Abstract: International Journal of Quantum Information, Volume 13, Issue 08, December 2015. Landsburg method of classifying mixed Nash equilibria for maximally entangled Eisert–Lewenstein–Wilkens (ELW) game is analyzed with special emphasis on symmetries inherent to the problem. Nash equilibria for the original ELW game are determined. Citation: International Journal of Quantum Information PubDate: 2016-03-07T09:11:51Z DOI: 10.1142/S0219749915500665

Authors:Yinzhu Wang, Danxia Wang, Li Huang Abstract: International Journal of Quantum Information, Ahead of Print. In this paper, an extended negativity entanglement measure for multipartite k-nonseparable states with respect to k-partition was proposed. We show that this measure is well-defined, i.e. it satisfies some basic properties as an entanglement measure. In addition, we give a relation between this measure and k-ME concurrence, and obtain a lower bound of this measure. Citation: International Journal of Quantum Information PubDate: 2016-04-18T09:13:56Z DOI: 10.1142/S0219749916500015

Authors:Brian R. La Cour, Corey I. Ostrove, Granville E. Ott, Michael J. Starkey, Gary R. Wilson Abstract: International Journal of Quantum Information, Ahead of Print. This paper describes a novel approach to emulate a universal quantum computer with a wholly classical system, one that uses a signal of bounded duration and amplitude to represent an arbitrary quantum state. The signal may be of any modality (e.g. acoustic, electromagnetic, etc.) but this paper will focus on electronic signals. Individual qubits are represented by in-phase and quadrature sinusoidal signals, while unitary gate operations are performed using simple analog electronic circuit devices. In this manner, the Hilbert space structure of a multi-qubit quantum state, as well as a universal set of gate operations, may be fully emulated classically. Results from a programmable prototype system are presented and discussed. Citation: International Journal of Quantum Information PubDate: 2016-04-07T08:50:53Z DOI: 10.1142/S0219749916400049

Abstract: International Journal of Quantum Information, Ahead of Print. We discuss the recently observed “loophole free” violation of Bell’s inequalities in the framework of a physically realist view of quantum mechanics (QM), which requires that physical properties are attributed jointly to a system, and to the context in which it is embedded. This approach is clearly different from classical realism, but it does define a meaningful “quantum realism” from a general philosophical point of view. Consistently with Bell test experiments, this quantum realism embeds some form of non-locality, but does not contain any action at a distance, in agreement with QM. Citation: International Journal of Quantum Information PubDate: 2016-04-07T08:50:52Z DOI: 10.1142/S0219749916400025

Authors:S. A. Rashkovskiy Abstract: International Journal of Quantum Information, Ahead of Print. It is shown that the Schrödinger equation can be written in the form of the diffusion equation for classical particles moving in a continuous space. A class of classical random processes described by the Schrödinger equation is considered. It is shown that such classical random processes can be used as a tool for the numerical solution of the Schrödinger equation. Citation: International Journal of Quantum Information PubDate: 2016-04-07T08:50:50Z DOI: 10.1142/S0219749916400062

Authors:Song Lin, Hui Wang, Gong-De Guo, Guo-Hua Ye, Hong-Zhen Du, Xiao-Fen Liu Abstract: International Journal of Quantum Information, Ahead of Print. Quantum key distribution (QKD) has been growing rapidly in recent years and becomes one of the hottest issues in quantum information science. During the implementation of QKD on a network, identity authentication has been one main problem. In this paper, an efficient authenticated multi-user quantum key distribution (MQKD) protocol with single particles is proposed. In this protocol, any two users on a quantum network can perform mutual authentication and share a secure session key with the assistance of a semi-honest center. Meanwhile, the particles, which are used as quantum information carriers, are not required to be stored, therefore the proposed protocol is feasible with current technology. Finally, security analysis shows that this protocol is secure in theory. Citation: International Journal of Quantum Information PubDate: 2016-03-29T07:03:48Z DOI: 10.1142/S0219749916500027

Abstract: International Journal of Quantum Information, Ahead of Print. In order to assess the susceptibility of the quantum key distribution (QKD) systems to the hacking attack including simultaneous and frequent system self-decalibrations, we analyze the stability of the QKD transmission organized in two commercially available systems. The first one employs non-entangled photons as flying qubits in the dark quantum channel for communication whereas the second one utilizes the entangled photon pairs to secretly share the cryptographic key. Applying standard methods of the statistical data analysis to the characteristic indicators of the quality of the QKD communication (the raw key exchange rate [RKER] and the quantum bit error rate [QBER]), we have estimated the pace of the self-decalibration of both systems and the repeatability rate in the case of controlled worsening of the dark channel quality. Citation: International Journal of Quantum Information PubDate: 2016-02-23T03:18:37Z DOI: 10.1142/S0219749915500641

Authors:Won Sang Chung Abstract: International Journal of Quantum Information, Ahead of Print. In this paper, we consider the generalized Schrödinger cat states. Using these states, we obtain the corresponding quasi-Bell states and the reduced density operator. For these quasi-Bell states, we investigate the non-classical effects such as oscillatory photon statistics, sub-Poissonian property and violation of the Cauchy–Schwarz inequality. Citation: International Journal of Quantum Information PubDate: 2016-02-23T03:18:36Z DOI: 10.1142/S0219749915500653

Authors:Jian Gao Abstract: International Journal of Quantum Information, Ahead of Print. We give a construction of quantum codes over [math] from cyclic codes over a finite non-chain ring [math], where [math], p is a prime, [math] and [math]. Citation: International Journal of Quantum Information PubDate: 2016-02-23T03:18:33Z DOI: 10.1142/S021974991550063X

Abstract: International Journal of Quantum Information, Ahead of Print. We present a study of extremal entanglement witnesses on a bipartite composite quantum system. We define the cone of witnesses as the dual of the set of separable density matrices, thus [math] when [math] is a witness and [math] is a pure product state, [math] with [math]. The set of witnesses of unit trace is a compact convex set, uniquely defined by its extremal points. The expectation value [math] as a function of vectors [math] and [math] is a positive semidefinite biquadratic form. Every zero of [math] imposes strong real-linear constraints on f and [math]. The real and symmetric Hessian matrix at the zero must be positive semidefinite. Its eigenvectors with zero eigenvalue, if such exist, we call Hessian zeros. A zero of [math] is quadratic if it has no Hessian zeros, otherwise it is quartic. We call a witness quadratic if it has only quadratic zeros, and quartic if it has at least one quartic zero. A main result we prove is that a witness is extremal if and only if no other witness has the same, or a larger, set of zeros and Hessian zeros. A quadratic extremal witness has a minimum number of isolated zeros depending on dimensions. If a witness is not extremal, then the constraints defined by its zeros and Hessian zeros determine all directions in which we may search for witnesses having more zeros or Hessian zeros. A finite number of iterated searches in random directions, by numerical methods, leads to an extremal witness which is nearly always quadratic and has the minimum number of zeros. We discuss briefly some topics related to extremal witnesses, in particular the relation between the facial structures of the dual sets of witnesses and separable states. We discuss the relation between extremality and optimality of witnesses, and a conjecture of separability of the so-called structural physical approximation (SPA) of an optimal witness. Finally, we discuss how to treat the entanglement witnesses on a complex Hilbert space as a subset of the witnesses on a real Hilbert space. Citation: International Journal of Quantum Information PubDate: 2016-02-23T03:16:12Z DOI: 10.1142/S0219749915500604

Authors:Zhen Wang, Zhi-Xi Wang Abstract: International Journal of Quantum Information, Ahead of Print. It is strictly proved that a two-qubit [math]-invariant state reaches its relative entropy of entanglement (REE) by the separable state having the same matrix structure. We also formulate three quadratic equations for the corresponding closest separable state (CSS) of [math]-invariant states by their symmetric property. Thus, the CSS of [math]-invariant state can be provided. Furthermore, to illustrate our result we consider two concrete examples. Citation: International Journal of Quantum Information PubDate: 2016-01-27T01:35:41Z DOI: 10.1142/S0219749915500586

Authors:Y. Ben-Aryeh, A. Mann Abstract: International Journal of Quantum Information, Ahead of Print. Explicitly separable density matrices are constructed for all separable two-qubits states based on Hilbert–Schmidt (HS) decompositions. For density matrices which include only two-qubits correlations the number of HS parameters is reduced to 3 by using local rotations, and for two-qubits states which include single qubit measurements, the number of parameters is reduced to 4 by local Lorentz transformations. For both cases, we related the absolute values of the HS parameters to probabilities, and the outer products of various Pauli matrices were transformed to pure state density matrices products. We discuss related problems for three-qubits. For n-qubits correlation systems ([math]) the sufficient condition for separability may be improved by local transformations, related to high order singular value decompositions (SVDs). Citation: International Journal of Quantum Information PubDate: 2016-01-27T01:35:38Z DOI: 10.1142/S0219749915500616

Authors:Constantin V. Usenko Abstract: International Journal of Quantum Information, Ahead of Print. In the direct communication quantum channels, the authorized recipient (Bob) and the non-authorized recipient (Eve) have different abilities for verification of received information. Bob can apply the feedback to commit the sender (Alice) to perform verification. Eve has to use for verification an indirect method based on the measurement of a set of incompatible observables enough for determination of the coding basis used by Alice. In the protocol of direct communication, regular modification of coding basis and masking it with an equilibrium in average information carrier density matrix prevents reconstruction of coding basis by the results of Eve’s measurements of an arbitrary set of observables. This provides unconditional security of the channel. Citation: International Journal of Quantum Information PubDate: 2016-01-27T01:35:35Z DOI: 10.1142/S0219749915500628