Two-mode Gaussian states as resource of secure quantum teleportation in open systems

For secure quantum teleportation (SQT) of coherent states two conditions are necessary to be fulfilled: Gaussian-state resources with two-way steering and teleportation fidelity higher than 2/3. We investigate and compare squeezed thermal states and squeezed vacuum states as initial resource states for SQT in an open quantum system, consisting of two uncoupled harmonic oscillators interacting with a thermal environment. The evolution of the open system is obtained in terms of the covariance matrix, by using the Gorini-Kossakowski-Lindblad-Sudarshan master equation. The SQT conditions are satisfied in a longer period of time in the case of initial squeezed vacuum states, therefore these states are better resource states for SQT than squeezed thermal states. We show that the admissible time for SQT decreases by increasing temperature, dissipation coefficient and average number of thermal photons, while for greater values of the squeezing parameter, SQT conditions are satisfied in a longer period of time.     

虚拟流体方法中界面处Riemann问题定义方式的改进

对RGFM中定义Riemann问题的方式进行改进,取距离界面适当远处的插值点处的状态作为Riemann问题的初值.并用数值算例对改进前后的RGFM进行比较.     

Helstrom Bound for Squeezed Coherent States in Binary Communication

In quantum information processing, using a receiver device to differentiate between two non-orthogonal states leads to a quantum error probability. The minimum possible error is known as the Helstrom bound. In this work, we study the conditions for state discrimination using an alphabet of squeezed coherent states and compare them with conditions using the Glauber-Sudarshan, i.e., standard, coherent states.     

On the uniqueness of the Invariant Equilibrium State and surface tension

Symmetric Equilibrium States and their properties under duality transformation are investigated. Necessary and sufficient conditions are derived for equilibrium states to be transformed into equilibrium states by duality. It is shown that ferromagnetic systems satisfying those conditions have correlation functions bounded by those corresponding to the (+) and free boundary conditions. It is then proved than any Invariant Equilibrium State of a ferromagnetic system is transformed into an equilibrium state by duality and is thus unique if the states defined by the (+), and free boundary conditions coincide on the symmetric algebra. The existence of surface tension between two pure phases is established.     

Stability,equilibrium and metastability in statistical mechanics

We survey a body of work, containing some new material, concerning the characterisation of equilibrium and metastable states of large assemblies of particles in terms of a variety of stability conditions. The theory is formulated in the thermodynamic limit and is based on the premise that the former states are those that are stable against all dynamical and thermodynamical perturbations, whereas the latter ones are endowed with only limited stability, sufficing to guarantee their long lifetimes and good thermodynamical behaviour. The Kubo-Martin-Schwinger (KMS) fluctuation-dissipation conditions play a central role in the developments stemming from this viewpoint, since it turns out that these conditions represent stability against localised disturbances of both the dynamical and thermo-dynamical kinds. Consequently, the stability arguments invoked here lead us to the following principal conclusions: (1) The equilibrium states are those that minimise the free energy density of the system and also satisfy the KMS conditions. This substantiates Gibbs's hypothesis that these states correspond to the standard ensembles. (2) Metastable states are of two kinds, that we term “ideal” and “normal”. Those of the former type satisfy the KMS conditions but minimise only the restriction of the free energy density to some reduced state space: those of the latter type are characterised by a still lower grade of stability. (3) The conditions on the forces under which ideal metastable states can exist are very restrictive, and thus the normal ones generally correspond to those observed in nature.     

Changes in the state of polarization of partially coherent flat-topped beam in turbulent atmosphere for different source conditions

The polarization states, i.e. the size, the shape and the orientation of the polarization ellipse of partially coherent flat-topped (PCFT) beams passing through atmospheric turbulence are studied in detail. The effects are studied of different source conditions on the polarization states of a PCFT beam propagating through atmospheric turbulence. Based on the unified theory of the polarization states for random electromagnetic beams, we have established the detailed formula for calculating the change of the polarization states of such beams. The polarization states behavior of PCFT beams passing through atmospheric turbulence for any arbitrary order of a flat-topped beam “N” under different source conditions were investigated.     

Stability of Quantum Systems at Three Scales: Passivity, Quantum Weak Energy Inequalities and the Microlocal Spectrum Condition

Quantum weak energy inequalities have recently been extensively discussed as a condition on the dynamical stability of quantum field states, particularly on curved spacetimes. We formulate the notion of a quantum weak energy inequality for general dynamical systems on static background spacetimes and establish a connection between quantum weak energy inequalities and thermodynamics. Namely, for such a dynamical system, we show that the existence of a class of states satisfying a quantum weak inequality implies that passive states (e.g., mixtures of ground- and thermal equilibrium states) exist for the time-evolution of the system and, therefore, that the second law of thermodynamics holds. As a model system, we consider the free scalar quantum field on a static spacetime. Although the Weyl algebra does not satisfy our general assumptions, our abstract results do apply to a related algebra which we construct, following a general method which we carefully describe, in Hilbert-space representations induced by quasifree Hadamard states. We discuss the problem of reconstructing states on the Weyl algebra from states on the new algebra and give conditions under which this may be accomplished. Previous results for linear quantum fields show that, on one hand, quantum weak energy inequalities follow from the Hadamard condition (or microlocal spectrum condition) imposed on the states, and on the other hand, that the existence of passive states implies that there is a class of states fulfilling the microlocal spectrum condition. Thus, the results of this paper indicate that these three conditions of dynamical stability are essentially equivalent. This observation is significant because the three conditions become effective at different length scales: The microlocal spectrum condition constrains the short-distance behaviour of quantum states (microscopic stability), quantum weak energy inequalities impose conditions at finite distance (mesoscopic stability), and the existence of passive states is a statement on the global thermodynamic stability of the system (macroscopic stability).Max-Planck-Institute for Mathematics in the Sciences, Inselstr. 22, 04103 Leipzig, Germany. verch@mis.mpg.de     

Quantum States as Objective Informational Bridges

A quantum state represents neither properties of a physical system nor anyone’s knowledge of its properties. The important question is not what quantum states represent but how they are used—as informational bridges. Knowing about some physical situations (its backing conditions), an agent may assign a quantum state to form expectations about other possible physical situations (its advice conditions). Quantum states are objective: only expectations based on correct state assignments are generally reliable. If a quantum state represents anything, it is the objective probabilistic relations between its backing conditions and its advice conditions. This paper offers an account of quantum states and their function as informational bridges, in quantum teleportation and elsewhere.     

Boundary conditions of continuum states in characterizing photocurrent of GaAs/AlGaAs quantum well infrared photodetector

We study the optical transition between bound-to-continuum states in a GaAs/AlGaAs multiple quantum well infrared photodetector (QWIP) by analyzing three possible boundary conditions for the continuum states. Comparing with experimental results, it has been suggested that the Bloch-state boundary conditions are proper for continuum states in the QWIPs consisting of multiple quantum wells and the fine structures in the responsivity spectrum result from the energy dispersion relationship of the multiple quantum wells.     

Monogamy of Measurement-Induced Nonlocality Based on Relative Entropy

In this paper, using relative entropy, we study monogamous properties of measurement-induced nonlocality based on relative entropy. Depending on different measurement sides, we provide necessary and sufficient conditions for two types of monogamy inequalities. By the concept of nonlocality monogamy score, we find a necessary condition of the vanished nonlocality monogamy score for arbitrary three-party states. In addition, two types of necessary and sufficient conditions of the vanished nonlocality monogamy scores are obtained for any pure states. As an application, we show that measurement-induced nonlocality based on relative entropy can be viewed as a "nonlocality witness" to distinguish generalized GHZ states from the generalized W states.     

Multimode uncertainty relations and separability of continuous variable states

A multimode uncertainty relation (generalizing the Robertson-Schr?dinger relation) is derived as a necessary constraint on the second moments of n pairs of canonical operators. In turn, necessary conditions for the separability of multimode continuous variable states under (m+n)-mode bipartitions are derived from the uncertainty relation. These conditions are proven to be necessary and sufficient for (1+n)-mode Gaussian states and for (m+n)-mode bisymmetric Gaussian states.     

Generalized Heisenberg algebra coherent states for power-law potentials

Coherent states for power-law potentials are constructed using generalized Heisenberg algebra. Klauder's minimal set of conditions required to obtain coherent states are satisfied. The statistical properties of these states are investigated through the evaluation of the Mandel's parameter. It is shown that these coherent states are useful for describing the states of real and ideal lasers.     

The quantization of the relativistic string

The classical field-dependent parametrization covariant Hamiltonian formulation of the open and the closed string is discussed. The formalism is not applicable to the open string. A conformally covariant formalism is developed for the open string. The Rohrlich gauge conditions are justified and applied. The parametrization of classical solutions is not uniquely fixed; the generators of rigid time translation in the parameter space remain first class. The constraints and gauge conditions are taken into account in the quantum theory as conditions on physical states. The required invariance of physical states under rigid displacement of parameter time leads to a mass superselection rule. The set of physical string quantum states is analogous to the set of states constructed by Di Vecchia, Del Guidice, and Fubini. A recursive construction is presented which permits the counting of physical states of any given mass, spin, and parity. Physical states lie on linearly rising Regge trajectories with one universal slope. The intercept of the leading trajectory is constrained only by the requirement that there be no tachyonic physical states. The quantization is carried out in four space-time dimensions.Supported by NSF Grant No. MPS74-15246 and DFG/Az 287/6. A portion of this work has been accepted by Syracuse University in partial fulfillment of the requirements of the doctorate degree.     

A rigorous proof for non-existence of edge state in the semi-infinite armchair edged graphene

Within the transfer matrix method, we study the conditions for the existence of the edge states in the semi-infinite armchair edged graphene. We discuss zero-energy and non-zero-energy edge states, respectively, and show the non-existence of the edge states in the model analytically and rigorously.     

Absence of current-density-wave excitonic states

It is shown that certain conditions on the anomalous quasiaverages of electron-hole pairing are satisfied by all eigenstates of the hamiltonian. These conditions are imposed on approximate states with electron-hole pairing such as those in the Hartree-Fock theory of Halperin and Rice. In Hartree-Fock theory at least, no current-density-wave excitonic states exist.     

Virtual surface states

Under conditions appropriate to a field emission experiment true surface states cannot exist. This paper demonstrates that virtual surface states do exist and have properties which for most practical purposes are identical to those of true surface states.     

混合迭加态的高阶压缩

本文详细计算一般的混合迭加态中△a₁和△a₂的k阶矩,应用Bloch矢量方法详细讨论混合迭加态中的高阶压缩,描写并定量计算,各阶压缩的压缩区域及压缩条件,讨论最佳压缩的条件,指出在高阶压缩的迭加态中,两个正交的分量a₁和a₂在某些条件可望同时被压缩,最后,试图对迭加态压缩的本质作一些探讨。 关键词：     

Generation of pure states in a nondegenerate two-photon micromaser

The generation of two-mode pure states in a lossless nondegenerate two-photon micromaser has been analyzed. The results show that under appropriate conditions, the field may evolve to pure states which can exhibit two-mode squeezing, or evolve to two-mode number states.     

Energy dissipation and stability of propagating surfaces

Thermodynamic equilibrium states are given by the minimum of a convex free energy function with suitable boundary conditions. Nonconvexity may lead to the coexistence of several phases and the classical Gibbs phase rule allows constructing their equilibrium properties (e.g., density or pressure). Within the framework of nonequilibrium thermodynamics, the maximization of energy dissipation (under suitable boundary conditions) can be used as an extremal principle to find stationary states. We show that stationary states generally exist for convex energy dissipation functions and that nonconvexity leads to metastable and unstable states. A geometric argument, similar in spirit to Gibbs' double-tangent construction, yields the stability limits of stationary states. This argument is applied to study a classical problem of materials science, namely the motion of a grain boundary under the influence of solute drag.     

一个全局耦合不连续映像格子中的奇异态

文章研究了一类由既不可逆又不连续映像构成的全局耦合映像格子系统中的奇异态行为,计算了系统的同步序参量和空间振幅变化图.结果表明,在某些特定的参数区间内,耦合映像格子系统会出现奇异态或团簇态,并且敏感地依赖于耦合强度的选择.上述丰富的动力学现象是由于单映像中不连续、不可逆性以及空间耦合相互作用的结果.通过数值模拟找到了奇异态或团簇态出现的特定参数区域.