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 International Journal of Quantum Information   [SJR: 0.588]   [H-I: 18]   Follow         Hybrid journal (It can contain Open Access articles)    ISSN (Print) 0219-7499 - ISSN (Online) 1793-6918    Published by World Scientific  [114 journals]
• Implementation of a quantum $\sqrt{{\rm swap}}$ gate for two distant atoms
trapped in separate cavities
• Authors: Xiu Lin, Rong-Can Yang, Xiang Chen
Abstract: International Journal of Quantum Information, Ahead of Print. We present a scheme to implement a quantum $\sqrt{{\rm swap}}$ gate for two-atom trapped in distant cavities connected via an optical fiber. In the whole process, the atomic system, the cavity modes and the fiber are not excited ensuring that the operation is insensitive to atomic spontaneous emission, cavity decay and the fiber loss. This scheme is significant for distributed and scalable quantum computation.
Citation: International Journal of Quantum Information
PubDate: Fri, 27 Feb 2015 03:32:23 GMT
DOI: 10.1142/S0219749915500033

• Minimum remote state preparation of an arbitrary two-level one-atom state
via cavity QED
• Authors: Yahong Wang, Changshui Yu
Abstract: International Journal of Quantum Information, Ahead of Print. In this paper, we propose three schemes for remotely state preparation (RSP) an arbitrary two-level one-atom state via cavity quantum electro dynamics (QED) with minimal resources consumption. In the first case, a Greenberger–Horne–Zeilinger (GHZ) state is used as quantum channel; in the second case, the sender needs to construct an quantum channel with both of the assistant of cavity QED and the knowledge about the state to be remotely prepared. In each scheme, only 1 cbit and 1 ebit are needed with the aid of cavity QED. In the third case, we combine the first two protocols and give a theoretical proposal for controlled RSP with only 2 cbits and 1 ebit resources consumption.
Citation: International Journal of Quantum Information
PubDate: Fri, 27 Feb 2015 03:32:23 GMT
DOI: 10.1142/S0219749915500094

• Entanglement entropy in quasi-symmetric multi-qubit states
• Authors: Zhi-Hua Li, An-Min Wang
Abstract: International Journal of Quantum Information, Ahead of Print. We generalize the symmetric multi-qubit states to their q-analogs, whose basis vectors are identified with the q-Dicke states. We study the entanglement entropy in these states and find that entanglement is extruded towards certain regions of the system due to the inhomogeneity aroused by q-deformation. We also calculate entanglement entropy in ground states of a related q-deformed Lipkin–Meshkov–Glick (LMG) model and show that the singularities of entanglement can correctly signify the quantum phase transition points for different strengths of q-deformation.
Citation: International Journal of Quantum Information
PubDate: Wed, 25 Feb 2015 02:17:12 GMT
DOI: 10.1142/S0219749915500070

• An achievable rate for private classical information over a quantum
• Authors: Alireza Nadem Ghazvini, Seyed Vahab AL-Din Makki, Shahpoor Alirezaee
Abstract: International Journal of Quantum Information, Ahead of Print. The rate region for transmission of classical information over a quantum broadcast channel and an inner bound for the rate of transmission of private classical information over a single-user quantum channel have been achieved in the previous paper. In this work, we extended the proofs of them to obtain an achievable private classical capacity for a two receivers quantum broadcast channel.
Citation: International Journal of Quantum Information
PubDate: Wed, 25 Feb 2015 02:17:11 GMT
DOI: 10.1142/S0219749915500057

• Manipulation of the stationary entanglement of three atoms coupled to a
common environment
• Authors: Fang Su
Abstract: International Journal of Quantum Information, Ahead of Print. In this work, we study the dynamics of three entangled atoms coupled to a common structured reservoir. The atoms are initially prepared in different W-like states characterized by different relative phases. We examine the roles of initial relative phases on the energy transfers among the individual atoms as well as atomic entanglement dynamics. We show that the features of quantum interferences induced by initial relative phases greatly affect the energy transfers and entanglement dynamics. In particular, a suitable choice of initial phases can increase atomic stationary entanglement over their initial value. The results imply a possible control strategy for atomic entanglement dynamics.
Citation: International Journal of Quantum Information
PubDate: Tue, 24 Feb 2015 07:59:47 GMT
DOI: 10.1142/S0219749915500082

• The lower bound to the concurrence for four-qubit W state under noisy
channels
• Authors: Pakhshan Espoukeh, Pouria Pedram
Abstract: International Journal of Quantum Information, Ahead of Print. We study the dynamics of four-qubit W state under various noisy environments by solving analytically the master equation in the Lindblad form in which the Lindblad operators correspond to the Pauli matrices and describe the decoherence of states. Also, we investigate the dynamics of the entanglement using the lower bound to the concurrence. It is found that while the entanglement decreases monotonically for Pauli-Z noise, it decays suddenly for other three noises. Moreover, by studying the time evolution of entanglement of various maximally entangled four-qubit states, we indicate that the four-qubit W state is more robust under same-axis Pauli channels. Furthermore, three-qubit W state preserves more entanglement with respect to the four-qubit W state, except for the Pauli-Z noise.
Citation: International Journal of Quantum Information
PubDate: Wed, 18 Feb 2015 02:48:52 GMT
DOI: 10.1142/S0219749915500045

• Maximal entanglement entanglement-assisted quantum codes of distance three
• Authors: Luobin Guo, Qiang Fu, Ruihu Li, Liangdong Lu
Abstract: International Journal of Quantum Information, Ahead of Print. Entanglement-assisted quantum error correcting code (EAQECC) is a generalization of standard stabilizer quantum code. Maximal entanglement EAQECCs can achieve the EA-hashing bound asymptotically. In this work, we give elementary recursive constructions of quaternary zero radical codes with dual distance three for all n ≥ 4. Consequently, good maximal entanglement EAQECCs of minimum distance three for such length n are obtained. Almost all of these EAQECCs are optimal or near optimal according to the EA-quantum Hamming bound.
Citation: International Journal of Quantum Information
PubDate: Wed, 18 Feb 2015 02:48:50 GMT
DOI: 10.1142/S0219749915500021

• Quantum-state transfer between atom and macroscopically distinguishable
cavity field in Jaynes–Cummings model
• Authors: Gang Zhang, Guan-Rong Li, Zhi Song
Abstract: International Journal of Quantum Information, Ahead of Print. We present a scheme for transferring quantum state between atom and cavity field in Jaynes–Cummings model (JC) in the aid of spin-echo-like technique. It is based on the facts that the atom in a cavity can induce the generation of modified coherent states (MCSs), which can be shown to be macroscopically distinguishable, and the anti-commutation relation between the Hamiltonian and the z-component Pauli matrix. We show that this scheme is applicable for a class of cavity field states. The application on two-cavity system provides an alternative scheme for preparation of non-local superpositions of quasi-classical light states. Numerical simulation shows that the proposed schemes are efficient.
Citation: International Journal of Quantum Information
PubDate: Tue, 17 Feb 2015 09:36:56 GMT
DOI: 10.1142/S021974991550001X

• A statistical model of information evaporation of perfectly reflecting
black holes
• Authors: Laszlo Gyongyosi
Abstract: International Journal of Quantum Information, Ahead of Print. We provide a statistical communication model for the phenomenon of quantum information evaporation from black holes (BHs). A BH behaves as a reflecting quantum channel in a very special regime, which allows for a receiver to perfectly recover the absorbed quantum information. The quantum channel of a perfectly reflecting (PR) BH is the probabilistically weighted sum of infinitely many qubit cloning channels. In this work, we reveal the statistical communication background of the information evaporation process of PR BHs. We show that the density of the cloned quantum particles in function of the PR BH's mass approximates a Chi-square distribution, while the stimulated emission process is characterized by zero-mean, circular symmetric complex Gaussian random variables. The results lead to the existence of Rayleigh random distributed coefficients in the probability density evolution, which confirms the presence of Rayleigh fading (a special type of random fluctuation) in the statistical communication model of BH information evaporation.
Citation: International Journal of Quantum Information
PubDate: Tue, 17 Feb 2015 09:36:56 GMT
DOI: 10.1142/S0219749915600254

• Energy and information propagation in a finite coupled bosonic heat bath
• Authors: Fernando Galve, Roberta Zambrini
Abstract: International Journal of Quantum Information, Ahead of Print. The finite coupled bosonic model of reservoir introduced by Vasile et al. [Phys. Rev. A89 (2014) 022109] to characterize non-Markovianity, is used to study the different dissipative behaviors of a harmonic oscillator coupled to it when it is in resonance, close to resonance or far detuned. We show that information and energy exchange between system and heat bath go hand in hand because phonons are the carriers of both: in resonance free propagation of excitations is achieved, and therefore pure dissipation, while when far detuned the system can only correlate with the first oscillator in the bath's chain, leading to almost unitary evolution. In the intermediate situation, we show the penetration of correlations and the formation of oscillatory (dressed state) behavior, which lies at the root of non-Markovianity.
Citation: International Journal of Quantum Information
PubDate: Mon, 16 Feb 2015 08:25:01 GMT
DOI: 10.1142/S0219749915600229

• Analytic symmetric information-theoretical discord for one class of
two-qubit states
• Authors: Jun Zhang, Shao-Xiong Wu, Chang-Shui Yu, Xiaoguang Wang
Abstract: International Journal of Quantum Information, Ahead of Print. We give the analytic expression for the information-theoretical symmetric discord of one type of two-qubit X states which depend on only four real parameters. As an application, we study the symmetric discord in a model, which shows that the numerical and analytic results are well consistent.
Citation: International Journal of Quantum Information
PubDate: Thu, 12 Feb 2015 06:16:02 GMT
DOI: 10.1142/S0219749915500069

• Generation of optical-terahertz biphoton pairs via spontaneous parametric
down-conversion
• Authors: V. V. Kornienko, S. A. Germanskiy, G. Kh. Kitaeva, A. N. Penin
Abstract: International Journal of Quantum Information, Ahead of Print. We examine the features of parametric down-conversion for generating non-classical optical-terahertz biphoton fields. The calculations were performed for a second-order correlation function and noise reduction factor (NRF), which were selected as measures of non-classicality of the field states. NRF measurement schemes were found to be less advantageous. Overall system temperature at which non-classical effects are still observable has been estimated as about 10 K. The priority of the main complicating factors for the quantum-optical measurements in the terahertz range has been determined. Thus, the most important parameter is the temperature of the system, after that come the absorption losses at terahertz frequencies, and the parametric conversion efficiency has the lowest impact. Increasing the pump radiation power has been found to be inefficient for "noise" suppression in this case. The calculations performed were based on lithium niobate dispersion properties due to its outstanding nonlinear optical properties and because it is frequently used for optical-to-terahertz frequency conversion.
Citation: International Journal of Quantum Information
PubDate: Fri, 06 Feb 2015 01:51:30 GMT
DOI: 10.1142/S0219749915600230

• Phase randomization and typicality in the interference of two condensates
• Authors: Paolo Facchi, Hiromichi Nakazato, Saverio Pascazio, Francesco V. Pepe, Golam Ali Sekh, Kazuya Yuasa
Abstract: International Journal of Quantum Information, Ahead of Print. Interference is observed when two independent Bose–Einstein condensates expand and overlap. This phenomenon is typical, in the sense that the overwhelming majority of wave functions of the condensates, uniformly sampled out of a suitable portion of the total Hilbert space, display interference with maximal visibility. We focus here on the phases of the condensates and their (pseudo) randomization, which naturally emerges when two-body scattering processes are considered. Relationship to typicality is discussed and analyzed.
Citation: International Journal of Quantum Information
PubDate: Thu, 05 Feb 2015 09:28:41 GMT
DOI: 10.1142/S0219749915600199

• Orthogonal-state-based cryptography in quantum mechanics and local
post-quantum theories
• Authors: S. Aravinda, Anindita Banerjee, Anirban Pathak, R. Srikanth
Abstract: International Journal of Quantum Information, Ahead of Print. We introduce the concept of cryptographic reduction, in analogy with a similar concept in computational complexity theory. In this framework, class A of crypto-protocols reduces to protocol class B in a scenario X, if for every instance a of A, there is an instance b of B and a secure transformation X that reproduces a given b, such that the security of b guarantees the security of a. Here we employ this reductive framework to study the relationship between security in quantum key distribution (QKD) and quantum secure direct communication (QSDC). We show that replacing the streaming of independent qubits in a QKD scheme by block encoding and transmission (permuting the order of particles block by block) of qubits, we can construct a QSDC scheme. This forms the basis for the block reduction from a QSDC class of protocols to a QKD class of protocols, whereby if the latter is secure, then so is the former. Conversely, given a secure QSDC protocol, we can of course construct a secure QKD scheme by transmitting a random key as the direct message. Then the QKD class of protocols is secure, assuming the security of the QSDC class which it is built from. We refer to this method of deduction of security for this class of QKD protocols, as key reduction. Finally, we propose an orthogonal-state-based deterministic key distribution (KD) protocol which is secure in some local post-quantum theories. Its security arises neither from geographic splitting of a code state nor from Heisenberg uncertainty, but from post-measurement disturbance.
Citation: International Journal of Quantum Information
PubDate: Thu, 05 Feb 2015 02:35:25 GMT
DOI: 10.1142/S0219749915600205

• Quantum oblivion: A master key for many quantum riddles
• Authors: Avshalom C. Elitzur, Eliahu Cohen
Abstract: International Journal of Quantum Information, Ahead of Print. A simple quantum interaction is analyzed, where the paths of two superposed particles asymmetrically cross, while a detector set to detect an interaction between them remains silent. Despite this negative result, the particles' states leave no doubt that a peculiar interaction has occurred: One particle's momentum is changed while the other's remains unaffected, in apparent violation of momentum conservation. Revisiting the foundations of the standard quantum measurement process offers the resolution. Prior to the macroscopic recording of no interaction, a brief critical interval (CI) prevails, during which the particles and the detector's pointer form a subtle entanglement which immediately dissolves. It is this self-cancellation, henceforth "quantum oblivion (QO)," that lies at the basis of some well-known intriguing quantum effects. Such is interaction-free measurement (IFM)1 and its more paradoxical variants like Hardy's Paradox2 and the quantum liar paradox.3 Even the Aharonov–Bohm (AB) effect4 and weak measurement (WM)5 turn out to belong to this group. We next study interventions within the CI that produce some other peculiar effects. Finally, we discuss some of the conceptual issues involved. Under a greater time-resolution of the CI, some non-local phenomena turn out to be local. Momentum is conserved due to the quantum uncertainties inflicted by the particle–pointer interaction, which sets the experiment's final boundary condition.
Citation: International Journal of Quantum Information
PubDate: Thu, 05 Feb 2015 02:35:24 GMT
DOI: 10.1142/S0219749915600242

• Entangled states implemented by Bn group operators, including properties
based on HS decompositions, separability and concurrence
• Authors: Y. Ben-Aryeh
Abstract: International Journal of Quantum Information, Ahead of Print. The use of the Bn group operators is developed for implementing entangling processes for large n-qubits systems (n > 2). By operating with the Bn group operators on the computational basis of states, entangled states are obtained with properties analogous to those of the 2-qubits Bell states. Tracing any qubit from the 3-qubits Bn entangled states, we get mixed states which are separable with zero concurrence, and correspondingly with only classical correlations. These properties are generalized to larger Bn entangled states (n > 3). The properties of the Bn entangled states are analyzed by the use of Hilbert–Schmidt (HS) decompositions.
Citation: International Journal of Quantum Information
PubDate: Thu, 05 Feb 2015 02:35:24 GMT
DOI: 10.1142/S0219749914500452

• New Minkowski type inequalities and entropic inequalities for quantum
states of qudits
• Authors: V. I. Man'ko, L. A. Markovich
Abstract: International Journal of Quantum Information, Ahead of Print. The two-parameter Minkowski like inequality written for composite quantum system state is obtained for arbitrary Hermitian non-negative matrix with trace equal to unity. The inequality can be used as entropic and information inequality for density matrix of noncomposite finite quantum system, e.g. for a single qudit state. The analogs of strong subadditivity condition for the single qudit is discussed in context of obtained Minkowski like inequality.
Citation: International Journal of Quantum Information
PubDate: Thu, 05 Feb 2015 02:35:22 GMT
DOI: 10.1142/S0219749915600217

• Quantum reading for the practical man
• Authors: Michele Dall'Arno
Abstract: International Journal of Quantum Information, Ahead of Print. Quantum reading is the art of exploiting the quantum properties of light to retrieve classical information stored in an optical memory with low energy and high accuracy. It was shown that the optimal strategy for quantum reading of beamsplitters largely outperforms coherent strategies, further allowing for perfect quantum reading, but requires a source challenging from the experimental viewpoint. Focusing on probes — i.e. BAT states and entangled coherent states (ECS) — which are experimentally feasible with present quantum optical technology, but still allow for perfect quantum reading, we evaluate the tradeoffs between the energy and the probability of error (failure) in ambiguous (unambiguous) quantum reading. It turns out that BAT states outperform ECS in any regime except for the case of high-energy discrimination of two beamsplitters with similar reflectivities.
Citation: International Journal of Quantum Information
PubDate: Thu, 05 Feb 2015 02:35:19 GMT
DOI: 10.1142/S0219749915600187

• Spatio-spectral characterization of twin-beam states of light for quantum
state engineering
• Authors: Alessia Allevi, Marco Lamperti, Ottavia Jedrkiewicz, Justinas Galinis, Radek Machulka, Ondřej Haderka, Jan Peřina, Maria Bondani
Abstract: International Journal of Quantum Information, Ahead of Print. We present an experimental investigation of the spatio-spectral coherence properties of bright twin-beam states (TWBs) as functions of different parameters, such as pump mean power and tuning angle of the employed nonlinear crystal. Our attention is mainly focused on the possible relations among the different quantities under investigation. Particular attention is devoted to the evolution of the number of spatio-spectral modes describing the radiation field, as it represents an interesting property to be controlled in view of possible applications to quantum state engineering protocols.
Citation: International Journal of Quantum Information
PubDate: Thu, 05 Feb 2015 02:35:18 GMT
DOI: 10.1142/S0219749915600278

• Controlling entanglement of two qubits by quantum-jump-based feedback
beyond rotating-wave approximation
• Authors: Qing Yang, Hui Liu, Xiu-Lan Zhen, Ming Yang, Zhuo-Liang Cao
Abstract: International Journal of Quantum Information, Ahead of Print. The entanglement dynamics of two identical atoms coupled to a single-mode cavity is considered. Based on the reduced non-perturbative quantum master equation method, the entanglement evolution of the two atoms with spontaneous emission under the quantum-jump-based feedback control is investigated beyond the conventional rotating-wave approximation (RWA). The research of entanglement evolution beyond RWA is a significant problem because of its importance to the field of strong coupling. The result of numerical simulations shows that an appropriate feedback control can prolong the entanglement time and increase the entanglement amplitude. The effect of synchronous control on two atoms is superior to that of one control.
Citation: International Journal of Quantum Information
PubDate: Thu, 05 Feb 2015 02:35:18 GMT
DOI: 10.1142/S0219749914500464

• Preface
• Authors: Marco Genovese, Giorgio Brida, Maria Luisa Rastello, Augusto Garuccio
Abstract: International Journal of Quantum Information, Ahead of Print.
Citation: International Journal of Quantum Information
PubDate: Thu, 29 Jan 2015 09:19:56 GMT
DOI: 10.1142/S0219749915020013

• Experimental violation of a d-dimensional bell inequality using
energy-time entangled photons
• Authors: Sacha Schwarz, Bänz Bessire, André Stefanov
Abstract: International Journal of Quantum Information, Ahead of Print. We experimentally study the violation of the CGLMP inequality for entangled 2-qubit and 2-qutrit states with different degrees of entanglement using numerically optimized measurement settings. The qudits are encoded and manipulated in the frequency spectrum of broadband energy-time entangled photons by taking into account a spatial light modulator (SLM). The latter allows to discretize the spectrum into bins. By controlling each frequency bin individually, the generation of maximally and non-maximally entangled qutrits is verified through quantum state tomography (QST).
Citation: International Journal of Quantum Information
PubDate: Thu, 29 Jan 2015 09:19:56 GMT
DOI: 10.1142/S0219749915600266

• Wavelet analysis on developable surface base on area preserving projection
• Authors: BaoQin Wang, Gang Wang, XiaoHui Zhou, Yu Su
Abstract: International Journal of Quantum Information, Ahead of Print. In this paper, a simple method is given in order to construct an area preserving mapping from a developable surface M to a plane. Based on the area preserving projection, we give some important formulas on M, and define a multi-resolution analysis on L2(M). We provide the conditions to further discuss the continuous wavelet transform and discrete wavelet transform on developable surface. At the same time, we derived two-scale equations that the scaling function and wavelet function on developable surface satisfied, we also define and discuss the orthogonality, and several important theorems are given. Finally, we construct the numerical examples. The focus of this paper is the area preserving mapping that from developable surface M to a plane, and the discrete wavelet transform on developable surface.
Citation: International Journal of Quantum Information
PubDate: Wed, 21 Jan 2015 03:13:58 GMT
DOI: 10.1142/S0219691315500071

• Sampling of bosonic qubits
• Authors: Vincenzo Tamma
Abstract: International Journal of Quantum Information, Ahead of Print. The boson sampling problem has brought a lot of attention in the quantum information field because it is not efficiently solvable with a classical computer; nonetheless it can be implementable with linear optical interferometers with single-boson sources. Recently, we introduced a more general problem, the multi-boson correlation sampling problem, which allows to take advantage of the muti-mode spectral distribution of the bosonic sources together with time-correlated measurements in order to achieve a sampling not only over the output channels of the interferometer but also over the joint detection times. This problem was analyzed for both single-photon sources and thermal sources. In this work, we demonstrate that it is possible to use single qubit bosonic sources in order to sample not only in the described “space-time” degree of freedom but also over all the possible exponential number of multi-qubit output states.
Citation: International Journal of Quantum Information
PubDate: Wed, 31 Dec 2014 03:56:52 GMT
DOI: 10.1142/S0219749915600175

• Entanglement generation in the ultra-strongly coupled Rabi model
• Authors: Matteo Bina, Stefano Maffezzoli Felis, Stefano Olivares
Abstract: International Journal of Quantum Information, Ahead of Print. We analyze the dynamics of the quantum Rabi model for two qubits interacting through a common bosonic field (resonator), focusing on the generation and detection of maximally entangled states. We obtain analytical results for the unitary dynamics of this system in the slow-qubit (or degenerate) regime, considering ultra-strong coupling between qubits and resonator mode, for which the rotating wave approximation (RWA) is no longer applicable. We also numerically investigate the dynamics beyond the slow-qubit condition in order to study the validity of the model in the presence of less strict conditions.
Citation: International Journal of Quantum Information
PubDate: Thu, 18 Dec 2014 07:09:18 GMT
DOI: 10.1142/S0219749915600163

• Experimental hybrid entanglement between quantum and classical states of
light
• Authors: Luca S. Costanzo, Alessandro Zavatta, Samuele Grandi, Marco Bellini, Hyunseok Jeong, Minsu Kang, Seung-Woo Lee, Timothy C. Ralph
Abstract: International Journal of Quantum Information, Ahead of Print. The realization of hybrid entanglement between a microscopic (quantum) and a macroscopic (classical) system, in analogy to the situation of the famous Schrödinger's cat paradox, is an important milestone, both from the fundamental perspective and for possible applications in the processing of quantum information. The most straightforward optical implementation of this condition is that of the entanglement between a single-photon and a coherent state. In this work, we describe the first step towards the generation of this type of hybrid entanglement from the experimental perspective.
Citation: International Journal of Quantum Information
PubDate: Wed, 17 Dec 2014 08:57:58 GMT
DOI: 10.1142/S0219749915600151

• Entanglement generation and dynamics for a Bose–Hubbard model in a
double-well potential
• Authors: F. Gentile, A. Montorsi, M. Roncaglia
Abstract: International Journal of Quantum Information, Ahead of Print. The study of entanglement between bosonic systems is of primary importance for establishing feasible resources needed for implementing quantum information protocols, both in their interacting atomic or photonic realizations. Atomic systems are particularly efficient in the production of large amounts of entanglement, providing higher information density than conventional qubit entangled states. Such increased quantum resources pave the way to novel fundamental tests of nature and efficient applications in quantum information, metrology and sensing. We consider a basic setup made up of two parties A and B, each one populated by a single level bosonic variable. The bosons are interacting and can hop between A and B, thus describing a two-site Bose–Hubbard Hamiltonian. We consider the generation of quantum states in several situations that cover the majority of physical realizations: ground state, finite temperature, unitary dynamics, dissipation through dephasing and loss of particles. The system is analyzed through truncated exact diagonalization, as a function of the microscopic parameters. The nonseparability of the obtained quantum states is estimated by means of the negativity, which has recently been proven to be a suitable measure of entanglement [M. Roncaglia, A. Montorsi and M. Genovese, Phys. Rev. A90 (2014) 062303]. Finally, we calculate lower bounds of the entanglement of formation (EOF), an indicator that quantifies the minimal amount of entanglement resources needed to build up such states.
Citation: International Journal of Quantum Information
PubDate: Wed, 10 Dec 2014 09:56:34 GMT
DOI: 10.1142/S021974991560014X

• Quantum discord in spin-1/2 Heisenberg chains with
Dzyaloshinkii–Moriya interaction
• Authors: Xiao San Ma, An Min Wang
Abstract: International Journal of Quantum Information, Ahead of Print. We have investigated the quantum discord (QD) of the thermal density matrix of spin-1/2 Heisenberg chains with Dzyaloshinskii–Moriya (DM) interaction. With fermionization technique, we study the mutual effect of DM interaction and the external magnetic field on the QD and the entanglement. Our analysis implies that the DM interaction can enhance the QD while the external magnetic field will shrink the QD. By a comparison between the entanglement and the QD, we find that the QD is more robust to the temperature and to the external magnetic field than the entanglement of formation (EoF) in the sense that the EoF takes a zero value while the QD does not for high temperature and strong external magnetic field. This point confirms the conclusion that there exist some separable states containing non-zero QD.
Citation: International Journal of Quantum Information
PubDate: Wed, 10 Dec 2014 09:56:33 GMT
DOI: 10.1142/S0219749914500439

• Single-photon emitters based on NIR color centers in diamond coupled with
solid immersion lenses
• Authors: D. Gatto Monticone, J. Forneris, M. Levi, A. Battiato, F. Picollo, P. Olivero, P. Traina, E. Moreva, E. Enrico, G. Brida, I. P. Degiovanni, M. Genovese, G. Amato, L. Boarino
Abstract: International Journal of Quantum Information, Ahead of Print. Single-photon sources represent a key enabling technology in quantum optics, and single color centers in diamond are a promising platform to serve this purpose, due to their high quantum efficiency and photostability at room temperature. The widely studied nitrogen-vacancy (NV) centers are characterized by several limitations, thus other defects have recently been considered, with a specific focus of centers emitting in the near-infra red (NIR). In the present work, we report on the coupling of native NIR-emitting centers in high-quality single-crystal diamond with solid immersion lens (SIL) structures fabricated by focused ion beam (FIB) lithography. The reported improvements in terms of light collection efficiency make the proposed system an ideal platform for the development of single-photon emitters with appealing photophysical and spectral properties.
Citation: International Journal of Quantum Information
PubDate: Wed, 10 Dec 2014 09:56:33 GMT
DOI: 10.1142/S0219749915600114

• High-capacity imaging and rotationally insensitive object identification
with correlated orbital angular momentum states
• Authors: Casey A. Fitzpatrick, David S. Simon, Alexander V. Sergienko
Abstract: International Journal of Quantum Information, Ahead of Print. Using no conventional measurements in position space, information extraction rates exceeding one bit per photon are achieved by employing high-dimensional correlated orbital angular momentum (OAM) states for object recognition. The correlations are shown to be insensitive to axial rotation of the target object: The information structure of an object's joint OAM coincidence spectrum is unchanged even when the object undergoes random rotations between each measurement. Additionally, OAM correlations alone are shown to be sufficient for full image reconstruction of complex, off-axis objects, and novel object symmetries are observed in the phases of OAM-object interaction transition amplitudes. Variations in mutual information rates, due to off-axis translation in the beam field, are studied, and it is shown that object symmetry signatures and information rates are independent of environmental factors sufficiently far from the beam center. The results motivate dynamic scanning applications in contexts where symmetry and small numbers of noninvasive measurements are desired.
Citation: International Journal of Quantum Information
PubDate: Tue, 09 Dec 2014 10:14:58 GMT
DOI: 10.1142/S0219749915600138

• Hunting the "impossible atoms" Pauli exclusion principle violation and
spontaneous collapse of the wave function at test
• Authors: Catalina Curceanu, Sergio Bartalucci, Angelo Bassi, Sergio Bertolucci, Carolina Berucci, Alexandru Mario Bragadireanu, Michael Cargnelli, Alberto Clozza, Sergio Di Matteo, S. Donadi, Alessandro D'uffizi, J.-P. Egger, Carlo Guaraldo, Mihail Iliescu, Tomoichi Ishiwatari, Matthias Laubenstein, Johann Marton, Edoardo Milotti, Dorel Pietreanu, Kristian Piscicchia, Titus Ponta, Emanuele Sbardella, Alessandro Scordo, Hexi Shi, Diana Sirghi, Florin Sirghi, Laura Sperandio, Oton Vazquez Doce, Johann Zmeskal
Abstract: International Journal of Quantum Information, Ahead of Print. The Pauli exclusion principle (PEP) and, more generally, the spin-statistics connection, are at the very basis of our understanding of matter, life and Universe. The PEP spurs, presently, a lively debate on its possible limits, deeply rooted in the very foundations of Quantum Mechanics. It is, therefore, extremely important to test the limits of its validity. The Violation of the PEP (VIP) experiment established the best limit on the probability that PEP is violated by electrons, using the method of searching for PEP forbidden atomic transitions in copper. We describe the experimental method, the obtained results, and plans to go beyond the actual limit by upgrading the experimental apparatus. We discuss the possibility of using a similar experimental technique to search for X-rays as a signature of the spontaneous collapse of the wave function predicted by continuous spontaneous localization (CSL) theories.
Citation: International Journal of Quantum Information
PubDate: Tue, 09 Dec 2014 10:14:55 GMT
DOI: 10.1142/S0219749915600126

• The su(1,1)-like intensity-dependent Rabi model: A perturbative analysis
of weak and strong-coupling regimes
• Authors: Vittorio Penna, Francesco A. Raffa
Abstract: International Journal of Quantum Information, Ahead of Print. We present a perturbative analysis of a Rabi model where the coupling between the quantized single-mode electromagnetic field and the two-level atom depends on the field intensity. Upon modeling the matter–radiation coupling through the Holstein–Primakoff realization of algebra su(1,1), we evaluate first- and second-order eigenenergies and eigenstates both in the weak-coupling regime (atom transition frequency smaller than the coupling strength) and in the strong-coupling regime. In the first case, among various effects, we observe a quadratic dependence on the photon number of energy eigenvalues and the possible formation of level doublets. In the strong-coupling case, the perturbative analysis becomes considerably complex due to the su(1,1)-valued form of the unperturbed Hamiltonian. The critical condition for the transition to an almost continuous spectrum is found in terms of the model parameters.
Citation: International Journal of Quantum Information
PubDate: Wed, 03 Dec 2014 04:06:43 GMT
DOI: 10.1142/S0219749915600102

• Features of three-photon polarization states: Entanglement and
polarization
• Authors: M. V. Fedorov
Abstract: International Journal of Quantum Information, Ahead of Print. In a general form, three-photon polarization states are superpositions of contributions from four three-photon polarization modes with four arbitrary complex coefficients. Entanglement of such states is defined as entanglement between their one-photon and two-photon parts. The degree of entanglement is found explicitly in terms of such entanglement quantifiers as the generalized concurrence, entropy of reduced states and the Schmidt parameter. Polarization Stokes vectors, as well as the Schmidt decompositions of three-photon states are found and discussed. Similarity and differences with respect to biphoton polarization states are discussed too.
Citation: International Journal of Quantum Information
PubDate: Wed, 03 Dec 2014 04:00:01 GMT
DOI: 10.1142/S0219749915600096

• Quantifying the leakage of quantum protocols for classical two-party
cryptography
• Authors: Louis Salvail, Christian Schaffner, Miroslava Sotáková
Abstract: International Journal of Quantum Information, Ahead of Print. We study quantum protocols among two distrustful parties. By adopting a rather strict definition of correctness — guaranteeing that honest players obtain their correct outcomes only — we can show that every strictly correct quantum protocol implementing a non-trivial classical primitive necessarily leaks information to a dishonest player. This extends known impossibility results to all non-trivial primitives. We provide a framework for quantifying this leakage and argue that leakage is a good measure for the privacy provided to the players by a given protocol. Our framework also covers the case where the two players are helped by a trusted third party. We show that despite the help of a trusted third party, the players cannot amplify the cryptographic power of any primitive. All our results hold even against quantum honest-but-curious adversaries who honestly follow the protocol but purify their actions and apply a different measurement at the end of the protocol. As concrete examples, we establish lower bounds on the leakage of standard universal two-party primitives such as oblivious transfer.
Citation: International Journal of Quantum Information
PubDate: Wed, 03 Dec 2014 04:00:01 GMT
DOI: 10.1142/S0219749914500415

• Is quantum simulation of turbulence within reach'
• Authors: Mario Rasetti
Abstract: International Journal of Quantum Information, Ahead of Print. The possibility of approaching quantum simulation of "topological turbulence" is discussed. In the latter, the topological features of turbulent flow are ascribed to a purely group-theoretic and topological view through the group SDiff of volume-preserving diffeomorphisms and the Mapping Class Group for the 2D surfaces that foliate the 3D flow domain. A class of representations of the group of mapping classes for compact boundaryless surfaces is explicitly constructed in terms of the Witt–Virasoro Hopf-coalgebra and implemented in terms of su(1,1). This leads to a complex, nonlinear Hamiltonian naturally associated with the fluid diffeomorphisms that could lend itself to the quantum simulation of turbulence in Fock space.
Citation: International Journal of Quantum Information
PubDate: Mon, 01 Dec 2014 06:09:05 GMT
DOI: 10.1142/S0219749915600084

• Quantum dissonance and deterministic quantum computation with a single
qubit
• Authors: Mazhar Ali
Abstract: International Journal of Quantum Information, Ahead of Print. Mixed state quantum computation can perform certain tasks which are believed to be efficiently intractable on a classical computer. For a specific model of mixed state quantum computation, namely, deterministic quantum computation with a single qubit (DQC1), recent investigations suggest that quantum correlations other than entanglement might be responsible for the power of DQC1 model. However, strictly speaking, the role of entanglement in this model of computation was not entirely clear. We provide conclusive evidence that there are instances where quantum entanglement is not present in any part of this model, nevertheless we have advantage over classical computation. This establishes the fact that quantum dissonance (a kind of quantum correlations) present in fully separable (FS) states provide power to DQC1 model.
Citation: International Journal of Quantum Information
PubDate: Mon, 01 Dec 2014 06:09:05 GMT
DOI: 10.1142/S0219749914500373

• Quantum codes from cyclic codes over F3 + vF3
• 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
DOI: 10.1142/S0219749914500427

• Emerging quantum mechanics: Coefficient of second-order coherence from
classical random fields interacting with threshold type detectors
• 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
DOI: 10.1142/S0219749915600072

• Entanglement and other quantum correlations of a single qudit state
• 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
DOI: 10.1142/S0219749915600060

• Engineering nonlinear coherent states as photon-added and
photon-subtracted coherent states
• 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
DOI: 10.1142/S0219749915600059

• Dimension-independent bounds for Hardy's experiment
• 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
DOI: 10.1142/S0219749914500397

• One-party controlled minimum remote state preparation of equatorial
n-qubit states
• 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
DOI: 10.1142/S0219749914500385

• Quantum nonlocality enhanced by homogenization
• 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
DOI: 10.1142/S0219749914500403

• Comment on "Cryptanalysis and improvement of the secure quantum sealed-bid
auction with post confirmation"
• 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
DOI: 10.1142/S021974991475001X

• Pairwise quantum and classical correlations in multi-qubits states via
linear relative entropy
• 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
DOI: 10.1142/S021974991450035X

• Time exponents of asymptotic entanglement of discrete quantum walk in one
dimension
• 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
DOI: 10.1142/S0219749914500361

• A bonding model of entanglement for N-qubit graph states
• 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
DOI: 10.1142/S0219749914300058

• The intrinsic helicity of elementary particles and the spin-statistic
connection
• 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
DOI: 10.1142/S0219749915600047

• Universal optimal quantum correlator
• 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
DOI: 10.1142/S0219749915600023

• Engineering decoherence for two-qubit systems interacting with a classical
environment
• 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
DOI: 10.1142/S0219749915600035

• If time is a local observable, then Hawking radiation is unitary
• 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
DOI: 10.1142/S0219749915600011

• Limitations on quantum dimensionality reduction
• 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
DOI: 10.1142/S0219749914400012

• EXPLICIT RELATION BETWEEN ALL LOWER BOUND TECHNIQUES FOR QUANTUM QUERY
COMPLEXITY
• 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
DOI: 10.1142/S0219749913500597

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