superposition of coherent states on an ellipse in the α plane are constructed. The statistical properties of the states are investigated by using sub-Poissonian photon statistics, quadrature squeezing, Wigner function and phase distribution. It is shown that the elliptical states exhibit stronger quadrature squeezing. The interference fringes between the coherent states form the elliptic annuli of Fock states in the Wigner function picture. The phase distribution is no longer uniform as the circular states. An experimental scheme is proposed for generating equidistant coherent-state superpositions on an ellipse for the motion of the center of mass of a trapped ion.     

Teleportation of Mixture of Diagonal Bell States via Bound Entangled States

We propose a protocol for teleportation of arbitrary mixture of diagonal Bell states, it is shown that the channel can be constructed with either pure maximally entangled states or mixed bound entangled states. We also present protocols to realize the controlled teleportation of mixture of diagonal Bell states via multi-particle mixed states. Our results show that bound entangled states are also important and useful resources in quantum communication tasks.     

Majorization criterion for distillability of a bipartite quantum state

Bipartite quantum states are classified into three categories: separable states, bound entangled states, and free entangled states. It is of great importance to characterize these families of states for the development of quantum information science. In this Letter, I show that the separable states and the bound entangled states have a common spectral property. More precisely, I prove that for undis-tillable-separable and bound entangled-states, the eigenvalue vector of the global system is majorized by that of the local system. This result constitutes a new sufficient condition for distillability of bipartite quantum states. This is achieved by proving that if a bipartite quantum state satisfies the reduction criterion for distillability, then it satisfies the majorization criterion for separability.