Controlled Dense Coding using Generalized GHZ-type State

Two schemes for controlled dense coding with a extended GHZ-type state are investigated. In this protocol, the supervisor (Cliff) can control the channel and the average amount of information transmitted from the sender (Alice) to the receiver (Bob) by adjusting the local measurement angle θ. It is shown that the results for the average amounts of information are unique from the different two schemes.     

Dense Coding with Cluster State Via Local Measurements

Two schemes, introducing generalized measurement and entanglement concentration respectively, for dense coding are investigated by using a one-dimensional four-particle cluster state, where the supervisors (Cliff and David) can control the average amount of information transmitted from the sender (Alice) to the receiver (Bob) by adjusting the local measurement angles θ ₃ and θ ₄. It is shown that the results for the average amounts of information are unique from the different two schemes.     

Dense Coding with Extended GHZ-W State via Local Measurements

Two schemes, with entanglement concentration and via generalized measurement, for dense coding are investigated by using a extended four-qubit GHZ-W state, where the supervisors (David and Cliff) can control the average amount of information transmitted from the sender (Alice) to the receiver (Bob) by adjusting the measurement angles θ ₃ and θ ₄. We show that the results for the average amounts of information are unique from the different two schemes.     

Controlled Dense Coding with Five-Qubit Cluster State

Two schemes, via entanglement concentration and with generalized measurement respectively, for controlled dense coding with a one-dimensional five-qubit cluster state are investigated. In this protocol, the supervisor (Cliff) can control the entanglement of the channel and the average amount of information transmitted from the sender (Alice) to the receiver (Bob) by adjusting the local measurement angle θ. It is shown that the results for the average amounts of information are unique from the different two schemes.     

Controlled Dense Coding with Six-Qubit Cluster State

Two schemes, via generalized measurement and with entanglement concentration respectively, for controlled dense coding with a six-qubit cluster state are investigated in detail. In these protocols, the supervisor (Cliff) can control the average amount of information transmitted from the senders (Alice and David) to the receiver (Bob) by adjusting the local measurement angle θ. It is shown that the results for the average amounts of information are unique from the different two schemes.     

Controlled Dense Coding with a Four-Particle Non-maximally Entangled State

Two schemes for controlled dense coding with a four-particle entangled state are investigated, one with entanglement concentration and the other with generalized measurement. In these protocols, the supervisor (Cliff) can control the average amount of information transmitted from the sender (Alice and David) to the receiver (Bob) only by adjusting his local measurement angle θ. It is shown that the results for the average amounts of information are unique from the different two schemes.     

Controlled Dense Coding with Four-Qubit Entangled State

Two schemes, via generalized measurement and with entanglement concentration respectively, for controlled dense coding with a four-qubit entangled state are investigated in detail. In the two schemes, the supervisor (Cliff) can control the average amount of information transmitted from the sender (Alice) to the receiver (Bob) by adjusting the local measurement angle θ. It is shown that the results for the average amounts of information are unique from the different two schemes.     

Dense Coding via Local Measurement with Extended GHZ-Type State

Two schemes for dense coding via local measurement with an extended GHZ-type state are investigated. In this protocol, the supervisor (Cliff) can control the channel and the average amount of information transmitted from the sender (Alice) to the receiver (Bob) by adjusting the local measurement angle θ. It is shown that the results for the average amounts of information are unique from the different two schemes.     

Dense Coding with Nonmaximally Entangled Cluster State via Local Measurement

We present two schemes for dense coding with nonmaximally entangled cluster state via local measurement. The average amounts of information are unique from the different two schemes. The average amount of information transmitted from Alice to Bob depends not only on the measurement angle θ, but also on the superposition coefficients of the state. For a given nonmaximally entangled cluster state, the supervisor can control the average amount of information transmitted from the sender to the receiver by adjusting the measurement angle.     

High order accurate, explicit, difference formulas for the classical wave equation

This article presents a simple and yet very novel approach to developing difference schemes for wave equations. The schemes that are developed are explicit in nature. The schemes are of such generality that one can transform from one difference scheme to another with only the slightest of computational effort. The schemes exhibit dispersive errors. The errors can be minimized, however, by increasing the order of truncation error. Numerical results are presented for two linear model equations with truncation error ranging up to O(h⁵). Numerical results are also presented for a system of shallow water equations. By choosing the appropriate a for a first order linear equation (a defines the geometry of an element) we may generate stable schemes for an arbitrary Courant number.     

Controlled Dense Coding with Four-Particle Entangled State

Two schemes, via generalized measurement and entanglement concentration respectively, for dense coding are investigated by using a four-particle entangled state, in which the supervisor can control the average amount of information transmitted from the sender to the receiver by adjusting the local measurement angle. It is shown that the results for the average amounts of information are unique from the different two schemes.     

Quantum secret sharing based on quantum error-correcting codes

Quantum secret sharing(QSS) is a procedure of sharing classical information or quantum information by using quantum states.This paper presents how to use a [2k-1,1,k] quantum error-correcting code(QECC) to implement a quantum(k,2k 1) threshold scheme.It also takes advantage of classical enhancement of the [2k-1,1,k] QECC to establish a QSS scheme which can share classical information and quantum information simultaneously.Because information is encoded into QECC,these schemes can prevent intercept-resend attacks and be implemented on some noisy channels.     

Scaling of mean first-passage time as efficiency measure of nodes sending information on scale-free Koch networks

Random walks on complex networks, especially scale-free networks, have attracted considerable interest in the past few years. A lot of previous work showed that the average receiving time (ART), i.e., the average of mean first-passage time (MFPT) for random walks to a given hub node (node with maximum degree) averaged over all starting points in scale-free small-world networks exhibits a sublinear or linear dependence on network order N (number of nodes), which indicates that hub nodes are very efficient in receiving information if one looks upon the random walker as an information messenger. Thus far, the efficiency of a hub node sending information on scale-free small-world networks has not been addressed yet. In this paper, we study random walks on the class of Koch networks with scale-free behavior and small-world effect. We derive some basic properties for random walks on the Koch network family, based on which we calculate analytically the average sending time (AST) defined as the average of MFPTs from a hub node to all other nodes, excluding the hub itself. The obtained closed-form expression displays that in large networks the AST grows with network order as N ln N, which is larger than the linear scaling of ART to the hub from other nodes. On the other hand, we also address the case with the information sender distributed uniformly among the Koch networks, and derive analytically the global mean first-passage time, namely, the average of MFPTs between all couples of nodes, the leading scaling of which is identical to that of AST. From the obtained results, we present that although hub nodes are more efficient for receiving information than other nodes, they display a qualitatively similar speed for sending information as non-hub nodes. Moreover, we show that that AST from a starting point (sender) to all possible targets is not sensitively affected by the sender’s location. The present findings are helpful for better understanding random walks performed on scale-free small-world networks.     

Artificial compressibility, characteristics-based schemes for variable density, incompressible, multi-species flows. Part I. Derivation of different formulations and constant density limit

The paper presents various formulations of characteristics-based schemes in the framework of the artificial-compressibility method for variable-density incompressible flows. In contrast to constant-density incompressible flows, where the characteristics-based variables reconstruction leads to a single formulation, in the case of variable density flows three different schemes can be obtained henceforth labeled as: transport, conservative and hybrid schemes. The conservative scheme results in pseudo-compressibility terms in the (multi-species) density reconstruction. It is shown that in the limit of constant density, the transport scheme becomes the (original) characteristics-based scheme for incompressible flows, but the conservative and hybrid schemes lead to a new characteristics-based variant for constant density flows. The characteristics-based schemes are combined with second and third-order interpolation for increasing the computational accuracy locally at the cell faces of the control volume. Numerical experiments for constant density flows reveal that all the characteristics-based schemes result in the same flow solution, but they exhibit different convergence behavior. The multigrid implementation and numerical studies for variable density flows are presented in Part II of this study.     

Simultaneous Measurement,Phase-Space Distributions,and Quantum State Determination

Noting that a classical phase-space probability distribution w(q, p) may be calculated from moment expectation values {q^mpⁿ}, we inquire as to whether similar data in quantum mechanics would be adequate to determine the statistical operator ?. For the family of simultaneous (q, p) measurement schemes investigated, it turns out that such moments do not suffice to fix ?. Comparison of the empirical information that is adequate to determine ? with that required to find w(q, p) reveals that in a sense more data are needed for state determination in quantum statistics than are needed in the classical case.     

量子纠缠态的普适远程克隆

提出一种任意两粒子纠缠态1→2普适远程克隆方案. 此方案仅需一个特殊的四粒子纠缠态作为量子信道, 就可使处于空间不同位置的两个接收者分别以5/6的保真度得到任意输入态的近似拷贝, 该保真度远高于已有方案中的保真度. 将方案推广到任意两粒子纠缠态1→N(N>2)普适远程克隆的情况, 可使处于不同地点的N个接收者分别以(2N+1)/(3N)的保真度得到输入态的近似拷贝. 另外, 提出一种以上述单个特殊四粒子纠缠态作为量子信道, 在多目标量子比特受控非门和 关键词： 量子纠缠态 普适远程克隆 保真度     

Algorithmic information and simplicity in statistical physics

Applications of algorithmic information theory to statistical physics rely (a) on the fact that average conditional algorithmic information can be approximated by Shannon information and (b) on the existence ofsimple states described by short programs. More precisely, given a list ofN states with probabilities 0<p ₁ ≤ ... ≤ p _N , the average conditional algorithmic informationĪ to specify one of these states obeys the inequalityH≤ Ī<H+O(1), whereH=−Σp _j log₂ p _j andO(1) is a computer-dependent constant. We show how any universal computer can be slightly modified in such a way that (a) the inequality becomesH≤ Ī<H+1 and (b) states that are simple with respect to the original computer remain simple with respect to the modified computer, thereby eliminating the computer-dependent constant from statistical physics.     

Quantum logic operations on two distant atoms trapped in two optical-fibre-connected cavities

Based on the coupling of two distant three-level atoms in two separate optical cavities connected with two optical fibres, schemes on the generation of several two-qubit logic gates are discussed under the conditions of Δ = δ - 2ν cos πk/2 >> g/2 and ν ~ g. Discussion and analysis of the fidelity, gate time and experimental setups show that our schemes are feasible with current optical cavity, atomic trap and optical fibre techniques. Moreover, the atom-cavity- fibre coupling can be used to generate an N-qubit nonlocal entanglement and transfer quantum information among N distant atoms by arranging N atom-cavity assemblages in a line and connecting each two adjacent cavities with two optical fibres.     

Even-parity states of the Sm atom with stepwise excitation

Two-colour stepwise excitation and photoionization schemes are adopted to study the spectra of high-lying states of the Sm atom. These bound even-parity states are excited with three different excitation paths from the 4f66s6p7DJ (J = 1, 2, 3) intermediate states, respectively. They are probed by photoionization process with an extra photon driving them to the continuum states. In this experiment, 270 states are detected in an energy range from 36160 cm-1 to 42250 cm-1, 109 of which are newly discovered, while the rest of them are confirmed to be the energy levels reported previously. Furthermore, based on the J-momentum selection rules of three excitation paths, a unique assignment of J-momentum for all observed states is determined, eliminating all remaining ambiguities in the literature. Finally, 53 single-colour transitions originating from the scanning laser are also identified. For all the relevant transitions, the information about their relative intensities is also given in the paper.     

Analysis of a kind of quantum cryptographic schemes based on secret sharing

Recently, Yang et al. proposed a kind of quantum cryptographic schemes based on secret sharing. The main idea is drawn from the case, where any n participants who share a secret K can co-operate as K does. This process can be applied to encryption, authentication, signature and so on. Unfortunately, since there is no identity authentication of the share’s holder, these schemes inherit the limitation of secret sharing in practice. If some participants do not follow the protocol, the protocol would be a failu...