Authors:Mohammad Ashraf et al Abstract: International Journal of Quantum Information, Ahead of Print.
Let R = F3 + vF3 be a finite commutative ring, where v2 = 1. It is a finite semi-local ring, not a chain ring. In this paper, we give a construction for quantum codes from cyclic codes over R. We derive self-orthogonal codes over F3 as Gray images of linear and cyclic codes over R. In particular, we use two codes associated with a cyclic code over R of arbitrary length to determine the parameters of the corresponding quantum code. PubDate: Thu, 20 Nov 2014 08:53:12 GMT

Authors:Andrei Khrennikov Abstract: International Journal of Quantum Information, Ahead of Print.
This paper is a contribution to the project "emergent quantum mechanics" unifying a variety of attempts to treat quantum mechanics (QMs) as emergent from other theories pretending on finer descriptions of quantum phenomena. More concretely it is about an attempt to model detection probabilities predicted by QM for single photon states by using classical random fields interacting with detectors of the threshold type. Continuous field model, prequantum classical statistical field theory (PCSFT), was developed in recent years and its predictions about probabilities and correlations match well with QM. The main problem is to develop the corresponding measurement theory which would describe the transition from continuous fields to discrete events, "clicks of detectors". Some success was achieved and the click-probabilities for quantum observables can be derived from PCSFT by modeling interaction of fields with the threshold type detectors. However, already for the coefficient of second-order coherence g2(0) calculations are too complicated and only an estimation of g2(0) was obtained. In this paper, we present results of numerical simulation based on PCSFT and modeling of interaction with threshold type detectors. The "prequantum random field" interacting with a detector is modeled as the Browninan motion in the space of classical fields (Wiener process in complex Hilbert space). Simulation for g2(0) shows that this coefficient approaches zero with increase of the number of detections. PubDate: Tue, 18 Nov 2014 09:07:28 GMT

Authors:Margarita A. Man'ko et al Abstract: International Journal of Quantum Information, Ahead of Print.
The approach to extend the notion of entanglement for characterizing the properties of quantum correlations in the state of a single qudit is presented. New information and entropic inequalities, such as the subadditivity condition, strong subadditivity condition, and monotonicity of relative entropy for a single qudit corresponding to an arbitrary spin state with spin j are discussed. The idea to employ quantum correlations in the single-qudit state, such as the entanglement, for developing a new quantum technique in quantum computing and quantum communication is proposed. Examples of qutrit and qudit with j = 3/2 are considered. PubDate: Tue, 18 Nov 2014 09:07:25 GMT

Authors:I. Ramos-Prieto et al Abstract: International Journal of Quantum Information, Ahead of Print.
We propose a class of nonlinear coherent states which are experimentally feasible in cavity or ion-trap quantum electrodynamics. These quantum field states arise from a new type of photon addition and subtraction based on London phase operators, also known as Susskind–Glogower operators, that just displaces the mean photon number without scaling the photon distribution. PubDate: Tue, 11 Nov 2014 08:02:08 GMT

Authors:Zhen-Peng Xu et al Abstract: International Journal of Quantum Information, Ahead of Print.
Hardy's paradox is of fundamental importance in quantum information theory. So far, there have been two types of its extensions into higher dimensions: in the first type the maximum probability of nonlocal events is roughly 9% and remains the same as the dimension changes (dimension-independent), while in the second type the probability becomes larger as the dimension increases, reaching approximately 40% in the infinite limit. Here, we (i) give an alternative proof of the first type, (ii) study the situation in which the maximum probability of nonlocal events can also be dimension-independent in the second type and (iii) conjecture how the situation could be changed in order that (ii) still holds. PubDate: Tue, 11 Nov 2014 08:02:07 GMT

Authors:Yahong Wang et al Abstract: International Journal of Quantum Information, Ahead of Print.
This paper offers a theoretical protocol for one-party controlled remote state preparation (RSP) of n-qubit states with minimum resources consumption. We are mainly focused on the case of the n-qubit state chosen from equatorial circle on a Bloch sphere. We use n - 1 EPR pairs and one GHZ state as quantum channel and show that only n + 1 cbits, n ebits and 2n + 1 qubits are consumed during the controlled RSP processing. PubDate: Tue, 11 Nov 2014 08:02:03 GMT

Authors:Xu Chen et al Abstract: International Journal of Quantum Information, Ahead of Print.
Homogenization proposed in [Y.-C Wu and M. Żukowski, Phys. Rev. A85 (2012) 022119] is a procedure to transform a tight Bell inequality with partial correlations into a full-correlation form that is also tight. In this paper, we check the homogenizations of two families of n-partite Bell inequalities: the Hardy inequality and the tight Bell inequality without quantum violation. For Hardy's inequalities, their homogenizations bear stronger quantum violation for the maximally entangled state; the tight Bell inequalities without quantum violation give the boundary of quantum and supra-quantum, but their homogenizations do not have the similar properties. We find their homogenization are violated by the maximally entangled state. Numerically computation shows the the domains of quantum violation of homogenized Hardy's inequalities for the generalized GHZ states are smaller than those of Hardy's inequalities. PubDate: Tue, 11 Nov 2014 08:02:02 GMT

Authors:Zhangji Zhao et al Abstract: International Journal of Quantum Information, Ahead of Print.
In a recent paper,1 an improvement of quantum sealed-bid auction protocol is proposed by introducing hash function. However, in this comment, it is shown that the improvement brings in other problems which would not complete the task of a sealed-bid auction fairly. PubDate: Fri, 07 Nov 2014 09:28:49 GMT

Authors:S. Balakrishnan Abstract: International Journal of Quantum Information, Volume 12, Issue 05, August 2014.
Linear entropy is widely used as a measure of operator entanglement of two-qubit gates. In this paper, we characterize the two-qubit gates of same linear entropy using the majorization criteria of the Schmidt coefficients of the gates. It is found that the gates with same linear entropy must have set of same Schmidt coefficients or set of different Schmidt coefficients which are not ordered according to the majorization relation. PubDate: Fri, 07 Nov 2014 08:22:46 GMT

Authors:M. Daoud et al Abstract: International Journal of Quantum Information, Ahead of Print.
The pairwise correlations in a multi-qubit state are quantified through a linear variant of relative entropy. In particular, we derive the explicit expressions of total, quantum and classical bipartite correlations. Two different bi-partioning schemes are considered. We discuss the derivation of closest product, quantum–classical and quantum–classical product states. We also investigate the additivity relation between the various pairwise correlations existing in pure and mixed states. As illustration, some special cases are examined. PubDate: Wed, 05 Nov 2014 03:45:36 GMT

Authors:Recep Eryiğit et al Abstract: International Journal of Quantum Information, Ahead of Print.
We report a systematic study of asymptotic behavior of entanglement between the position and coin degrees of freedom for a one-dimensional discrete quantum walk. Effects of coin bias, initial coin asymmetry and phase difference and non-locality of initial position state on the fluctuations and asymptotic value of entanglement are investigated by using Fourier approach. Fluctuations in entropy are found to die out as power law in time as t-α with α = 1/2,3/2 and 5/2 depending on the initial state parameters of the system. PubDate: Wed, 05 Nov 2014 03:45:36 GMT

Authors:Charlie Beil Abstract: International Journal of Quantum Information, Ahead of Print.
We introduce new mathematical aspects of the Bell states using matrix factorizations, non-noetherian singularities, and noncommutative blowups. A matrix factorization of a polynomial p consists of two matrices ϕ1,ϕ2 such that ϕ1ϕ2 = ϕ2ϕ1 = p id. Using this notion, we show how the Bell states emerge from the separable product of two mixtures, by defining pure states over complex matrices rather than just the complex numbers. We then show in an idealized algebraic setting that pure states are supported on non-noetherian singularities. Moreover, we find that the collapse of a Bell state is intimately related to the representation theory of the noncommutative blowup along its singular support. This presents an exchange in geometry: the nonlocal commutative spacetime of the entangled state emerges from an underlying local noncommutative spacetime. PubDate: Fri, 31 Oct 2014 04:14:36 GMT

Authors:Zhiqiang Li et al Abstract: International Journal of Quantum Information, Ahead of Print.
Since non-permutative quantum gates have more complex rules than permutative quantum gates, it is very hard to synthesize quantum logic circuits using non-permutative quantum gates, such as controlled-square-root-of-NOT gates (CV/CV+ gates). In the efficient synthesis algorithm, direct use of quantum non-permutative gates should be avoided. Rather, the key method is to use quantum gates to create new permutative quantum gates that then replace non-permutative quantum gates. This method assumes the library of quantum gate primitives are constructed so as to have the lowest possible quantum cost. In this paper, we first propose some new CV/CV+-like gates, i.e. controlled-kth-root-of-NOT gates where k = 2,4,8,…, and give all corresponding matrixes. Further, we also present a novel generic method to quickly and directly construct this new optimal quantum logic gate library using CNOT and these non-permutative quantum gates. Our method introduces new means to find permutative quantum gates with lower quantum cost. PubDate: Fri, 31 Oct 2014 04:14:31 GMT

Authors:Mordecai Waegell Abstract: International Journal of Quantum Information, Ahead of Print.
The class of entangled N-qubit states known as graph states, and the corresponding stabilizer groups of N-qubit Pauli observables, have found a wide range of applications in quantum information processing and the foundations of quantum mechanics. A review of the properties of graph states is given and core spaces of graph states are introduced and discussed. A bonding model of entanglement for generalized graph states is then presented, in which the presence or absence of a bond between two qubits unequivocally specifies whether or not they are entangled. A physical interpretation of these bonds is given, along with a characterization of how they can be created or destroyed by entangling unitary operations and how they can be destroyed by local Pauli measurements. It is shown that local unitary operations do not affect the bond structure of a graph state, and therefore that if two graph states have nonisomorphic bond structures, then local unitary operations and/or reordering of qubits cannot change one into the other. Color multigraphs are introduced to depict the bond structures of graph states and to make some of their properties more apparent. PubDate: Fri, 31 Oct 2014 04:14:30 GMT

Authors:Francesco De Martini et al Abstract: International Journal of Quantum Information, Ahead of Print.
The traditional standard quantum mechanics (SQM) is unable to solve the spin-statistics problem, i.e. to justify the utterly important "Pauli exclusion principle". The present paper presents a simple and complete solution of the spin-statistics problem on the basis of the "conformal quantum geometrodynamics (CQG)", a theory that was found to reproduce successfully all relevant processes of the SQM based on Dirac's or Schrödinger's equations, including Heisenberg's uncertainty relations and non-local Einstein–Podolsky–Rosen (EPR) correlations. When applied to a system made of many identical particles, an additional property of all elementary particles enters naturally into play: the "intrinsic helicity". This property, not considered in the SQM, determines the correct spin-statistics connection (SSC) observed in nature. PubDate: Wed, 29 Oct 2014 04:22:03 GMT

Authors:Francesco Buscemi et al Abstract: International Journal of Quantum Information, Ahead of Print.
Recently, a novel operational strategy to access quantum correlation functions of the form Tr[AρB] was provided in [F. Buscemi, M. Dall'Arno, M. Ozawa and V. Vedral, arXiv:1312.4240]. Here we propose a realization scheme, that we call partial expectation values, implementing such strategy in terms of a unitary interaction with an ancillary system followed by the measurement of an observable on the ancilla. Our scheme is universal, being independent of ρ, A, and B, and it is optimal in a statistical sense. Our scheme is suitable for implementation with present quantum optical technology, and provides a new way to test uncertainty relations. PubDate: Tue, 28 Oct 2014 09:40:50 GMT

Authors:Fedor Herbut Abstract: International Journal of Quantum Information, Ahead of Print.
Measurement of a degenerate (or non-degenerate) discrete observable is investigated in the framework of quantum measurement theory short of collapse, i.e. premeasurement theory, based on a unitary evolution operator that includes the measurement interaction between object and measuring instrument. A pointer observable with eigen-projectors of, in general, many (or even infinitely) dimensional ranges is introduced as a new approach. It leads to redundant entanglement in the final state. As the first main result, the basic dynamical relation of the approach is derived. It is shown to be equivalent to the calibration condition, which is known to define general exact measurement. The latter is given a practical form. Complete measurement (premeasurement with objectification or collapse), which is in some sense implied by the premeasurement theory, performed on a subsystem of a bipartite object in a pure state is studied with particular attention to its effect on the opposite, interactionally unaffected subsystem. The change of state of the latter is derived for exact complete subsystem measurement, and it is shown that the change is the same as for the simplest, i.e. ideal measurement (this is the second main result). It is applied to the case of twin observables and thus distant measurement obtains a new, more satisfactory, foundation (the third main result). Distant measurement is a basic concept in the EPR phenomenon. The well-known importance of the latter implies importance of the former. PubDate: Tue, 21 Oct 2014 08:49:45 GMT

Authors:Matteo A. C. Rossi et al Abstract: International Journal of Quantum Information, Ahead of Print.
We address the dynamics of a two-qubit system interacting with a classical dephasing environment driven by a Gaussian stochastic process. Upon introducing the concept of entanglement-preserving time, we compare the degrading effects of different environments, e.g. those described by Ornstein–Uhlenbeck (OU) or fractional noise. In particular, we consider pure Bell states and mixtures of Bell states and study the typical values of the entanglement-preserving time for both independent and common environments. We found that engineering environments towards fractional Gaussian noise is useful to preserve entanglement as well as to improve its robustness against noise. We also address entanglement sudden death by studying the sudden-death time as a function of the initial negativity. We found that: (i) the sudden-death time is bounded from below by an increasing function of the initial negativity, (ii) the sudden-death time depends only slightly on the process used to describe the environment and exhibits typicality. Overall, our results show that engineering the environment has only a slight influence over the entanglement sudden-death time, while it represents a valuable resource to increase the entanglement-preserving time, i.e. to maintain entanglement closer to the initial level for a longer interaction time. PubDate: Tue, 21 Oct 2014 08:49:45 GMT

Authors:Yosi Atia et al Abstract: International Journal of Quantum Information, Ahead of Print.
We demonstrate the use of optimal control to design two entropy-manipulating quantum gates which are more complex than the corresponding, commonly used, gates, such as CNOT and Toffoli (CCNOT): A two-qubit gate called polarization exchange (PE) and a three-qubit gate called polarization compression (COMP) were designed using GRAPE, an optimal control algorithm. Both gates were designed for a three-spin system. Our design provided efficient and robust nuclear magnetic resonance (NMR) radio frequency (RF) pulses for 13C2-trichloroethylene (TCE), our chosen three-spin system. We then experimentally applied these two quantum gates onto TCE at the NMR lab. Such design of these gates and others could be relevant for near-future applications of quantum computing devices. PubDate: Tue, 14 Oct 2014 03:56:45 GMT

Authors:Anmer Daskin et al Abstract: International Journal of Quantum Information, Ahead of Print.
Entanglement plays an important role in quantum communication, algorithms, and error correction. Schmidt coefficients are correlated to the eigenvalues of the reduced density matrix. These eigenvalues are used in von Neumann entropy to quantify the amount of the bipartite entanglement. In this paper, we map the Schmidt basis and the associated coefficients to quantum circuits to generate random quantum states. We also show that it is possible to adjust the entanglement between subsystems by changing the quantum gates corresponding to the Schmidt coefficients. In this manner, random quantum states with predefined bipartite entanglement amounts can be generated using random Schmidt basis. This provides a technique for generating equivalent quantum states for given weighted graph states, which are very useful in the study of entanglement, quantum computing, and quantum error correction. PubDate: Wed, 08 Oct 2014 03:49:20 GMT

Authors:Nikos Iliopoulos et al Abstract: International Journal of Quantum Information, Ahead of Print.
We theoretically investigate the quantum correlations (in terms of concurrence of indistinguishable electrons) in a prototype molecular system (hydrogen molecule). With the assistance of the standard approximations of the linear combination of atomic orbitals and the configuration interaction methods we describe the electronic wavefunction of the ground state of the H2 molecule. Moreover, we managed to find a rather simple analytic expression for the concurrence (the most used measure of quantum entanglement) of the two electrons when the molecule is in its lowest energy. We have found that concurrence does not really show any relation to the construction of the chemical bond. PubDate: Thu, 28 Aug 2014 12:06:51 GMT

Authors:Bao Liu et al Abstract: International Journal of Quantum Information, Ahead of Print.
The characterization of quantum discord (QD) and geometric discord (GD) has mostly concentrated on two-qubit states since the minimization in both discords is a daunting task for high-dimensional states. Numerical calculations of both discords are carried out for a generic bipartite state. When one-dimensional orthogonal projectors for a local measurement on n-dimensional Hilbert space are realized by the generators and the Euler angles of SU(n), the optimal measurements have a figure of merit that includes n(n - 1) Euler parameters. As an representative example, such projectors and two kinds of algorithms are used to estimate both discords for two-qutrit mixed states in recent literature. The generalized negativity as a measure of quantum entanglement is calculated for reference purposes. For those states with one parameter the discords and the negativity respectively display the nonlinear and the linear function of the parameter, with different turning points. However, they are positively correlated in the suitable ranges of the parameter for those states. The hierarchy of those quantities is discussed as well. Those shed new light on the understanding of QDs and quantum entanglement of mixed states in high-dimensions. PubDate: Mon, 25 Aug 2014 07:12:30 GMT

Authors:Hrvoje Nikolić Abstract: International Journal of Quantum Information, Ahead of Print.
In the usual formulation of quantum theory, time is a global classical evolution parameter, not a local quantum observable. On the other hand, both canonical quantum gravity (which lacks fundamental time-evolution parameter) and the principle of spacetime covariance (which insists that time should be treated on an equal footing with space) suggest that quantum theory should be slightly reformulated, in a manner that promotes time to a local observable. Such a reformulated quantum theory is unitary in a more general sense than the usual quantum theory. In particular, this promotes the non-unitary Hawking radiation to a unitary phenomenon, which avoids the black-hole information paradox. PubDate: Tue, 19 Aug 2014 11:39:12 GMT

Authors:M. A. Khan et al Abstract: International Journal of Quantum Information, Ahead of Print.
Any dielectric nanoparticle moving inside an optical cavity generates an optomechanical interaction. In this paper, we theoretically analyze the light scattering of an optomechanical cavity which strongly interacts with a dielectric nanoparticle. The cavity is driven by an external laser field. This interaction gives rise to different dynamics that can be used to cool, trap and levitate nanoparticle. We analytically calculate reflection and transmission rate of the cavity field, and study the time evolution of the intracavity field, momentum and position of the nanoparticle. We find the nanoparticle occupies a discrete position inside the cavity. This effect can be exploited to separate nanoparticle and couplings between classical particles and quantized fields. PubDate: Wed, 23 Jul 2014 03:07:32 GMT

Authors:Tomoyuki Morimae Abstract: International Journal of Quantum Information, Ahead of Print.
In the circuit model of quantum computation, a desired unitary gate can be implemented deterministically, whereas in the measurement-based model the unitary gate is implemented up to a byproduct operator. In order to compensate byproducts, following measurement angles must be adjusted, or classical results must be corrected. Such a feed-forwarding requires some classical processing and tuning of the measurement device, which cause the delay of computation and the additional decoherence. We show that if we respect the no-signaling principle, which is one of the most fundamental principles in physics, byproducts cannot be avoided in measurement-based quantum computation. Furthermore, we also show by using the idea of the quantum error correcting code that due to the no-signaling principle, not all byproducts are allowed in measurement-based quantum computation. PubDate: Wed, 16 Jul 2014 08:29:57 GMT

Authors:sales@wspc.com.sg (Aram W. Harrow) Abstract: International Journal of Quantum Information, Ahead of Print.
The Johnson–Lindenstrauss Lemma is a classic result which implies that any set of n real vectors can be compressed to O(logn) dimensions while only distorting pairwise Euclidean distances by a constant factor. Here we consider potential extensions of this result to the compression of quantum states. We show that, by contrast with the classical case, there does not exist any distribution over quantum channels that significantly reduces the dimension of quantum states while preserving the 2-norm distance with high probability. We discuss two tasks for which the 2-norm distance is indeed the correct figure of merit. In the case of the trace norm, we show that the dimension of low-rank mixed states can be reduced by up to a square root, but that essentially no dimensionality reduction is possible for highly mixed states. PubDate: Wed, 04 Jun 2014 03:58:56 GMT

Authors:LOÏCK MAGNIN et al Abstract: International Journal of Quantum Information, Volume 0, Issue 0, Ahead of Print. PubDate: Mon, 25 Nov 2013 06:28:10 GMT