Authors:Gerd Niestegge Abstract: International Journal of Quantum Information, Volume 15, Issue 06, September 2017. A well-known feature of quantum mechanics is the secure exchange of secret bit strings which can then be used as keys to encrypt messages transmitted over any classical communication channel. It is demonstrated that this quantum key distribution allows a much more general and abstract access than commonly thought. The results include some generalizations of the Hilbert space version of quantum key distribution, but are based upon a general nonclassical extension of conditional probability. A special state-independent conditional probability is identified as origin of the superior security of quantum key distribution; this is a purely algebraic property of the quantum logic and represents the transition probability between the outcomes of two consecutive quantum measurements. Citation: International Journal of Quantum Information PubDate: 2017-10-09T03:00:08Z DOI: 10.1142/S0219749917500484

Authors:M. A. Jafarizadeh, F. Eghbalifam, S. Nami, M. Yahyavi Abstract: International Journal of Quantum Information, Ahead of Print. In this paper, entanglement classification shared among the spins of localized fermions in the noninteracting Fermi gas is studied. It is proven that the Fermi gas density matrix is block diagonal on the basis of the projection operators to the irreducible representations of symmetric group [math]. Every block of density matrix is in the form of the direct product of a matrix and identity matrix. Then it is useful to study entanglement in every block of density matrix separately. The basis of corresponding Hilbert space are identified from the Schur–Weyl duality theorem. Also, it can be shown that the symmetric part of the density matrix is fully separable. Then it has been shown that the entanglement measure which is introduced in Eltschka et al. [New J. Phys. 10, 043104 (2008)] and Guhne et al. [New J. Phys. 7, 229 (2005)], is zero for the even [math] qubit Fermi gas density matrix. Then by focusing on three spin reduced density matrix, the entanglement classes have been investigated. In three qubit states there is an entanglement measure which is called 3-tangle. It can be shown that 3-tangle is zero for three qubit density matrix, but the density matrix is not biseparable for all possible values of its parameters and its eigenvectors are in the form of W-states. Then an entanglement witness for detecting non-separable state and an entanglement witness for detecting nonbiseparable states, have been introduced for three qubit density matrix by using convex optimization problem. Finally, the four spin reduced density matrix has been investigated by restricting the density matrix to the irreducible representations of [math]. The restricted density matrix to the subspaces of the irreducible representations: [math], [math] and [math] are denoted by [math], [math] and [math], respectively. It has been shown that some highly entangled classes (by using the results of Miyake [Phys. Rev. A 67, 012108 (2003)] for entanglement classification) do not exist in the blocks of density matrix [math] and [math], so these classes do not exist in the total Fermi gas density matrix. Citation: International Journal of Quantum Information PubDate: 2017-11-15T08:06:31Z DOI: 10.1142/S0219749917500551

Authors:Florio Maria Ciaglia, Alberto Ibort, Giuseppe Marmo Abstract: International Journal of Quantum Information, Ahead of Print. On the affine space containing the space [math] of quantum states of finite-dimensional systems, there are contravariant tensor fields by means of which it is possible to define Hamiltonian and gradient vector fields encoding the relevant geometrical properties of [math]. Guided by Dirac’s analogy principle, we will use them as inspiration to define contravariant tensor fields, Hamiltonian and gradient vector fields on the affine space containing the space of fair probability distributions on a finite sample space and analyze their geometrical properties. Most of our considerations will be dealt with for the simple example of a three-level system. Citation: International Journal of Quantum Information PubDate: 2017-11-10T02:42:25Z DOI: 10.1142/S021974991740007X

Authors:Milajiguli Rexiti, Stefano Mancini Abstract: International Journal of Quantum Information, Ahead of Print. We consider the estimation of two-qubit interactions when initial states of both qubit can be locally controlled, while the final state of only one qubit can be measured. This amounts to realize a model of quantum channel communication with environment assistance. In such a framework, the unitaries’ parameters space results a tetrahedron in [math]. On its edges the problem, becoming of single parameter estimation, can be exactly solved and we derive optimal probe states and estimators. Our results show that the possibility of environment assistance is always beneficial, while the usage of entanglement at channels’ input is not. Citation: International Journal of Quantum Information PubDate: 2017-11-08T08:29:12Z DOI: 10.1142/S0219749917500538

Authors:Mohammad Hossein Zarei, Yahya Khalili Abstract: International Journal of Quantum Information, Ahead of Print. The completeness of some classical statistical mechanical (SM) models is a recent result that has been developed by quantum formalism for the partition functions. In this paper, we consider a 2D classical [math] filed theory whose completeness has been proved in [V. Karimipour and M. H. Zarei, Phys. Rev. A 85 (2012) 032316]. We give a new and general systematic proof for the completeness of such a model where, by a few simple steps, we show how the partition function of an arbitrary classical field theory can be derived from a 2D classical [math] model. To this end, we start from various classical field theories containing models on arbitrary lattices and also [math] lattice gauge theories. Then we convert them to a new classical field model on a nonplanar bipartite graph with imaginary kinetic terms. After that, we show that any polynomial function of the field in the corresponding Hamiltonian can approximately be converted to a [math] term by adding enough numbers of vertices to the bipartite graph. In the next step, we give a few graphical transformations to convert the final nonplanar graph to a 2D rectangular lattice. We also show that the number of vertices which should be added grows polynomially with the number of vertices in the original model. Citation: International Journal of Quantum Information PubDate: 2017-11-07T09:21:07Z DOI: 10.1142/S0219749917500514

Authors:Dario Tamascelli, Alessia Segati, Stefano Olivares Abstract: International Journal of Quantum Information, Ahead of Print. We address two-level systems (TLSs) arranged in ring configurations affected by static disorder. In particular, we investigate the role of dephasing in the transport of an excitation along the ring. We compare the efficiency of the transfer process on isotropic rings and on biomimetic rings modeled according to the structure of light-harvesting (LH) complexes. Our analysis provides a simple but clear and interesting example of how an interplay between the coherent dynamics of the system and the incoherent action of the environment can enhance the transfer capabilities of disordered lattices. Citation: International Journal of Quantum Information PubDate: 2017-11-07T09:21:06Z DOI: 10.1142/S0219749917400068

Authors:Filippo Giraldi Abstract: International Journal of Quantum Information, Ahead of Print. The flow of quantum information in local dephasing channels is analyzed over short and long times in case the structured reservoir of frequency modes exhibits a spectral gap in the density of modes over low frequencies. The presence of the low-frequency gap with upper cut-off frequency [math] produces an infinite sequence of long-time intervals over which information backflow appears. Though generally irregular, the time intervals exhibit, under certain conditions, upper bounds: the [math]th episode of information backflow has already started at the instant [math], and already ended at the instant [math], for every [math]. The intervals become regular over long times, tend to the asymptotic length [math], as the supremum value, and are described analytically in terms of the structure of the spectral density near the upper cut-off frequency of the spectral gap. Consequently, engineering structured reservoirs of frequency modes with a spectral gap over low frequencies produces in local dephasing channels regular sequences of information backflow and recoherence over long times, along with non-Markovian evolution. Citation: International Journal of Quantum Information PubDate: 2017-11-07T09:21:06Z DOI: 10.1142/S0219749917500502

Authors:Y. Akbari-Kourbolagh Abstract: International Journal of Quantum Information, Ahead of Print. We present sufficient criteria for the entanglement of three-qubit states. For some special families of states, the criteria are also necessary for the entanglement. They are formulated as simple sets of inequalities for the mean values of certain observables defined as tensor products of Pauli matrices. The criteria are good indicators of the entanglement in the vicinity of three-qubit GHZ and W states and enjoy the capability of detecting the entangled states with positive partial transpositions. Furthermore, they improve the best known result for the case of W state mixed with the white noise. The efficiency of the criteria is illustrated through several examples. Citation: International Journal of Quantum Information PubDate: 2017-11-07T09:21:05Z DOI: 10.1142/S0219749917500496

Authors:Yang Liu, Ruihu Li, Liangdong Lü, Luobin Guo Abstract: International Journal of Quantum Information, Ahead of Print. The Bose–Chaudhuri–Hocquenghem (BCH) codes have been studied for more than 57 years and have found wide application in classical communication system and quantum information theory. In this paper, we study the construction of quantum codes from a family of [math]-ary BCH codes with length [math] (also called antiprimitive BCH codes in the literature), where [math] is a power of 2 and [math]. By a detailed analysis of some useful properties about [math]-ary cyclotomic cosets modulo [math], Hermitian dual-containing conditions for a family of non-narrow-sense antiprimitive BCH codes are presented, which are similar to those of [math]-ary primitive BCH codes. Consequently, via Hermitian Construction, a family of new quantum codes can be derived from these dual-containing BCH codes. Some of these new antiprimitive quantum BCH codes are comparable with those derived from primitive BCH codes. Citation: International Journal of Quantum Information PubDate: 2017-11-07T09:21:05Z DOI: 10.1142/S0219749917500526

Authors:Constantin Meis, Pierre Richard Dahoo Abstract: International Journal of Quantum Information, Ahead of Print. We employ here the enhancement of the vector potential amplitude quantization at a single photon state. The analysis of the general solution of the vector potential, obtained by resolving Maxwell’s equations, implies that the amplitude is proportional to the angular frequency. The photon vector potential function [math] can be written in the plane wave representation satisfying the classical wave propagation equation, Schrödinger’s equation for the energy with the relativistic massless field Hamiltonian and a linear time-dependent equation for the vector potential amplitude operator. Thus, the vector potential [math] with the quantized amplitude may play the role of a real wave function for the photon in a nonlocal representation that can be suitably normalized. We then deduce that the amplitudes of the electric and magnetic fields, respectively, of a single free photon are proportional to the square of the angular frequency. This might open perspectives for the development of nondestructive photon detection methods based on the influence of the electric and/or magnetic fields of photons on the energy levels of atoms and molecules. Citation: International Journal of Quantum Information PubDate: 2017-11-01T08:43:17Z DOI: 10.1142/S0219749917400032

Authors:Andrzej Chrostowski, Rafał Demkowicz-Dobrzański, Marcin Jarzyna, Konrad Banaszek Abstract: International Journal of Quantum Information, Ahead of Print. We consider the problem of characterizing the spatial extent of a composite light source using the super-resolution imaging technique based on mode demultiplexing when the centroid of the source is not known precisely. We show that the essential features of this problem can be mapped onto a simple qubit model for joint estimation of a phase shift and a dephasing strength. Citation: International Journal of Quantum Information PubDate: 2017-11-01T08:43:16Z DOI: 10.1142/S0219749917400056

Authors:Tsamouo Tsokeng Arthur, Tchoffo Martin, Lukong Cornelius Fai Abstract: International Journal of Quantum Information, Ahead of Print. We investigate the dynamics of entanglement, quantum discord (QD) and state coherence in a bipartite and noninteracting spin-qutrits system under mixed classical noises. Specifically, the collective effects of static noise (SN) and random telegraphic noise (RTN) each being coupled with a marginal system, are analyzed. While the static noise models a non-Markovian environment, the dynamic noise can model both a Markovian or a non-Markovian environment, and both dynamics are studied. We show that quantum correlations and coherence may survive the noise degrading effects at sufficiently long time when the Markovian regime of the RTN is considered. Meanwhile, the opposite is found in the non-Markovian regime, wherein the nonmonotonic dynamics of quantum features avoid sudden death phenomena. However, the static noise is more fatal to the survival of quantum correlations and quantum state coherence as compared to the RTN. Citation: International Journal of Quantum Information PubDate: 2017-09-29T03:39:21Z DOI: 10.1142/S0219749917500472

Authors:Song-Song Li Abstract: International Journal of Quantum Information, Ahead of Print. We investigate the influence of one-body losses on the dynamics of squeezing and entanglement in two-mode Bose–Einstein condensates. We show that one-body losses play an important role in the dynamical process of generating squeezing and quantum entanglement. The stronger one-body losses induce smaller squeezing and lesser entanglement, but maintain in a longer time interval. Citation: International Journal of Quantum Information PubDate: 2017-09-20T03:32:36Z DOI: 10.1142/S0219749917500460

Authors:Swarnamala Sirsi, Karthik Bharath, S. P. Shilpashree, H. S. Smitha Rao Abstract: International Journal of Quantum Information, Ahead of Print. We propose a simple method for constructing positive operator-valued measures (POVMs) using any set of matrices which form an orthonormal basis for the space of complex matrices. Considering the orthonormal set of irreducible spherical tensors, we examine the properties of the construction on the [math]-dimensional subspace of the [math]-dimensional Hilbert space of [math] qubits comprising the permutationally symmetric states. Using the notion of vectorization, the constructed POVMs are interpretable as projection operators in a higher-dimensional space. We then describe a method to physically realize the constructed POVMs for symmetric states using the Clebsch–Gordan decomposition of the tensor product of irreducible representations of the rotation group. We illustrate the proposed construction on a spin-1 system, and show that it is possible to generate entangled states from separable ones. Citation: International Journal of Quantum Information PubDate: 2017-09-14T08:14:01Z DOI: 10.1142/S0219749917500423

Authors:Edson C. Nogueira, Gustavo de Souza, Adalberto D. Varizi, Marcos D. Sampaio Abstract: International Journal of Quantum Information, Ahead of Print. In this work, we analyze two-flavor neutrino oscillations within the framework of quantum estimation theory (QET). We compute the quantum Fischer information (QFI) for the mixing angle [math] and show that mass measurements are the ones that achieve optimal precision. We also study the Fischer information (FI) associated with flavor measurements and show that they are optimized at specific neutrino times-of-flight. Therefore, although the usual population measurement does not realize the precision limit set by the QFI, it can in principle be implemented with the best possible sensitivity to [math]. We investigate how these quantifiers relate to the single-particle, mode entanglement in neutrino oscillations. We demonstrate that this form of entanglement does not enhance either of them. In particular, our results show that in single-particle settings, entanglement is not directly connected with the enhancement of precision in metrological tasks. Citation: International Journal of Quantum Information PubDate: 2017-09-14T08:14:01Z DOI: 10.1142/S0219749917500459

Authors:Iman Sargolzahi, Sayyed Yahya Mirafzali Abstract: International Journal of Quantum Information, Ahead of Print. We consider a bipartite quantum system [math] (including parties [math] and [math]), interacting with an environment [math] through a localized quantum dynamics [math]. We call a quantum dynamics [math] localized if, e.g. the party [math] is isolated from the environment and only [math] interacts with the environment: [math], where [math] is the identity map on the part [math] and [math] is a completely positive (CP) map on the both [math] and [math]. We will show that the reduced dynamics of the system is also localized as [math], where [math] is a CP map on [math], if and only if the initial state of the system-environment is a Markov state. We then generalize this result to the two following cases: when both [math] and [math] interact with a same environment, and when each party interacts with its local environment. Citation: International Journal of Quantum Information PubDate: 2017-09-12T08:06:08Z DOI: 10.1142/S0219749917500435

Authors:Y. Ben-Aryeh, A. Mann Abstract: International Journal of Quantum Information, Ahead of Print. Explicit separability of general two qubits density matrices is related to Lorentz transformations. We use the 4-dimensional form [math] of the Hilbert–Schmidt (HS) decomposition of the density matrix. For the generic case, in which Lorentz transformations diagonalize [math] into [math], we give relations between the [math] and the [math]. In particular, we consider two cases: (a) Two qubits density matrices with one pair of linear terms in the HS decomposition. (b) Two qubits density matrices with two or three symmetric pairs of linear terms. Some of the theoretical results are demonstrated by numerical calculations. The four non-generic cases (which may be reduced to case (a) are analyzed and the non-generic property is related explicitly to Lorentz velocity [math] which is not reachable physically. Citation: International Journal of Quantum Information PubDate: 2017-09-12T08:06:08Z DOI: 10.1142/S0219749917500447

Authors:Yong Siah Teo, Christian R. Müller, Hyunseok Jeong, Zdeněk Hradil, Jaroslav Řeháček, Luis L. Sánchez-Soto Abstract: International Journal of Quantum Information, Ahead of Print. Wigner and Husimi quasi-distributions, owing to their functional regularity, give the two archetypal and equivalent representations of all observable-parameters in continuous-variable quantum information. Balanced homodyning (HOM) and heterodyning (HET) that correspond to their associated sampling procedures, on the other hand, fare very differently concerning their state or parameter reconstruction accuracies. We present a general theory of a now-known fact that HET can be tomographically more powerful than balanced homodyning to many interesting classes of single-mode quantum states, and discuss the treatment for two-mode sources. Citation: International Journal of Quantum Information PubDate: 2017-08-29T06:28:18Z DOI: 10.1142/S0219749917400020

Authors:Hrvoje Nikolić Abstract: International Journal of Quantum Information, Ahead of Print. Most physicists do not have patience for reading long and obscure interpretation arguments and disputes. Hence, to attract attention of a wider physics community, in this paper various old and new aspects of quantum interpretations are explained in a concise and simple (almost trivial) form. About the “Copenhagen” interpretation, we note that there are several different versions of it and explain how to make sense of “local nonreality” interpretation. About the many-world interpretation (MWI), we explain that it is neither local nor nonlocal, that it cannot explain the Born rule, that it suffers from the preferred basis problem, and that quantum suicide cannot be used to test it. About the Bohmian interpretation, we explain that it is analogous to dark matter, use it to explain that there is no big difference between nonlocal correlation and nonlocal causation, and use some condensed-matter ideas to outline how nonrelativistic Bohmian theory could be a theory of everything. We also explain how different interpretations can be used to demystify the delayed choice experiment, to resolve the problem of time in quantum gravity, and to provide alternatives to quantum nonlocality. Finally, we explain why is life compatible with the second law. Citation: International Journal of Quantum Information PubDate: 2017-08-29T06:28:16Z DOI: 10.1142/S0219749917400019

Authors:Yangyang Wang, Jinchuan Hou, Xiaofei Qi Abstract: International Journal of Quantum Information, Ahead of Print. A quantum correlation [math] based on weak measurements for bipartite systems is introduced. It is shown that the product states do not contain this quantum correlation. Also, the necessary and sufficient condition for any two-qubit state becoming a product state is obtained. The quantum correlation [math] and other quantum correlation for two-qubit entangled pure state, Werner states and isotropic states are compared. Citation: International Journal of Quantum Information PubDate: 2017-08-23T07:53:47Z DOI: 10.1142/S0219749917500411