Entanglement in neutrino oscillations

International Nuclear Information System (INIS)

Blasone, M.; Dell'Anno, F.; De Siena, S.; Illuminati, F.; Dell'Anno, F.; De Siena, S.; Illuminati, F.; Blasone, M.

2009-01-01

Flavor oscillations in elementary particle physics are related to multimode entanglement of single-particle states. We show that mode entanglement can be expressed in terms of flavor transition probabilities, and therefore that single-particle entangled states acquire a precise operational characterization in the context of particle mixing. We treat in detail the physically relevant cases of two- and three-flavor neutrino oscillations, including the effective measure of CP violation. We discuss experimental schemes for the transfer of the quantum information encoded in single-neutrino states to spatially delocalized two-flavor charged-lepton states, thus showing, at least in principle, that single-particle entangled states of neutrino mixing are legitimate physical resources for quantum information tasks. (authors)

Relay entanglement and clusters of correlated spins

Science.gov (United States)

Doronin, S. I.; Zenchuk, A. I.

2018-06-01

Considering a spin-1/2 chain, we suppose that the entanglement passes from a given pair of particles to another one, thus establishing the relay transfer of entanglement along the chain. Therefore, we introduce the relay entanglement as a sum of all pairwise entanglements in a spin chain. For more detailed studying the effects of remote pairwise entanglements, we use the partial sums collecting entanglements between the spins separated by up to a certain number of nodes. The problem of entangled cluster formation is considered, and the geometric mean entanglement is introduced as a characteristic of quantum correlations in a cluster. Generally, the lifetime of a cluster decreases with an increase in its size.

Entanglement in mutually unbiased bases

Energy Technology Data Exchange (ETDEWEB)

Wiesniak, M; Zeilinger, A [Vienna Center for Quantum Science and Technology (VCQ), Faculty of Physics, University of Vienna, Boltzmanngasse 5, 1090 Vienna (Austria); Paterek, T, E-mail: tomasz.paterek@nus.edu.sg [Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, 117543 Singapore (Singapore)

2011-05-15

One of the essential features of quantum mechanics is that most pairs of observables cannot be measured simultaneously. This phenomenon manifests itself most strongly when observables are related to mutually unbiased bases. In this paper, we shed some light on the connection between mutually unbiased bases and another essential feature of quantum mechanics, quantum entanglement. It is shown that a complete set of mutually unbiased bases of a bipartite system contains a fixed amount of entanglement, independent of the choice of the set. This has implications for entanglement distribution among the states of a complete set. In prime-squared dimensions we present an explicit experiment-friendly construction of a complete set with a particularly simple entanglement distribution. Finally, we describe the basic properties of mutually unbiased bases composed of product states only. The constructions are illustrated with explicit examples in low dimensions. We believe that the properties of entanglement in mutually unbiased bases may be one of the ingredients to be taken into account to settle the question of the existence of complete sets. We also expect that they will be relevant to applications of bases in the experimental realization of quantum protocols in higher-dimensional Hilbert spaces.

Multipartite entangled quantum states: Transformation, Entanglement monotones and Application

Science.gov (United States)

Cui, Wei

Entanglement is one of the fundamental features of quantum information science. Though bipartite entanglement has been analyzed thoroughly in theory and shown to be an important resource in quantum computation and communication protocols, the theory of entanglement shared between more than two parties, which is called multipartite entanglement, is still not complete. Specifically, the classification of multipartite entanglement and the transformation property between different multipartite states by local operators and classical communications (LOCC) are two fundamental questions in the theory of multipartite entanglement. In this thesis, we present results related to the LOCC transformation between multipartite entangled states. Firstly, we investigate the bounds on the LOCC transformation probability between multipartite states, especially the GHZ class states. By analyzing the involvement of 3-tangle and other entanglement measures under weak two-outcome measurement, we derive explicit upper and lower bound on the transformation probability between GHZ class states. After that, we also analyze the transformation between N-party W type states, which is a special class of multipartite entangled states that has an explicit unique expression and a set of analytical entanglement monotones. We present a necessary and sufficient condition for a known upper bound of transformation probability between two N-party W type states to be achieved. We also further investigate a novel entanglement transformation protocol, the random distillation, which transforms multipartite entanglement into bipartite entanglement ii shared by a non-deterministic pair of parties. We find upper bounds for the random distillation protocol for general N-party W type states and find the condition for the upper bounds to be achieved. What is surprising is that the upper bounds correspond to entanglement monotones that can be increased by Separable Operators (SEP), which gives the first set of

Optimal simulation of a perfect entangler

International Nuclear Information System (INIS)

Yu Nengkun; Duan Runyao; Ying Mingsheng

2010-01-01

A 2 x 2 unitary operation is called a perfect entangler if it can generate a maximally entangled state from some unentangled input. We study the following question: How many runs of a given two-qubit entangling unitary operation are required to simulate some perfect entangler with one-qubit unitary operations as free resources? We completely solve this problem by presenting an analytical formula for the optimal number of runs of the entangling operation. Our result reveals an entanglement strength of two-qubit unitary operations.

Distributed wireless quantum communication networks with partially entangled pairs

International Nuclear Information System (INIS)

Yu Xu-Tao; Zhang Zai-Chen; Xu Jin

2014-01-01

Wireless quantum communication networks transfer quantum state by teleportation. Existing research focuses on maximal entangled pairs. In this paper, we analyse the distributed wireless quantum communication networks with partially entangled pairs. A quantum routing scheme with multi-hop teleportation is proposed. With the proposed scheme, is not necessary for the quantum path to be consistent with the classical path. The quantum path and its associated classical path are established in a distributed way. Direct multi-hop teleportation is conducted on the selected path to transfer a quantum state from the source to the destination. Based on the feature of multi-hop teleportation using partially entangled pairs, if the node number of the quantum path is even, the destination node will add another teleportation at itself. We simulated the performance of distributed wireless quantum communication networks with a partially entangled state. The probability of transferring the quantum state successfully is statistically analyzed. Our work shows that multi-hop teleportation on distributed wireless quantum networks with partially entangled pairs is feasible. (general)

Establishing and storing of deterministic quantum entanglement among three distant atomic ensembles.

Science.gov (United States)

Yan, Zhihui; Wu, Liang; Jia, Xiaojun; Liu, Yanhong; Deng, Ruijie; Li, Shujing; Wang, Hai; Xie, Changde; Peng, Kunchi

2017-09-28

It is crucial for the physical realization of quantum information networks to first establish entanglement among multiple space-separated quantum memories and then, at a user-controlled moment, to transfer the stored entanglement to quantum channels for distribution and conveyance of information. Here we present an experimental demonstration on generation, storage, and transfer of deterministic quantum entanglement among three spatially separated atomic ensembles. The off-line prepared multipartite entanglement of optical modes is mapped into three distant atomic ensembles to establish entanglement of atomic spin waves via electromagnetically induced transparency light-matter interaction. Then the stored atomic entanglement is transferred into a tripartite quadrature entangled state of light, which is space-separated and can be dynamically allocated to three quantum channels for conveying quantum information. The existence of entanglement among three released optical modes verifies that the system has the capacity to preserve multipartite entanglement. The presented protocol can be directly extended to larger quantum networks with more nodes.Continuous-variable encoding is a promising approach for quantum information and communication networks. Here, the authors show how to map entanglement from three spatial optical modes to three separated atomic samples via electromagnetically induced transparency, releasing it later on demand.

Quantum entanglement of high angular momenta.

Science.gov (United States)

Fickler, Robert; Lapkiewicz, Radek; Plick, William N; Krenn, Mario; Schaeff, Christoph; Ramelow, Sven; Zeilinger, Anton

2012-11-02

Single photons with helical phase structures may carry a quantized amount of orbital angular momentum (OAM), and their entanglement is important for quantum information science and fundamental tests of quantum theory. Because there is no theoretical upper limit on how many quanta of OAM a single photon can carry, it is possible to create entanglement between two particles with an arbitrarily high difference in quantum number. By transferring polarization entanglement to OAM with an interferometric scheme, we generate and verify entanglement between two photons differing by 600 in quantum number. The only restrictive factors toward higher numbers are current technical limitations. We also experimentally demonstrate that the entanglement of very high OAM can improve the sensitivity of angular resolution in remote sensing.

General individual attack on the ping-pong protocol with completely entangled pairs of qutrits

OpenAIRE

Vasiliu, E. V.

2009-01-01

The general individual (non-coherent) attack on the ping-pong protocol with completely entangled pairs of three-dimensional quantum systems (qutrits) is analyzed. The expression for amount of the eavesdropper's information as functions from probability of attack detection is derived. It is shown, that the security of the ping-pong protocol with pairs of qutrits is higher the security of the protocol with pairs of qubits. It is also shown, that with the use by legitimate users in a control mod...

Quantum Entanglement and Reduced Density Matrices

Science.gov (United States)

Purwanto, Agus; Sukamto, Heru; Yuwana, Lila

2018-05-01

We investigate entanglement and separability criteria of multipartite (n-partite) state by examining ranks of its reduced density matrices. Firstly, we construct the general formula to determine the criterion. A rank of origin density matrix always equals one, meanwhile ranks of reduced matrices have various ranks. Next, separability and entanglement criterion of multipartite is determined by calculating ranks of reduced density matrices. In this article we diversify multipartite state criteria into completely entangled state, completely separable state, and compound state, i.e. sub-entangled state and sub-entangledseparable state. Furthermore, we also shorten the calculation proposed by the previous research to determine separability of multipartite state and expand the methods to be able to differ multipartite state based on criteria above.

Thermal entanglement and teleportation of a thermally mixed entangled state of a Heisenberg chain through a Werner state

Institute of Scientific and Technical Information of China (English)

Huang Li-Yuan; Fang Mao-Fa

2008-01-01

The thermal entanglement and teleportation of a thermally mixed entangled state of a two-qubit Heisenberg XXX chain under the Dzyaloshinski-Moriya (DM) anisotropic antisymmetric interaction through a noisy quantum channel given by a Werner state is investigated. The dependences of the thermal entanglement of the teleported state on the DM coupling constant, the temperature and the entanglement of the noisy quantum channel are studied in detail for both the ferromagnetic and the antiferromagnetic cases. The result shows that a minimum entanglement of the noisy quantum channel must be provided in order to realize the entanglement teleportation. The values of fidelity of the teleported state are also studied for these two cases. It is found that under certain conditions, we can transfer an initial state with a better fidelity than that for any classical communication protocol.

Separability criteria for genuine multiparticle entanglement

NARCIS (Netherlands)

Guhne, O.; Seevinck, M.P.|info:eu-repo/dai/nl/304847399

2010-01-01

We present a method to derive separability criteria for different classes of multiparticle entanglement, especially genuine multiparticle entanglement. The resulting criteria are necessary and sufficient for certain families of states. This, for example, completely solves the problem of classifying

Separability Criteria for Genuine Multiparticle Entanglement

NARCIS (Netherlands)

Guehne, O.; Seevinck, M.P.

2010-01-01

We present a method to derive separability criteria for different classes of multiparticle entanglement, especially genuine multiparticle entanglement. The resulting criteria are necessary and sufficient for certain families of states. This, for example, completely solves the problem of classifying

Teleportation of Squeezed Entangled State

Institute of Scientific and Technical Information of China (English)

HU Li-Yun; ZHOU Nan-Run

2007-01-01

Based on the coherent entangled state |α, x＞ we introduce the squeezed entangled state (SES). Then we propose a teleportation protocol for the SES by using Einstein-Podolsky-Rosen entangled state |η＞as a quantum channel.The calculation is greatly simplified by virtue of the Schmidt decompositions of both |α, x＞and |η＞. Any bipartite states that can be expanded in terms of |α, x＞may be teleported in this way due to the completeness of |α, x＞.

Computing quantum discord is NP-complete

International Nuclear Information System (INIS)

Huang, Yichen

2014-01-01

We study the computational complexity of quantum discord (a measure of quantum correlation beyond entanglement), and prove that computing quantum discord is NP-complete. Therefore, quantum discord is computationally intractable: the running time of any algorithm for computing quantum discord is believed to grow exponentially with the dimension of the Hilbert space so that computing quantum discord in a quantum system of moderate size is not possible in practice. As by-products, some entanglement measures (namely entanglement cost, entanglement of formation, relative entropy of entanglement, squashed entanglement, classical squashed entanglement, conditional entanglement of mutual information, and broadcast regularization of mutual information) and constrained Holevo capacity are NP-hard/NP-complete to compute. These complexity-theoretic results are directly applicable in common randomness distillation, quantum state merging, entanglement distillation, superdense coding, and quantum teleportation; they may offer significant insights into quantum information processing. Moreover, we prove the NP-completeness of two typical problems: linear optimization over classical states and detecting classical states in a convex set, providing evidence that working with classical states is generically computationally intractable. (paper)

Studying entanglement-assisted entanglement transformation

International Nuclear Information System (INIS)

Hsu Liyi

2004-01-01

In this paper, we study catalysis of entanglement transformations for n-level pure entangled states. We propose an algorithm of finding the required catalystic entanglement. We introduce several examples by way of demonstration. We evaluate the lower and upper bound of the required inequalities for deciding whether there are m-level appropriate catalyst states for entanglement transformations for two n-level pure entangled states

Hybrid entanglement concentration assisted with single coherent state

International Nuclear Information System (INIS)

Guo Rui; Zhou Lan; Sheng Yu-Bo; Gu Shi-Pu; Wang Xing-Fu

2016-01-01

Hybrid entangled state (HES) is a new type of entanglement, which combines the advantages of an entangled polarization state and an entangled coherent state. HES is widely discussed in the applications of quantum communication and computation. In this paper, we propose three entanglement concentration protocols (ECPs) for Bell-type HES, W-type HES, and cluster-type HES, respectively. After performing these ECPs, we can obtain the maximally entangled HES with some success probability. All the ECPs exploit the single coherent state to complete the concentration. These protocols are based on the linear optics, which are feasible in future experiments. (paper)

Entanglement and quantum state transfer between two atoms trapped in two indirectly coupled cavities

Science.gov (United States)

Zheng, Bin; Shen, Li-Tuo; Chen, Ming-Feng

2016-05-01

We propose a one-step scheme for implementing entanglement generation and the quantum state transfer between two atomic qubits trapped in two different cavities that are not directly coupled to each other. The process is realized through engineering an effective asymmetric X-Y interaction for the two atoms involved in the gate operation and an auxiliary atom trapped in an intermediate cavity, induced by virtually manipulating the atomic excited states and photons. We study the validity of the scheme as well as the influences of the dissipation by numerical simulation and demonstrate that it is robust against decoherence.

Teleportation of a three-particle entangled W state

Institute of Scientific and Technical Information of China (English)

郑亦庄; 顾永建; 郭光灿

2002-01-01

We have investigated the problem of teleporting a three-particle entangled W state and we propose a scheme based on entanglement swapping to complete the teleportation. We also put forward a scheme for the teleportation of a general W state by using nonmaximally entangled quantum channels. The probability of success of the latter scheme is obtained.

A chiroptical switch based on supramolecular chirality transfer through alkyl chain entanglement and dynamic covalent bonding.

Science.gov (United States)

Lv, Kai; Qin, Long; Wang, Xiufeng; Zhang, Li; Liu, Minghua

2013-12-14

Chirality transfer is an interesting phenomenon in Nature, which represents an important step to understand the evolution of chiral bias and the amplification of the chirality. In this paper, we report the chirality transfer via the entanglement of the alkyl chains between chiral gelator molecules and achiral amphiphilic Schiff base. We have found that although an achiral Schiff base amphiphile could not form organogels in any kind of organic solvents, it formed co-organogels when mixed with a chiral gelator molecule. Interestingly, the chirality of the gelator molecules was transferred to the Schiff base chromophore in the mixed co-gels and there was a maximum mixing ratio for the chirality transfer. Furthermore, the supramolecular chirality was also produced based on a dynamic covalent chemistry of an imine formed by the reaction between an aldehyde and an amine. Such a covalent bond of imine was formed reversibly depending on the pH variation. When the covalent bond was formed the chirality transfer occurred, when it was destroyed, the transfer stopped. Thus, a supramolecular chiroptical switch is obtained based on supramolecular chirality transfer and dynamic covalent chemistry.

Dynamics and manipulation of entanglement in coupled harmonic systems with many degrees of freedom

Science.gov (United States)

Plenio, M. B.; Hartley, J.; Eisert, J.

2004-03-01

We study the entanglement dynamics of a system consisting of a large number of coupled harmonic oscillators in various configurations and for different types of nearest-neighbour interactions. For a one-dimensional chain, we provide compact analytical solutions and approximations to the dynamical evolution of the entanglement between spatially separated oscillators. Key properties such as the speed of entanglement propagation, the maximum amount of transferred entanglement and the efficiency for the entanglement transfer are computed. For harmonic oscillators coupled by springs, corresponding to a phonon model, we observe a non-monotonic transfer efficiency in the initially prepared amount of entanglement, i.e. an intermediate amount of initial entanglement is transferred with the highest efficiency. In contrast, within the framework of the rotating-wave approximation (as appropriate, e.g. in quantum optical settings) one finds a monotonic behaviour. We also study geometrical configurations that are analogous to quantum optical devices (such as beamsplitters and interferometers) and observe characteristic differences when initially thermal or squeezed states are entering these devices. We show that these devices may be switched on and off by changing the properties of an individual oscillator. They may therefore be used as building blocks of large fixed and pre-fabricated but programmable structures in which quantum information is manipulated through propagation. We discuss briefly possible experimental realizations of systems of interacting harmonic oscillators in which these effects may be confirmed experimentally.

Rank-dependant factorization of entanglement evolution

International Nuclear Information System (INIS)

Siomau, Michael

2016-01-01

Highlights: • In some cases the complex entanglement evolution can be factorized on simple terms. • We suggest factorization equations for multiqubit entanglement evolution. • The factorization is solely defined by the rank of the final state density matrices. • The factorization is independent on the local noisy channels and initial pure states. - Abstract: The description of the entanglement evolution of a complex quantum system can be significantly simplified due to the symmetries of the initial state and the quantum channels, which simultaneously affect parts of the system. Using concurrence as the entanglement measure, we study the entanglement evolution of few qubit systems, when each of the qubits is affected by a local unital channel independently on the others. We found that for low-rank density matrices of the final quantum state, such complex entanglement dynamics can be completely described by a combination of independent factors representing the evolution of entanglement of the initial state, when just one of the qubits is affected by a local channel. We suggest necessary conditions for the rank of the density matrices to represent the entanglement evolution through the factors. Our finding is supported with analytical examples and numerical simulations.

Multiple-copy entanglement transformation and entanglement catalysis

International Nuclear Information System (INIS)

Duan Runyao; Feng Yuan; Li Xin; Ying Mingsheng

2005-01-01

We prove that any multiple-copy entanglement transformation [S. Bandyopadhyay, V. Roychowdhury, and U. Sen, Phys. Rev. A 65, 052315 (2002)] can be implemented by a suitable entanglement-assisted local transformation [D. Jonathan and M. B. Plenio, Phys. Rev. Lett. 83, 3566 (1999)]. Furthermore, we show that the combination of multiple-copy entanglement transformation and the entanglement-assisted one is still equivalent to the pure entanglement-assisted one. The mathematical structure of multiple-copy entanglement transformations then is carefully investigated. Many interesting properties of multiple-copy entanglement transformations are presented, which exactly coincide with those satisfied by the entanglement-assisted ones. Most interestingly, we show that an arbitrarily large number of copies of state should be considered in multiple-copy entanglement transformations

Dynamics of Quantum Entanglement in Reservoir with Memory Effects

International Nuclear Information System (INIS)

Hao Xiang; Sha Jinqiao; Sun Jian; Zhu Shiqun

2012-01-01

The non-Markovian dynamics of quantum entanglement is studied by the Shabani-Lidar master equation when one of entangled quantum systems is coupled to a local reservoir with memory effects. The completely positive reduced dynamical map can be constructed in the Kraus representation. Quantum entanglement decays more slowly in the non-Markovian environment. The decoherence time for quantum entanglement can be markedly increased with the change of the memory kernel. It is found out that the entanglement sudden death between quantum systems and entanglement sudden birth between the system and reservoir occur at different instants. (general)

Entanglement, purity, and energy: Two qubits versus two modes

International Nuclear Information System (INIS)

McHugh, Derek; Ziman, Mario; Buzek, Vladimir

2006-01-01

We study the relationship between the entanglement, mixedness, and energy of two-qubit and two-mode Gaussian quantum states. We parametrize the set of allowed states of these two fundamentally different physical systems using measures of entanglement, mixedness, and energy that allow us to compare and contrast the two systems using a phase diagram. This phase diagram enables one to clearly identify not only the physically allowed states, but the set of states connected under an arbitrary quantum operation. We pay particular attention to the maximally entangled mixed states of each system. Following this we investigate how efficiently one may transfer entanglement from two-mode to two-qubit states

Efficient quantum entanglement distribution over an arbitrary collective-noise channel

Science.gov (United States)

Sheng, Yu-Bo; Deng, Fu-Guo

2010-04-01

We present an efficient quantum entanglement distribution over an arbitrary collective-noise channel. The basic idea in the present scheme is that two parties in quantum communication first transmit the entangled states in the frequency degree of freedom which suffers little from the noise in an optical fiber. After the two parties share the photon pairs, they add some operations and equipments to transfer the frequency entanglement of pairs into the polarization entanglement with the success probability of 100%. Finally, they can get maximally entangled polarization states with polarization independent wavelength division multiplexers and quantum frequency up-conversion which can erase distinguishability for frequency. Compared with conventional entanglement purification protocols, the present scheme works in a deterministic way in principle. Surprisingly, the collective noise leads to an additional advantage.

Entangled entanglement: A construction procedure

Energy Technology Data Exchange (ETDEWEB)

Uchida, Gabriele, E-mail: Gabriele.Uchida@univie.ac.at [University of Vienna, Faculty of Computer Science, Währinger Strasse 29, 1090 Vienna (Austria); Bertlmann, Reinhold A., E-mail: Reinhold.Bertlmann@univie.ac.at [University of Vienna, Faculty of Physics, Boltzmanngasse 5, 1090 Vienna (Austria); Hiesmayr, Beatrix C., E-mail: Beatrix.Hiesmayr@univie.ac.at [University of Vienna, Faculty of Physics, Boltzmanngasse 5, 1090 Vienna (Austria)

2015-10-30

The familiar Greenberger–Horne–Zeilinger (GHZ) states can be rewritten by entangling the Bell states for two qubits with a third qubit state, which is dubbed entangled entanglement. We show that in a constructive way we obtain all eight independent GHZ states that form the simplex of entangled entanglement, the magic simplex. The construction procedure allows a generalization to higher dimensions both, in the degrees of freedom (considering qudits) as well as in the number of particles (considering n-partite states). Such bases of GHZ-type states exhibit a cyclic geometry, a Merry Go Round, that is relevant for experimental and quantum information theoretic applications.

Multi-particle entanglement via two-party entanglement

Science.gov (United States)

Brassard, Gilles; Mor, Tal

2001-09-01

Entanglement between n particles is a generalization of the entanglement between two particles, and a state is considered entangled if it cannot be written as a mixture of tensor products of the n particles' states. We present the key notion of semi-separability, used to investigate n-particle entanglement by looking at two-party entanglement between its various subsystems. We provide necessary conditions for n-particle separability (that is, sufficient conditions for n-particle entanglement). We also provide necessary and sufficient conditions in the case of pure states. By surprising examples, we show that such conditions are not sufficient for separability in the case of mixed states, suggesting entanglement of a strange type.

Generalized Entanglement Entropies of Quantum Designs

Science.gov (United States)

Liu, Zi-Wen; Lloyd, Seth; Zhu, Elton Yechao; Zhu, Huangjun

2018-03-01

The entanglement properties of random quantum states or dynamics are important to the study of a broad spectrum of disciplines of physics, ranging from quantum information to high energy and many-body physics. This Letter investigates the interplay between the degrees of entanglement and randomness in pure states and unitary channels. We reveal strong connections between designs (distributions of states or unitaries that match certain moments of the uniform Haar measure) and generalized entropies (entropic functions that depend on certain powers of the density operator), by showing that Rényi entanglement entropies averaged over designs of the same order are almost maximal. This strengthens the celebrated Page's theorem. Moreover, we find that designs of an order that is logarithmic in the dimension maximize all Rényi entanglement entropies and so are completely random in terms of the entanglement spectrum. Our results relate the behaviors of Rényi entanglement entropies to the complexity of scrambling and quantum chaos in terms of the degree of randomness, and suggest a generalization of the fast scrambling conjecture.

Manipulating mesoscopic multipartite entanglement with atom-light interfaces

International Nuclear Information System (INIS)

Stasinska, J.; Rodo, C.; Paganelli, S.; Birkl, G.; Sanpera, A.

2009-01-01

Entanglement between two macroscopic atomic ensembles induced by measurement on an ancillary light system has proven to be a powerful method for engineering quantum memories and quantum state transfer. Here we investigate the feasibility of such methods for generation, manipulation, and detection of genuine multipartite entanglement (Greenberger-Horne-Zeilinger and clusterlike states) between mesoscopic atomic ensembles without the need of individual addressing of the samples. Our results extend in a nontrivial way the Einstein-Podolsky-Rosen entanglement between two macroscopic gas samples reported experimentally in [B. Julsgaard, A. Kozhekin, and E. Polzik, Nature (London) 413, 400 (2001)]. We find that under realistic conditions, a second orthogonal light pulse interacting with the atomic samples, can modify and even reverse the entangling action of the first one leaving the samples in a separable state.

Entanglement Evolution of Three-Qubit States under Local Decoherence

International Nuclear Information System (INIS)

Ma Xiaosan; Liu Gaosheng; Wang Anmin

2010-01-01

By using negativity as entanglement measure, we have investigated the effect of local decoherence from a non-Markovian environment on the time evolution of entanglement of three-qubit states including the GHZ state, the W state, and the Werner state. From the results, we find that the entanglement dynamics depends not only on the coupling strengths but also on the specific states of concern. Specifically, the entanglement takes different behaviors under weak or strong coupling and it varies with the quantum states under study. The entanglement of the GHZ state and the Werner state can be destroyed completely by the local decoherence, while the entanglement of the W state can survive through the local decoherence partially. (general)

The entanglement evolution between two entangled atoms

Indian Academy of Sciences (India)

... entanglement between the two atoms changes periodically and undergoes the entanglement sudden death (ESD) and sudden birth at some time. The entanglement properties between the field and the atom insidethe cavity are dependent on the photon number. Most interestingly, the entanglement between the field and ...

Squeezing and entangling nuclear spins in helium 3

DEFF Research Database (Denmark)

Reinaudi, Gael; Sinatra, Alice; Dantan, Aurelien Romain

2007-01-01

We present a realistic model for transferring the squeezing or the entanglement of optical field modes to the collective ground state nuclear spin of 3He using metastability exchange collisions. We discuss in detail the requirements for obtaining good quantum state transfer efficiency and study t...

Minimal tomography with entanglement witnesses

OpenAIRE

Zhu, Huangjun; Teo, Yong Siah; Englert, Berthold-Georg

2009-01-01

We introduce informationally complete measurements whose outcomes are entanglement witnesses and so answer the question of how many witnesses need to be measured to decide whether an arbitrary state is entangled or not: as many as the dimension of the state space. The optimized witness-based measurement can provide exponential improvement with respect to witness efficiency in high-dimensional Hilbert spaces, at the price of a reduction in the tomographic efficiency. We describe a systematic c...

Probing Entanglement in Adiabatic Quantum Optimization with Trapped Ions

Directory of Open Access Journals (Sweden)

Philipp eHauke

2015-04-01

Full Text Available Adiabatic quantum optimization has been proposed as a route to solve NP-complete problems, with a possible quantum speedup compared to classical algorithms. However, the precise role of quantum effects, such as entanglement, in these optimization protocols is still unclear. We propose a setup of cold trapped ions that allows one to quantitatively characterize, in a controlled experiment, the interplay of entanglement, decoherence, and non-adiabaticity in adiabatic quantum optimization. We show that, in this way, a broad class of NP-complete problems becomes accessible for quantum simulations, including the knapsack problem, number partitioning, and instances of the max-cut problem. Moreover, a general theoretical study reveals correlations of the success probability with entanglement at the end of the protocol. From exact numerical simulations for small systems and linear ramps, however, we find no substantial correlations with the entanglement during the optimization. For the final state, we derive analytically a universal upper bound for the success probability as a function of entanglement, which can be measured in experiment. The proposed trapped-ion setups and the presented study of entanglement address pertinent questions of adiabatic quantum optimization, which may be of general interest across experimental platforms.

Generalizing entanglement

Science.gov (United States)

Jia, Ding

2017-12-01

The expected indefinite causal structure in quantum gravity poses a challenge to the notion of entanglement: If two parties are in an indefinite causal relation of being causally connected and not, can they still be entangled? If so, how does one measure the amount of entanglement? We propose to generalize the notions of entanglement and entanglement measure to address these questions. Importantly, the generalization opens the path to study quantum entanglement of states, channels, networks, and processes with definite or indefinite causal structure in a unified fashion, e.g., we show that the entanglement distillation capacity of a state, the quantum communication capacity of a channel, and the entanglement generation capacity of a network or a process are different manifestations of one and the same entanglement measure.

Entangling movable mirrors in a double cavity system

DEFF Research Database (Denmark)

Pinard, Michel; Dantan, Aurelien Romain; Vitali, David

2005-01-01

We propose a double-cavity set-up capable of generating a stationary entangled state of two movable mirrors at cryogenic temperatures. The scheme is based on the optimal transfer of squeezing of input optical fields to mechanical vibrational modes of the mirrors, realized by the radiation pressure...... of the intracavity light. We show that the presence of macroscopic entanglement can be demonstrated by an appropriate readout of the output light of the two cavities....

Entanglement dynamics in random media

Science.gov (United States)

Menezes, G.; Svaiter, N. F.; Zarro, C. A. D.

2017-12-01

We study how the entanglement dynamics between two-level atoms is impacted by random fluctuations of the light cone. In our model the two-atom system is envisaged as an open system coupled with an electromagnetic field in the vacuum state. We employ the quantum master equation in the Born-Markov approximation in order to describe the completely positive time evolution of the atomic system. We restrict our investigations to the situation in which the atoms are coupled individually to two spatially separated cavities, one of which displays the emergence of light-cone fluctuations. In such a disordered cavity, we assume that the coefficients of the Klein-Gordon equation are random functions of the spatial coordinates. The disordered medium is modeled by a centered, stationary, and Gaussian process. We demonstrate that disorder has the effect of slowing down the entanglement decay. We conjecture that in a strong-disorder environment the mean life of entangled states can be enhanced in such a way as to almost completely suppress quantum nonlocal decoherence.

Local cloning of entangled states

International Nuclear Information System (INIS)

Gheorghiu, Vlad; Yu Li; Cohen, Scott M.

2010-01-01

We investigate the conditions under which a set S of pure bipartite quantum states on a DxD system can be locally cloned deterministically by separable operations, when at least one of the states is full Schmidt rank. We allow for the possibility of cloning using a resource state that is less than maximally entangled. Our results include that: (i) all states in S must be full Schmidt rank and equally entangled under the G-concurrence measure, and (ii) the set S can be extended to a larger clonable set generated by a finite group G of order |G|=N, the number of states in the larger set. It is then shown that any local cloning apparatus is capable of cloning a number of states that divides D exactly. We provide a complete solution for two central problems in local cloning, giving necessary and sufficient conditions for (i) when a set of maximally entangled states can be locally cloned, valid for all D; and (ii) local cloning of entangled qubit states with nonvanishing entanglement. In both of these cases, we show that a maximally entangled resource is necessary and sufficient, and the states must be related to each other by local unitary 'shift' operations. These shifts are determined by the group structure, so need not be simple cyclic permutations. Assuming this shifted form and partially entangled states, then in D=3 we show that a maximally entangled resource is again necessary and sufficient, while for higher-dimensional systems, we find that the resource state must be strictly more entangled than the states in S. All of our necessary conditions for separable operations are also necessary conditions for local operations and classical communication (LOCC), since the latter is a proper subset of the former. In fact, all our results hold for LOCC, as our sufficient conditions are demonstrated for LOCC, directly.

Quantum entanglement and quantum teleportation

International Nuclear Information System (INIS)

Shih, Y.H.

2001-01-01

One of the most surprising consequences of quantum mechanics is the entanglement of two or more distance particles. The ''ghost'' interference and the ''ghost'' image experiments demonstrated the astonishing nonlocal behavior of an entangled photon pair. Even though we still have questions in regard to fundamental issues of the entangled quantum systems, quantum entanglement has started to play important roles in quantum information and quantum computation. Quantum teleportation is one of the hot topics. We have demonstrated a quantum teleportation experiment recently. The experimental results proved the working principle of irreversibly teleporting an unknown arbitrary quantum state from one system to another distant system by disassembling into and then later reconstructing from purely classical information and nonclassical EPR correlations. The distinct feature of this experiment is that the complete set of Bell states can be distinguished in the Bell state measurement. Teleportation of a quantum state can thus occur with certainty in principle. (orig.)

Teleportation of a Kind of Three-Mode Entangled States of Continuous Variables

Institute of Scientific and Technical Information of China (English)

无

2005-01-01

A quantum teleportation scheme to teleport a kind of tripartite entangled states of continuous variables by using a quantum channel composed of three bipartite entangled states is proposed. The joint Bell measurement is feasible because the bipartite entangled states are complete and the squeezed state has a natural representation in the entangled state basis. The calculation is greatly simplified by using the Schmidt decomposition of the entangled states.

Entanglement degradation in depolarizing light scattering

International Nuclear Information System (INIS)

Aiello, A.; Woerdman, J.P.

2005-01-01

Full text: In the classical regime, when a beam of light is scattered by a medium, it may emerge partially or completely depolarized depending on the optical properties of the medium. Correspondingly, in the quantum regime, when an entangled two-photon pair is scattered, the classical depolarization may result in an entanglement degradation. Here, relations between photon scattering, entanglement and multi-mode detection are investigated. We establish a general framework in which one- and two-photon elastic scattering processes can be discussed, and we focus on the study of the intrinsic entanglement degradation caused by a multi-mode detection. We show that any multi-mode scattered state cannot maximally violate the Bell-CHSH inequality because of the momentum spread. The results presented here have general validity and can be applied to both deterministic and random scattering processes. (author)

Entanglement dynamics in quantum information theory

International Nuclear Information System (INIS)

Cubitt, T.S.

2007-01-01

This thesis contributes to the theory of entanglement dynamics, that is, the behaviour of entanglement in systems that are evolving with time. Progressively more complex multipartite systems are considered, starting with low-dimensional tripartite systems, whose entanglement dynamics can nonetheless display surprising properties, progressing through larger networks of interacting particles, and finishing with infinitely large lattice models. Firstly, what is perhaps the most basic question in entanglement dynamics is considered: what resources are necessary in order to create entanglement between distant particles? The answer is surprising: sending separable states between the parties is sufficient; entanglement can be created without it being carried by a ''messenger'' particle. The analogous result also holds in the continuous-time case: two particles interacting indirectly via a common ancilla particle can be entangled without the ancilla ever itself becoming entangled. The latter result appears to discount any notion of entanglement flow. However, for pure states, this intuitive idea can be recovered, and even made quantitative. A ''bottleneck'' inequality is derived that relates the entanglement rate of the end particles in a tripartite chain to the entanglement of the middle one. In particular, no entanglement can be created if the middle particle is not entangled. However, although this result can be applied to general interaction networks, it does not capture the full entanglement dynamics of these more complex systems. This is remedied by the derivation of entanglement rate equations, loosely analogous to the rate equations describing a chemical reaction. A complete set of rate equations for a system reflects the full structure of its interaction network, and can be used to prove a lower bound on the scaling with chain length of the time required to entangle the ends of a chain. Finally, in contrast with these more abstract results, the entanglement and

Superadditivity of distillable entanglement from quantum teleportation

Science.gov (United States)

Bandyopadhyay, Somshubhro; Roychowdhury, Vwani

2005-12-01

We show that the phenomenon of superadditivity of distillable entanglement observed in multipartite quantum systems results from the consideration of states created during the execution of the standard end-to-end quantum teleportation protocol [and a few additional local operations and classical communication (LOCC) steps] on a linear chain of singlets. Some of these intermediate states are tensor products of bound entangled (BE) states, and hence, by construction possess distillable entanglement, which can be unlocked by simply completing the rest of the LOCC operations required by the underlying teleportation protocol. We use this systematic approach to construct both new and known examples of superactivation of bound entanglement, and examples of activation of BE states using other BE states. A surprising outcome is the construction of noiseless quantum relay channels with no distillable entanglement between any two parties, except for that between the two end nodes.

Superadditivity of distillable entanglement from quantum teleportation

International Nuclear Information System (INIS)

Bandyopadhyay, Somshubhro; Roychowdhury, Vwani

2005-01-01

We show that the phenomenon of superadditivity of distillable entanglement observed in multipartite quantum systems results from the consideration of states created during the execution of the standard end-to-end quantum teleportation protocol [and a few additional local operations and classical communication (LOCC) steps] on a linear chain of singlets. Some of these intermediate states are tensor products of bound entangled (BE) states, and hence, by construction possess distillable entanglement, which can be unlocked by simply completing the rest of the LOCC operations required by the underlying teleportation protocol. We use this systematic approach to construct both new and known examples of superactivation of bound entanglement, and examples of activation of BE states using other BE states. A surprising outcome is the construction of noiseless quantum relay channels with no distillable entanglement between any two parties, except for that between the two end nodes

Discussion of entanglement entropy in quantum gravity

International Nuclear Information System (INIS)

Ma, Chen-Te

2018-01-01

We study entanglement entropy in gravity theory with quantum effects. A simplest model is a two dimensional Einstein gravity theory. We use an n-sheet manifold to obtain an area term of entanglement entropy by summing over all background fields. Based on AdS/CFT correspondence, strongly coupled conformal field theory is expected to describe perturbative quantum gravity theory. An ultraviolet complete quantum gravity theory should not depend on a choice of an entangling surface. To analysis the problem explicitly, we analyze two dimensional conformal field theory. We find that a coefficient of a universal term of entanglement entropy is independent of a choice of an entangling surface in two dimensional conformal field theory for one interval to show a tentative evidence. Finally, we discuss that translational invariance in a quantum system at zero temperature, size goes to infinity and no mass scales, except for cut-off, possibly be a necessary condition in quantum gravity theory by ruing out a volume law of entanglement entropy. (copyright 2018 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

General form of genuine multipartite entanglement quantum channels for teleportation

International Nuclear Information System (INIS)

Chen Pingxing; Zhu Shiyao; Guo, Guangcan

2006-01-01

Recently Yeo and Chua [Phys. Rev. Lett. 96, 060502 (2006)] presented an explicit protocol for faithfully teleporting an arbitrary two-qubit state via a genuine four-qubit entanglement channel. Here we generalize completely their results to teleporting an arbitrary N-qubit state via genuine N-qubit entanglement channels. And we present the general form of the genuine multipartite entanglement channels, namely, the sufficient and necessary condition the genuine N-qubit entanglement channels must satisfy to teleport an arbitrary N-qubit state

Entanglement purification of multi-mode quantum states

International Nuclear Information System (INIS)

Clausen, J; Knoell, L; Welsch, D-G

2003-01-01

An iterative random procedure is considered allowing entanglement purification of a class of multi-mode quantum states. In certain cases, complete purification may be achieved using only a single signal state preparation. A physical implementation based on beam splitter arrays and non-linear elements is suggested. The influence of loss is analysed in the example of purification of entangled N-mode coherent states

Deterministic chaos in entangled eigenstates

Science.gov (United States)

Schlegel, K. G.; Förster, S.

2008-05-01

We investigate the problem of deterministic chaos in connection with entangled states using the Bohmian formulation of quantum mechanics. We show for a two particle system in a harmonic oscillator potential, that in a case of entanglement and three energy eigen-values the maximum Lyapunov-parameters of a representative ensemble of trajectories for large times develops to a narrow positive distribution, which indicates nearly complete chaotic dynamics. We also present in short results from two time-dependent systems, the anisotropic and the Rabi oscillator.

Deterministic chaos in entangled eigenstates

Energy Technology Data Exchange (ETDEWEB)

Schlegel, K.G. [Fakultaet fuer Physik, Universitaet Bielefeld, Postfach 100131, D-33501 Bielefeld (Germany)], E-mail: guenter.schlegel@arcor.de; Foerster, S. [Fakultaet fuer Physik, Universitaet Bielefeld, Postfach 100131, D-33501 Bielefeld (Germany)

2008-05-12

We investigate the problem of deterministic chaos in connection with entangled states using the Bohmian formulation of quantum mechanics. We show for a two particle system in a harmonic oscillator potential, that in a case of entanglement and three energy eigen-values the maximum Lyapunov-parameters of a representative ensemble of trajectories for large times develops to a narrow positive distribution, which indicates nearly complete chaotic dynamics. We also present in short results from two time-dependent systems, the anisotropic and the Rabi oscillator.

Deterministic chaos in entangled eigenstates

International Nuclear Information System (INIS)

Schlegel, K.G.; Foerster, S.

2008-01-01

We investigate the problem of deterministic chaos in connection with entangled states using the Bohmian formulation of quantum mechanics. We show for a two particle system in a harmonic oscillator potential, that in a case of entanglement and three energy eigen-values the maximum Lyapunov-parameters of a representative ensemble of trajectories for large times develops to a narrow positive distribution, which indicates nearly complete chaotic dynamics. We also present in short results from two time-dependent systems, the anisotropic and the Rabi oscillator

Entanglement in open quantum systems

International Nuclear Information System (INIS)

Isar, A.

2007-01-01

In the framework of the theory of open systems based on quantum dynamical semigroups, we solve the master equation for two independent bosonic oscillators interacting with an environment in the asymptotic long-time regime. We give a description of the continuous-variable entanglement in terms of the covariance matrix of the quantum states of the considered system for an arbitrary Gaussian input state. Using the Peres-Simon necessary and sufficient condition for separability of two-mode Gaussian states, we show that the two non-interacting systems immersed in a common environment and evolving under a Markovian, completely positive dynamics become asymptotically entangled for certain environments, so that their non-local quantum correlations exist in the long-time regime. (author) Key words: quantum information theory, open systems, quantum entanglement, inseparable states

Entanglement detection

Energy Technology Data Exchange (ETDEWEB)

Guehne, Otfried [Institut fuer Quantenoptik und Quanteninformation, Osterreichische Akademie der Wissenschaften, Technikerstrasse 21A, A-6020 Innsbruck (Austria); Institut fuer theoretische Physik, Universitaet Innsbruck, Technikerstrasse 25, A-6020 Innsbruck (Austria)], E-mail: otfried.guehne@uibk.ac.at; Toth, Geza [Department of Theoretical Physics, University of the Basque Country, P.O. Box 644, E-48080 Bilbao (Spain); Ikerbasque-Basque Foundation for Science, Alameda Urquijo 36, E-48011 Bilbao (Spain); ICFO-Institute of Photonic Sciences, Mediterranean Technology Park, E-08860 Castelldefels (Barcelona) (Spain); Research Institute for Solid State Physics and Optics, Hungarian Academy of Sciences, P.O. Box 49, H-1525 Budapest (Hungary)

2009-04-15

How can one prove that a given quantum state is entangled? In this paper we review different methods that have been proposed for entanglement detection. We first explain the basic elements of entanglement theory for two or more particles and then entanglement verification procedures such as Bell inequalities, entanglement witnesses, the determination of nonlinear properties of a quantum state via measurements on several copies, and spin squeezing inequalities. An emphasis is given to the theory and application of entanglement witnesses. We also discuss several experiments, where some of the presented methods have been implemented.

Entanglement of three-qubit Greenberger-Horne-Zeilinger-symmetric states.

Science.gov (United States)

Eltschka, Christopher; Siewert, Jens

2012-01-13

The first characterization of mixed-state entanglement was achieved for two-qubit states in Werner's seminal work [Phys. Rev. A 40, 4277 (1989)]. A physically important extension concerns mixtures of a pure entangled state [such as the Greenberger-Horne-Zeilinger (GHZ) state] and the unpolarized state. These mixed states serve as benchmark for the robustness of multipartite entanglement. They share the symmetries of the GHZ state. We call such states GHZ symmetric. Here we give a complete description of the entanglement in the family of three-qubit GHZ-symmetric states and, in particular, of the three-qubit generalized Werner states. Our method relies on the appropriate parametrization of the states and on the invariance of entanglement properties under general local operations. An application is the definition of a symmetrization witness for the entanglement class of arbitrary three-qubit states.

Entanglement dynamics in quantum information theory

Energy Technology Data Exchange (ETDEWEB)

Cubitt, T.S.

2007-03-29

This thesis contributes to the theory of entanglement dynamics, that is, the behaviour of entanglement in systems that are evolving with time. Progressively more complex multipartite systems are considered, starting with low-dimensional tripartite systems, whose entanglement dynamics can nonetheless display surprising properties, progressing through larger networks of interacting particles, and finishing with infinitely large lattice models. Firstly, what is perhaps the most basic question in entanglement dynamics is considered: what resources are necessary in order to create entanglement between distant particles? The answer is surprising: sending separable states between the parties is sufficient; entanglement can be created without it being carried by a ''messenger'' particle. The analogous result also holds in the continuous-time case: two particles interacting indirectly via a common ancilla particle can be entangled without the ancilla ever itself becoming entangled. The latter result appears to discount any notion of entanglement flow. However, for pure states, this intuitive idea can be recovered, and even made quantitative. A ''bottleneck'' inequality is derived that relates the entanglement rate of the end particles in a tripartite chain to the entanglement of the middle one. In particular, no entanglement can be created if the middle particle is not entangled. However, although this result can be applied to general interaction networks, it does not capture the full entanglement dynamics of these more complex systems. This is remedied by the derivation of entanglement rate equations, loosely analogous to the rate equations describing a chemical reaction. A complete set of rate equations for a system reflects the full structure of its interaction network, and can be used to prove a lower bound on the scaling with chain length of the time required to entangle the ends of a chain. Finally, in contrast with these more

Entanglement entropy for 2D gauge theories with matters

Science.gov (United States)

Aoki, Sinya; Iizuka, Norihiro; Tamaoka, Kotaro; Yokoya, Tsuyoshi

2017-08-01

We investigate the entanglement entropy in 1 +1 -dimensional S U (N ) gauge theories with various matter fields using the lattice regularization. Here we use extended Hilbert space definition for entanglement entropy, which contains three contributions; (1) classical Shannon entropy associated with superselection sector distribution, where sectors are labeled by irreducible representations of boundary penetrating fluxes, (2) logarithm of the dimensions of their representations, which is associated with "color entanglement," and (3) EPR Bell pairs, which give "genuine" entanglement. We explicitly show that entanglement entropies (1) and (2) above indeed appear for various multiple "meson" states in gauge theories with matter fields. Furthermore, we employ transfer matrix formalism for gauge theory with fundamental matter field and analyze its ground state using hopping parameter expansion (HPE), where the hopping parameter K is roughly the inverse square of the mass for the matter. We evaluate the entanglement entropy for the ground state and show that all (1), (2), (3) above appear in the HPE, though the Bell pair part (3) appears in higher order than (1) and (2) do. With these results, we discuss how the ground state entanglement entropy in the continuum limit can be understood from the lattice ground state obtained in the HPE.

Experimental Determination of Multipartite Entanglement with Incomplete Information

Directory of Open Access Journals (Sweden)

G. H. Aguilar

2015-09-01

Full Text Available Multipartite entanglement is very poorly understood despite all the theoretical and experimental advances of the last decades. Preparation, manipulation, and identification of this resource is crucial for both practical and fundamental reasons. However, the difficulty in the practical manipulation and the complexity of the data generated by measurements on these systems increase rapidly with the number of parties. Therefore, we would like to experimentally address the problem of how much information about multipartite entanglement we can access with incomplete measurements. In particular, it was shown that some types of pure multipartite entangled states can be witnessed without measuring the correlations [M. Walter et al., Science 340, 1205 (2013] between parties, which is strongly demanding experimentally. We explore this method using an optical setup that permits the preparation and the complete tomographic reconstruction of many inequivalent classes of three- and four-partite entangled states, and compare complete versus incomplete information. We show that the method is useful in practice, even for nonpure states or nonideal measurement conditions.

Monogamy inequality for distributed gaussian entanglement.

Science.gov (United States)

Hiroshima, Tohya; Adesso, Gerardo; Illuminati, Fabrizio

2007-02-02

We show that for all n-mode Gaussian states of continuous variable systems, the entanglement shared among n parties exhibits the fundamental monogamy property. The monogamy inequality is proven by introducing the Gaussian tangle, an entanglement monotone under Gaussian local operations and classical communication, which is defined in terms of the squared negativity in complete analogy with the case of n-qubit systems. Our results elucidate the structure of quantum correlations in many-body harmonic lattice systems.

Remote entanglement distribution

International Nuclear Information System (INIS)

Sanders, B.C.; Gour, G.; Meyer, D.A.

2005-01-01

Full text: Shared bipartite entanglement is a crucial shared resource for many quantum information tasks such as teleportation, entanglement swapping, and remote state preparation. In general different nodes of a quantum network share an entanglement resource, such as ebits, that are consumed during the task. In practice, generating entangled states is expensive, but here we establish a protocol by which a quantum network requires only a single supplier of entanglement to all nodes who, by judicious measurements and classical communication, provides the nodes with a unique pair wise entangled state independent of the measurement outcome. Furthermore, we extend this result to a chain of suppliers and nodes, which enables an operational interpretation of concurrence. In the special case that the supplier shares bipartite states with two nodes, and such states are pure and maximally entangled, our protocol corresponds to entanglement swapping. However, in the practical case that initial shared entanglement between suppliers and nodes involves partially entangled or mixed states, we show that general local operations and classical communication by all parties (suppliers and nodes) yields distributions of entangled states between nodes. In general a distribution of bipartite entangled states between any two nodes will include states that do not have the same entanglement; thus we name this general process remote entanglement distribution. In our terminology entanglement swapping with partially entangled states is a particular class of remote entanglement distribution protocols. Here we identify which distributions of states that can or cannot be created by remote entanglement distribution. In particular we prove a powerful theorem that establishes an upper bound on the entanglement of formation that can be produced between two qubit nodes. We extend this result to the case of a linear chain of parties that play the roles of suppliers and nodes; this extension provides

Entanglement enhances security in quantum communication

International Nuclear Information System (INIS)

Demkowicz-Dobrzanski, Rafal; Sen, Aditi; Sen, Ujjwal; Lewenstein, Maciej

2009-01-01

Secret sharing is a protocol in which a 'boss' wants to send a classical message secretly to two 'subordinates', such that none of the subordinates is able to know the message alone, while they can find it if they cooperate. Quantum mechanics is known to allow for such a possibility. We analyze tolerable quantum bit error rates in such secret sharing protocols in the physically relevant case when the eavesdropping is local with respect to the two channels of information transfer from the boss to the two subordinates. We find that using entangled encoding states is advantageous to legitimate users of the protocol. We therefore find that entanglement is useful for secure quantum communication. We also find that bound entangled states with positive partial transpose are not useful as a local eavesdropping resource. Moreover, we provide a criterion for security in secret sharing--a parallel of the Csiszar-Koerner criterion in single-receiver classical cryptography.

Modular entanglement.

Science.gov (United States)

Gualdi, Giulia; Giampaolo, Salvatore M; Illuminati, Fabrizio

2011-02-04

We introduce and discuss the concept of modular entanglement. This is the entanglement that is established between the end points of modular systems composed by sets of interacting moduli of arbitrarily fixed size. We show that end-to-end modular entanglement scales in the thermodynamic limit and rapidly saturates with the number of constituent moduli. We clarify the mechanisms underlying the onset of entanglement between distant and noninteracting quantum systems and its optimization for applications to quantum repeaters and entanglement distribution and sharing.

Probabilistic Teleportation of the Three-Particle Entangled State viaEntanglement Swapping

Institute of Scientific and Technical Information of China (English)

路洪

2001-01-01

A scheme of teleportation of a three-particle entangled state via entanglement swapping is proposed. It is shown that if a two-particle entangled state and a three-particle entangled state (both are not maximum entangled states) are used as quantum channels, probabilistic teleportation of the three-particle entangled state can be realized.

Storage and retrieval of time-entangled soliton trains in a three-level atom system coupled to an optical cavity

Science.gov (United States)

Welakuh, Davis D. M.; Dikandé, Alain M.

2017-11-01

The storage and subsequent retrieval of coherent pulse trains in the quantum memory (i.e. cavity-dark state) of three-level Λ atoms, are considered for an optical medium in which adiabatic photon transfer occurs under the condition of quantum impedance matching. The underlying mechanism is based on intracavity Electromagnetically-Induced Transparency, by which properties of a cavity filled with three-level Λ-type atoms are manipulated by an external control field. Under the impedance matching condition, we derive analytic expressions that suggest a complete transfer of an input field into the cavity-dark state by varying the mixing angle in a specific way, and its subsequent retrieval at a desired time. We illustrate the scheme by demonstrating the complete transfer and retrieval of a Gaussian, a single hyperbolic-secant and a periodic train of time-entangled hyperbolic-secant input photon pulses in the atom-cavity system. For the time-entangled hyperbolic-secant input field, a total controllability of the periodic evolution of the dark state population is made possible by changing the Rabi frequency of the classical driving field, thus allowing to alternately store and retrieve high-intensity photons from the optically dense Electromagnetically-Induced transparent medium. Such multiplexed photon states, which are expected to allow sharing quantum information among many users, are currently of very high demand for applications in long-distance and multiplexed quantum communication.

Quantum Entanglement in Neural Network States

Directory of Open Access Journals (Sweden)

Dong-Ling Deng

2017-05-01

Full Text Available Machine learning, one of today’s most rapidly growing interdisciplinary fields, promises an unprecedented perspective for solving intricate quantum many-body problems. Understanding the physical aspects of the representative artificial neural-network states has recently become highly desirable in the applications of machine-learning techniques to quantum many-body physics. In this paper, we explore the data structures that encode the physical features in the network states by studying the quantum entanglement properties, with a focus on the restricted-Boltzmann-machine (RBM architecture. We prove that the entanglement entropy of all short-range RBM states satisfies an area law for arbitrary dimensions and bipartition geometry. For long-range RBM states, we show by using an exact construction that such states could exhibit volume-law entanglement, implying a notable capability of RBM in representing quantum states with massive entanglement. Strikingly, the neural-network representation for these states is remarkably efficient, in the sense that the number of nonzero parameters scales only linearly with the system size. We further examine the entanglement properties of generic RBM states by randomly sampling the weight parameters of the RBM. We find that their averaged entanglement entropy obeys volume-law scaling, and the meantime strongly deviates from the Page entropy of the completely random pure states. We show that their entanglement spectrum has no universal part associated with random matrix theory and bears a Poisson-type level statistics. Using reinforcement learning, we demonstrate that RBM is capable of finding the ground state (with power-law entanglement of a model Hamiltonian with a long-range interaction. In addition, we show, through a concrete example of the one-dimensional symmetry-protected topological cluster states, that the RBM representation may also be used as a tool to analytically compute the entanglement spectrum. Our

Displacement-enhanced entanglement distillation of single-mode-squeezed entangled states

DEFF Research Database (Denmark)

Tipsmark, Anders; Neergaard-Nielsen, Jonas Schou; Andersen, Ulrik Lund

2013-01-01

It has been shown that entanglement distillation of Gaussian entangled states by means of local photon subtraction can be improved by local Gaussian transformations. Here we show that a similar effect can be expected for the distillation of an asymmetric Gaussian entangled state that is produced...... by a single squeezed beam. We show that for low initial entanglement, our largely simplified protocol generates more entanglement than previous proposed protocols. Furthermore, we show that the distillation scheme also works efficiently on decohered entangled states as well as with a practical photon...

Device-independent entanglement certification of all entangled states

OpenAIRE

Bowles, Joseph; Šupić, Ivan; Cavalcanti, Daniel; Acín, Antonio

2018-01-01

We present a method to certify the entanglement of all bipartite entangled quantum states in a device-independent way. This is achieved by placing the state in a quantum network and constructing a correlation inequality based on an entanglement witness for the state. Our method is device-independent, in the sense that entanglement can be certified from the observed statistics alone, under minimal assumptions on the underlying physics. Conceptually, our results borrow ideas from the field of s...

Two-Photon Quantum Entanglement from Type-II Spontaneous Parametric Down-Conversion

Science.gov (United States)

Pittman, Todd Butler

The concept of two (or more) particle entanglement lies at the heart of many fascinating questions concerning the foundations of quantum mechanics. The counterintuitive nonlocal behavior of entangled states led Einstein, Podolsky, and Rosen (EPR) to ask their famous 1935 question, "Can quantum mechanical description of reality be considered complete?". Although the debate has been raging on for more than 60 years, there is still no absolutely conclusive answer to this question. For if entangled states exist and can be observed, then accepting quantum mechanics as a complete theory requires a drastic overhaul of one's physical intuition with regards to the common sense notions of locality and reality put forth by EPR. Contained herein are the results of research investigating various non-classical features of the two-photon entangled states produced in Type-II Spontaneous Parametric Down -Conversion (SPDC). Through a series of experiments we have manifest the nonlocal nature of the quantum mechanical "two-photon effective wavefunction" (or Biphoton) realized by certain photon-counting coincidence measurements performed on these states. In particular, we examine a special double entanglement, in which the states are seen to be simultaneously entangled in both spin and space-time variables. The observed phenomena based on this double entanglement lead to many interesting results which defy classical explanation, but are well described within the framework of quantum mechanics. The implications provide a unique perspective concerning the nature of the photon, and the concept of quantum entanglement.

Subdecoherence time generation and detection of orbital entanglement in quantum dots.

Science.gov (United States)

Brange, F; Malkoc, O; Samuelsson, P

2015-05-01

Recent experiments have demonstrated subdecoherence time control of individual single-electron orbital qubits. Here we propose a quantum-dot-based scheme for generation and detection of pairs of orbitally entangled electrons on a time scale much shorter than the decoherence time. The electrons are entangled, via two-particle interference, and transferred to the detectors during a single cotunneling event, making the scheme insensitive to charge noise. For sufficiently long detector dot lifetimes, cross-correlation detection of the dot charges can be performed with real-time counting techniques, providing for an unambiguous short-time Bell inequality test of orbital entanglement.

Minimal tomography with entanglement witnesses

International Nuclear Information System (INIS)

Zhu Huangjun; Teo Yong Siah; Englert, Berthold-Georg

2010-01-01

We introduce informationally complete measurements whose outcomes are entanglement witnesses and so answer the question of how many witnesses need to be measured to decide whether an arbitrary state is entangled or not: as many as the dimension of the state space. The witnesses can be measured successively; if all of them give an inconclusive result, one exploits their tomographic completeness for a reconstruction of the quantum state and can then determine its entanglement properties by data processing. There are witnesses that are optimal for this purpose. The optimized witness-based measurement can provide exponential improvement with respect to witness efficiency in high-dimensional Hilbert spaces, at the price of a reduction in the tomographic efficiency. We describe a systematic construction and illustrate the matter with the example of two qubits. For the case of two polarization qubits of photons, we show how existing technology can be used to implement the optimized witnesses in a very efficient way. Owing to the details of the implementation, which actually measures the eigenstate basis of the witness rather than solely determining the expectation value of the witness, one does not need to measure more than six witnesses in this example of a 16-dimensional state space.

Minimal tomography with entanglement witnesses

Science.gov (United States)

Zhu, Huangjun; Teo, Yong Siah; Englert, Berthold-Georg

2010-05-01

We introduce informationally complete measurements whose outcomes are entanglement witnesses and so answer the question of how many witnesses need to be measured to decide whether an arbitrary state is entangled or not: as many as the dimension of the state space. The witnesses can be measured successively; if all of them give an inconclusive result, one exploits their tomographic completeness for a reconstruction of the quantum state and can then determine its entanglement properties by data processing. There are witnesses that are optimal for this purpose. The optimized witness-based measurement can provide exponential improvement with respect to witness efficiency in high-dimensional Hilbert spaces, at the price of a reduction in the tomographic efficiency. We describe a systematic construction and illustrate the matter with the example of two qubits. For the case of two polarization qubits of photons, we show how existing technology can be used to implement the optimized witnesses in a very efficient way. Owing to the details of the implementation, which actually measures the eigenstate basis of the witness rather than solely determining the expectation value of the witness, one does not need to measure more than six witnesses in this example of a 16-dimensional state space.

Quantifying tripartite entanglement for three-qubit generalized Werner states

Energy Technology Data Exchange (ETDEWEB)

Siewert, Jens [Departamento de Quimica Fisica, Universidad del Pais Vasco, 48080 Bilbao (Spain); Ikerbasque, Basque Foundation for Science, 48011 Bilbao (Spain); Eltschka, Christopher [Institut fuer Theoretische Physik, Universitaet Regensburg, D-93040 Regensburg (Germany)

2012-07-01

The adequate quantification of entanglement in multipartite mixed states is still a theoretically unsolved problem, even in the case of three qubits. In order to investigate the robustness of entanglement against noise one often employs the so-called generalized Werner states, i.e., pure maximally entangled states mixed with the completely unpolarized state. Even for those states there are no quantitative results available. In this contribution, we present the solution of the problem for three-qubit generalized Werner states (as well as for the whole family of full-rank mixed states which obey the Greenberger-Horne-Zeilinger symmetry) by providing an exact quantitative account of the tripartite entanglement contained in those states.

Controlling transfer of quantum correlations among bi-partitions of a composite quantum system by combining different noisy environments

International Nuclear Information System (INIS)

Zhang Xiu-Xing; Li Fu-Li

2011-01-01

The correlation dynamics are investigated for various bi-partitions of a composite quantum system consisting of two qubits and two independent and non-identical noisy environments. The two qubits have no direct interaction with each other and locally interact with their environments. Classical and quantum correlations including the entanglement are initially prepared only between the two qubits. We find that contrary to the identical noisy environment case, the quantum correlation transfer direction can be controlled by combining different noisy environments. The amplitude-damping environment determines whether there exists the entanglement transfer among bi-partitions of the system. When one qubit is coupled to an amplitude-damping environment and the other one to a bit-flip one, we find a very interesting result that all the quantum and the classical correlations, and even the entanglement, originally existing between the qubits, can be completely transferred without any loss to the qubit coupled to the bit-flit environment and the amplitude-damping environment. We also notice that it is possible to distinguish the quantum correlation from the classical correlation and the entanglement by combining different noisy environments. (general)

Entanglement branching operator

Science.gov (United States)

Harada, Kenji

2018-01-01

We introduce an entanglement branching operator to split a composite entanglement flow in a tensor network which is a promising theoretical tool for many-body systems. We can optimize an entanglement branching operator by solving a minimization problem based on squeezing operators. The entanglement branching is a new useful operation to manipulate a tensor network. For example, finding a particular entanglement structure by an entanglement branching operator, we can improve a higher-order tensor renormalization group method to catch a proper renormalization flow in a tensor network space. This new method yields a new type of tensor network states. The second example is a many-body decomposition of a tensor by using an entanglement branching operator. We can use it for a perfect disentangling among tensors. Applying a many-body decomposition recursively, we conceptually derive projected entangled pair states from quantum states that satisfy the area law of entanglement entropy.

Teleportation of N-particle entangled W state via entanglement swapping

Institute of Scientific and Technical Information of China (English)

Zhan You-Bang

2004-01-01

A scheme for teleporting an unknown N-particle entangled W state is proposed via entanglement swapping. In this scheme, N maximally entangled particle pairs are used as quantum channel. As a special case, the teleportation of an unknown four-particle entangled W state is studied.

Quantum communication for satellite-to-ground networks with partially entangled states

International Nuclear Information System (INIS)

Chen Na; Quan Dong-Xiao; Pei Chang-Xing; Yang-Hong

2015-01-01

To realize practical wide-area quantum communication, a satellite-to-ground network with partially entangled states is developed in this paper. For efficiency and security reasons, the existing method of quantum communication in distributed wireless quantum networks with partially entangled states cannot be applied directly to the proposed quantum network. Based on this point, an efficient and secure quantum communication scheme with partially entangled states is presented. In our scheme, the source node performs teleportation only after an end-to-end entangled state has been established by entanglement swapping with partially entangled states. Thus, the security of quantum communication is guaranteed. The destination node recovers the transmitted quantum bit with the help of an auxiliary quantum bit and specially defined unitary matrices. Detailed calculations and simulation analyses show that the probability of successfully transferring a quantum bit in the presented scheme is high. In addition, the auxiliary quantum bit provides a heralded mechanism for successful communication. Based on the critical components that are presented in this article an efficient, secure, and practical wide-area quantum communication can be achieved. (paper)

Renormalizing Entanglement Distillation

Science.gov (United States)

Waeldchen, Stephan; Gertis, Janina; Campbell, Earl T.; Eisert, Jens

2016-01-01

Entanglement distillation refers to the task of transforming a collection of weakly entangled pairs into fewer highly entangled ones. It is a core ingredient in quantum repeater protocols, which are needed to transmit entanglement over arbitrary distances in order to realize quantum key distribution schemes. Usually, it is assumed that the initial entangled pairs are identically and independently distributed and are uncorrelated with each other, an assumption that might not be reasonable at all in any entanglement generation process involving memory channels. Here, we introduce a framework that captures entanglement distillation in the presence of natural correlations arising from memory channels. Conceptually, we bring together ideas from condensed-matter physics—ideas from renormalization and matrix-product states and operators—with those of local entanglement manipulation, Markov chain mixing, and quantum error correction. We identify meaningful parameter regions for which we prove convergence to maximally entangled states, arising as the fixed points of a matrix-product operator renormalization flow.

Entanglement without nonlocality

International Nuclear Information System (INIS)

Hewitt-Horsman, C.; Vedral, V.

2007-01-01

We consider the characterization of entanglement from the perspective of a Heisenberg formalism. We derive a two-party generalized separability criterion, and from this describe a physical understanding of entanglement. We find that entanglement may be considered as fundamentally a local effect, and therefore as a separate computational resource from nonlocality. We show how entanglement differs from correlation physically, and explore the implications of this concept of entanglement for the notion of classicality. We find that this understanding of entanglement extends naturally to multipartite cases

Estimating Time To Complete for ATLAS data transfers

CERN Document Server

Bogado Garcia, Joaquin Ignacio; The ATLAS collaboration; Monticelli, Fernando

2018-01-01

Transfer Time To Complete (T³C) is a new extension for the data management system Rucio that allows to make predictions about the duration of a file transfer. The extension has a modular architecture which allows to make predictions based on simple to more sophisticated models, depending on available data and computation power. The ability to predict file transfer times with reasonable accuracy provides a tool for better transfer scheduling  and thus reduces both the load on storage systems and the associated networks. The accuracy of the model requires fine tuning for its parameters on a link basis. As the underlying infrastructure varies depending on the source and destination of the transfer, the parameters modelling the network between these sites will also be studied.

Partial recovery of entanglement in bipartite-entanglement transformations

International Nuclear Information System (INIS)

Bandyopadhyay, Somshubhro; Roychowdhury, Vwani; Vatan, Farrokh

2002-01-01

Any deterministic bipartite-entanglement transformation involving finite copies of pure states and carried out using local operations and classical communication (LOCC) results in a net loss of entanglement. We show that for almost all such transformations, partial recovery of lost entanglement is achievable by using 2x2 auxiliary entangled states, no matter how large the dimensions of the parent states are. For the rest of the special cases of deterministic LOCC transformations, we show that the dimension of the auxiliary entangled state depends on the presence of equalities in the majorization relations of the parent states. We show that genuine recovery is still possible using auxiliary states in dimensions less than that of the parent states for all patterns of majorization relations except only one special case

Entanglement diversion and quantum teleportation of entangled coherent states

Institute of Scientific and Technical Information of China (English)

Cai Xin-Hua; Guo Jie-Rong; Nie Jian-Jun; Jia Jin-Ping

2006-01-01

The proposals on entanglement diversion and quantum teleportation of entangled coherent states are presented.In these proposals,the entanglement between two coherent states,|α〉and |-α〉,with the same amplitude but a phase difference of π is utilized as a quantum channel.The processes of the entanglement diversion and the teleportation are achieved by using the 5050 symmetric beam splitters,the phase shifters and the photodetectors with the help of classical information.

Calibration robust entanglement detection beyond Bell inequalities

Energy Technology Data Exchange (ETDEWEB)

Moroder, Tobias [Institut fuer Quantenoptik und Quanteninformation, Oesterreichische Akademie der Wissenschaften, Technikerstrasse 21A, A-6020 Innsbruck (Austria); Gittsovich, Oleg [Department of Physics and Astronomy, Institute for Quantum Computing, University of Waterloo, 200 University Avenue West, N2L 3G1 Waterloo, Ontario (Canada)

2012-07-01

In its vast majority entanglement verification is examined either in the complete characterized or totally device independent scenario. The assumptions imposed by these extreme cases are often either too weak or strong for real experiments. Here we investigate this detection task for the intermediate regime where partial knowledge of the measured observables is known, considering cases like orthogonal, sharp or only dimension bounded measurements. We show that for all these assumptions it is not necessary to violate a corresponding Bell inequality in order to detect entanglement. We derive strong detection criteria that can be directly evaluated for experimental data and which are robust against large classes of calibration errors. The conditions are even capable of detecting bound entanglement under the sole assumption of dimension bounded measurements.

Einstein-Podolsky-Rosen-entangled motion of two massive objects

Science.gov (United States)

Schnabel, Roman

2015-07-01

In 1935, Einstein, Podolsky, and Rosen (EPR) considered two particles in an entangled state of motion to illustrate why they questioned the completeness of quantum theory. In past decades, microscopic systems with entanglement in various degrees of freedom have successfully been generated, representing compelling evidence to support the completeness of quantum theory. Today, the generation of an EPR-entangled state of motion of two massive objects of up to the kilogram scale seems feasible with state-of-the-art technology. Recently, the generation and verification of EPR-entangled mirror motion in interferometric gravitational wave detectors was proposed, with the aim of testing quantum theory in the regime of macroscopic objects, and to make available nonclassical probe systems for future tests of modified quantum theories that include (nonrelativistic) gravity. The work presented here builds on these earlier results and proposes a specific Michelson interferometer that includes two high-quality laser mirrors of about 0.1 kg mass each. The mirrors are individually suspended as pendula and located close to each other, and cooled to about 4 K. The physical concepts for the generation of the EPR-entangled center-of-mass motion of these two mirrors are described. Apart from a test of quantum mechanics in the macroscopic world, the setup is envisioned to test predictions of yet-to-be-elaborated modified quantum theories that include gravitational effects.

Entanglement and thermodynamics after a quantum quench in integrable systems.

Science.gov (United States)

Alba, Vincenzo; Calabrese, Pasquale

2017-07-25

Entanglement and entropy are key concepts standing at the foundations of quantum and statistical mechanics. Recently, the study of quantum quenches revealed that these concepts are intricately intertwined. Although the unitary time evolution ensuing from a pure state maintains the system at zero entropy, local properties at long times are captured by a statistical ensemble with nonzero thermodynamic entropy, which is the entanglement accumulated during the dynamics. Therefore, understanding the entanglement evolution unveils how thermodynamics emerges in isolated systems. Alas, an exact computation of the entanglement dynamics was available so far only for noninteracting systems, whereas it was deemed unfeasible for interacting ones. Here, we show that the standard quasiparticle picture of the entanglement evolution, complemented with integrability-based knowledge of the steady state and its excitations, leads to a complete understanding of the entanglement dynamics in the space-time scaling limit. We thoroughly check our result for the paradigmatic Heisenberg chain.

Charcterization of multipartite entanglement

Energy Technology Data Exchange (ETDEWEB)

Chong, Bo

2006-06-23

In this thesis, we discuss several aspects of the characterization of entanglement in multipartite quantum systems, including detection, classification and quantification of entanglement. First, we discuss triqubit pure entanglement and propose a special true tripartite entanglement, the mixed entanglement, besides the Greenberger-Horne-Zeilinger (GHZ) entanglement and the W entanglement. Then, based on quantitative complementarity relations, we draw entanglement Venn diagrams for triqubit pure states with different entanglements and introduce the total tangle {tau}{sup (T)} to quantify total entanglement of triqubit pure states by defining the union I that is equivalent to the total tangle {tau}{sup (T)} from the mathematical point of view. The generalizations of entanglement Venn diagrams and the union I to N-qubit pure states are also discussed. Finally, based on the ranks of reduced density matrices, we discuss the separability of multiparticle arbitrary-dimensional pure and mixed states, respectively. (orig.)

Charcterization of multipartite entanglement

International Nuclear Information System (INIS)

Chong, Bo

2006-01-01

In this thesis, we discuss several aspects of the characterization of entanglement in multipartite quantum systems, including detection, classification and quantification of entanglement. First, we discuss triqubit pure entanglement and propose a special true tripartite entanglement, the mixed entanglement, besides the Greenberger-Horne-Zeilinger (GHZ) entanglement and the W entanglement. Then, based on quantitative complementarity relations, we draw entanglement Venn diagrams for triqubit pure states with different entanglements and introduce the total tangle τ (T) to quantify total entanglement of triqubit pure states by defining the union I that is equivalent to the total tangle τ (T) from the mathematical point of view. The generalizations of entanglement Venn diagrams and the union I to N-qubit pure states are also discussed. Finally, based on the ranks of reduced density matrices, we discuss the separability of multiparticle arbitrary-dimensional pure and mixed states, respectively. (orig.)

Teleportation of a Coherent Superposition State Via a nonmaximally Entangled Coherent Xhannel

Institute of Scientific and Technical Information of China (English)

无

2002-01-01

@@ We investigate the problemm of teleportation of a superposition coherent state with nonmaximally entangled coherent channel. Two strategies are considered to complete the task. The first one uses entanglement concentration to purify the channel to a maximally entangled one. The second one teleports the state through the nonmaximally entangled coherent channel directly. We find that the probabilities of successful teleportations for the two strategies are depend on the amplitudes of the coherent states and the mean fidelity of teleportation using the first strategy is always less than that of the second strategy.

Circuit QED: generation of two-transmon-qutrit entangled states via resonant interaction

Science.gov (United States)

Ye, Xi-Mei; Zheng, Zhen-Fei; Lu, Dao-Ming; Yang, Chui-Ping

2018-04-01

We present a way to create entangled states of two superconducting transmon qutrits based on circuit QED. Here, a qutrit refers to a three-level quantum system. Since only resonant interaction is employed, the entanglement creation can be completed within a short time. The degree of entanglement for the prepared entangled state can be controlled by varying the weight factors of the initial state of one qutrit, which allows the prepared entangled state to change from a partially entangled state to a maximally entangled state. Because a single cavity is used, only resonant interaction is employed, and none of identical qutrit-cavity coupling constant, measurement, and auxiliary qutrit is needed, this proposal is easy to implement in experiments. The proposal is quite general and can be applied to prepare a two-qutrit partially or maximally entangled state with two natural or artificial atoms of a ladder-type level structure, coupled to an optical or microwave cavity.

Detecting quantum entanglement. Entanglement witnesses and uncertainty relations

International Nuclear Information System (INIS)

Guehne, O.

2004-01-01

This thesis deals with methods of the detection of entanglement. After recalling some facts and definitions concerning entanglement and separability, we investigate two methods of the detection of entanglement. In the first part of this thesis we consider so-called entanglement witnesses, mainly in view of the detection of multipartite entanglement. Entanglement witnesses are observables for which a negative expectation value indicates entanglement. We first present a simple method to construct these witnesses. Since witnesses are nonlocal observables, they are not easy to measure in a real experiment. However, as we will show, one can circumvent this problem by decomposing the witness into several local observables which can be measured separately. We calculate the local decompositions for several interesting witnesses for two, three and four qubits. Local decompositions can be optimized in the number of measurement settings which are needed for an experimental implementation. We present a method to prove that a given local decomposition is optimal and discuss with this the optimality of our decompositions. Then we present another method of designing witnesses which are by construction measurable with local measurements. Finally, we shortly report on experiments where some of the witnesses derived in this part have been used to detect three- and four-partite entanglement of polarized photons. The second part of this thesis deals with separability criteria which are written in terms of uncertainty relations. There are two different formulations of uncertainty relations since one can measure the uncertainty of an observable by its variance as well as by entropic quantities. We show that both formulations are useful tools for the derivation of separability criteria for finite-dimensional systems and investigate the resulting criteria. Our results in this part exhibit also some more fundamental properties of entanglement: We show how known separability criteria for

Quantum teleportation and entanglement distribution over 100-kilometre free-space channels.

Science.gov (United States)

Yin, Juan; Ren, Ji-Gang; Lu, He; Cao, Yuan; Yong, Hai-Lin; Wu, Yu-Ping; Liu, Chang; Liao, Sheng-Kai; Zhou, Fei; Jiang, Yan; Cai, Xin-Dong; Xu, Ping; Pan, Ge-Sheng; Jia, Jian-Jun; Huang, Yong-Mei; Yin, Hao; Wang, Jian-Yu; Chen, Yu-Ao; Peng, Cheng-Zhi; Pan, Jian-Wei

2012-08-09

Transferring an unknown quantum state over arbitrary distances is essential for large-scale quantum communication and distributed quantum networks. It can be achieved with the help of long-distance quantum teleportation and entanglement distribution. The latter is also important for fundamental tests of the laws of quantum mechanics. Although quantum teleportation and entanglement distribution over moderate distances have been realized using optical fibre links, the huge photon loss and decoherence in fibres necessitate the use of quantum repeaters for larger distances. However, the practical realization of quantum repeaters remains experimentally challenging. Free-space channels, first used for quantum key distribution, offer a more promising approach because photon loss and decoherence are almost negligible in the atmosphere. Furthermore, by using satellites, ultra-long-distance quantum communication and tests of quantum foundations could be achieved on a global scale. Previous experiments have achieved free-space distribution of entangled photon pairs over distances of 600 metres (ref. 14) and 13 kilometres (ref. 15), and transfer of triggered single photons over a 144-kilometre one-link free-space channel. Most recently, following a modified scheme, free-space quantum teleportation over 16 kilometres was demonstrated with a single pair of entangled photons. Here we report quantum teleportation of independent qubits over a 97-kilometre one-link free-space channel with multi-photon entanglement. An average fidelity of 80.4 ± 0.9 per cent is achieved for six distinct states. Furthermore, we demonstrate entanglement distribution over a two-link channel, in which the entangled photons are separated by 101.8 kilometres. Violation of the Clauser-Horne-Shimony-Holt inequality is observed without the locality loophole. Besides being of fundamental interest, our results represent an important step towards a global quantum network. Moreover, the high

Holographic entanglement entropy in superconductor phase transition with dark matter sector

Directory of Open Access Journals (Sweden)

Yan Peng

2015-11-01

Full Text Available In this paper, we investigate the holographic phase transition with dark matter sector in the AdS black hole background away from the probe limit. We discuss the properties of phases mostly from the holographic topological entanglement entropy of the system. We find the entanglement entropy is a good probe to the critical temperature and the order of the phase transition in the general model. The behaviors of entanglement entropy at large strip size suggest that the area law still holds when including dark matter sector. We also conclude that the holographic topological entanglement entropy is useful in detecting the stability of the phase transitions. Furthermore, we derive the complete diagram of the effects of coupled parameters on the critical temperature through the entanglement entropy and analytical methods.

The entanglement evolution between two entangled atoms

Indian Academy of Sciences (India)

Entanglement is an important resource for quantum information processing. [1–3] and also one of the most important nonclassical properties in quantum theory. ... consideration, which consists of two entangled two-level atoms A and B with ...

Irreversibility of entanglement distillation for a class of symmetric states

International Nuclear Information System (INIS)

Vollbrecht, Karl Gerd H.; Wolf, Michael M.; Werner, Reinhard F.

2004-01-01

We investigate the irreversibility of entanglement distillation for a symmetric (d+1)-parameter family of mixed bipartite quantum states acting on Hilbert spaces of arbitrary dimension dxd. We prove that in this family the entanglement cost is generically strictly larger than the distillable entanglement, so that the set of states for which the distillation process is asymptotically reversible is of measure zero. This remains true even if the distillation process is catalytically assisted by pure-state entanglement and every operation is allowed, which preserves the positivity of the partial transpose. It is shown that reversibility occurs only in cases where the state is a tagged mixture. The reversible cases are shown to be completely characterized by minimal uncertainty vectors for entropic uncertainty relations

Entanglement and co-tunneling of two equivalent protons in hydrogen bond pairs

Science.gov (United States)

Smedarchina, Zorka; Siebrand, Willem; Fernández-Ramos, Antonio

2018-03-01

A theoretical study is reported of a system of two identical symmetric hydrogen bonds, weakly coupled such that the two mobile protons can move either separately (stepwise) or together (concerted). It is modeled by two equivalent quartic potentials interacting through dipolar and quadrupolar coupling terms. The tunneling Hamiltonian has two imaginary modes (reaction coordinates) and a potential with a single maximum that may turn into a saddle-point of second order and two sets of (inequivalent) minima. Diagonalization is achieved via a modified Jacobi-Davidson algorithm. From this Hamiltonian the mechanism of proton transfer is derived. To find out whether the two protons move stepwise or concerted, a new tool is introduced, based on the distribution of the probability flux in the dividing plane of the transfer mode. While stepwise transfer dominates for very weak coupling, it is found that concerted transfer (co-tunneling) always occurs, even when the coupling vanishes since the symmetry of the Hamiltonian imposes permanent entanglement on the motions of the two protons. We quantify this entanglement and show that, for a wide range of parameters of interest, the lowest pair of states of the Hamiltonian represents a perfect example of highly entangled quantum states in continuous variables. The method is applied to the molecule porphycene for which the observed tunneling splitting is calculated in satisfactory agreement with experiment, and the mechanism of double-proton tunneling is found to be predominantly concerted. We show that, under normal conditions, when they are in the ground state, the two porphycene protons are highly entangled, which may have interesting applications. The treatment also identifies the conditions under which such a system can be handled by conventional one-instanton techniques.

The entanglement purification for entangled multi-particle states

CERN Document Server

Ye, Liu; Guo Guang Can

2002-01-01

We present two purification schemes for nonmaximally entangled states. We first show that two parties, Alice and Bob, start with shared less-entangled three-particle states to probabilistically produce a three-particle Greenberger-Horne-Zeilinger state by Bell state measurements and positive operator valued measure (POVM) or a unitary transformation. Then, by a straightforward generalization of the schemes, the purification of a multi-particle entangled state can be realized. 25 Refs. --- 35 --- AN

Entanglement dynamics in a Kerr spacetime

Science.gov (United States)

Menezes, G.

2018-04-01

We consider the entanglement dynamics between two-level atoms in a rotating black hole background. In our model the two-atom system is envisaged as an open system coupled with a massless scalar field prepared in one of the physical vacuum states of interest. We employ the quantum master equation in the Born-Markov approximation in order to describe the time evolution of the atomic subsystem. We investigate two different states of motion for the atoms, namely static atoms and also stationary atoms with zero angular momentum. The purpose of this work is to expound the impact on the creation of entanglement coming from the combined action of the different physical processes underlying the Hawking effect and the Unruh-Starobinskii effect. We demonstrate that, in the scenario of rotating black holes, the degree of quantum entanglement is significantly modified due to the phenomenon of superradiance in comparison with the analogous cases in a Schwarzschild spacetime. In the perspective of a zero angular momentum observer (ZAMO), one is allowed to probe entanglement dynamics inside the ergosphere, since static observers cannot exist within such a region. On the other hand, the presence of superradiant modes could be a source for violation of complete positivity. This is verified when the quantum field is prepared in the Frolov-Thorne vacuum state. In this exceptional situation, we raise the possibility that the loss of complete positivity is due to the breakdown of the Markovian approximation, which means that any arbitrary physically admissible initial state of the two atoms would not be capable to hold, with time evolution, its interpretation as a physical state inasmuch as negative probabilities are generated by the dynamical map.

Detecting nonlocal Cooper pair entanglement by optical Bell inequality violation

Energy Technology Data Exchange (ETDEWEB)

Nigg, Simon E.; Tiwari, Rakesh P.; Walter, Stefan; Schmidt, Thomas L. [Department of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel (Switzerland)

2015-07-01

Based on the Bardeen Cooper Schrieffer (BCS) theory of superconductivity, the coherent splitting of Cooper pairs from a superconductor to two spatially separated quantum dots has been predicted to generate nonlocal pairs of entangled electrons. In order to test this hypothesis, we propose a scheme to transfer the spin state of a split Cooper pair onto the polarization state of a pair of optical photons. We show that the produced photon pairs can be used to violate a Bell inequality, unambiguously demonstrating the entanglement of the split Cooper pairs.

Detecting nonlocal Cooper pair entanglement by optical Bell inequality violation

Science.gov (United States)

Nigg, Simon E.; Tiwari, Rakesh P.; Walter, Stefan; Schmidt, Thomas L.

2015-03-01

Based on the Bardeen-Cooper-Schrieffer theory of superconductivity, the coherent splitting of Cooper pairs from a superconductor to two spatially separated quantum dots has been predicted to generate nonlocal pairs of entangled electrons. In order to test this hypothesis, we propose a scheme to transfer the spin state of a split Cooper pair onto the polarization state of a pair of optical photons. We show that the photon pairs produced can be used to violate a Bell inequality, unambiguously demonstrating the entanglement of the split Cooper pairs.

Complete family of separability criteria

International Nuclear Information System (INIS)

Doherty, Andrew C.; Spedalieri, Federico M.; Parrilo, Pablo A.

2004-01-01

We introduce a family of separability criteria that are based on the existence of extensions of a bipartite quantum state ρ to a larger number of parties satisfying certain symmetry properties. It can be easily shown that all separable states have the required extensions, so the nonexistence of such an extension for a particular state implies that the state is entangled. One of the main advantages of this approach is that searching for the extension can be cast as a convex optimization problem known as a semidefinite program. Whenever an extension does not exist, the dual optimization constructs an explicit entanglement witness for the particular state. These separability tests can be ordered in a hierarchical structure whose first step corresponds to the well-known positive partial transpose (Peres-Horodecki) criterion, and each test in the hierarchy is at least as powerful as the preceding one. This hierarchy is complete, in the sense that any entangled state is guaranteed to fail a test at some finite point in the hierarchy, thus showing it is entangled. The entanglement witnesses corresponding to each step of the hierarchy have well-defined and very interesting algebraic properties that, in turn, allow for a characterization of the interior of the set of positive maps. Coupled with some recent results on the computational complexity of the separability problem, which has been shown to be NP hard, this hierarchy of tests gives a complete and also computationally and theoretically appealing characterization of mixed bipartite entangled states

Entanglement and quantum teleportation via decohered tripartite entangled states

Energy Technology Data Exchange (ETDEWEB)

Metwally, N., E-mail: nmohamed31@gmail.com

2014-12-15

The entanglement behavior of two classes of multi-qubit system, GHZ and GHZ like states passing through a generalized amplitude damping channel is discussed. Despite this channel causes degradation of the entangled properties and consequently their abilities to perform quantum teleportation, one can always improve the lower values of the entanglement and the fidelity of the teleported state by controlling on Bell measurements, analyzer angle and channel’s strength. Using GHZ-like state within a generalized amplitude damping channel is much better than using the normal GHZ-state, where the decay rate of entanglement and the fidelity of the teleported states are smaller than those depicted for GHZ state.

Entanglement between two interacting CFTs and generalized holographic entanglement entropy

International Nuclear Information System (INIS)

Mollabashi, Ali; Shiba, Noburo; Takayanagi, Tadashi

2014-01-01

In this paper we discuss behaviors of entanglement entropy between two interacting CFTs and its holographic interpretation using the AdS/CFT correspondence. We explicitly perform analytical calculations of entanglement entropy between two free scalar field theories which are interacting with each other in both static and time-dependent ways. We also conjecture a holographic calculation of entanglement entropy between two interacting N=4 super Yang-Mills theories by introducing a minimal surface in the S 5 direction, instead of the AdS 5 direction. This offers a possible generalization of holographic entanglement entropy

Majorana entanglement bridge

Science.gov (United States)

Plugge, Stephan; Zazunov, Alex; Sodano, Pasquale; Egger, Reinhold

2015-06-01

We study the concurrence of entanglement between two quantum dots in contact to Majorana bound states on a floating superconducting island. The distance between the Majorana states, the charging energy of the island, and the average island charge are shown to be decisive parameters for the efficiency of entanglement generation. We find that long-range entanglement with basically distance-independent concurrence is possible over wide parameter regions, where the proposed setup realizes a "Majorana entanglement bridge." We also study the time-dependent concurrence obtained after one of the tunnel couplings is suddenly switched on, which reveals the time scales for generating entanglement. Accurate analytical expressions for the concurrence are derived both for the static and the time-dependent cases. Our results indicate that entanglement formation in interacting Majorana devices can be fully understood in terms of an interplay of elastic cotunneling (also referred to as "teleportation") and crossed Andreev reflection processes.

The Entangled Cosmos: an experiment in physical theopoetics

Science.gov (United States)

Keller, Catherine

2012-09-01

As an experiment in constructive transdisciplinary relationality, a theology of nonseparable difference here engages a physics of quantum entanglement. The metaphoric potential of "spooky action at a distance" to intensify a cosmology resistant to the dominant individualism and conducive to ethical ecologies of interdependence has only begun to develop across multiple discourses. This essay contemplates the specific unfolding of a theory of nonlocal superpositions by physicists such as Stapp, Bohm and Barad. It does not literalize any God-trope, but rather entangles theology in the mysterious uncertainty of our widest interdependencies. This essay, first presented as a lecture at the American Academy of Religion "Science, Technology and Religion" Group, San Francisco, November 2011, forms the core of a chapter in a book I am currently completing, The Cloud of the Impossible: Theological Entanglements.

Entanglement negativity in the multiverse

Energy Technology Data Exchange (ETDEWEB)

Kanno, Sugumi [Department of Theoretical Physics and History of Science, University of the Basque Country UPV/EHU, 48080 Bilbao (Spain); Shock, Jonathan P. [Laboratory for Quantum Gravity and Strings and Astrophysics, Cosmology and Gravity Center, Department of Mathematics and Applied Mathematics, University of Cape Town, Private Bag, Rondebosch 7701 (South Africa); Soda, Jiro, E-mail: sugumi.kanno@ehu.es, E-mail: jonathan.shock@uct.ac.za, E-mail: jiro@phys.sci.kobe-u.ac.jp [Department of Physics, Kobe University, Kobe 657-8501 (Japan)

2015-03-01

We explore quantum entanglement between two causally disconnected regions in the multiverse. We first consider a free massive scalar field, and compute the entanglement negativity between two causally separated open charts in de Sitter space. The qualitative feature of it turns out to be in agreement with that of the entanglement entropy. We then introduce two observers who determine the entanglement between two causally disconnected de Sitter spaces. When one of the observers remains constrained to a region of the open chart in a de Sitter space, we find that the scale dependence enters into the entanglement. We show that a state which is initially maximally entangled becomes more entangled or less entangled on large scales depending on the mass of the scalar field and recovers the initial entanglement in the small scale limit. We argue that quantum entanglement may provide some evidence for the existence of the multiverse.

Entanglement negativity in the multiverse

International Nuclear Information System (INIS)

Kanno, Sugumi; Shock, Jonathan P.; Soda, Jiro

2015-01-01

We explore quantum entanglement between two causally disconnected regions in the multiverse. We first consider a free massive scalar field, and compute the entanglement negativity between two causally separated open charts in de Sitter space. The qualitative feature of it turns out to be in agreement with that of the entanglement entropy. We then introduce two observers who determine the entanglement between two causally disconnected de Sitter spaces. When one of the observers remains constrained to a region of the open chart in a de Sitter space, we find that the scale dependence enters into the entanglement. We show that a state which is initially maximally entangled becomes more entangled or less entangled on large scales depending on the mass of the scalar field and recovers the initial entanglement in the small scale limit. We argue that quantum entanglement may provide some evidence for the existence of the multiverse

Entanglement negativity in the multiverse

Energy Technology Data Exchange (ETDEWEB)

Kanno, Sugumi [Department of Theoretical Physics and History of Science, University of the Basque Country UPV/EHU, 48080 Bilbao (Spain); IKERBASQUE, Basque Foundation for Science, Maria Diaz de Haro 3, 48013, Bilbao (Spain); Laboratory for Quantum Gravity & Strings and Astrophysics, Cosmology & Gravity Center, Department of Mathematics & Applied Mathematics, University of Cape Town, Private Bag, Rondebosch 7701 (South Africa); Shock, Jonathan P. [Laboratory for Quantum Gravity & Strings and Astrophysics, Cosmology & Gravity Center, Department of Mathematics & Applied Mathematics, University of Cape Town, Private Bag, Rondebosch 7701 (South Africa); National Institute for Theoretical Physics, Private Bag X1, Matieland, 7602 (South Africa); Soda, Jiro [Department of Physics, Kobe University, Kobe 657-8501 (Japan)

2015-03-10

We explore quantum entanglement between two causally disconnected regions in the multiverse. We first consider a free massive scalar field, and compute the entanglement negativity between two causally separated open charts in de Sitter space. The qualitative feature of it turns out to be in agreement with that of the entanglement entropy. We then introduce two observers who determine the entanglement between two causally disconnected de Sitter spaces. When one of the observers remains constrained to a region of the open chart in a de Sitter space, we find that the scale dependence enters into the entanglement. We show that a state which is initially maximally entangled becomes more entangled or less entangled on large scales depending on the mass of the scalar field and recovers the initial entanglement in the small scale limit. We argue that quantum entanglement may provide some evidence for the existence of the multiverse.

Newton's Cradle and Entanglement Transport in a Flexible Rydberg Chain

International Nuclear Information System (INIS)

Wuester, S.; Ates, C.; Eisfeld, A.; Rost, J. M.

2010-01-01

In a regular, flexible chain of Rydberg atoms, a single electronic excitation localizes on two atoms that are in closer mutual proximity than all others. We show how the interplay between excitonic and atomic motion causes electronic excitation and diatomic proximity to propagate through the Rydberg chain as a combined pulse. In this manner entanglement is transferred adiabatically along the chain, reminiscent of momentum transfer in Newton's cradle.

Experimental quantum teleportation and multiphoton entanglement via interfering narrowband photon sources

International Nuclear Information System (INIS)

Yang Jian; Zhang Han; Peng Chengzhi; Chen Zengbing; Bao Xiaohui; Chen Shuai; Pan Jianwei

2009-01-01

In this paper, we report a realization of synchronization-free quantum teleportation and narrowband three-photon entanglement through interfering narrowband photon sources. Since both the single-photon and the entangled photon pair utilized are completely autonomous, it removes the requirement of high-demanding synchronization techniques in long-distance quantum communication with pulsed spontaneous parametric down-conversion sources. The frequency linewidth of the three-photon entanglement realized is on the order of several MHz, which matches the requirement of atomic ensemble based quantum memories. Such a narrowband multiphoton source will have applications in some advanced quantum communication protocols and linear optical quantum computation.

Voltage-Controlled Quantum Dynamics and Generation Entanglement between Two Separated Quantum-Dot Molecules Embedded in Photonic Crystal Cavities

International Nuclear Information System (INIS)

Cheng Mu-Tian; Song Yan-Yan; Ma Xiao-San; Wang Xia

2014-01-01

Voltage-controlled quantum dynamics of two quantum-dot molecules (QDMs) embedded in two separated photonic crystal cavities are theoretically investigated. We show numerically that generation of entangled states and population transfer between the two QDMs can be realized with the same coupling parameters. The effects of parameters deviation and dissipations on generation entangled states and populations transfer are also discussed. The results may be used for realization of new-type of solid state quantum devices and integrated electro-optical devices

Unitarily localizable entanglement of Gaussian states

International Nuclear Information System (INIS)

Serafini, Alessio; Adesso, Gerardo; Illuminati, Fabrizio

2005-01-01

We consider generic (mxn)-mode bipartitions of continuous-variable systems, and study the associated bisymmetric multimode Gaussian states. They are defined as (m+n)-mode Gaussian states invariant under local mode permutations on the m-mode and n-mode subsystems. We prove that such states are equivalent, under local unitary transformations, to the tensor product of a two-mode state and of m+n-2 uncorrelated single-mode states. The entanglement between the m-mode and the n-mode blocks can then be completely concentrated on a single pair of modes by means of local unitary operations alone. This result allows us to prove that the PPT (positivity of the partial transpose) condition is necessary and sufficient for the separability of (m+n)-mode bisymmetric Gaussian states. We determine exactly their negativity and identify a subset of bisymmetric states whose multimode entanglement of formation can be computed analytically. We consider explicit examples of pure and mixed bisymmetric states and study their entanglement scaling with the number of modes

Gaussian measures of entanglement versus negativities: Ordering of two-mode Gaussian states

International Nuclear Information System (INIS)

Adesso, Gerardo; Illuminati, Fabrizio

2005-01-01

We study the entanglement of general (pure or mixed) two-mode Gaussian states of continuous-variable systems by comparing the two available classes of computable measures of entanglement: entropy-inspired Gaussian convex-roof measures and positive partial transposition-inspired measures (negativity and logarithmic negativity). We first review the formalism of Gaussian measures of entanglement, adopting the framework introduced in M. M. Wolf et al., Phys. Rev. A 69, 052320 (2004), where the Gaussian entanglement of formation was defined. We compute explicitly Gaussian measures of entanglement for two important families of nonsymmetric two-mode Gaussian state: namely, the states of extremal (maximal and minimal) negativities at fixed global and local purities, introduced in G. Adesso et al., Phys. Rev. Lett. 92, 087901 (2004). This analysis allows us to compare the different orderings induced on the set of entangled two-mode Gaussian states by the negativities and by the Gaussian measures of entanglement. We find that in a certain range of values of the global and local purities (characterizing the covariance matrix of the corresponding extremal states), states of minimum negativity can have more Gaussian entanglement of formation than states of maximum negativity. Consequently, Gaussian measures and negativities are definitely inequivalent measures of entanglement on nonsymmetric two-mode Gaussian states, even when restricted to a class of extremal states. On the other hand, the two families of entanglement measures are completely equivalent on symmetric states, for which the Gaussian entanglement of formation coincides with the true entanglement of formation. Finally, we show that the inequivalence between the two families of continuous-variable entanglement measures is somehow limited. Namely, we rigorously prove that, at fixed negativities, the Gaussian measures of entanglement are bounded from below. Moreover, we provide some strong evidence suggesting that they

Quantum dialogue using non-maximally entangled states based on entanglement swapping

International Nuclear Information System (INIS)

Xia Yan; Song Jie; Song Heshan

2007-01-01

We present a secure quantum dialogue protocol using non-maximally entangled two-particle states via entanglement swapping at first, and then discuss the requirements for a real quantum dialogue. Within the present version two authorized users can exchange their faithful secret messages securely and simultaneously based on the method of entanglement purification

Efficient multipartite entanglement purification with the entanglement link from a subspace

Energy Technology Data Exchange (ETDEWEB)

Deng Fuguo [Department of Physics, Applied Optics Beijing Area Major Laboratory, Beijing Conventional University, Beijing 100875 (China)

2011-11-15

We present an efficient multipartite entanglement purification protocol (MEPP) for N-photon systems in a Greenberger-Horne-Zeilinger state with parity-check detectors. It contains two parts. One is the conventional MEPP with which the parties can obtain a high-fidelity N-photon ensemble directly, similar to the MEPP with controlled-not gates. The other is our recycling MEPP in which the entanglement link is used to produce some N-photon entangled systems from entangled N{sup '}-photon subsystems (2{<=}N{sup '}entangled N{sup '}-photon subsystems are obtained efficiently by measuring the photons with potential bit-flip errors. With these two parts, the present MEPP has a higher efficiency than all other conventional MEPPs.

Entanglement reactivation in separable environments

International Nuclear Information System (INIS)

Pirandola, Stefano

2013-01-01

Combining two entanglement-breaking channels into a correlated-noise environment restores the distribution of entanglement. Surprisingly, this reactivation can be induced by the injection of separable correlations from the composite environment. In any dimension (finite or infinite), we can construct classically correlated ‘twirling’ environments which are entanglement-breaking in the transmission of single systems but entanglement-preserving when two systems are transmitted. Here entanglement is simply preserved by the existence of decoherence-free subspaces. Remarkably, even when such subspaces do not exist, a fraction of the input entanglement can still be distributed. This is found in separable Gaussian environments, where distillable entanglement is able to survive the two-mode transmission, despite being broken in any single-mode transmission by the strong thermal noise. In the Gaussian setting, entanglement restoration is a threshold process, occurring only after a critical amount of correlations has been injected. Such findings suggest new perspectives for distributing entanglement in realistic environments with extreme decoherence, identifying separable correlations and classical memory effects as physical resources for ‘breaking entanglement-breaking’. (paper)

Mutual preservation of entanglement

International Nuclear Information System (INIS)

Veitia, Andrzej; Jing, Jun; Yu, Ting; Wong, Chee Wei

2012-01-01

We study a generalized double Jaynes–Cummings (JC) model where two entangled pairs of two-level atoms interact indirectly. We show that there exist initial states of the qubit system so that two entangled pairs are available at all times. In particular, the minimum entanglement in the pairs as a function of the initial state is studied. Finally, we extend our findings to a model consisting of multi-mode atom–cavity interactions. We use a non-Markovian quantum state diffusion (QSD) equation to obtain the steady-state density matrix for the qubits. We show that the multi-mode model also displays dynamical preservation of entanglement. -- Highlights: ► Entanglement dynamics is studied in a generalized double Jaynes–Cummings model. ► We show that for certain initial states, the atoms remain entangled at all times. ► We extend the results to the case of multi-mode atom–cavity interactions. ► The model suggest that indirect interaction may help to preserve entanglement.

Thermal excitation spectrum from entanglement in an expanding quantum string

Directory of Open Access Journals (Sweden)

Jürgen Berges

2018-03-01

Full Text Available A surprising result in e+e− collisions is that the particle spectra from the string formed between the expanding quark–antiquark pair have thermal properties even though scatterings appear not to be frequent enough to explain this. We address this problem by considering the finite observable interval of a relativistic quantum string in terms of its reduced density operator by tracing over the complement region. We show how quantum entanglement in the presence of a horizon in spacetime for the causal transfer of information leads locally to a reduced mixed-state density operator. For very early proper time τ, we show that the entanglement entropy becomes extensive and scales with the rapidity. At these early times, the reduced density operator is of thermal form, with an entanglement temperature Tτ=ħ/(2πkBτ, even in the absence of any scatterings.

Entanglement properties between two atoms in the binomial optical field interacting with two entangled atoms

International Nuclear Information System (INIS)

Liu Tang-Kun; Zhang Kang-Long; Tao Yu; Shan Chuan-Jia; Liu Ji-Bing

2016-01-01

The temporal evolution of the degree of entanglement between two atoms in a system of the binomial optical field interacting with two arbitrary entangled atoms is investigated. The influence of the strength of the dipole–dipole interaction between two atoms, probabilities of the Bernoulli trial, and particle number of the binomial optical field on the temporal evolution of the atomic entanglement are discussed. The result shows that the two atoms are always in the entanglement state. Moreover, if and only if the two atoms are initially in the maximally entangled state, the entanglement evolution is not affected by the parameters, and the degree of entanglement is always kept as 1. (paper)

Braiding transformation, entanglement swapping, and Berry phase in entanglement space

International Nuclear Information System (INIS)

Chen Jingling; Ge Molin; Xue Kang

2007-01-01

We show that braiding transformation is a natural approach to describe quantum entanglement by using the unitary braiding operators to realize entanglement swapping and generate the Greenberger-Horne-Zeilinger states as well as the linear cluster states. A Hamiltonian is constructed from the unitary R i,i+1 (θ,φ) matrix, where φ=ωt is time-dependent while θ is time-independent. This in turn allows us to investigate the Berry phase in the entanglement space

Entanglement purification and concentration of electron-spin entangled states using quantum-dot spins in optical microcavities

International Nuclear Information System (INIS)

Wang Chuan; Zhang Yong; Jin Guangsheng

2011-01-01

We present an entanglement purification protocol and an entanglement concentration protocol for electron-spin entangled states, resorting to quantum-dot spin and optical-microcavity-coupled systems. The parity-check gates (PCGs) constructed by the cavity-spin-coupling system provide a different method for the entanglement purification of electron-spin entangled states. This protocol can efficiently purify an electron ensemble in a mixed entangled state. The PCGs can also concentrate electron-spin pairs in less-entangled pure states efficiently. The proposed methods are more flexible as only single-photon detection and single-electron detection are needed.

Characterization of two-qubit perfect entanglers

International Nuclear Information System (INIS)

Rezakhani, A.T.

2004-01-01

Here we consider perfect entanglers from another perspective. It is shown that there are some special perfect entanglers which can maximally entangle a full product basis. We explicitly construct a one-parameter family of such entanglers together with the proper product basis that they maximally entangle. This special family of perfect entanglers contains some well-known operators such as controlled-NOT (CNOT) and double-CNOT, but not √(SWAP). In addition, it is shown that all perfect entanglers with entangling power equal to the maximal value (2/9) are also special perfect entanglers. It is proved that the one-parameter family is the only possible set of special perfect entanglers. Also we provide an analytic way to implement any arbitrary two-qubit gate, given a proper special perfect entangler supplemented with single-qubit gates. Such gates are shown to provide a minimum universal gate construction in that just two of them are necessary and sufficient in implementation of a generic two-qubit gate

The relation between majorization theory and quantum information from entanglement monotones perspective

Energy Technology Data Exchange (ETDEWEB)

Erol, V. [Department of Computer Engineering, Institute of Science, Okan University, Istanbul (Turkey); Netas Telecommunication Inc., Istanbul (Turkey)

2016-04-21

Entanglement has been studied extensively for understanding the mysteries of non-classical correlations between quantum systems. In the bipartite case, there are well known monotones for quantifying entanglement such as concurrence, relative entropy of entanglement (REE) and negativity, which cannot be increased via local operations. The study on these monotones has been a hot topic in quantum information [1-7] in order to understand the role of entanglement in this discipline. It can be observed that from any arbitrary quantum pure state a mixed state can obtained. A natural generalization of this observation would be to consider local operations classical communication (LOCC) transformations between general pure states of two parties. Although this question is a little more difficult, a complete solution has been developed using the mathematical framework of the majorization theory [8]. In this work, we analyze the relation between entanglement monotones concurrence and negativity with respect to majorization for general two-level quantum systems of two particles.

A scheme for distributed quantum search through simultaneous state transfer mechanism

International Nuclear Information System (INIS)

Gupta, M.; Pathak, A.

2007-01-01

Using a quantum network model, we present a scheme for distributed implementation of Grover's algorithm. The proposed scheme can implement a quantum search over data bases stored in different computers. Entanglement is used to carry out different non-local operations over the spatially distributed quantum computers. A method to transfer the combined state of many qubits over the entanglement and subsequently refreshing the entangled pair is presented. This method of simultaneous s tate transfer from one computer to the other, is shown to result in a constant communication complexity. (Abstract Copyright [2007], Wiley Periodicals, Inc.)

Atoms and cavities: Explorations of quantum entanglement

International Nuclear Information System (INIS)

Raimond, J. M.; Hagley, E.; Maitre, X.; Nogues, G.; Wunderlich, C.; Brune, M.; Haroche, S.

1999-01-01

The interaction of circular Rydberg atoms with a high-quality microwave cavity makes it possible to realize complex quantum state manipulations. The state of an atom can be 'copied' onto the cavity. Reversing this operation at a later time with a second atom, we realize an elementary 'quantum memory' holding an atomic quantum coherence for a while in a cavity mode. We have also generated two-atom entangled states of the Einstein-Podolsky-Rosen type. At variance with previous experiments, this one implies massive particles in a completely controlled process. These entanglement manipulations can be generalized to more complex or to mesoscopic systems and open the way to new tests of fundamental aspects of the quantum world

Detecting faked continuous-variable entanglement using one-sided device-independent entanglement witnesses

Science.gov (United States)

Opanchuk, B.; Arnaud, L.; Reid, M. D.

2014-06-01

We demonstrate the principle of one-sided device-independent continuous-variable (CV) quantum information. In situations of no trust, we show by enactment how the use of standard CV entanglement criteria can mislead Charlie into thinking that Alice and Bob share entanglement, when the data are actually generated classically using a local-hidden-variable theory based on the Wigner function. We distinguish between criteria that demonstrate CV entanglement, and criteria that demonstrate the CV Einstein-Podolsky-Rosen (EPR) steering paradox. We show that the latter, but not the former, are necessarily one-sided device-independent entanglement witnesses, and can be used by Charlie to signify genuine EPR entanglement, if he trusts only Alice. A monogamy result for the EPR steering paradox confirms the security of the shared amplitude values in that case.

Photon Entanglement Through Brain Tissue.

Science.gov (United States)

Shi, Lingyan; Galvez, Enrique J; Alfano, Robert R

2016-12-20

Photon entanglement, the cornerstone of quantum correlations, provides a level of coherence that is not present in classical correlations. Harnessing it by study of its passage through organic matter may offer new possibilities for medical diagnosis technique. In this work, we study the preservation of photon entanglement in polarization, created by spontaneous parametric down-conversion, after one entangled photon propagates through multiphoton-scattering brain tissue slices with different thickness. The Tangle-Entropy (TS) plots show the strong preservation of entanglement of photons propagating in brain tissue. By spatially filtering the ballistic scattering of an entangled photon, we find that its polarization entanglement is preserved and non-locally correlated with its twin in the TS plots. The degree of entanglement correlates better with structure and water content than with sample thickness.

Heralded entangling quantum gate via cavity-assisted photon scattering

Science.gov (United States)

Borges, Halyne S.; Rossatto, Daniel Z.; Luiz, Fabrício S.; Villas-Boas, Celso J.

2018-01-01

We theoretically investigate the generation of heralded entanglement between two identical atoms via cavity-assisted photon scattering in two different configurations, namely, either both atoms confined in the same cavity or trapped into locally separated ones. Our protocols are given by a very simple and elegant single-step process, the key mechanism of which is a controlled-phase-flip gate implemented by impinging a single photon on single-sided cavities. In particular, when the atoms are localized in remote cavities, we introduce a single-step parallel quantum circuit instead of the serial process extensively adopted in the literature. We also show that such parallel circuit can be straightforwardly applied to entangle two macroscopic clouds of atoms. Both protocols proposed here predict a high entanglement degree with a success probability close to unity for state-of-the-art parameters. Among other applications, our proposal and its extension to multiple atom-cavity systems step toward a suitable route for quantum networking, in particular for quantum state transfer, quantum teleportation, and nonlocal quantum memory.

Entanglement dynamics of two electron-spin qubits in a strongly detuned and dissipative quantum-dot-cavity system

International Nuclear Information System (INIS)

Xiang Shaohua; Deng Xiaopeng; Song Kehui; Wen Wei; Shi Zhengang

2011-01-01

We investigate the entanglement dynamics of two electron-spin qubits in the quantum-dot (QD)-microcavity system in the large-detuning limit and subjected to two different noise sources: electron-spin dephasing and relaxation. We show that when one of the two dots is prepared initially in the excited state, the created entanglement exhibits oscillatory behavior at the beginning of evolution and then completely disappears over time. For two QDs that are initially in either the Einstein-Podolsky-Rosen-Bell states or the Werner states, their entanglement evolution exhibits the same behavior in the presence of pure dephasing, but is completely different under the relaxation process. We also show that the interdot interaction induced by a single-mode cavity field does not contribute to the dynamics of entanglement for these Bell states and Werner states.

Mixtures of maximally entangled pure states

Energy Technology Data Exchange (ETDEWEB)

Flores, M.M., E-mail: mflores@nip.up.edu.ph; Galapon, E.A., E-mail: eric.galapon@gmail.com

2016-09-15

We study the conditions when mixtures of maximally entangled pure states remain entangled. We found that the resulting mixed state remains entangled when the number of entangled pure states to be mixed is less than or equal to the dimension of the pure states. For the latter case of mixing a number of pure states equal to their dimension, we found that the mixed state is entangled provided that the entangled pure states to be mixed are not equally weighted. We also found that one can restrict the set of pure states that one can mix from in order to ensure that the resulting mixed state is genuinely entangled. Also, we demonstrate how these results could be applied as a way to detect entanglement in mixtures of the entangled pure states with noise.

Statistical properties of quantum entanglement and information entropy

International Nuclear Information System (INIS)

Abdel-Aty, M.M.A.

2007-03-01

Key words: entropy, entanglement, atom-field interaction, trapped ions, cold atoms, information entropy. Objects of research: Pure state entanglement, entropy squeezing mazer. The aim of the work: Study of the new entanglement features and new measures for both pure-state and mixed state of particle-field interaction. Also, the impact of the information entropy on the quantum information theory. Method of investigation: Methods of theoretical physics and applied mathematics (statistical physics, quantum optics) are used. Results obtained and their novelty are: All the results of the dissertation are new and many new features have been discovered. Particularly: the most general case of the pure state entanglement has been introduced. Although various special aspects of the quantum entropy have been investigated previously, the general features of the dynamics, when a multi-level system and a common environment are considered, have not been treated before and our work therefore, field a gap in the literature. Specifically: 1) A new entanglement measure due to quantum mutual entropy (mixed-state entanglement) we called it DEM, has been introduced, 2) A new treatment of the atomic information entropy in higher level systems has been presented. The problem has been completely solved in the case of three-level system, 3) A new solution of the interaction between the ultra cold atoms and cavity field has been discovered, 4) Some new models of the atom-field interaction have been adopted. Practical value: The subject carries out theoretic character. Application region: Results can be used in quantum computer developments. Also, the presented results can be used for further developments of the quantum information and quantum communications. (author)

Protecting single-photon entanglement with practical entanglement source

Science.gov (United States)

Zhou, Lan; Ou-Yang, Yang; Wang, Lei; Sheng, Yu-Bo

2017-06-01

Single-photon entanglement (SPE) is important for quantum communication and quantum information processing. However, SPE is sensitive to photon loss. In this paper, we discuss a linear optical amplification protocol for protecting SPE. Different from the previous protocols, we exploit the practical spontaneous parametric down-conversion (SPDC) source to realize the amplification, for the ideal entanglement source is unavailable in current quantum technology. Moreover, we prove that the amplification using the entanglement generated from SPDC source as auxiliary is better than the amplification assisted with single photons. The reason is that the vacuum state from SPDC source will not affect the amplification, so that it can be eliminated automatically. This protocol may be useful in future long-distance quantum communications.

Quantum entanglement and nonlocality properties of two-mode Gaussian squeezed states

International Nuclear Information System (INIS)

Shao-Hua, Xiang; Bin, Shao; Ke-Hui, Song

2009-01-01

Quantum entanglement and nonlocality properties of a family of two-mode Gaussian pure states have been investigated. The results show that the entanglement of these states is determined by both the two-mode squeezing parameter and the difference of the two single-mode squeezing parameters. For the same two-mode squeezing parameter, these states show larger entanglement than the usual two-mode squeezed vacuum state. The violation of Bell inequality depends strongly on all the squeezing parameters of these states and disappears completely in the limit of large squeezing. In particular, these states can exhibit much stronger violation of local realism than two-mode squeezed vacuum state in the range of experimentally available squeezing values. (general)

Benchmarks and statistics of entanglement dynamics

International Nuclear Information System (INIS)

Tiersch, Markus

2009-01-01

In the present thesis we investigate how the quantum entanglement of multicomponent systems evolves under realistic conditions. More specifically, we focus on open quantum systems coupled to the (uncontrolled) degrees of freedom of an environment. We identify key quantities that describe the entanglement dynamics, and provide efficient tools for its calculation. For quantum systems of high dimension, entanglement dynamics can be characterized with high precision. In the first part of this work, we derive evolution equations for entanglement. These formulas determine the entanglement after a given time in terms of a product of two distinct quantities: the initial amount of entanglement and a factor that merely contains the parameters that characterize the dynamics. The latter is given by the entanglement evolution of an initially maximally entangled state. A maximally entangled state thus benchmarks the dynamics, and hence allows for the immediate calculation or - under more general conditions - estimation of the change in entanglement. Thereafter, a statistical analysis supports that the derived (in-)equalities describe the entanglement dynamics of the majority of weakly mixed and thus experimentally highly relevant states with high precision. The second part of this work approaches entanglement dynamics from a topological perspective. This allows for a quantitative description with a minimum amount of assumptions about Hilbert space (sub-)structure and environment coupling. In particular, we investigate the limit of increasing system size and density of states, i.e. the macroscopic limit. In this limit, a universal behaviour of entanglement emerges following a ''reference trajectory'', similar to the central role of the entanglement dynamics of a maximally entangled state found in the first part of the present work. (orig.)

Benchmarks and statistics of entanglement dynamics

Energy Technology Data Exchange (ETDEWEB)

Tiersch, Markus

2009-09-04

In the present thesis we investigate how the quantum entanglement of multicomponent systems evolves under realistic conditions. More specifically, we focus on open quantum systems coupled to the (uncontrolled) degrees of freedom of an environment. We identify key quantities that describe the entanglement dynamics, and provide efficient tools for its calculation. For quantum systems of high dimension, entanglement dynamics can be characterized with high precision. In the first part of this work, we derive evolution equations for entanglement. These formulas determine the entanglement after a given time in terms of a product of two distinct quantities: the initial amount of entanglement and a factor that merely contains the parameters that characterize the dynamics. The latter is given by the entanglement evolution of an initially maximally entangled state. A maximally entangled state thus benchmarks the dynamics, and hence allows for the immediate calculation or - under more general conditions - estimation of the change in entanglement. Thereafter, a statistical analysis supports that the derived (in-)equalities describe the entanglement dynamics of the majority of weakly mixed and thus experimentally highly relevant states with high precision. The second part of this work approaches entanglement dynamics from a topological perspective. This allows for a quantitative description with a minimum amount of assumptions about Hilbert space (sub-)structure and environment coupling. In particular, we investigate the limit of increasing system size and density of states, i.e. the macroscopic limit. In this limit, a universal behaviour of entanglement emerges following a ''reference trajectory'', similar to the central role of the entanglement dynamics of a maximally entangled state found in the first part of the present work. (orig.)

Remarks on entanglement swapping

International Nuclear Information System (INIS)

Song, Daegene

2004-01-01

In two partially entangled states, entanglement swapping by Bell measurement will yield the weaker entanglement of the two. This scheme is optimal because the average entanglement cannot increase under local operation and classical communication. However, for more than two states, this scheme does not always yield the weakest link. We consider projective measurements other than Bell-type measurement and show, numerically, that while Bell measurement may not be unique, it is indeed optimal among these projective measurements. We also discuss the non-uniqueness of Bell measurements. (letter to the editor)

Experimental test of entangled histories

Science.gov (United States)

Cotler, Jordan; Duan, Lu-Ming; Hou, Pan-Yu; Wilczek, Frank; Xu, Da; Yin, Zhang-Qi; Zu, Chong

2017-12-01

Entangled histories arise when a system partially decoheres in such a way that its past cannot be described by a sequence of states, but rather a superposition of sequences of states. Such entangled histories have not been previously observed. We propose and demonstrate the first experimental scheme to create entangled history states of the Greenberger-Horne-Zeilinger (GHZ) type. In our experiment, the polarization states of a single photon at three different times are prepared as a GHZ entangled history state. We define a GHZ functional which attains a maximum value 1 on the ideal GHZ entangled history state and is bounded above by 1 / 16 for any three-time history state lacking tripartite entanglement. We have measured the GHZ functional on a state we have prepared experimentally, yielding a value of 0 . 656 ± 0 . 005, clearly demonstrating the contribution of entangled histories.

Pseudo-entanglement evaluated in noninertial frames

International Nuclear Information System (INIS)

Mehri-Dehnavi, Hossein; Mirza, Behrouz; Mohammadzadeh, Hosein; Rahimi, Robabeh

2011-01-01

Research highlights: → We study pseudo-entanglement in noninertial frames. → We examine different measures of entanglement and nonclassical correlation for the state. → We find the threshold for entanglement is changed in noninertial frames. → We also describe the behavior of local unitary classes of states in noninertial frames. - Abstract: We study quantum discord, in addition to entanglement, of bipartite pseudo-entanglement in noninertial frames. It is shown that the entanglement degrades from its maximum value in a stationary frame to a minimum value in an infinite accelerating frame. There is a critical region found in which, for particular cases, entanglement of states vanishes for certain accelerations. The quantum discord of pseudo-entanglement decreases by increasing the acceleration. Also, for a physically inaccessible region, entanglement and nonclassical correlation are evaluated and shown to match the corresponding values of the physically accessible region for an infinite acceleration.

Entanglement in the Bogoliubov vacuum

DEFF Research Database (Denmark)

Poulsen, Uffe Vestergaard; Meyer, T.; Lewenstein, M.

2005-01-01

We analyze the entanglement properties of the Bogoliubov vacuum, which is obtained as a second-order approximation to the ground state of an interacting Bose-Einstein condensate. We work in one- and two-dimensional lattices and study the entanglement between two groups of sites as a function...... of the geometry of the configuration and the strength of the interactions. As our measure of entanglement we use the logarithmic negativity, supplemented by an algorithmic check for bound entanglement where appropiate. The short-range entanglement is found to grow approximately linearly with the group sizes...

Entangled network and quantum communication

Energy Technology Data Exchange (ETDEWEB)

Metwally, Nasser, E-mail: Nmetwally@gmail.com [Math. Dept., Faculty of Science, South Valley University, Aswan (Egypt); Math. Dept., College of Science, University of Bahrain, P.O. Box 32038 (Bahrain)

2011-11-21

A theoretical scheme is introduced to generate entangled network via Dzyaloshinskii–Moriya (DM) interaction. The dynamics of entanglement between different nodes, which is generated by direct or indirect interaction, is investigated. It is shown that, the direction of (DM) interaction and the locations of the nodes have a sensational effect on the degree of entanglement. The minimum entanglement generated between all the nodes is quantified. The upper and lower bounds of the entanglement depend on the direction of DM interaction, and the repetition of the behavior depends on the strength of DM. The generated entangled nodes are used as quantum channel to perform quantum teleportation, where it is shown that the fidelity of teleporting unknown information between the network members depends on the locations of the members.

Experimental Entanglement Distribution by Separable States

Science.gov (United States)

Vollmer, Christina E.; Schulze, Daniela; Eberle, Tobias; Händchen, Vitus; Fiurášek, Jaromír; Schnabel, Roman

2013-12-01

Distribution of entanglement between macroscopically separated parties is crucial for future quantum information networks. Surprisingly, it has been theoretically shown that two distant systems can be entangled by sending a third system that is not entangled with either of them. Here, we experimentally distribute entanglement and successfully prove that our transmitted light beam is indeed not entangled with the parties’ local systems. Our work demonstrates an unexpected variant of entanglement distribution and improves the understanding necessary to engineer multipartite quantum networks.

Quantum entanglement for systems of identical bosons: II. Spin squeezing and other entanglement tests

International Nuclear Information System (INIS)

Dalton, B J; Goold, J; Garraway, B M; Reid, M D

2017-01-01

These two accompanying papers are concerned with entanglement for systems of identical massive bosons and the relationship to spin squeezing and other quantum correlation effects. The main focus is on two mode entanglement, but multi-mode entanglement is also considered. The bosons may be atoms or molecules as in cold quantum gases. The previous paper I dealt with the general features of quantum entanglement and its specific definition in the case of systems of identical bosons. Entanglement is a property shared between two (or more) quantum sub-systems. In defining entanglement for systems of identical massive particles, it was concluded that the single particle states or modes are the most appropriate choice for sub-systems that are distinguishable, that the general quantum states must comply both with the symmetrization principle and the super-selection rules (SSR) that forbid quantum superpositions of states with differing total particle number (global SSR compliance). Further, it was concluded that (in the separable states) quantum superpositions of sub-system states with differing sub-system particle number (local SSR compliance) also do not occur. The present paper II determines possible tests for entanglement based on the treatment of entanglement set out in paper I. Several inequalities involving variances and mean values of operators have been previously proposed as tests for entanglement between two sub-systems. These inequalities generally involve mode annihilation and creation operators and include the inequalities that define spin squeezing. In this paper, spin squeezing criteria for two mode systems are examined, and spin squeezing is also considered for principle spin operator components where the covariance matrix is diagonal. The proof, which is based on our SSR compliant approach shows that the presence of spin squeezing in any one of the spin components requires entanglement of the relevant pair of modes. A simple Bloch vector test for

Quantum entanglement for systems of identical bosons: II. Spin squeezing and other entanglement tests

Science.gov (United States)

Dalton, B. J.; Goold, J.; Garraway, B. M.; Reid, M. D.

2017-02-01

These two accompanying papers are concerned with entanglement for systems of identical massive bosons and the relationship to spin squeezing and other quantum correlation effects. The main focus is on two mode entanglement, but multi-mode entanglement is also considered. The bosons may be atoms or molecules as in cold quantum gases. The previous paper I dealt with the general features of quantum entanglement and its specific definition in the case of systems of identical bosons. Entanglement is a property shared between two (or more) quantum sub-systems. In defining entanglement for systems of identical massive particles, it was concluded that the single particle states or modes are the most appropriate choice for sub-systems that are distinguishable, that the general quantum states must comply both with the symmetrization principle and the super-selection rules (SSR) that forbid quantum superpositions of states with differing total particle number (global SSR compliance). Further, it was concluded that (in the separable states) quantum superpositions of sub-system states with differing sub-system particle number (local SSR compliance) also do not occur. The present paper II determines possible tests for entanglement based on the treatment of entanglement set out in paper I. Several inequalities involving variances and mean values of operators have been previously proposed as tests for entanglement between two sub-systems. These inequalities generally involve mode annihilation and creation operators and include the inequalities that define spin squeezing. In this paper, spin squeezing criteria for two mode systems are examined, and spin squeezing is also considered for principle spin operator components where the covariance matrix is diagonal. The proof, which is based on our SSR compliant approach shows that the presence of spin squeezing in any one of the spin components requires entanglement of the relevant pair of modes. A simple Bloch vector test for

Entanglement entropy with a time-dependent Hamiltonian

Science.gov (United States)

Sivaramakrishnan, Allic

2018-03-01

The time evolution of entanglement tracks how information propagates in interacting quantum systems. We study entanglement entropy in CFT2 with a time-dependent Hamiltonian. We perturb by operators with time-dependent source functions and use the replica trick to calculate higher-order corrections to entanglement entropy. At first order, we compute the correction due to a metric perturbation in AdS3/CFT2 and find agreement on both sides of the duality. Past first order, we find evidence of a universal structure of entanglement propagation to all orders. The central feature is that interactions entangle unentangled excitations. Entanglement propagates according to "entanglement diagrams," proposed structures that are motivated by accessory spacetime diagrams for real-time perturbation theory. To illustrate the mechanisms involved, we compute higher-order corrections to free fermion entanglement entropy. We identify an unentangled operator, one which does not change the entanglement entropy to any order. Then, we introduce an interaction and find it changes entanglement entropy by entangling the unentangled excitations. The entanglement propagates in line with our conjecture. We compute several entanglement diagrams. We provide tools to simplify the computation of loop entanglement diagrams, which probe UV effects in entanglement propagation in CFT and holography.

Entangled spins and ghost-spins

Directory of Open Access Journals (Sweden)

Dileep P. Jatkar

2017-09-01

Full Text Available We study patterns of quantum entanglement in systems of spins and ghost-spins regarding them as simple quantum mechanical toy models for theories containing negative norm states. We define a single ghost-spin as in [20] as a 2-state spin variable with an indefinite inner product in the state space. We find that whenever the spin sector is disentangled from the ghost-spin sector (both of which could be entangled within themselves, the reduced density matrix obtained by tracing over all the ghost-spins gives rise to positive entanglement entropy for positive norm states, while negative norm states have an entanglement entropy with a negative real part and a constant imaginary part. However when the spins are entangled with the ghost-spins, there are new entanglement patterns in general. For systems where the number of ghost-spins is even, it is possible to find subsectors of the Hilbert space where positive norm states always lead to positive entanglement entropy after tracing over the ghost-spins. With an odd number of ghost-spins however, we find that there always exist positive norm states with negative real part for entanglement entropy after tracing over the ghost-spins.

Interface between path and orbital angular momentum entanglement for high-dimensional photonic quantum information.

Science.gov (United States)

Fickler, Robert; Lapkiewicz, Radek; Huber, Marcus; Lavery, Martin P J; Padgett, Miles J; Zeilinger, Anton

2014-07-30

Photonics has become a mature field of quantum information science, where integrated optical circuits offer a way to scale the complexity of the set-up as well as the dimensionality of the quantum state. On photonic chips, paths are the natural way to encode information. To distribute those high-dimensional quantum states over large distances, transverse spatial modes, like orbital angular momentum possessing Laguerre Gauss modes, are favourable as flying information carriers. Here we demonstrate a quantum interface between these two vibrant photonic fields. We create three-dimensional path entanglement between two photons in a nonlinear crystal and use a mode sorter as the quantum interface to transfer the entanglement to the orbital angular momentum degree of freedom. Thus our results show a flexible way to create high-dimensional spatial mode entanglement. Moreover, they pave the way to implement broad complex quantum networks where high-dimensionally entangled states could be distributed over distant photonic chips.

Error exponents for entanglement concentration

International Nuclear Information System (INIS)

Hayashi, Masahito; Koashi, Masato; Matsumoto, Keiji; Morikoshi, Fumiaki; Winter, Andreas

2003-01-01

Consider entanglement concentration schemes that convert n identical copies of a pure state into a maximally entangled state of a desired size with success probability being close to one in the asymptotic limit. We give the distillable entanglement, the number of Bell pairs distilled per copy, as a function of an error exponent, which represents the rate of decrease in failure probability as n tends to infinity. The formula fills the gap between the least upper bound of distillable entanglement in probabilistic concentration, which is the well-known entropy of entanglement, and the maximum attained in deterministic concentration. The method of types in information theory enables the detailed analysis of the distillable entanglement in terms of the error rate. In addition to the probabilistic argument, we consider another type of entanglement concentration scheme, where the initial state is deterministically transformed into a (possibly mixed) final state whose fidelity to a maximally entangled state of a desired size converges to one in the asymptotic limit. We show that the same formula as in the probabilistic argument is valid for the argument on fidelity by replacing the success probability with the fidelity. Furthermore, we also discuss entanglement yield when optimal success probability or optimal fidelity converges to zero in the asymptotic limit (strong converse), and give the explicit formulae for those cases

The minimal entanglement of bipartite decompositions as a witness of strong entanglement in a quantum system

OpenAIRE

Zenchuk, A. I.

2010-01-01

We {characterize the multipartite entanglement in a quantum system by the quantity} which vanishes if only the quantum system may be decomposed into two weakly entangled subsystems, unlike measures of multipartite entanglement introduced before. We refer to this {quantity} as the minimal entanglement of bipartite decompositions (MEBD). Big MEBD means that the system may not be decomposed into two weakly entangled subsystems. MEBD allows one to define, for instance, whether the given quantum s...

Multipartite entanglement in neutrino oscillations

International Nuclear Information System (INIS)

Blasone, Massimo; Dell'Anno, Fabio; De Siena, Silvio; Illuminati, Fabrizio

2009-01-01

Particle mixing is related to multi-mode entanglement of single-particle states The occupation number of both flavor eigenstates and mass eigenstates can be used to define a multiqubit space. In such a framework, flavor neutrino states can be interpreted as multipartite mode-entangled states. By using two different entanglement measures, we analyze the behavior of multipartite entanglement in the phenomenon of neutrino oscillations.

Multipartite entanglement in neutrino oscillations

Energy Technology Data Exchange (ETDEWEB)

Blasone, Massimo; Dell' Anno, Fabio; De Siena, Silvio; Illuminati, Fabrizio, E-mail: blasone@sa.infn.i [Dipartimento di Matematica e Informatica, Universita degli Studi di Salerno, Via Ponte don Melillo, I-84084 Fisciano (Italy)

2009-06-01

Particle mixing is related to multi-mode entanglement of single-particle states The occupation number of both flavor eigenstates and mass eigenstates can be used to define a multiqubit space. In such a framework, flavor neutrino states can be interpreted as multipartite mode-entangled states. By using two different entanglement measures, we analyze the behavior of multipartite entanglement in the phenomenon of neutrino oscillations.

Geometric multipartite entanglement measures

International Nuclear Information System (INIS)

Paz-Silva, Gerardo A.; Reina, John H.

2007-01-01

Within the framework of constructions for quantifying entanglement, we build a natural scenario for the assembly of multipartite entanglement measures based on Hopf bundle-like mappings obtained through Clifford algebra representations. Then, given the non-factorizability of an arbitrary two-qubit density matrix, we give an alternate quantity that allows the construction of two types of entanglement measures based on their arithmetical and geometrical averages over all pairs of qubits in a register of size N, and thus fully characterize its degree and type of entanglement. We find that such an arithmetical average is both additive and strongly super additive

Holographic entanglement entropy and entanglement thermodynamics of 'black' non-susy D3 brane

Science.gov (United States)

Bhattacharya, Aranya; Roy, Shibaji

2018-06-01

Like BPS D3 brane, the non-supersymmetric (non-susy) D3 brane of type IIB string theory is also known to have a decoupling limit and leads to a non-supersymmetric AdS/CFT correspondence. The throat geometry in this case represents a QFT which is neither conformal nor supersymmetric. The 'black' version of the non-susy D3 brane in the decoupling limit describes a QFT at finite temperature. Here we first compute the entanglement entropy for small subsystem of such QFT from the decoupled geometry of 'black' non-susy D3 brane using holographic technique. Then we study the entanglement thermodynamics for the weakly excited states of this QFT from the asymptotically AdS geometry of the decoupled 'black' non-susy D3 brane. We observe that for small subsystem this background indeed satisfies a first law like relation with a universal (entanglement) temperature inversely proportional to the size of the subsystem and an (entanglement) pressure normal to the entangling surface. Finally we show how the entanglement entropy makes a cross-over to the thermal entropy at high temperature.

Completing the proof of “Generic quantum nonlocality”

Energy Technology Data Exchange (ETDEWEB)

Gachechiladze, Mariami; Gühne, Otfried, E-mail: otfried.guehne@uni-siegen.de

2017-04-18

In a paper by Popescu and Rohrlich a proof has been presented showing that any pure entangled multiparticle quantum state violates some Bell inequality. We point out a gap in this proof, but we also give a construction to close this gap. It turns out that with some extra effort all the results from the aforementioned publication can be proven. Our construction shows how two-particle entanglement can be generated via performing local projections on a multiparticle state. - Highlights: • A proof is completed, showing that any pure entangled multiparticle quantum state violates some Bell inequality. • The results demonstrate how an multi-qubit state can be transformed by local measurements to a two-qubit entangled state. • The extension to higher dimensions is discussed.

Completing the proof of “Generic quantum nonlocality”

International Nuclear Information System (INIS)

Gachechiladze, Mariami; Gühne, Otfried

2017-01-01

In a paper by Popescu and Rohrlich a proof has been presented showing that any pure entangled multiparticle quantum state violates some Bell inequality. We point out a gap in this proof, but we also give a construction to close this gap. It turns out that with some extra effort all the results from the aforementioned publication can be proven. Our construction shows how two-particle entanglement can be generated via performing local projections on a multiparticle state. - Highlights: • A proof is completed, showing that any pure entangled multiparticle quantum state violates some Bell inequality. • The results demonstrate how an multi-qubit state can be transformed by local measurements to a two-qubit entangled state. • The extension to higher dimensions is discussed.

Scheme for entanglement concentration of unknown atomic entangled states by interference of polarized photons

Energy Technology Data Exchange (ETDEWEB)

Wang, Hong-Fu; Zhu, Ai-Dong; Zhang, Shou [Department of Physics, College of Science, Yanbian University, Yanji, Jilin 133002 (China); Yeon, Kyu-Hwang, E-mail: hfwang@ybu.edu.c, E-mail: szhang@ybu.edu.c [Department of Physics and BK21 Program for Device Physics, College of Natural Science, Chungbuk National University, Cheongju, Chungbuk 361-763 (Korea, Republic of)

2010-12-14

Based on the interference effect of polarized photons, we propose a practical scheme for entanglement concentration of unknown atomic entangled states. In the scheme, two {lambda}{lambda}-type atoms belonging to different entangled pairs are individually trapped in two spatially separated cavities. By the subsequent detection of the polarized photons leaking out of the separate optical cavities, Alice and Bob as two distant parties can probabilistically extract one maximally entangled four-atom Greenberger-Horne-Zeilinger (GHZ) state from two identical partially entangled Einstein-Podolsky-Rosen (EPR) pairs. We also discuss the influence of cavity decay on the success probability of the scheme. The scheme is feasible and within the reach of current experimental technology.

Time-To-Complete Prediction for Data Transfers

CERN Document Server

Toler, Wesley

2016-01-01

Currently, there is no prediction provided to users for the amount of time a particular data transfer from one site in the Worldwide LHC Computing Grid to another will take to complete. To develop a time-to-complete prediction, network performance data and per-file information is gathered from two separate databases and fused, and the resulting cleaned data is fitted using random forest regression. Results are shown for two separate links: the link from CERN Data Centre to Brookhaven National Laboratory’s ATLAS data center, and the link from CERN Data Centre to SARA-MATRIX in Amsterdam. A total RMS error of 25.93 minutes between predicted and test data is found for the CERN-PROD -> BNL-ATLAS link, while the CERN-PROD -> SARA-MATRIX link yields a total RMS error of 3.00 minutes.

Squashed entanglement in infinite dimensions

International Nuclear Information System (INIS)

Shirokov, M. E.

2016-01-01

We analyse two possible definitions of the squashed entanglement in an infinite-dimensional bipartite system: direct translation of the finite-dimensional definition and its universal extension. It is shown that the both definitions produce the same lower semicontinuous entanglement measure possessing all basis properties of the squashed entanglement on the set of states having at least one finite marginal entropy. It is also shown that the second definition gives an adequate lower semicontinuous extension of this measure to all states of the infinite-dimensional bipartite system. A general condition relating continuity of the squashed entanglement to continuity of the quantum mutual information is proved and its corollaries are considered. Continuity bound for the squashed entanglement under the energy constraint on one subsystem is obtained by using the tight continuity bound for quantum conditional mutual information (proved in the Appendix by using Winter’s technique). It is shown that the same continuity bound is valid for the entanglement of formation. As a result the asymptotic continuity of the both entanglement measures under the energy constraint on one subsystem is proved.

Volume-law scaling for the entanglement entropy in spin-1/2 chains

International Nuclear Information System (INIS)

Vitagliano, G; Riera, A; Latorre, J I

2010-01-01

Entanglement entropy obeys area law scaling for typical physical quantum systems. This may naively be argued to follow from the locality of interactions. We show that this is not the case by constructing an explicit simple spin chain Hamiltonian with nearest-neighbor interactions that presents an entanglement volume scaling law. This non-translational model is contrived to have couplings that force the accumulation of singlet bonds across the half-chain. This configuration of the couplings is suggested by real-space renormalization group arguments. Computation of the entanglement entropy is performed by mapping the system to free fermions and diagonalizing numerically its correlation matrix. An analytical relationship between the entanglement entropy and the Frobenius norm of the correlation matrix is also established. Our result is complementary to the known relationship between non-translational invariant, nearest-neighbor interacting Hamiltonians and quantum Merlin-Arthur (QMA)-complete problems.

Correcting quantum errors with entanglement.

Science.gov (United States)

Brun, Todd; Devetak, Igor; Hsieh, Min-Hsiu

2006-10-20

We show how entanglement shared between encoder and decoder can simplify the theory of quantum error correction. The entanglement-assisted quantum codes we describe do not require the dual-containing constraint necessary for standard quantum error-correcting codes, thus allowing us to "quantize" all of classical linear coding theory. In particular, efficient modern classical codes that attain the Shannon capacity can be made into entanglement-assisted quantum codes attaining the hashing bound (closely related to the quantum capacity). For systems without large amounts of shared entanglement, these codes can also be used as catalytic codes, in which a small amount of initial entanglement enables quantum communication.

Entangled Cloud Storage

DEFF Research Database (Denmark)

Ateniese, Giuseppe; Dagdelen, Özgür; Damgård, Ivan Bjerre

2012-01-01

keeps the files in it private but still lets each client P_i recover his own data by interacting with S; no cooperation from other clients is needed. At the same time, the cloud provider is discouraged from altering or overwriting any significant part of c as this will imply that none of the clients can......Entangled cloud storage enables a set of clients {P_i} to “entangle” their files {f_i} into a single clew c to be stored by a (potentially malicious) cloud provider S. The entanglement makes it impossible to modify or delete significant part of the clew without affecting all files in c. A clew...... recover their files. We provide theoretical foundations for entangled cloud storage, introducing the notion of an entangled encoding scheme that guarantees strong security requirements capturing the properties above. We also give a concrete construction based on privacy-preserving polynomial interpolation...

Entanglement distribution in quantum networks

International Nuclear Information System (INIS)

Perseguers, Sebastien

2010-01-01

This Thesis contributes to the theory of entanglement distribution in quantum networks, analyzing the generation of long-distance entanglement in particular. We consider that neighboring stations share one partially entangled pair of qubits, which emphasizes the difficulty of creating remote entanglement in realistic settings. The task is then to design local quantum operations at the stations, such that the entanglement present in the links of the whole network gets concentrated between few parties only, regardless of their spatial arrangement. First, we study quantum networks with a two-dimensional lattice structure, where quantum connections between the stations (nodes) are described by non-maximally entangled pure states (links). We show that the generation of a perfectly entangled pair of qubits over an arbitrarily long distance is possible if the initial entanglement of the links is larger than a threshold. This critical value highly depends on the geometry of the lattice, in particular on the connectivity of the nodes, and is related to a classical percolation problem. We then develop a genuine quantum strategy based on multipartite entanglement, improving both the threshold and the success probability of the generation of long-distance entanglement. Second, we consider a mixed-state definition of the connections of the quantum networks. This formalism is well-adapted for a more realistic description of systems in which noise (random errors) inevitably occurs. New techniques are required to create remote entanglement in this setting, and we show how to locally extract and globally process some error syndromes in order to create useful long-distance quantum correlations. Finally, we turn to networks that have a complex topology, which is the case for most real-world communication networks such as the Internet for instance. Besides many other characteristics, these systems have in common the small-world feature, stating that any two nodes are separated by a

Entanglement distribution in quantum networks

Energy Technology Data Exchange (ETDEWEB)

Perseguers, Sebastien

2010-04-15

This Thesis contributes to the theory of entanglement distribution in quantum networks, analyzing the generation of long-distance entanglement in particular. We consider that neighboring stations share one partially entangled pair of qubits, which emphasizes the difficulty of creating remote entanglement in realistic settings. The task is then to design local quantum operations at the stations, such that the entanglement present in the links of the whole network gets concentrated between few parties only, regardless of their spatial arrangement. First, we study quantum networks with a two-dimensional lattice structure, where quantum connections between the stations (nodes) are described by non-maximally entangled pure states (links). We show that the generation of a perfectly entangled pair of qubits over an arbitrarily long distance is possible if the initial entanglement of the links is larger than a threshold. This critical value highly depends on the geometry of the lattice, in particular on the connectivity of the nodes, and is related to a classical percolation problem. We then develop a genuine quantum strategy based on multipartite entanglement, improving both the threshold and the success probability of the generation of long-distance entanglement. Second, we consider a mixed-state definition of the connections of the quantum networks. This formalism is well-adapted for a more realistic description of systems in which noise (random errors) inevitably occurs. New techniques are required to create remote entanglement in this setting, and we show how to locally extract and globally process some error syndromes in order to create useful long-distance quantum correlations. Finally, we turn to networks that have a complex topology, which is the case for most real-world communication networks such as the Internet for instance. Besides many other characteristics, these systems have in common the small-world feature, stating that any two nodes are separated by a

Entanglement entropy and duality

Energy Technology Data Exchange (ETDEWEB)

Radičević, Ðorđe [Stanford Institute for Theoretical Physics and Department of Physics, Stanford University, Stanford, CA 94305-4060 (United States)

2016-11-22

Using the algebraic approach to entanglement entropy, we study several dual pairs of lattice theories and show how the entropy is completely preserved across each duality. Our main result is that a maximal algebra of observables in a region typically dualizes to a non-maximal algebra in a dual region. In particular, we show how the usual notion of tracing out external degrees of freedom dualizes to a tracing out coupled to an additional summation over superselection sectors. We briefly comment on possible extensions of our results to more intricate dualities, including holographic ones.

Cosmological quantum entanglement

International Nuclear Information System (INIS)

Martín-Martínez, Eduardo; Menicucci, Nicolas C

2012-01-01

We review recent literature on the connection between quantum entanglement and cosmology, with an emphasis on the context of expanding universes. We discuss recent theoretical results reporting on the production of entanglement in quantum fields due to the expansion of the underlying spacetime. We explore how these results are affected by the statistics of the field (bosonic or fermionic), the type of expansion (de Sitter or asymptotically stationary), and the coupling to spacetime curvature (conformal or minimal). We then consider the extraction of entanglement from a quantum field by coupling to local detectors and how this procedure can be used to distinguish curvature from heating by their entanglement signature. We review the role played by quantum fluctuations in the early universe in nucleating the formation of galaxies and other cosmic structures through their conversion into classical density anisotropies during and after inflation. We report on current literature attempting to account for this transition in a rigorous way and discuss the importance of entanglement and decoherence in this process. We conclude with some prospects for further theoretical and experimental research in this area. These include extensions of current theoretical efforts, possible future observational pursuits, and experimental analogues that emulate these cosmic effects in a laboratory setting. (paper)

Experimental entanglement distillation of mesoscopic quantum states

DEFF Research Database (Denmark)

Dong, Ruifang; Lassen, Mikael Østergaard; Heersink, Joel

2008-01-01

channel, the distribution of loss-intolerant entangled states is inevitably afflicted by decoherence, which causes a degradation of the transmitted entanglement. To combat the decoherence, entanglement distillation, a process of extracting a small set of highly entangled states from a large set of less...... entangled states, can be used(4-14). Here we report on the distillation of deterministically prepared light pulses entangled in continuous variables that have undergone non-Gaussian noise. The entangled light pulses(15-17) are sent through a lossy channel, where the transmission is varying in time similarly...

Holographic entanglement entropy in two-order insulator/superconductor transitions

Energy Technology Data Exchange (ETDEWEB)

Peng, Yan, E-mail: yanpengphy@163.com; Liu, Guohua

2017-04-10

We study holographic superconductor model with two orders in the five dimensional AdS soliton background away from the probe limit. We disclose properties of phase transitions mostly from the holographic topological entanglement entropy approach. Our results show that the entanglement entropy is useful in investigating transitions in this general model and in particular, there is a new type of first order phase transition in the insulator/superconductor system. We also give some qualitative understanding and obtain the analytical condition for this first order phase transition to occur. As a summary, we draw the complete phase diagram representing effects of the scalar charge on phase transitions.

Entanglement hamiltonian and entanglement contour in inhomogeneous 1D critical systems

Science.gov (United States)

Tonni, Erik; Rodríguez-Laguna, Javier; Sierra, Germán

2018-04-01

Inhomogeneous quantum critical systems in one spatial dimension have been studied by using conformal field theory in static curved backgrounds. Two interesting examples are the free fermion gas in the harmonic trap and the inhomogeneous XX spin chain called rainbow chain. For conformal field theories defined on static curved spacetimes characterised by a metric which is Weyl equivalent to the flat metric, with the Weyl factor depending only on the spatial coordinate, we study the entanglement hamiltonian and the entanglement spectrum of an interval adjacent to the boundary of a segment where the same boundary condition is imposed at the endpoints. A contour function for the entanglement entropies corresponding to this configuration is also considered, being closely related to the entanglement hamiltonian. The analytic expressions obtained by considering the curved spacetime which characterises the rainbow model have been checked against numerical data for the rainbow chain, finding an excellent agreement.

Continuous-Variable Entanglement Swapping

Directory of Open Access Journals (Sweden)

Kevin Marshall

2015-05-01

Full Text Available We present a very brief overview of entanglement swapping as it relates to continuous-variable quantum information. The technical background required is discussed and the natural link to quantum teleportation is established before discussing the nature of Gaussian entanglement swapping. The limitations of Gaussian swapping are introduced, along with the general applications of swapping in the context of to quantum communication and entanglement distribution. In light of this, we briefly summarize a collection of entanglement swapping schemes which incorporate a non-Gaussian ingredient and the benefits of such schemes are noted. Finally, we motivate the need to further study and develop such schemes by highlighting requirements of a continuous-variable repeater.

Entanglement criterion for tripartite systems based on local sum uncertainty relations

Science.gov (United States)

Akbari-Kourbolagh, Y.; Azhdargalam, M.

2018-04-01

We propose a sufficient criterion for the entanglement of tripartite systems based on local sum uncertainty relations for arbitrarily chosen observables of subsystems. This criterion generalizes the tighter criterion for bipartite systems introduced by Zhang et al. [C.-J. Zhang, H. Nha, Y.-S. Zhang, and G.-C. Guo, Phys. Rev. A 81, 012324 (2010), 10.1103/PhysRevA.81.012324] and can be used for both discrete- and continuous-variable systems. It enables us to detect the entanglement of quantum states without having a complete knowledge of them. Its utility is illustrated by some examples of three-qubit, qutrit-qutrit-qubit, and three-mode Gaussian states. It is found that, in comparison with other criteria, this criterion is able to detect some three-qubit bound entangled states more efficiently.

Holographic Entanglement Entropy

CERN Document Server

Rangamani, Mukund

2016-01-01

We review the developments in the past decade on holographic entanglement entropy, a subject that has garnered much attention owing to its potential to teach us about the emergence of spacetime in holography. We provide an introduction to the concept of entanglement entropy in quantum field theories, review the holographic proposals for computing the same, providing some justification for where these proposals arise from in the first two parts. The final part addresses recent developments linking entanglement and geometry. We provide an overview of the various arguments and technical developments that teach us how to use field theory entanglement to detect geometry. Our discussion is by design eclectic; we have chosen to focus on developments that appear to us most promising for further insights into the holographic map. This is a preliminary draft of a few chapters of a book which will appear sometime in the near future, to be published by Springer. The book in addition contains a discussion of application o...

Multipartite entanglement and firewalls

Science.gov (United States)

Luo, Shengqiao; Stoltenberg, Henry; Albrecht, Andreas

2017-03-01

Black holes offer an exciting area to explore the nature of quantum gravity. The classic work on Hawking radiation indicates that black holes should decay via quantum effects, but our ideas about how this might work at a technical level are incomplete. Recently Almheiri-Marolf-Polchinski-Sully (AMPS) have noted an apparent paradox in reconciling fundamental properties of quantum mechanics with standard beliefs about black holes. One way to resolve the paradox is to postulate the existence of a "firewall" inside the black hole horizon which prevents objects from falling smoothly toward the singularity. A fundamental limitation on the behavior of quantum entanglement known as "monogamy" plays a key role in the AMPS argument. Our goal is to study and apply many-body entanglement theory to consider the entanglement among different parts of Hawking radiation and black holes. Using the multipartite entanglement measure called negativity, we identify an example which could change the AMPS accounting of quantum entanglement and perhaps eliminate the need for a firewall. Specifically, we constructed a toy model for black hole decay which has different entanglement behavior than that assumed by AMPS. We discuss the additional steps that would be needed to bring lessons from our toy model to our understanding of realistic black holes.

Entanglement in Gaussian matrix-product states

International Nuclear Information System (INIS)

Adesso, Gerardo; Ericsson, Marie

2006-01-01

Gaussian matrix-product states are obtained as the outputs of projection operations from an ancillary space of M infinitely entangled bonds connecting neighboring sites, applied at each of N sites of a harmonic chain. Replacing the projections by associated Gaussian states, the building blocks, we show that the entanglement range in translationally invariant Gaussian matrix-product states depends on how entangled the building blocks are. In particular, infinite entanglement in the building blocks produces fully symmetric Gaussian states with maximum entanglement range. From their peculiar properties of entanglement sharing, a basic difference with spin chains is revealed: Gaussian matrix-product states can possess unlimited, long-range entanglement even with minimum number of ancillary bonds (M=1). Finally we discuss how these states can be experimentally engineered from N copies of a three-mode building block and N two-mode finitely squeezed states

Quantum entanglement via nilpotent polynomials

International Nuclear Information System (INIS)

Mandilara, Aikaterini; Akulin, Vladimir M.; Smilga, Andrei V.; Viola, Lorenza

2006-01-01

We propose a general method for introducing extensive characteristics of quantum entanglement. The method relies on polynomials of nilpotent raising operators that create entangled states acting on a reference vacuum state. By introducing the notion of tanglemeter, the logarithm of the state vector represented in a special canonical form and expressed via polynomials of nilpotent variables, we show how this description provides a simple criterion for entanglement as well as a universal method for constructing the invariants characterizing entanglement. We compare the existing measures and classes of entanglement with those emerging from our approach. We derive the equation of motion for the tanglemeter and, in representative examples of up to four-qubit systems, show how the known classes appear in a natural way within our framework. We extend our approach to qutrits and higher-dimensional systems, and make contact with the recently introduced idea of generalized entanglement. Possible future developments and applications of the method are discussed

Quantum entanglement of identical particles

International Nuclear Information System (INIS)

Shi Yu

2003-01-01

We consider entanglement in a system with a fixed number of identical particles. Since any operation should be symmetrized over all the identical particles and there is the precondition that the spatial wave functions overlap, the meaning of identical-particle entanglement is fundamentally different from that of distinguishable particles. The identical-particle counterpart of the Schmidt basis is shown to be the single-particle basis in which the one-particle reduced density matrix is diagonal. But it does not play a special role in the issue of entanglement, which depends on the single-particle basis chosen. The nonfactorization due to (anti)symmetrization is naturally excluded by using the (anti)symmetrized basis or, equivalently, the particle number representation. The natural degrees of freedom in quantifying the identical-particle entanglement in a chosen single-particle basis are occupation numbers of different single-particle basis states. The entanglement between effectively distinguishable spins is shown to be a special case of the occupation-number entanglement

Entanglement conservation, ER=EPR, and a new classical area theorem for wormholes

Energy Technology Data Exchange (ETDEWEB)

Remmen, Grant N. [Walter Burke Institute for Theoretical PhysicsCalifornia Institute of Technology, Pasadena, CA 91125 (United States); Bao, Ning [Walter Burke Institute for Theoretical PhysicsCalifornia Institute of Technology, Pasadena, CA 91125 (United States); Institute for Quantum Information and Matter,California Institute of Technology, Pasadena, CA 91125 (United States); Pollack, Jason [Walter Burke Institute for Theoretical PhysicsCalifornia Institute of Technology, Pasadena, CA 91125 (United States)

2016-07-11

We consider the question of entanglement conservation in the context of the ER=EPR correspondence equating quantum entanglement with wormholes. In quantum mechanics, the entanglement between a system and its complement is conserved under unitary operations that act independently on each; ER=EPR suggests that an analogous statement should hold for wormholes. We accordingly prove a new area theorem in general relativity: for a collection of dynamical wormholes and black holes in a spacetime satisfying the null curvature condition, the maximin area for a subset of the horizons (giving the largest area attained by the minimal cross section of the multi-wormhole throat separating the subset from its complement) is invariant under classical time evolution along the outermost apparent horizons. The evolution can be completely general, including horizon mergers and the addition of classical matter satisfying the null energy condition. This theorem is the gravitational dual of entanglement conservation and thus constitutes an explicit characterization of the ER=EPR duality in the classical limit.

Entanglement rules for holographic Fermi surfaces

Directory of Open Access Journals (Sweden)

Dibakar Roychowdhury

2016-08-01

Full Text Available In this paper, based on the notion of Gauge/Gravity duality, we explore the laws of entanglement thermodynamics for most generic classes of Quantum Field Theories with hyperscaling violation. In our analysis, we note that for Quantum Field Theories with compressible quark like excitation, the first law of entanglement thermodynamics gets modified due to the presence of an additional term that could be identified as the entanglement chemical potential associated with hidden Fermi surfaces of the boundary theory. Most notably, we find that the so called entanglement chemical potential does not depend on the size of the entangling region and is purely determined by the quark d.o.f. encoded within the entangling region.

Entanglement rules for holographic Fermi surfaces

Energy Technology Data Exchange (ETDEWEB)

Roychowdhury, Dibakar, E-mail: dibakarphys@gmail.com

2016-08-15

In this paper, based on the notion of Gauge/Gravity duality, we explore the laws of entanglement thermodynamics for most generic classes of Quantum Field Theories with hyperscaling violation. In our analysis, we note that for Quantum Field Theories with compressible quark like excitation, the first law of entanglement thermodynamics gets modified due to the presence of an additional term that could be identified as the entanglement chemical potential associated with hidden Fermi surfaces of the boundary theory. Most notably, we find that the so called entanglement chemical potential does not depend on the size of the entangling region and is purely determined by the quark d.o.f. encoded within the entangling region.

Entanglement in a parametric converter

Energy Technology Data Exchange (ETDEWEB)

Lee, Su-Yong; Qamar, Shahid; Lee, Hai-Woong; Zubairy, M Suhail [Center for Quantum Physics, COMSATS Institute of Information Technology, Islamabad (Pakistan)], E-mail: shahid_qamar@pieas.edu.pk, E-mail: zubairy@physics.tamu.edu

2008-07-28

In this paper, we consider a parametric converter as a source of entangled radiation. We examine recently derived conditions (Hillery and Zubairy 2006 Phys. Rev. Lett. 96 050503, Duan et al 2000 Phys. Rev. Lett. 84 2722) for determining when the two output modes in a parametric converter are entangled. We show that for different initial field states, the two criteria give different conditions that ensure that the output states are entangled. We also present an input-output calculation for the entanglement of the output field.

Quantum entanglement helps in improving economic efficiency

International Nuclear Information System (INIS)

Du Jiangfeng; Ju Chenyong; Li Hui

2005-01-01

We propose an economic regulation approach based on quantum game theory for the government to reduce the abuses of oligopolistic competition. Theoretical analysis shows that this approach can help government improve the economic efficiency of the oligopolistic market, and help prevent monopoly due to incorrect information. These advantages are completely attributed to the quantum entanglement, a unique quantum mechanical character

Quantum entanglement helps in improving economic efficiency

Science.gov (United States)

Du, Jiangfeng; Ju, Chenyong; Li, Hui

2005-02-01

We propose an economic regulation approach based on quantum game theory for the government to reduce the abuses of oligopolistic competition. Theoretical analysis shows that this approach can help government improve the economic efficiency of the oligopolistic market, and help prevent monopoly due to incorrect information. These advantages are completely attributed to the quantum entanglement, a unique quantum mechanical character.

Energy localization in maximally entangled two- and three-qubit phase space

International Nuclear Information System (INIS)

Pashaev, Oktay K; Gurkan, Zeynep N

2012-01-01

Motivated by the Möbius transformation for symmetric points under the generalized circle in the complex plane, the system of symmetric spin coherent states corresponding to antipodal qubit states is introduced. In terms of these states, we construct the maximally entangled complete set of two-qubit coherent states, which in the limiting cases reduces to the Bell basis. A specific property of our symmetric coherent states is that they never become unentangled for any value of ψ from the complex plane. Entanglement quantifications of our states are given by the reduced density matrix and the concurrence determinant, and it is shown that our basis is maximally entangled. Universal one- and two-qubit gates in these new coherent state basis are calculated. As an application, we find the Q symbol of the XY Z model Hamiltonian operator H as an average energy function in maximally entangled two- and three-qubit phase space. It shows regular finite-energy localized structure with specific local extremum points. The concurrence and fidelity of quantum evolution with dimerization of double periodic patterns are given. (paper)

Hawking radiation, entanglement, and teleportation in the background of an asymptotically flat static black hole

International Nuclear Information System (INIS)

Pan Qiyuan; Jing Jiliang

2008-01-01

The effect of the Hawking temperature on the entanglement and teleportation for the scalar field in a most general, static, and asymptotically flat black hole with spherical symmetry has been investigated. It has been shown that the same 'initial entanglement' for the state parameter α and its 'normalized partners'√(1-α 2 ) will be degraded by the Hawking effect with increasing Hawking temperature along two different trajectories except for the maximally entangled state. In the infinite Hawking temperature limit, corresponding to the case of the black hole evaporating completely, the state no longer has distillable entanglement for any α. It is interesting to note that the mutual information in this limit is equal to just half of the 'initially mutual information'. It has also been demonstrated that the fidelity of teleportation decreases as the Hawking temperature increases, which indicates the degradation of entanglement.

Classical-driving-assisted entanglement dynamics control

Energy Technology Data Exchange (ETDEWEB)

Zhang, Ying-Jie, E-mail: yingjiezhang@qfnu.edu.cn [Shandong Provincial Key Laboratory of Laser Polarization and Information Technology, Department of Physics, Qufu Normal University, Qufu 273165 (China); Han, Wei [Shandong Provincial Key Laboratory of Laser Polarization and Information Technology, Department of Physics, Qufu Normal University, Qufu 273165 (China); Xia, Yun-Jie, E-mail: yjxia@qfnu.edu.cn [Shandong Provincial Key Laboratory of Laser Polarization and Information Technology, Department of Physics, Qufu Normal University, Qufu 273165 (China); Fan, Heng, E-mail: hfan@iphy.ac.cn [Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190 (China); Collaborative Innovation Center of Quantum Matter, Beijing, 100190 (China)

2017-04-15

We propose a scheme of controlling entanglement dynamics of a quantum system by applying the external classical driving field for two atoms separately located in a single-mode photon cavity. It is shown that, with a judicious choice of the classical-driving strength and the atom–photon detuning, the effective atom–photon interaction Hamiltonian can be switched from Jaynes–Cummings model to anti-Jaynes–Cummings model. By tuning the controllable atom–photon interaction induced by the classical field, we illustrate that the evolution trajectory of the Bell-like entanglement states can be manipulated from entanglement-sudden-death to no-entanglement-sudden-death, from no-entanglement-invariant to entanglement-invariant. Furthermore, the robustness of the initial Bell-like entanglement can be improved by the classical driving field in the leaky cavities. This classical-driving-assisted architecture can be easily extensible to multi-atom quantum system for scalability.

Manipulation of entanglement and its realisation using trapped ions

International Nuclear Information System (INIS)

Jonathan, Daniel

2001-01-01

Entanglement is a fundamental physical resource at the heart of quantum information theory. This Thesis contributes to its study by approaching it from two separate directions: the laws governing its manipulation, and its creation within a concrete physical setting. I begin by studying the manipulation of entangled pure states of two quantum systems when (i) only a single copy of each system is available and (ii) only a restricted class of physical operations are allowed to be performed on them. One physically reasonable class, denoted LQCC, is the set of all possible quantum operations realised on each system by local agents, who are allowed to communicate with each other only by classical means. Given these conditions, I find a minimal set of entropic-like state functions that completely determine which manipulations can be realised. Applications to useful protocols such as entanglement concentration are discussed. Further elaboration allows also the determination of the most faithful approximation to a given target state that can be attained under LQCC, and the most faithful teleportation protocol achievable when only partial entanglement is available. The study of a more general class of transformations demonstrates that entanglement can also be a re-usable resource. Specifically, I show that the mere presence of further entanglement allows the realisation of transformations which are impossible under LQCC alone. The extra entanglement is not consumed in any way, acting as a 'catalyst'. Applications of this counter-intuitive effect are discussed. In the second part of the Thesis, I turn to the concrete creation and manipulation of entanglement within the system of laser-cooled, trapped ions. After a brief survey of known schemes, I propose a new method for realising two-qubit quantum logic gates within this system. The scheme is based on the AC Stark shift (lightshift) induced by laser light resonant with the ionic transition frequency. At specific laser

Transverse entanglement migration in Hilbert space

International Nuclear Information System (INIS)

Chan, K. W.; Torres, J. P.; Eberly, J. H.

2007-01-01

We show that, although the amount of mutual entanglement of photons propagating in free space is fixed, the type of correlations between the photons that determine the entanglement can dramatically change during propagation. We show that this amounts to a migration of entanglement in Hilbert space, rather than real space. For the case of spontaneous parametric down-conversion, the migration of entanglement in transverse coordinates takes place from modulus to phase of the biphoton state and back again. We propose an experiment to observe this migration in Hilbert space and to determine the full entanglement

Inter-Universal Quantum Entanglement

Science.gov (United States)

Robles-Pérez, S. J.; González-Díaz, P. F.

2015-01-01

The boundary conditions to be imposed on the quantum state of the whole multiverse could be such that the universes would be created in entangled pairs. Then, interuniversal entanglement would provide us with a vacuum energy for each single universe that might be fitted with observational data, making testable not only the multiverse proposal but also the boundary conditions of the multiverse. Furthermore, the second law of the entanglement thermodynamics would enhance the expansion of the single universes.

Entanglement as a signature of quantum chaos.

Science.gov (United States)

Wang, Xiaoguang; Ghose, Shohini; Sanders, Barry C; Hu, Bambi

2004-01-01

We explore the dynamics of entanglement in classically chaotic systems by considering a multiqubit system that behaves collectively as a spin system obeying the dynamics of the quantum kicked top. In the classical limit, the kicked top exhibits both regular and chaotic dynamics depending on the strength of the chaoticity parameter kappa in the Hamiltonian. We show that the entanglement of the multiqubit system, considered for both the bipartite and the pairwise entanglement, yields a signature of quantum chaos. Whereas bipartite entanglement is enhanced in the chaotic region, pairwise entanglement is suppressed. Furthermore, we define a time-averaged entangling power and show that this entangling power changes markedly as kappa moves the system from being predominantly regular to being predominantly chaotic, thus sharply identifying the edge of chaos. When this entangling power is averaged over all states, it yields a signature of global chaos. The qualitative behavior of this global entangling power is similar to that of the classical Lyapunov exponent.

Searching for highly entangled multi-qubit states

International Nuclear Information System (INIS)

Brown, Iain D K; Stepney, Susan; Sudbery, Anthony; Braunstein, Samuel L

2005-01-01

We present a simple numerical optimization procedure to search for highly entangled states of 2, 3, 4 and 5 qubits. We develop a computationally tractable entanglement measure based on the negative partial transpose criterion, which can be applied to quantum systems of an arbitrary number of qubits. The search algorithm attempts to optimize this entanglement cost function to find the maximal entanglement in a quantum system. We present highly entangled 4-qubit and 5-qubit states discovered by this search. We show that the 4-qubit state is not quite as entangled, according to two separate measures, as the conjectured maximally entangled Higuchi-Sudbery state. Using this measure, these states are more highly entangled than the 4-qubit and 5-qubit GHZ states. We also present a conjecture about the NPT measure, inspired by some of our numerical results, that the single-qubit reduced states of maximally entangled states are all totally mixed

Entanglement property in matrix product spin systems

International Nuclear Information System (INIS)

Zhu Jingmin

2012-01-01

We study the entanglement property in matrix product spin-ring systems systemically by von Neumann entropy. We find that: (i) the Hilbert space dimension of one spin determines the upper limit of the maximal value of the entanglement entropy of one spin, while for multiparticle entanglement entropy, the upper limit of the maximal value depends on the dimension of the representation matrices. Based on the theory, we can realize the maximum of the entanglement entropy of any spin block by choosing the appropriate control parameter values. (ii) When the entanglement entropy of one spin takes its maximal value, the entanglement entropy of an asymptotically large spin block, i.e. the renormalization group fixed point, is not likely to take its maximal value, and so only the entanglement entropy S n of a spin block that varies with size n can fully characterize the spin-ring entanglement feature. Finally, we give the entanglement dynamics, i.e. the Hamiltonian of the matrix product system. (author)

Optimization of entanglement witnesses

Science.gov (United States)

Lewenstein, M.; Kraus, B.; Cirac, J. I.; Horodecki, P.

2000-11-01

An entanglement witness (EW) is an operator that allows the detection of entangled states. We give necessary and sufficient conditions for such operators to be optimal, i.e., to detect entangled states in an optimal way. We show how to optimize general EW, and then we particularize our results to the nondecomposable ones; the latter are those that can detect positive partial transpose entangled states (PPTES's). We also present a method to systematically construct and optimize this last class of operators based on the existence of ``edge'' PPTES's, i.e., states that violate the range separability criterion [Phys. Lett. A 232, 333 (1997)] in an extreme manner. This method also permits a systematic construction of nondecomposable positive maps (PM's). Our results lead to a sufficient condition for entanglement in terms of nondecomposable EW's and PM's. Finally, we illustrate our results by constructing optimal EW acting on H=C2⊗C4. The corresponding PM's constitute examples of PM's with minimal ``qubit'' domains, or-equivalently-minimal Hermitian conjugate codomains.

Universal distortion-free entanglement concentration

International Nuclear Information System (INIS)

Matsumoto, Keiji; Hayashi, Masahito

2007-01-01

We propose a new protocol of universal entanglement concentration, which converts many copies of an unknown pure state to an exact maximally entangled state. The yield of the protocol, which is outputted as a classical information, is probabilistic, and achieves the entropy rate with high probability, just as nonuniversal entanglement concentration protocols do

Universal entanglement transformations without communication

International Nuclear Information System (INIS)

Dam, Wim van; Hayden, Patrick

2003-01-01

We show that in the presence of finite catalysts, any pure bipartite entangled state can be converted into any other, to unlimited accuracy, without the use of any communication, quantum or classical. We call this process embezzling entanglement because it involves removing a small amount of entanglement from the catalyst in a physically unnoticeable way

Thermodynamic entanglement of magnonic condensates

Science.gov (United States)

Yuan, H. Y.; Yung, Man-Hong

2018-02-01

Over the past decade, significant progress has been achieved to create Bose-Einstein condensates (BECs) of magnetic excitations, i.e., magnons, at room temperature, which is a novel quantum many-body system with a strong spin-spin correlation, and contains potential applications in magnonic spintronics. For quantum information science, the magnonic condensates can become an attractive source of quantum entanglement, which plays a central role in most of the quantum information processing tasks. Here we theoretically study the entanglement properties of a magnon gas above and below the condensation temperature. We show that the thermodynamic entanglement of the spins is a manifestation of the off-diagonal long-range order; the entanglement of the condensate does not vanish, even if the spins are separated by an infinitely long distance, which is fundamentally distinct from the normal magnetic ordering below the Curie temperature. In addition, the phase-transition point occurs when the derivative of the entanglement changes abruptly. These results provide a theoretical foundation for a future investigation of the magnon BEC in terms of quantum entanglement.

Residual entanglement and sudden death: A direct connection

International Nuclear Information System (INIS)

Oliveira, J.G.G. de; Peixoto de Faria, J.G.; Nemes, M.C.

2011-01-01

We explore the results of [V. Coffman, et al., Phys. Rev. A 61 (2000) 052306] derived for general tripartite states in a dynamical context. We study a class of physically motivated tripartite systems. We show that whenever entanglement sudden death occurs in one of the partitions residual entanglement will appear. For fourpartite systems however, the appearance of residual entanglement is not conditioned by sudden death of entanglement. We can only say that if sudden death of entanglement occurs in some partition there will certainly be residual entanglement. -- Highlights: ► For tripartite systems we show there exists residual entanglement if sudden death occurs. ► For fourpartite systems, the residual entanglement is not conditioned by sudden death. ► If sudden death of entanglement occurs there will certainly be residual entanglement.

Minimal Entanglement Witness from Electrical Current Correlations.

Science.gov (United States)

Brange, F; Malkoc, O; Samuelsson, P

2017-01-20

Despite great efforts, an unambiguous demonstration of entanglement of mobile electrons in solid state conductors is still lacking. Investigating theoretically a generic entangler-detector setup, we here show that a witness of entanglement between two flying electron qubits can be constructed from only two current cross correlation measurements, for any nonzero detector efficiencies and noncollinear polarization vectors. We find that all entangled pure states, but not all mixed ones, can be detected with only two measurements, except the maximally entangled states, which require three. Moreover, detector settings for optimal entanglement witnessing are presented.

Optimal entanglement witnesses for qubits and qutrits

Science.gov (United States)

Bertlmann, Reinhold A.; Durstberger, Katharina; Hiesmayr, Beatrix C.; Krammer, Philipp

2005-11-01

We study the connection between the Hilbert-Schmidt measure of entanglement (that is the minimal distance of an entangled state to the set of separable states) and entanglement witness in terms of a generalized Bell inequality which distinguishes between entangled and separable states. A method for checking the nearest separable state to a given entangled one is presented. We illustrate the general results by considering isotropic states, in particular two-qubit and two-qutrit states—and their generalizations to arbitrary dimensions—where we calculate the optimal entanglement witnesses explicitly.

Optimal entanglement witnesses for qubits and qutrits

International Nuclear Information System (INIS)

Bertlmann, Reinhold A.; Durstberger, Katharina; Hiesmayr, Beatrix C.; Krammer, Philipp

2005-01-01

We study the connection between the Hilbert-Schmidt measure of entanglement (that is the minimal distance of an entangled state to the set of separable states) and entanglement witness in terms of a generalized Bell inequality which distinguishes between entangled and separable states. A method for checking the nearest separable state to a given entangled one is presented. We illustrate the general results by considering isotropic states, in particular two-qubit and two-qutrit states--and their generalizations to arbitrary dimensions--where we calculate the optimal entanglement witnesses explicitly

Minimal Entanglement Witness from Electrical Current Correlations

Science.gov (United States)

Brange, F.; Malkoc, O.; Samuelsson, P.

2017-01-01

Despite great efforts, an unambiguous demonstration of entanglement of mobile electrons in solid state conductors is still lacking. Investigating theoretically a generic entangler-detector setup, we here show that a witness of entanglement between two flying electron qubits can be constructed from only two current cross correlation measurements, for any nonzero detector efficiencies and noncollinear polarization vectors. We find that all entangled pure states, but not all mixed ones, can be detected with only two measurements, except the maximally entangled states, which require three. Moreover, detector settings for optimal entanglement witnessing are presented.

Experimental distribution of entanglement with separable carriers

Science.gov (United States)

Fedrizzi, Alessandro; Zuppardo, Margherita; Gillett, Geoff; Broome, Matthew; de Almeida, Marcelo; Paternostro, Mauro; White, Andrew; Paterek, Tomasz

2014-03-01

Quantum networks will allow us to overcome distance limitations in quantum communication, and to share quantum computing tasks between remote quantum processors. The key requirement for quantum networking is the distribution of entanglement between nodes. Surprisingly, entanglement can be generated across a network without directly being communicated between nodes. In contrast to information gain, which cannot exceed the communicated information, the entanglement gain is bounded by the communicated quantum discord, a more general measure of quantum correlation that includes but is not limited to entanglement. Here we report an experiment in which two communicating parties who share three initially separable photonic qubits are entangled by exchange of a carrier photon that is not entangled with either party at all times. We show that distributing entanglement with separable carriers is resilient to noise and in some cases becomes the only way of distributing entanglement over noisy environments.

Graphical Classification of Entangled Qutrits

Directory of Open Access Journals (Sweden)

Kentaro Honda

2012-10-01

Full Text Available A multipartite quantum state is entangled if it is not separable. Quantum entanglement plays a fundamental role in many applications of quantum information theory, such as quantum teleportation. Stochastic local quantum operations and classical communication (SLOCC cannot essentially change quantum entanglement without destroying it. Therefore, entanglement can be classified by dividing quantum states into equivalence classes, where two states are equivalent if each can be converted into the other by SLOCC. Properties of this classification, especially in the case of non two-dimensional quantum systems, have not been well studied. Graphical representation is sometimes used to clarify the nature and structural features of entangled states. SLOCC equivalence of quantum bits (qubits has been described graphically via a connection between tripartite entangled qubit states and commutative Frobenius algebras (CFAs in monoidal categories. In this paper, we extend this method to qutrits, i.e., systems that have three basis states. We examine the correspondence between CFAs and tripartite entangled qutrits. Using the symmetry property, which is required by the definition of a CFA, we find that there are only three equivalence classes that correspond to CFAs. We represent qutrits graphically, using the connection to CFAs. We derive equations that characterize the three equivalence classes. Moreover, we show that any qutrit can be represented as a composite of three graphs that correspond to the three classes.

On entanglement entropy in non-Abelian lattice gauge theory and 3D quantum gravity

Energy Technology Data Exchange (ETDEWEB)

Delcamp, Clement [Perimeter Institute for Theoretical Physics,31 Caroline Street North, Waterloo, Ontario N2L 2Y5 (Canada); Department of Physics & Astronomy and Guelph-Waterloo Physics Institute, University of Waterloo,200 University Avenue West, Waterloo, Ontario N2L 3G1 (Canada); Dittrich, Bianca; Riello, Aldo [Perimeter Institute for Theoretical Physics,31 Caroline Street North, Waterloo, Ontario N2L 2Y5 (Canada)

2016-11-18

Entanglement entropy is a valuable tool for characterizing the correlation structure of quantum field theories. When applied to gauge theories, subtleties arise which prevent the factorization of the Hilbert space underlying the notion of entanglement entropy. Borrowing techniques from extended topological field theories, we introduce a new definition of entanglement entropy for both Abelian and non-Abelian gauge theories. Being based on the notion of excitations, it provides a completely relational way of defining regions. Therefore, it naturally applies to background independent theories, e.g. gravity, by circumventing the difficulty of specifying the position of the entangling surface. We relate our construction to earlier proposals and argue that it brings these closer to each other. In particular, it yields the non-Abelian analogue of the ‘magnetic centre choice’, as obtained through an extended-Hilbert-space method, but applied to the recently introduced fusion basis for 3D lattice gauge theories. We point out that the different definitions of entanglement entropy can be related to a choice of (squeezed) vacuum state.

Entanglement in a Dimerized Antiferromagnetic Heisenberg Chain

OpenAIRE

Hao, Xiang; Zhu, Shiqun

2008-01-01

The entanglement properties in an antiferromagnetic dimerized Heisenberg spin-1/2 chain are investigated. The entanglement gap, which is the difference between the ground-state energy and the minimal energy that any separable state can attain, is calculated to detect the entanglement. It is found that the entanglement gap can be increased by varying the alternation parameter. Through thermal energy, the witness of the entanglement can determine a characteristic temperature below that an entan...

Witnessing entanglement by proxy

International Nuclear Information System (INIS)

Bäuml, Stefan; Bruß, Dagmar; Kampermann, Hermann; Huber, Marcus; Winter, Andreas

2016-01-01

Entanglement is a ubiquitous feature of low temperature systems and believed to be highly relevant for the dynamics of condensed matter properties and quantum computation even at higher temperatures. The experimental certification of this paradigmatic quantum effect in macroscopic high temperature systems is constrained by the limited access to the quantum state of the system. In this paper we show how macroscopic observables beyond the mean energy of the system can be exploited as proxy witnesses for entanglement detection. Using linear and semi-definite relaxations we show that all previous approaches to this problem can be outperformed by our proxies, i.e. entanglement can be certified at higher temperatures without access to any local observable. For an efficient computation of proxy witnesses one can resort to a generalised grand canonical ensemble, enabling entanglement certification even in complex systems with macroscopic particle numbers. (paper)

From entanglement witness to generalized Catalan numbers

Science.gov (United States)

Cohen, E.; Hansen, T.; Itzhaki, N.

2016-07-01

Being extremely important resources in quantum information and computation, it is vital to efficiently detect and properly characterize entangled states. We analyze in this work the problem of entanglement detection for arbitrary spin systems. It is demonstrated how a single measurement of the squared total spin can probabilistically discern separable from entangled many-particle states. For achieving this goal, we construct a tripartite analogy between the degeneracy of entanglement witness eigenstates, tensor products of SO(3) representations and classical lattice walks with special constraints. Within this framework, degeneracies are naturally given by generalized Catalan numbers and determine the fraction of states that are decidedly entangled and also known to be somewhat protected against decoherence. In addition, we introduce the concept of a “sterile entanglement witness”, which for large enough systems detects entanglement without affecting much the system’s state. We discuss when our proposed entanglement witness can be regarded as a sterile one.

Continuous variable polarization entanglement, experiment and analysis

International Nuclear Information System (INIS)

Bowen, Warwick P; Treps, Nicolas; Schnabel, Roman; Ralph, Timothy C; Lam, Ping Koy

2003-01-01

We generate and characterize continuous variable polarization entanglement between two optical beams. We first produce quadrature entanglement, and by performing local operations we transform it into a polarization basis. We extend two entanglement criteria, the inseparability criteria proposed by Duan et al (2000 Phys. Rev. Lett. 84 2722) and the Einstein-Podolsky-Rosen (EPR) paradox criteria proposed by Reid and Drummond (1988 Phys. Rev. Lett. 60 2731), to Stokes operators; and use them to characterize the entanglement. Our results for the EPR paradox criteria are visualized in terms of uncertainty balls on the Poincare sphere. We demonstrate theoretically that using two quadrature entangled pairs it is possible to entangle three orthogonal Stokes operators between a pair of beams, although with a bound √3 times more stringent than for the quadrature entanglement

Continuous variable polarization entanglement, experiment and analysis

Energy Technology Data Exchange (ETDEWEB)

Bowen, Warwick P [Department of Physics, Faculty of Science, Australian National University, ACT 0200 (Australia); Treps, Nicolas [Department of Physics, Faculty of Science, Australian National University, ACT 0200 (Australia); Schnabel, Roman [Department of Physics, Faculty of Science, Australian National University, ACT 0200 (Australia); Ralph, Timothy C [Department of Physics, Centre for Quantum Computer Technology, University of Queensland, St Lucia, QLD 4072 (Australia); Lam, Ping Koy [Department of Physics, Faculty of Science, Australian National University, ACT 0200 (Australia)

2003-08-01

We generate and characterize continuous variable polarization entanglement between two optical beams. We first produce quadrature entanglement, and by performing local operations we transform it into a polarization basis. We extend two entanglement criteria, the inseparability criteria proposed by Duan et al (2000 Phys. Rev. Lett. 84 2722) and the Einstein-Podolsky-Rosen (EPR) paradox criteria proposed by Reid and Drummond (1988 Phys. Rev. Lett. 60 2731), to Stokes operators; and use them to characterize the entanglement. Our results for the EPR paradox criteria are visualized in terms of uncertainty balls on the Poincare sphere. We demonstrate theoretically that using two quadrature entangled pairs it is possible to entangle three orthogonal Stokes operators between a pair of beams, although with a bound {radical}3 times more stringent than for the quadrature entanglement.

Entanglement and decoherence in high energy physics

International Nuclear Information System (INIS)

Bertlmann, R.

2005-01-01

Full text: The phenomenon of entanglement occurs in very heavy quantum systems of particle physics. We find analogies but also differences to the entangled spin-1/2 or photon systems. In particular we discuss the features of entangled 'strangeness', the K-meson system, where a Bell inequality exists which has a remarkable connection to CP (charge conjugation and parity) and its violation. Stability of entangled quantum states is studied by allowing the system to interact with an environment. We consider possible decoherence of entangled 'beauty', the B-meson system, produced at the particle colliders at very high energies (10 GeV). Finally, we discuss a criterion for detecting entangled/separable states, a generalized Bell inequality and entanglement witness. We illustrate its geometric features by the two-spin example Alice and Bob. (author)

Quantum Statistics and Entanglement Problems

OpenAIRE

Trainor, L. E. H.; Lumsden, Charles J.

2002-01-01

Interpretations of quantum measurement theory have been plagued by two questions, one concerning the role of observer consciousness and the other the entanglement phenomenon arising from the superposition of quantum states. We emphasize here the remarkable role of quantum statistics in describing the entanglement problem correctly and discuss the relationship to issues arising from current discussions of intelligent observers in entangled, decohering quantum worlds.

Gaussian maximally multipartite-entangled states

Science.gov (United States)

Facchi, Paolo; Florio, Giuseppe; Lupo, Cosmo; Mancini, Stefano; Pascazio, Saverio

2009-12-01

We study maximally multipartite-entangled states in the context of Gaussian continuous variable quantum systems. By considering multimode Gaussian states with constrained energy, we show that perfect maximally multipartite-entangled states, which exhibit the maximum amount of bipartite entanglement for all bipartitions, only exist for systems containing n=2 or 3 modes. We further numerically investigate the structure of these states and their frustration for n≤7 .

Gaussian maximally multipartite-entangled states

International Nuclear Information System (INIS)

Facchi, Paolo; Florio, Giuseppe; Pascazio, Saverio; Lupo, Cosmo; Mancini, Stefano

2009-01-01

We study maximally multipartite-entangled states in the context of Gaussian continuous variable quantum systems. By considering multimode Gaussian states with constrained energy, we show that perfect maximally multipartite-entangled states, which exhibit the maximum amount of bipartite entanglement for all bipartitions, only exist for systems containing n=2 or 3 modes. We further numerically investigate the structure of these states and their frustration for n≤7.

Entanglement criteria for microscopic-macroscopic systems

International Nuclear Information System (INIS)

Spagnolo, Nicolo; Vitelli, Chiara; Sciarrino, Fabio; De Martini, Francesco

2010-01-01

We discuss the conclusions that can be drawn on a recent experimental micro-macro entanglement test [De Martini, Sciarrino, and Vitelli, Phys. Rev. Lett. 100, 253601 (2008)]. The system under investigation is generated through optical parametric amplification of one photon belonging to an entangled pair. The adopted entanglement criterion makes it possible to infer the presence of entanglement before losses that occur on the macrostate under a specific assumption. In particular, an a priori knowledge of the system that generates the micro-macro pair is necessary to exclude a class of separable states that can reproduce the obtained experimental results. Finally, we discuss the feasibility of a micro-macro ''genuine'' entanglement test on the analyzed system by considering different strategies, which show that in principle a fraction ε, proportional to the number of photons that survive the lossy process, of the original entanglement persists in any loss regime.

Entanglement quantification by local unitary operations

Energy Technology Data Exchange (ETDEWEB)

Monras, A.; Giampaolo, S. M.; Gualdi, G.; Illuminati, F. [Dipartimento di Matematica e Informatica, Universita degli Studi di Salerno, CNISM, Unita di Salerno, and INFN, Sezione di Napoli-Gruppo Collegato di Salerno, Via Ponte don Melillo, I-84084 Fisciano (Italy); Adesso, G.; Davies, G. B. [School of Mathematical Sciences, University of Nottingham, University Park, Nottingham NG7 2RD (United Kingdom)

2011-07-15

Invariance under local unitary operations is a fundamental property that must be obeyed by every proper measure of quantum entanglement. However, this is not the only aspect of entanglement theory where local unitary operations play a relevant role. In the present work we show that the application of suitable local unitary operations defines a family of bipartite entanglement monotones, collectively referred to as ''mirror entanglement.'' They are constructed by first considering the (squared) Hilbert-Schmidt distance of the state from the set of states obtained by applying to it a given local unitary operator. To the action of each different local unitary operator there corresponds a different distance. We then minimize these distances over the sets of local unitary operations with different spectra, obtaining an entire family of different entanglement monotones. We show that these mirror-entanglement monotones are organized in a hierarchical structure, and we establish the conditions that need to be imposed on the spectrum of a local unitary operator for the associated mirror entanglement to be faithful, i.e., to vanish in and only in separable pure states. We analyze in detail the properties of one particularly relevant member of the family, the ''stellar mirror entanglement'' associated with the traceless local unitary operations with nondegenerate spectra and equispaced eigenvalues in the complex plane. This particular measure generalizes the original analysis of S. M. Giampaolo and F. Illuminati [Phys. Rev. A 76, 042301 (2007)], valid for qubits and qutrits. We prove that the stellar entanglement is a faithful bipartite entanglement monotone in any dimension and that it is bounded from below by a function proportional to the linear entropy and from above by the linear entropy itself, coinciding with it in two- and three-dimensional spaces.

Entanglement quantification by local unitary operations

International Nuclear Information System (INIS)

Monras, A.; Giampaolo, S. M.; Gualdi, G.; Illuminati, F.; Adesso, G.; Davies, G. B.

2011-01-01

Invariance under local unitary operations is a fundamental property that must be obeyed by every proper measure of quantum entanglement. However, this is not the only aspect of entanglement theory where local unitary operations play a relevant role. In the present work we show that the application of suitable local unitary operations defines a family of bipartite entanglement monotones, collectively referred to as ''mirror entanglement.'' They are constructed by first considering the (squared) Hilbert-Schmidt distance of the state from the set of states obtained by applying to it a given local unitary operator. To the action of each different local unitary operator there corresponds a different distance. We then minimize these distances over the sets of local unitary operations with different spectra, obtaining an entire family of different entanglement monotones. We show that these mirror-entanglement monotones are organized in a hierarchical structure, and we establish the conditions that need to be imposed on the spectrum of a local unitary operator for the associated mirror entanglement to be faithful, i.e., to vanish in and only in separable pure states. We analyze in detail the properties of one particularly relevant member of the family, the ''stellar mirror entanglement'' associated with the traceless local unitary operations with nondegenerate spectra and equispaced eigenvalues in the complex plane. This particular measure generalizes the original analysis of S. M. Giampaolo and F. Illuminati [Phys. Rev. A 76, 042301 (2007)], valid for qubits and qutrits. We prove that the stellar entanglement is a faithful bipartite entanglement monotone in any dimension and that it is bounded from below by a function proportional to the linear entropy and from above by the linear entropy itself, coinciding with it in two- and three-dimensional spaces.

Local copying of orthogonal entangled quantum states

International Nuclear Information System (INIS)

Anselmi, Fabio; Chefles, Anthony; Plenio, Martin B

2004-01-01

In classical information theory one can, in principle, produce a perfect copy of any input state. In quantum information theory, the no cloning theorem prohibits exact copying of non-orthogonal states. Moreover, if we wish to copy multiparticle entangled states and can perform only local operations and classical communication (LOCC), then further restrictions apply. We investigate the problem of copying orthogonal, entangled quantum states with an entangled blank state under the restriction to LOCC. Throughout, the subsystems have finite dimension D. We show that if all of the states to be copied are non-maximally entangled, then novel LOCC copying procedures based on entanglement catalysis are possible. We then study in detail the LOCC copying problem where both the blank state and at least one of the states to be copied are maximally entangled. For this to be possible, we find that all the states to be copied must be maximally entangled. We obtain a necessary and sufficient condition for LOCC copying under these conditions. For two orthogonal, maximally entangled states, we provide the general solution to this condition. We use it to show that for D = 2, 3, any pair of orthogonal, maximally entangled states can be locally copied using a maximally entangled blank state. However, we also show that for any D which is not prime, one can construct pairs of such states for which this is impossible

Optimized entanglement witnesses for Dicke states

Energy Technology Data Exchange (ETDEWEB)

Bergmann, Marcel; Guehne, Otfried [Naturwissenschaftlich-Technische Fakultaet, Universitaet Siegen, Department Physik, Walter-Flex-Strasse 3, D-57068 Siegen (Germany)

2013-07-01

Quantum entanglement is an important resource for applications in quantum information processing like quantum teleportation and cryptography. Moreover, the number of particles that can be entangled experimentally using polarized photons or ion traps has been significantly enlarged. Therefore, criteria to decide the question whether a given multi-particle state is entangled or not have to be improved. Our approach to this problem uses the notion of PPT mixtures which form an approximation to the set of bi-separable states. With this method, entanglement witnesses can be obtained in a natural manner via linear semi-definite programming. In our contribution, we will present analytical results for entanglement witnesses for Dicke states. This allows to overcome the limitations of convex optimization.

Entanglement-Gradient Routing for Quantum Networks.

Science.gov (United States)

Gyongyosi, Laszlo; Imre, Sandor

2017-10-27

We define the entanglement-gradient routing scheme for quantum repeater networks. The routing framework fuses the fundamentals of swarm intelligence and quantum Shannon theory. Swarm intelligence provides nature-inspired solutions for problem solving. Motivated by models of social insect behavior, the routing is performed using parallel threads to determine the shortest path via the entanglement gradient coefficient, which describes the feasibility of the entangled links and paths of the network. The routing metrics are derived from the characteristics of entanglement transmission and relevant measures of entanglement distribution in quantum networks. The method allows a moderate complexity decentralized routing in quantum repeater networks. The results can be applied in experimental quantum networking, future quantum Internet, and long-distance quantum communications.

Strong monotonicity in mixed-state entanglement manipulation

International Nuclear Information System (INIS)

Ishizaka, Satoshi

2006-01-01

A strong entanglement monotone, which never increases under local operations and classical communications (LOCC), restricts quantum entanglement manipulation more strongly than the usual monotone since the usual one does not increase on average under LOCC. We propose strong monotones in mixed-state entanglement manipulation under LOCC. These are related to the decomposability and one-positivity of an operator constructed from a quantum state, and reveal geometrical characteristics of entangled states. These are lower bounded by the negativity or generalized robustness of entanglement

Quantum teleportation. New wave of applications of quantum mechanics based on quantum entanglement: non-trivial transfer of quantum information

International Nuclear Information System (INIS)

Andrej, L.; Bednar, M.; Cernansky, M.

1999-01-01

The phenomenon of quantum teleportation is discussed with emphasis on its physical aspects. A brief introduction into the Einstein-Podolsky-Rosen (EPR) paradox is followed by Bohm's reformulation of the EPR paradox for the case of a physical system of two spins in the singlet state. A description of Bell's entangled spin states of two-particle systems of standard fermions as well as polarized photons is also given. In view of the fact that quantum teleportation has been realized experimentally mainly on photons, the next part of the paper is devoted to problems of generation and detection of two-photon Bell's entangled states. A detailed description of the process of quantum teleportation exploiting quantum entangled states follows. A classical formulation of the EPR paradox is given in the Appendix. (Z.J.)

Positive maps, majorization, entropic inequalities and detection of entanglement

International Nuclear Information System (INIS)

Augusiak, R; Stasinska, J

2009-01-01

In this paper, we discuss some general connections between the notions of positive map, weak majorization and entropic inequalities in the context of detection of entanglement among bipartite quantum systems. First, basing on the fact that any positive map Λ:M d (C)→M d (C) can be written as the difference between two completely positive maps Λ=Λ 1 -Λ 2 , we propose a possible way to generalize the Nielsen-Kempe majorization criterion. Then, we present two methods of derivation of some general classes of entropic inequalities useful for the detection of entanglement. While the first one follows from the aforementioned generalized majorization relation and the concept of Schur-concave decreasing functions, the second is based on some functional inequalities. What is important is that, contrary to the Nielsen-Kempe majorization criterion and entropic inequalities, our criteria allow for the detection of entangled states with positive partial transposition when using indecomposable positive maps. We also point out that if a state with at least one maximally mixed subsystem is detected by some necessary criterion based on the positive map Λ, then there exist entropic inequalities derived from Λ (by both procedures) that also detect this state. In this sense, they are equivalent to the necessary criterion [IxΛ](rhov AB )≥0. Moreover, our inequalities provide a way of constructing multi-copy entanglement witnesses and therefore are promising from the experimental point of view. Finally, we discuss some of the derived inequalities in the context of the recently introduced protocol of state merging and the possibility of approximating the mean value of a linear entanglement witness.

Global entanglement in multiparticle systems

International Nuclear Information System (INIS)

Meyer, David A.; Wallach, Nolan R.

2002-01-01

We define a polynomial measure of multiparticle entanglement which is scalable, i.e., which applies to any number of spin-(1/2) particles. By evaluating it for three particle states, for eigenstates of the one dimensional Heisenberg antiferromagnet and on quantum error correcting code subspaces, we illustrate the extent to which it quantifies global entanglement. We also apply it to track the evolution of entanglement during a quantum computation

Teleportation of Entangled States through Divorce of Entangled Pair Mediated by a Weak Coherent Field in a High-Q Cavity

Institute of Scientific and Technical Information of China (English)

W. B. Cardosol; N. G. de Almeida

2008-01-01

We propose a scheme to partially teleport an unknown entangled atomic state. A high-Q cavity, supporting one mode of a weak coherent state, is needed to accomplish this process. By partial teleportation we mean that teleportation will occur by changing one of the partners of the entangled state to be teleported. The entangled state to be teleported is composed by one pair of particles, we called this surprising characteristic of maintaining the entanglement, even when one of the particle of the entangled pair being teleported is changed, of divorce of entangled states.

Production and Detection of Spin-Entangled Electrons in Mesoscopic Conductors

Science.gov (United States)

Burkard, Guido

2006-03-01

Electron spins are an extremely versatile form of quantum bits. When localized in quantum dots, they can form a register for quantum computation. Moreover, being attached to a charge in a mesoscopic conductor allows the electron spin to play the role of a mobile carrier of quantum information similarly to photons in optical quantum communication. Since entanglement is a basic resource in quantum communication, the production and detection of spin-entangled Einstein-Podolsky-Rosen (EPR) pairs of electrons are of great interest. Besides the practical importance, it is of fundamental interest to test quantum non-locality for electrons. I review the theoretical schemes for the entanglement production in superconductor-normal junctions [1] and other systems. The electron spin entanglement can be detected and quantified from measurements of the fluctuations (shot noise) of the charge current after the electrons have passed through an electronic beam splitter [2,3]. This two-particle interference effect is related to the Hanbury-Brown and Twiss experiment and leads to a doubling of the shot noise SI=φ=0 for spin-entangled states, allowing their differentiation from unentangled pairs. I report on the role of spin-orbit coupling (Rashba and Dresselhaus) in a complete characterization of the spin entanglement [4]. Finally, I address the effects of a discrete level spectrum in the mesoscopic leads and of backscattering and decoherence.[1] P. Recher, E. V. Sukhorukov, D. Loss, Phys. Rev. B 63, 165314 (2001)[2] G. Burkard, D. Loss, E. V. Sukhorukov, Phys. Rev. B 61, R16303 (2000)[3] G. Burkard and D. Loss, Phys. Rev. Lett.91, 087903 (2003)[4] J. C. Egues, G. Burkard, D. Saraga, J. Schliemann, D. Loss, cond-mat/0509038, to appear in Phys.Rev.B (2005).

Generating stationary entangled states in superconducting qubits

International Nuclear Information System (INIS)

Zhang Jing; Liu Yuxi; Li Chunwen; Tarn, T.-J.; Nori, Franco

2009-01-01

When a two-qubit system is initially maximally entangled, two independent decoherence channels, one per qubit, would greatly reduce the entanglement of the two-qubit system when it reaches its stationary state. We propose a method on how to minimize such a loss of entanglement in open quantum systems. We find that the quantum entanglement of general two-qubit systems with controllable parameters can be controlled by tuning both the single-qubit parameters and the two-qubit coupling strengths. Indeed, the maximum fidelity F max between the stationary entangled state, ρ ∞ , and the maximally entangled state, ρ m , can be about 2/3≅max(tr(ρ ∞ ρ m ))=F max , corresponding to a maximum stationary concurrence, C max , of about 1/3≅C(ρ ∞ )=C max . This is significant because the quantum entanglement of the two-qubit system can be produced and kept, even for a long time. We apply our proposal to several types of two-qubit superconducting circuits and show how the entanglement of these two-qubit circuits can be optimized by varying experimentally controllable parameters.

Optimal Entanglement Witnesses for Qubits and Qutrits

International Nuclear Information System (INIS)

Bertlmann, R.A.; Durstberger, K.; Hiesmayr, B.C.; Krammer, P.

2005-01-01

Full text: We give a review of the connection between an optimal entanglement witness and the Hilbert-Schmidt measure of entanglement (that is the minimal distance of an entangled state to the set of separable states): a generalized Bell inequality is derived within the concept of entanglement witnesses, in the sense that a violation of the inequality detects entanglement and not non-locality liKEX usual Bell inequalities do. It can be seen that the maximal violation equals the Hilbert-Schmidt measure. Furthermore, since finding the nearest separable state to a given entangled state is rather difficult, a method for checking an estimated nearest separable state is presented. This is illustrated with isotropic qubit and qutrit states; the Hilbert-Schmidt measure, the optimal entanglement witness and the maximal violation of the GBI are calculated for those cases. Possible generalizations for arbitrary dimensions are discussed. (author)

Quantum entanglement and quantum computational algorithms

Indian Academy of Sciences (India)

Abstract. The existence of entangled quantum states gives extra power to quantum computers over their classical counterparts. Quantum entanglement shows up qualitatively at the level of two qubits. We demonstrate that the one- and the two-bit Deutsch-Jozsa algorithm does not require entanglement and can be mapped ...

Entanglement polygon inequality in qubit systems

Science.gov (United States)

Qian, Xiao-Feng; Alonso, Miguel A.; Eberly, J. H.

2018-06-01

We prove a set of tight entanglement inequalities for arbitrary N-qubit pure states. By focusing on all bi-partite marginal entanglements between each single qubit and its remaining partners, we show that the inequalities provide an upper bound for each marginal entanglement, while the known monogamy relation establishes the lower bound. The restrictions and sharing properties associated with the inequalities are further analyzed with a geometric polytope approach, and examples of three-qubit GHZ-class and W-class entangled states are presented to illustrate the results.

Entanglement, Bell inequality and all that

International Nuclear Information System (INIS)

Narnhofer, Heide; Thirring, Walter

2012-01-01

We start from the geometrical observation that a finite set of pure states correspond to some points on a sphere and their convex span cannot be the whole set of states. If we call the left over entangled we can pursue this picture from the simplest case of a two dimensional Hilbert space to the usual Alice-and-Bob game of entangled states and then move to bigger systems and finely to quantum field theory where almost everything is entangled. On the way we encounter more or less known old friends up from the shell structure of states to the monogamy of squashed entanglement. We study how entanglement can be concentrated on a small slice and how it depends on the particular factorization of the Hilbert space.

Entanglement, Bell inequality and all that

Energy Technology Data Exchange (ETDEWEB)

Narnhofer, Heide; Thirring, Walter [Fakultaet fuer Physik, Universitaet Wien, Boltzmanngasse 5, A-1090 Wien (Austria)

2012-09-15

We start from the geometrical observation that a finite set of pure states correspond to some points on a sphere and their convex span cannot be the whole set of states. If we call the left over entangled we can pursue this picture from the simplest case of a two dimensional Hilbert space to the usual Alice-and-Bob game of entangled states and then move to bigger systems and finely to quantum field theory where almost everything is entangled. On the way we encounter more or less known old friends up from the shell structure of states to the monogamy of squashed entanglement. We study how entanglement can be concentrated on a small slice and how it depends on the particular factorization of the Hilbert space.

Entanglement verification with detection efficiency mismatch

Science.gov (United States)

Zhang, Yanbao; Lütkenhaus, Norbert

Entanglement is a necessary condition for secure quantum key distribution (QKD). When there is an efficiency mismatch between various detectors used in the QKD system, it is still an open problem how to verify entanglement. Here we present a method to address this problem, given that the detection efficiency mismatch is characterized and known. The method works without assuming an upper bound on the number of photons going to each threshold detector. Our results suggest that the efficiency mismatch affects the ability to verify entanglement: the larger the efficiency mismatch is, the smaller the set of entangled states that can be verified becomes. When there is no mismatch, our method can verify entanglement even if the method based on squashing maps [PRL 101, 093601 (2008)] fails.

Entanglement entropy in top-down models

Energy Technology Data Exchange (ETDEWEB)

Jones, Peter A.R.; Taylor, Marika [Mathematical Sciences and STAG Research Centre, University of Southampton,Highfield, Southampton, SO17 1BJ (United Kingdom)

2016-08-26

We explore holographic entanglement entropy in ten-dimensional supergravity solutions. It has been proposed that entanglement entropy can be computed in such top-down models using minimal surfaces which asymptotically wrap the compact part of the geometry. We show explicitly in a wide range of examples that the holographic entanglement entropy thus computed agrees with the entanglement entropy computed using the Ryu-Takayanagi formula from the lower-dimensional Einstein metric obtained from reduction over the compact space. Our examples include not only consistent truncations but also cases in which no consistent truncation exists and Kaluza-Klein holography is used to identify the lower-dimensional Einstein metric. We then give a general proof, based on the Lewkowycz-Maldacena approach, of the top-down entanglement entropy formula.

Entanglement entropy in top-down models

International Nuclear Information System (INIS)

Jones, Peter A.R.; Taylor, Marika

2016-01-01

We explore holographic entanglement entropy in ten-dimensional supergravity solutions. It has been proposed that entanglement entropy can be computed in such top-down models using minimal surfaces which asymptotically wrap the compact part of the geometry. We show explicitly in a wide range of examples that the holographic entanglement entropy thus computed agrees with the entanglement entropy computed using the Ryu-Takayanagi formula from the lower-dimensional Einstein metric obtained from reduction over the compact space. Our examples include not only consistent truncations but also cases in which no consistent truncation exists and Kaluza-Klein holography is used to identify the lower-dimensional Einstein metric. We then give a general proof, based on the Lewkowycz-Maldacena approach, of the top-down entanglement entropy formula.

Entanglement temperature with Gauss–Bonnet term

Directory of Open Access Journals (Sweden)

Shesansu Sekhar Pal

2015-09-01

Full Text Available We compute the entanglement temperature using the first law-like of thermodynamics, ΔE=TentΔSEE, up to Gauss–Bonnet term in the Jacobson–Myers entropy functional in any arbitrary spacetime dimension. The computation is done when the entangling region is the geometry of a slab. We also show that such a Gauss–Bonnet term, which becomes a total derivative, when the co-dimension two hypersurface is four dimensional, does not contribute to the finite term in the entanglement entropy. We observe that the Weyl-squared term does not contribute to the entanglement entropy. It is important to note that the calculations are performed when the entangling region is very small and the energy is calculated using the normal Hamiltonian.

Spin-photon entangling diode

DEFF Research Database (Denmark)

Flindt, Christian; Sørensen, A. S.; Lukin, M. D.

2007-01-01

We propose a semiconductor device that can electrically generate entangled electron spin-photon states, providing a building block for entanglement of distant spins. The device consists of a p-i-n diode structure that incorporates a coupled double quantum dot. We show that electronic control of t...

Entanglement capacity of nonlocal Hamiltonians: A geometric approach

International Nuclear Information System (INIS)

Lari, Behzad; Hassan, Ali Saif M.; Joag, Pramod S.

2009-01-01

We develop a geometric approach to quantify the capability of creating entanglement for a general physical interaction acting on two qubits. We use the entanglement measure proposed by us for N-qubit pure states [Ali Saif M. Hassan and Pramod S. Joag, Phys. Rev. A 77, 062334 (2008)]. This geometric method has the distinct advantage that it gives the experimentally implementable criteria to ensure the optimal entanglement production rate without requiring a detailed knowledge of the state of the two qubit system. For the production of entanglement in practice, we need criteria for optimal entanglement production, which can be checked in situ without any need to know the state, as experimentally finding out the state of a quantum system is generally a formidable task. Further, we use our method to quantify the entanglement capacity in higher level and multipartite systems. We quantify the entanglement capacity for two qutrits and find the maximal entanglement generation rate and the corresponding state for the general isotropic interaction between qutrits, using the entanglement measure of N-qudit pure states proposed by us [Ali Saif M. Hassan and Pramod S. Joag, Phys. Rev. A 80, 042302 (2009)]. Next we quantify the genuine three qubit entanglement capacity for a general interaction between qubits. We obtain the maximum entanglement generation rate and the corresponding three qubit state for a general isotropic interaction between qubits. The state maximizing the entanglement generation rate is of the Greenberger-Horne-Zeilinger class. To the best of our knowledge, the entanglement capacities for two qutrit and three qubit systems have not been reported earlier.

Teleportation of Entangled States through Divorce of Entangled Pair Mediated by a Weak Coherent Field in a High-Q Cavity

International Nuclear Information System (INIS)

Cardoso, W. B.; Almeida, N. G. de

2008-01-01

We propose a scheme to partially teleport an unknown entangled atomic state. A high-Q cavity, supporting one mode of a weak coherent state, is needed to accomplish this process. By partial teleportation we mean that teleportation will occur by changing one of the partners of the entangled state to be teleported. The entangled state to be teleported is composed by one pair of particles, we called this surprising characteristic of maintaining the entanglement, even when one of the particle of the entangled pair being teleported is changed, of divorce of entangled states. (fundamental areas of phenomenology (including applications))

Teleportation of entanglement over 143 km.

Science.gov (United States)

Herbst, Thomas; Scheidl, Thomas; Fink, Matthias; Handsteiner, Johannes; Wittmann, Bernhard; Ursin, Rupert; Zeilinger, Anton

2015-11-17

As a direct consequence of the no-cloning theorem, the deterministic amplification as in classical communication is impossible for unknown quantum states. This calls for more advanced techniques in a future global quantum network, e.g., for cloud quantum computing. A unique solution is the teleportation of an entangled state, i.e., entanglement swapping, representing the central resource to relay entanglement between distant nodes. Together with entanglement purification and a quantum memory it constitutes a so-called quantum repeater. Since the aforementioned building blocks have been individually demonstrated in laboratory setups only, the applicability of the required technology in real-world scenarios remained to be proven. Here we present a free-space entanglement-swapping experiment between the Canary Islands of La Palma and Tenerife, verifying the presence of quantum entanglement between two previously independent photons separated by 143 km. We obtained an expectation value for the entanglement-witness operator, more than 6 SDs beyond the classical limit. By consecutive generation of the two required photon pairs and space-like separation of the relevant measurement events, we also showed the feasibility of the swapping protocol in a long-distance scenario, where the independence of the nodes is highly demanded. Because our results already allow for efficient implementation of entanglement purification, we anticipate our research to lay the ground for a fully fledged quantum repeater over a realistic high-loss and even turbulent quantum channel.

Entanglement between two spatially separated atomic modes

Science.gov (United States)

Lange, Karsten; Peise, Jan; Lücke, Bernd; Kruse, Ilka; Vitagliano, Giuseppe; Apellaniz, Iagoba; Kleinmann, Matthias; Tóth, Géza; Klempt, Carsten

2018-04-01

Modern quantum technologies in the fields of quantum computing, quantum simulation, and quantum metrology require the creation and control of large ensembles of entangled particles. In ultracold ensembles of neutral atoms, nonclassical states have been generated with mutual entanglement among thousands of particles. The entanglement generation relies on the fundamental particle-exchange symmetry in ensembles of identical particles, which lacks the standard notion of entanglement between clearly definable subsystems. Here, we present the generation of entanglement between two spatially separated clouds by splitting an ensemble of ultracold identical particles prepared in a twin Fock state. Because the clouds can be addressed individually, our experiments open a path to exploit the available entangled states of indistinguishable particles for quantum information applications.

Entanglement-based Free Space Quantum Cryptography in Daylight

Science.gov (United States)

Gerhardt, Ilja; Peloso, Matthew P.; Ho, Caleb; Lamas-Linares, Antia; Kurtsiefer, Christian

2009-05-01

In quantum key distribution (QKD) two families of protocols are established: One, based on preparing and sending approximations of single photons, the other based on measurements on entangled photon pairs, which allow to establish a secret key using less assumptions on the size of a Hilbert space. The larger optical bandwidth of photon pairs in comparison with light used for the first family makes establishing a free space link challenging. We present a complete entanglement based QKD system following the BBM92 protocol, which generates a secure key continuously 24 hours a day between distant parties. Spectral, spatial and temporal filtering schemes were introduced to a previous setup, suppressing more than 30,B of background. We are able to establish the link during daytime, and have developed an algorithm to start and maintain time synchronization with simple crystal oscillators.

Heralded entanglement of two remote atoms

Science.gov (United States)

Krug, Michael; Hofmann, Julian; Ortegel, Norbert; Gerard, Lea; Redeker, Kai; Henkel, Florian; Rosenfeld, Wenjamin; Weber, Markus; Weinfurter, Harald

2012-06-01

Entanglement between atomic quantum memories at remote locations will be a key resource for future applications in quantum communication. One possibility to generate such entanglement over large distances is entanglement swapping starting from two quantum memories each entangled with a photon. The photons can be transported to a Bell-state measurement where after the atomic quantum memories are projected onto an entangled state. We have set up two independently operated single atom experiments separated by 20 m. Via a spontaneous decay process each quantum memory, in our case a single Rb-87 atom, emits a single photon whose polarization is entangled with the atomic spin. The photons one emitted from each atom are collected into single-mode optical fibers guided to a non-polarizing 50-50 beam-splitter and detected by avalanche photodetectors. Bunching of indistinguishable photons allows to perform a Bell-state measurement on the photons. Conditioned on the registration of particular two-photon coincidences the spin states of both atoms are measured. The observed correlations clearly prove the entanglement of the two atoms. This is a first step towards creating a basic node of a quantum network as well as a key prerequisite for a future loophole-free test of Bell's inequality.

Images in quantum entanglement

International Nuclear Information System (INIS)

Bowden, G J

2009-01-01

A system for classifying and quantifying entanglement in spin 1/2 pure states is presented based on simple images. From the image point of view, an entangled state can be described as a linear superposition of separable object wavefunction Ψ O plus a portion of its own inverse image. Bell states can be defined in this way: Ψ= 1/√2 (Ψ O ±Ψ I ). Using the method of images, the three-spin 1/2 system is discussed in some detail. This system can exhibit exclusive three-particle ν 123 entanglement, two-particle entanglements ν 12 , ν 13 , ν 23 and/or mixtures of all four. All four image states are orthogonal both to each other and to the object wavefunction. In general, five entanglement parameters ν 12 , ν 13 , ν 23 , ν 123 and φ 123 are required to define the general entangled state. In addition, it is shown that there is considerable scope for encoding numbers, at least from the classical point of view but using quantum-mechanical principles. Methods are developed for their extraction. It is shown that concurrence can be used to extract even-partite, but not odd-partite information. Additional relationships are also presented which can be helpful in the decoding process. However, in general, numerical methods are mandatory. A simple roulette method for decoding is presented and discussed. But it is shown that if the encoder chooses to use transcendental numbers for the angles defining the target function (α 1 , β 1 ), etc, the method rapidly turns into the Devil's roulette, requiring finer and finer angular steps.

Images in quantum entanglement

Energy Technology Data Exchange (ETDEWEB)

Bowden, G J [School of Physics and Astronomy, University of Southampton, SO17 1BJ (United Kingdom)

2009-08-28

A system for classifying and quantifying entanglement in spin 1/2 pure states is presented based on simple images. From the image point of view, an entangled state can be described as a linear superposition of separable object wavefunction {psi}{sub O} plus a portion of its own inverse image. Bell states can be defined in this way: {psi}= 1/{radical}2 ({psi}{sub O}{+-}{psi}{sub I} ). Using the method of images, the three-spin 1/2 system is discussed in some detail. This system can exhibit exclusive three-particle {nu}{sub 123} entanglement, two-particle entanglements {nu}{sub 12}, {nu}{sub 13}, {nu}{sub 23} and/or mixtures of all four. All four image states are orthogonal both to each other and to the object wavefunction. In general, five entanglement parameters {nu}{sub 12}, {nu}{sub 13}, {nu}{sub 23}, {nu}{sub 123} and {phi}{sub 123} are required to define the general entangled state. In addition, it is shown that there is considerable scope for encoding numbers, at least from the classical point of view but using quantum-mechanical principles. Methods are developed for their extraction. It is shown that concurrence can be used to extract even-partite, but not odd-partite information. Additional relationships are also presented which can be helpful in the decoding process. However, in general, numerical methods are mandatory. A simple roulette method for decoding is presented and discussed. But it is shown that if the encoder chooses to use transcendental numbers for the angles defining the target function ({alpha}{sub 1}, {beta}{sub 1}), etc, the method rapidly turns into the Devil's roulette, requiring finer and finer angular steps.

Multipartite geometric entanglement in finite size XY model

Energy Technology Data Exchange (ETDEWEB)

Blasone, Massimo; Dell' Anno, Fabio; De Siena, Silvio; Giampaolo, Salvatore Marco; Illuminati, Fabrizio, E-mail: blasone@sa.infn.i [Dipartimento di Matematica e Informatica, Universita degli Studi di Salerno, Via Ponte don Melillo, I-84084 Fisciano (Italy)

2009-06-01

We investigate the behavior of the multipartite entanglement in the finite size XY model by means of the hierarchical geometric measure of entanglement. By selecting specific components of the hierarchy, we study both global entanglement and genuinely multipartite entanglement.

Gravity as Quantum Entanglement Force

OpenAIRE

Lee, Jae-Weon; Kim, Hyeong-Chan; Lee, Jungjai

2010-01-01

We conjecture that the total quantum entanglement of matter and vacuum in the universe tends to increase with time, like entropy, and that an effective force is associated with this tendency. We also suggest that gravity and dark energy are types of quantum entanglement forces, similar to Verlinde's entropic force, and give holographic dark energy with an equation of state comparable to current observational data. This connection between quantum entanglement and gravity could give some new in...

Quantum walks with entangled coins

International Nuclear Information System (INIS)

Venegas-Andraca, S E; Ball, J L; Burnett, K; Bose, S

2005-01-01

We present a mathematical formalism for the description of un- restricted quantum walks with entangled coins and one walker. The numerical behaviour of such walks is examined when using a Bell state as the initial coin state, with two different coin operators, two different shift operators, and one walker. We compare and contrast the performance of these quantum walks with that of a classical random walk consisting of one walker and two maximally correlated coins as well as quantum walks with coins sharing different degrees of entanglement. We illustrate that the behaviour of our walk with entangled coins can be very different in comparison to the usual quantum walk with a single coin. We also demonstrate that simply by changing the shift operator, we can generate widely different distributions. We also compare the behaviour of quantum walks with maximally entangled coins with that of quantum walks with non-entangled coins. Finally, we show that the use of different shift operators on two and three qubit coins leads to different position probability distributions in one- and two-dimensional graphs

Entanglement quantification by local unitary operations

Science.gov (United States)

Monras, A.; Adesso, G.; Giampaolo, S. M.; Gualdi, G.; Davies, G. B.; Illuminati, F.

2011-07-01

Invariance under local unitary operations is a fundamental property that must be obeyed by every proper measure of quantum entanglement. However, this is not the only aspect of entanglement theory where local unitary operations play a relevant role. In the present work we show that the application of suitable local unitary operations defines a family of bipartite entanglement monotones, collectively referred to as “mirror entanglement.” They are constructed by first considering the (squared) Hilbert-Schmidt distance of the state from the set of states obtained by applying to it a given local unitary operator. To the action of each different local unitary operator there corresponds a different distance. We then minimize these distances over the sets of local unitary operations with different spectra, obtaining an entire family of different entanglement monotones. We show that these mirror-entanglement monotones are organized in a hierarchical structure, and we establish the conditions that need to be imposed on the spectrum of a local unitary operator for the associated mirror entanglement to be faithful, i.e., to vanish in and only in separable pure states. We analyze in detail the properties of one particularly relevant member of the family, the “stellar mirror entanglement” associated with the traceless local unitary operations with nondegenerate spectra and equispaced eigenvalues in the complex plane. This particular measure generalizes the original analysis of S. M. Giampaolo and F. Illuminati [Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.76.042301 76, 042301 (2007)], valid for qubits and qutrits. We prove that the stellar entanglement is a faithful bipartite entanglement monotone in any dimension and that it is bounded from below by a function proportional to the linear entropy and from above by the linear entropy itself, coinciding with it in two- and three-dimensional spaces.

Entanglement entropy in the quantum networks of a coupled quantum harmonic oscillator

International Nuclear Information System (INIS)

Jafarizadeh, M A; Nami, S; Eghbalifam, F

2015-01-01

We investigate the entanglement of the ground state in the quantum networks that their nodes are considered as quantum harmonic oscillators. To this aim, the Schmidt numbers and entanglement entropy between two arbitrary partitions of a network are calculated.In partitioning an arbitrary graph into two parts there are some nodes in each part which are not connected to the nodes of the other part. So, these nodes of each part can be in distinct subsets. Therefore, the graph is separated into four subsets. The nodes of the first and last subsets are those which are not connected to the nodes of the other part. In theorem 1, by using the generalized Schur complement method in these four subsets, we prove that all the graphs whose connections between the two alternative subsets are complete, have the same entropy. A large number of graphs satisfy this theorem. Then the entanglement entropy in the limit of the large coupling and large size of the system is investigated in these graphs. Also, the asymptotic behaviors of the Schmidt numbers and entanglement entropy in the limit of infinite coupling are shown.One important quantity about partitioning is the conductance of the graph. The conductance of the graph is considered in various graphs. In these graphs we compare the conductance of the graph and the entanglement entropy. (paper)

Multiple quantum spin dynamics of entanglement

International Nuclear Information System (INIS)

Doronin, Serge I.

2003-01-01

The dynamics of entanglement is investigated on the basis of exactly solvable models of multiple quantum (MQ) NMR spin dynamics. It is shown that the time evolution of MQ coherences of systems of coupled nuclear spins in solids is directly connected with dynamics of the quantum entanglement. We studied analytically the dynamics of entangled states for two- and three-spin systems coupled by the dipole-dipole interaction. In this case the dynamics of the quantum entanglement is uniquely determined by the time evolution of MQ coherences of the second order. The real part of the density matrix describing MQ dynamics in solids is responsible for MQ coherences of the zeroth order while its imaginary part is responsible for the second order. Thus, one can conclude that the dynamics of the entanglement is connected with transitions from the real part of the density matrix to the imaginary one, and vice versa. A pure state which generalizes the Greenberger-Horne-Zeilinger (GHZ) and W states is found. Different measures of the entanglement of this state are analyzed for tripartite systems

Quantum teleportation and multi-photon entanglement

International Nuclear Information System (INIS)

Pan, J.-W.

1999-08-01

The present thesis is the result of theoretical and experimental work on the physics of multiparticle interference. The theoretical results show that a quantum network with simple quantum logic gates and a handful of qubits enables one to control and manipulate quantum entanglement. Because of the present absence of quantum gate for two independently produced photons, in the mean time we also present a practical way to generate and identify multiparticle entangled state. The experimental work has thoroughly developed the necessary techniques to study novel multiparticle interference phenomena. By making use of the pulsed source for polarization entangled photon pairs, in this thesis we report for the first time the experimental realization of quantum teleportation, of entanglement swapping and of production of these-particle entanglement. Using the three-particle entanglement source, here we also present the first experimental realization of a test of local realism without inequalities. The methods developed in these experiments are of great significance both for exploring the field of quantum information and for future experiments on the fundamental tests of quantum mechanics. (author)

Interuniversal entanglement in a cyclic multiverse

Science.gov (United States)

Robles-Pérez, Salvador; Balcerzak, Adam; Dąbrowski, Mariusz P.; Krämer, Manuel

2017-04-01

We study scenarios of parallel cyclic multiverses which allow for a different evolution of the physical constants, while having the same geometry. These universes are classically disconnected, but quantum-mechanically entangled. Applying the thermodynamics of entanglement, we calculate the temperature and the entropy of entanglement. It emerges that the entropy of entanglement is large at big bang and big crunch singularities of the parallel universes as well as at the maxima of the expansion of these universes. The latter seems to confirm earlier studies that quantum effects are strong at turning points of the evolution of the universe performed in the context of the timeless nature of the Wheeler-DeWitt equation and decoherence. On the other hand, the entropy of entanglement at big rip singularities is going to zero despite its presumably quantum nature. This may be an effect of total dissociation of the universe structures into infinitely separated patches violating the null energy condition. However, the temperature of entanglement is large/infinite at every classically singular point and at maximum expansion and seems to be a better measure of quantumness.

Cloning the entanglement of a pair of quantum bits

International Nuclear Information System (INIS)

Lamoureux, Louis-Philippe; Navez, Patrick; Cerf, Nicolas J.; Fiurasek, Jaromir

2004-01-01

It is shown that any quantum operation that perfectly clones the entanglement of all maximally entangled qubit pairs cannot preserve separability. This 'entanglement no-cloning' principle naturally suggests that some approximate cloning of entanglement is nevertheless allowed by quantum mechanics. We investigate a separability-preserving optimal cloning machine that duplicates all maximally entangled states of two qubits, resulting in 0.285 bits of entanglement per clone, while a local cloning machine only yields 0.060 bits of entanglement per clone

Transplanckian entanglement entropy

International Nuclear Information System (INIS)

Chang, Darwin; Chu, C.-S.; Lin Fengli

2004-01-01

The entanglement entropy of the event horizon is known to be plagued by the UV divergence due to the infinitely blue-shifted near horizon modes. In this Letter we calculate the entanglement entropy using the transplanckian dispersion relation, which has been proposed to model the quantum gravity effects. We show that, very generally, the entropy is rendered UV finite due to the suppression of high energy modes effected by the transplanckian dispersion relation

Exponentially Enhanced Light-Matter Interaction, Cooperativities, and Steady-State Entanglement Using Parametric Amplification

Science.gov (United States)

Qin, Wei; Miranowicz, Adam; Li, Peng-Bo; Lü, Xin-You; You, J. Q.; Nori, Franco

2018-03-01

We propose an experimentally feasible method for enhancing the atom-field coupling as well as the ratio between this coupling and dissipation (i.e., cooperativity) in an optical cavity. It exploits optical parametric amplification to exponentially enhance the atom-cavity interaction and, hence, the cooperativity of the system, with the squeezing-induced noise being completely eliminated. Consequently, the atom-cavity system can be driven from the weak-coupling regime to the strong-coupling regime for modest squeezing parameters, and even can achieve an effective cooperativity much larger than 100. Based on this, we further demonstrate the generation of steady-state nearly maximal quantum entanglement. The resulting entanglement infidelity (which quantifies the deviation of the actual state from a maximally entangled state) is exponentially smaller than the lower bound on the infidelities obtained in other dissipative entanglement preparations without applying squeezing. In principle, we can make an arbitrarily small infidelity. Our generic method for enhancing atom-cavity interaction and cooperativities can be implemented in a wide range of physical systems, and it can provide diverse applications for quantum information processing.

Entanglement in coined quantum walks on regular graphs

International Nuclear Information System (INIS)

Carneiro, Ivens; Loo, Meng; Xu, Xibai; Girerd, Mathieu; Kendon, Viv; Knight, Peter L

2005-01-01

Quantum walks, both discrete (coined) and continuous time, form the basis of several recent quantum algorithms. Here we use numerical simulations to study the properties of discrete, coined quantum walks. We investigate the variation in the entanglement between the coin and the position of the particle by calculating the entropy of the reduced density matrix of the coin. We consider both dynamical evolution and asymptotic limits for coins of dimensions from two to eight on regular graphs. For low coin dimensions, quantum walks which spread faster (as measured by the mean square deviation of their distribution from uniform) also exhibit faster convergence towards the asymptotic value of the entanglement between the coin and particle's position. For high-dimensional coins, the DFT coin operator is more efficient at spreading than the Grover coin. We study the entanglement of the coin on regular finite graphs such as cycles, and also show that on complete bipartite graphs, a quantum walk with a Grover coin is always periodic with period four. We generalize the 'glued trees' graph used by Childs et al (2003 Proc. STOC, pp 59-68) to higher branching rate (fan out) and verify that the scaling with branching rate and with tree depth is polynomial

Signalling, entanglement and quantum evolution beyond Cauchy horizons

International Nuclear Information System (INIS)

Yurtsever, Ulvi; Hockney, George

2005-01-01

Consider a bipartite entangled system, half of which falls through the event horizon of an evaporating black hole, while the other half remains coherently accessible to experiments in the exterior region. Beyond complete evaporation, the evolution of the quantum state past the Cauchy horizon cannot remain unitary, raising the questions: how can this evolution be described as a quantum map, and how is causality preserved? What are the possible effects of such non-standard quantum evolution maps on the behaviour of the entangled laboratory partner? More generally, the laws of quantum evolution under extreme conditions in remote regions (not just in evaporating black-hole interiors, but possibly near other naked singularities and regions of extreme spacetime structure) remain untested by observation, and might conceivably be non-unitary or even nonlinear, raising the same questions about the evolution of entangled states. The answers to these questions are subtle, and are linked in unexpected ways to the fundamental laws of quantum mechanics. We show that terrestrial experiments can be designed to probe and constrain exactly how the laws of quantum evolution might be altered, either by black-hole evaporation, or by other extreme processes in remote regions possibly governed by unknown physics

Entropy-driven phase transitions of entanglement

Science.gov (United States)

Facchi, Paolo; Florio, Giuseppe; Parisi, Giorgio; Pascazio, Saverio; Yuasa, Kazuya

2013-05-01

We study the behavior of bipartite entanglement at fixed von Neumann entropy. We look at the distribution of the entanglement spectrum, that is, the eigenvalues of the reduced density matrix of a quantum system in a pure state. We report the presence of two continuous phase transitions, characterized by different entanglement spectra, which are deformations of classical eigenvalue distributions.

Manipulating continuous variable photonic entanglement

International Nuclear Information System (INIS)

Plenio, M.B.

2005-01-01

I will review our work on photonic entanglement in the continuous variable regime including both Gaussian and non-Gaussian states. The feasibility and efficiency of various entanglement purification protocols are discussed this context. (author)

Multipartite entanglement detection with nonsymmetric probing

DEFF Research Database (Denmark)

Dellantonio, Luca; Das, Sumanta; Appel, Jürgen

2017-01-01

We show that spin-squeezing criteria commonly used for entanglement detection can be erroneous if the probe is not symmetric. We then derive a lower bound on squeezing for separable states in spin systems probed asymmetrically. Using this we further develop a procedure that allows us to verify th...... the degree of entanglement of a quantum state in the spin system. Finally, we apply our method for entanglement verification to existing experimental data, and use it to prove the existence of tripartite entanglement in a spin-squeezed atomic ensemble.......We show that spin-squeezing criteria commonly used for entanglement detection can be erroneous if the probe is not symmetric. We then derive a lower bound on squeezing for separable states in spin systems probed asymmetrically. Using this we further develop a procedure that allows us to verify...

Entanglement replication in driven dissipative many-body systems.

Science.gov (United States)

Zippilli, S; Paternostro, M; Adesso, G; Illuminati, F

2013-01-25

We study the dissipative dynamics of two independent arrays of many-body systems, locally driven by a common entangled field. We show that in the steady state the entanglement of the driving field is reproduced in an arbitrarily large series of inter-array entangled pairs over all distances. Local nonclassical driving thus realizes a scale-free entanglement replication and long-distance entanglement distribution mechanism that has immediate bearing on the implementation of quantum communication networks.

Entanglement witnesses arising from exposed positive linear maps

OpenAIRE

Ha, Kil-Chan; Kye, Seung-Hyeok

2011-01-01

We consider entanglement witnesses arising from positive linear maps which generate exposed extremal rays. We show that every entanglement can be detected by one of these witnesses, and this witness detects a unique set of entanglement among those. Therefore, they provide a minimal set of witnesses to detect all entanglement in a sense. Furthermore, if those maps are indecomposable then they detect large classes of entanglement with positive partial transposes which have nonempty relative int...

Quantum Entanglement Growth under Random Unitary Dynamics

Directory of Open Access Journals (Sweden)

Adam Nahum

2017-07-01

Full Text Available Characterizing how entanglement grows with time in a many-body system, for example, after a quantum quench, is a key problem in nonequilibrium quantum physics. We study this problem for the case of random unitary dynamics, representing either Hamiltonian evolution with time-dependent noise or evolution by a random quantum circuit. Our results reveal a universal structure behind noisy entanglement growth, and also provide simple new heuristics for the “entanglement tsunami” in Hamiltonian systems without noise. In 1D, we show that noise causes the entanglement entropy across a cut to grow according to the celebrated Kardar-Parisi-Zhang (KPZ equation. The mean entanglement grows linearly in time, while fluctuations grow like (time^{1/3} and are spatially correlated over a distance ∝(time^{2/3}. We derive KPZ universal behavior in three complementary ways, by mapping random entanglement growth to (i a stochastic model of a growing surface, (ii a “minimal cut” picture, reminiscent of the Ryu-Takayanagi formula in holography, and (iii a hydrodynamic problem involving the dynamical spreading of operators. We demonstrate KPZ universality in 1D numerically using simulations of random unitary circuits. Importantly, the leading-order time dependence of the entropy is deterministic even in the presence of noise, allowing us to propose a simple coarse grained minimal cut picture for the entanglement growth of generic Hamiltonians, even without noise, in arbitrary dimensionality. We clarify the meaning of the “velocity” of entanglement growth in the 1D entanglement tsunami. We show that in higher dimensions, noisy entanglement evolution maps to the well-studied problem of pinning of a membrane or domain wall by disorder.

Quantum Entanglement Growth under Random Unitary Dynamics

Science.gov (United States)

Nahum, Adam; Ruhman, Jonathan; Vijay, Sagar; Haah, Jeongwan

2017-07-01

Characterizing how entanglement grows with time in a many-body system, for example, after a quantum quench, is a key problem in nonequilibrium quantum physics. We study this problem for the case of random unitary dynamics, representing either Hamiltonian evolution with time-dependent noise or evolution by a random quantum circuit. Our results reveal a universal structure behind noisy entanglement growth, and also provide simple new heuristics for the "entanglement tsunami" in Hamiltonian systems without noise. In 1D, we show that noise causes the entanglement entropy across a cut to grow according to the celebrated Kardar-Parisi-Zhang (KPZ) equation. The mean entanglement grows linearly in time, while fluctuations grow like (time )1/3 and are spatially correlated over a distance ∝(time )2/3. We derive KPZ universal behavior in three complementary ways, by mapping random entanglement growth to (i) a stochastic model of a growing surface, (ii) a "minimal cut" picture, reminiscent of the Ryu-Takayanagi formula in holography, and (iii) a hydrodynamic problem involving the dynamical spreading of operators. We demonstrate KPZ universality in 1D numerically using simulations of random unitary circuits. Importantly, the leading-order time dependence of the entropy is deterministic even in the presence of noise, allowing us to propose a simple coarse grained minimal cut picture for the entanglement growth of generic Hamiltonians, even without noise, in arbitrary dimensionality. We clarify the meaning of the "velocity" of entanglement growth in the 1D entanglement tsunami. We show that in higher dimensions, noisy entanglement evolution maps to the well-studied problem of pinning of a membrane or domain wall by disorder.

Gain maximization in a probabilistic entanglement protocol

Science.gov (United States)

di Lorenzo, Antonio; Esteves de Queiroz, Johnny Hebert

Entanglement is a resource. We can therefore define gain as a monotonic function of entanglement G (E) . If a pair with entanglement E is produced with probability P, the net gain is N = PG (E) - (1 - P) C , where C is the cost of a failed attempt. We study a protocol where a pair of quantum systems is produced in a maximally entangled state ρm with probability Pm, while it is produced in a partially entangled state ρp with the complementary probability 1 -Pm . We mix a fraction w of the partially entangled pairs with the maximally entangled ones, i.e. we take the state to be ρ = (ρm + wUlocρpUloc+) / (1 + w) , where Uloc is an appropriate unitary local operation designed to maximize the entanglement of ρ. This procedure on one hand reduces the entanglement E, and hence the gain, but on the other hand it increases the probability of success to P =Pm + w (1 -Pm) , therefore the net gain N may increase. There may be hence, a priori, an optimal value for w, the fraction of failed attempts that we mix in. We show that, in the hypothesis of a linear gain G (E) = E , even assuming a vanishing cost C -> 0 , the net gain N is increasing with w, therefore the best strategy is to always mix the partially entangled states. Work supported by CNPq, Conselho Nacional de Desenvolvimento Científico e Tecnológico, proc. 311288/2014-6, and by FAPEMIG, Fundação de Amparo à Pesquisa de Minas Gerais, proc. IC-FAPEMIG2016-0269 and PPM-00607-16.

Gauge field entanglement in Kitaev's honeycomb model

Science.gov (United States)

Dóra, Balázs; Moessner, Roderich

2018-01-01

A spin fractionalizes into matter and gauge fermions in Kitaev's spin liquid on the honeycomb lattice. This follows from a Jordan-Wigner mapping to fermions, allowing for the construction of a minimal entropy ground-state wave function on the cylinder. We use this to calculate the entanglement entropy by choosing several distinct partitionings. First, by partitioning an infinite cylinder into two, the -ln2 topological entanglement entropy is reconfirmed. Second, the reduced density matrix of the gauge sector on the full cylinder is obtained after tracing out the matter degrees of freedom. This allows for evaluating the gauge entanglement Hamiltonian, which contains infinitely long-range correlations along the symmetry axis of the cylinder. The matter-gauge entanglement entropy is (Ny-1 )ln2 , with Ny the circumference of the cylinder. Third, the rules for calculating the gauge sector entanglement of any partition are determined. Rather small correctly chosen gauge partitions can still account for the topological entanglement entropy in spite of long-range correlations in the gauge entanglement Hamiltonian.

Cosmological perturbations in the entangled inflationary universe

Science.gov (United States)

Robles-Pérez, Salvador J.

2018-03-01

In this paper, the model of a multiverse made up of universes that are created in entangled pairs that conserve the total momentum conjugated to the scale factor is presented. For the background spacetime, assumed is a Friedmann-Robertson-Walker metric with a scalar field with mass m minimally coupled to gravity. For the fields that propagate in the entangled spacetimes, the perturbations of the spacetime and the scalar field, whose quantum states become entangled too, are considered. They turn out to be in a quasithermal state, and the corresponding thermodynamical magnitudes are computed. Three observables are expected to be caused by the creation of the universes in entangled pairs: a modification of the Friedmann equation because of the entanglement of the spacetimes, a modification of the effective value of the potential of the scalar field by the backreaction of the perturbation modes, and a modification of the spectrum of fluctuations because the thermal distribution is induced by the entanglement of the partner universes. The later would be a distinctive feature of the creation of universes in entangled pairs.

Measurement-Device-Independent Approach to Entanglement Measures

Science.gov (United States)

Shahandeh, Farid; Hall, Michael J. W.; Ralph, Timothy C.

2017-04-01

Within the context of semiquantum nonlocal games, the trust can be removed from the measurement devices in an entanglement-detection procedure. Here, we show that a similar approach can be taken to quantify the amount of entanglement. To be specific, first, we show that in this context, a small subset of semiquantum nonlocal games is necessary and sufficient for entanglement detection in the local operations and classical communication paradigm. Second, we prove that the maximum payoff for these games is a universal measure of entanglement which is convex and continuous. Third, we show that for the quantification of negative-partial-transpose entanglement, this subset can be further reduced down to a single arbitrary element. Importantly, our measure is measurement device independent by construction and operationally accessible. Finally, our approach straightforwardly extends to quantify the entanglement within any partitioning of multipartite quantum states.

Effect of two-qutrit entanglement on quantum speed limit time of a bipartite V-type open system

Energy Technology Data Exchange (ETDEWEB)

Behzadi, N., E-mail: n.behzadi@tabrizu.ac.ir [Research Institute for Fundamental Sciences, University of Tabriz (Iran, Islamic Republic of); Ahansaz, B.; Ektesabi, A.; Faizi, E. [Physics Department, Azarbaijan Shahid Madani University, Tabriz (Iran, Islamic Republic of)

2017-03-15

In the present paper, quantum speed limit (QSL) time of a bipartite V-type three-level atomic system under the effect of two-qutrit entanglement is investigated. Each party interacts with own independent reservoir. By considering two local unitarily equivalent Werner states and the Horodecki PPT state, as initial states, the QSL time is evaluated for each of them in the respective entangled regions. It is counterintuitively observed that the effect of entanglement on the QSL time driven from each of the initial Werner states are completely different when the degree of non-Markovianity is considerable. In addition, it is interesting that the effect of entanglement of the non-equivalent Horodecki state on the calculated QSL time displays an intermediate behavior relative to the cases obtained for the Werner states.

Minimal Entanglement Witness From Electrical Current Correlations

OpenAIRE

Brange, F.; Malkoc, O.; Samuelsson, P.

2016-01-01

Despite great efforts, an unambiguous demonstration of entanglement of mobile electrons in solid state conductors is still lacking. Investigating theoretically a generic entangler-detector setup, we here show that a witness of entanglement between two flying electron qubits can be constructed from only two current cross correlation measurements, for any nonzero detector efficiencies and non-collinear polarization vectors. We find that all entangled pure states, but not all mixed ones, can be ...

Bound entanglement and local realism

International Nuclear Information System (INIS)

Kaszlikowski, Dagomir; Zukowski, Marek; Gnacinski, Piotr

2002-01-01

We show using a numerical approach, which gives necessary and sufficient conditions for the existence of local realism, that the bound entangled state presented in Bennett et al. [Phys. Rev. Lett. 82, 5385 (1999)] admits a local and realistic description. We also find the lowest possible amount of some appropriate entangled state that must be ad-mixed to the bound entangled state so that the resulting density operator has no local and realistic description and as such can be useful in quantum communication and quantum computation

Entanglement fidelity of the standard quantum teleportation channel

Energy Technology Data Exchange (ETDEWEB)

Li, Gang; Ye, Ming-Yong, E-mail: myye@fjnu.edu.cn; Lin, Xiu-Min

2013-09-16

We consider the standard quantum teleportation protocol where a general bipartite state is used as entanglement resource. We use the entanglement fidelity to describe how well the standard quantum teleportation channel transmits quantum entanglement and give a simple expression for the entanglement fidelity when it is averaged on all input states.

Experimental demonstration of high fidelity entanglement distribution over decoherence channels via qubit transduction.

Science.gov (United States)

Lim, Hyang-Tag; Hong, Kang-Hee; Kim, Yoon-Ho

2015-10-21

Quantum coherence and entanglement, which are essential resources for quantum information, are often degraded and lost due to decoherence. Here, we report a proof-of-principle experimental demonstration of high fidelity entanglement distribution over decoherence channels via qubit transduction. By unitarily switching the initial qubit encoding to another, which is insensitive to particular forms of decoherence, we have demonstrated that it is possible to avoid the effect of decoherence completely. In particular, we demonstrate high-fidelity distribution of photonic polarization entanglement over quantum channels with two types of decoherence, amplitude damping and polarization-mode dispersion, via qubit transduction between polarization qubits and dual-rail qubits. These results represent a significant breakthrough in quantum communication over decoherence channels as the protocol is input-state independent, requires no ancillary photons and symmetries, and has near-unity success probability.

Maximally multipartite entangled states

Science.gov (United States)

Facchi, Paolo; Florio, Giuseppe; Parisi, Giorgio; Pascazio, Saverio

2008-06-01

We introduce the notion of maximally multipartite entangled states of n qubits as a generalization of the bipartite case. These pure states have a bipartite entanglement that does not depend on the bipartition and is maximal for all possible bipartitions. They are solutions of a minimization problem. Examples for small n are investigated, both analytically and numerically.

Entangled states in quantum mechanics

Science.gov (United States)

Ruža, Jānis

2010-01-01

In some circles of quantum physicists, a view is maintained that the nonseparability of quantum systems-i.e., the entanglement-is a characteristic feature of quantum mechanics. According to this view, the entanglement plays a crucial role in the solution of quantum measurement problem, the origin of the “classicality” from the quantum physics, the explanation of the EPR paradox by a nonlocal character of the quantum world. Besides, the entanglement is regarded as a cornerstone of such modern disciplines as quantum computation, quantum cryptography, quantum information, etc. At the same time, entangled states are well known and widely used in various physics areas. In particular, this notion is widely used in nuclear, atomic, molecular, solid state physics, in scattering and decay theories as well as in other disciplines, where one has to deal with many-body quantum systems. One of the methods, how to construct the basis states of a composite many-body quantum system, is the so-called genealogical decomposition method. Genealogical decomposition allows one to construct recurrently by particle number the basis states of a composite quantum system from the basis states of its forming subsystems. These coupled states have a structure typical for entangled states. If a composite system is stable, the internal structure of its forming basis states does not manifest itself in measurements. However, if a composite system is unstable and decays onto its forming subsystems, then the measurables are the quantum numbers, associated with these subsystems. In such a case, the entangled state has a dynamical origin, determined by the Hamiltonian of the corresponding decay process. Possible correlations between the quantum numbers of resulting subsystems are determined by the symmetries-conservation laws of corresponding dynamical variables, and not by the quantum entanglement feature.

Entanglement entropy and nonabelian gauge symmetry

International Nuclear Information System (INIS)

Donnelly, William

2014-01-01

Entanglement entropy has proven to be an extremely useful concept in quantum field theory. Gauge theories are of particular interest, but for these systems the entanglement entropy is not clearly defined because the physical Hilbert space does not factor as a tensor product according to regions of space. Here we review a definition of entanglement entropy that applies to abelian and nonabelian lattice gauge theories. This entanglement entropy is obtained by embedding the physical Hilbert space into a product of Hilbert spaces associated to regions with boundary. The latter Hilbert spaces include degrees of freedom on the entangling surface that transform like surface charges under the gauge symmetry. These degrees of freedom are shown to contribute to the entanglement entropy, and the form of this contribution is determined by the gauge symmetry. We test our definition using the example of two-dimensional Yang–Mills theory, and find that it agrees with the thermal entropy in de Sitter space, and with the results of the Euclidean replica trick. We discuss the possible implications of this result for more complicated gauge theories, including quantum gravity. (paper)

Quantum entanglement and special relativity

International Nuclear Information System (INIS)

Nishikawa, Yoshihisa

2008-01-01

Quantum entanglement was suggested by Einstein to indicate that quantum mechanics was incomplete. However, against Einstein's expectation, the phenomenon due to quantum entanglement has been verified by experiments. Recently, in quantum information theory, it has been also treated as a resource for quantum teleportation and so on. In around 2000, it is recognized that quantum correlations between two particles of one pair state in an entangled spin-state are affected by the non-trivial effect due to the successive Lorentz transformation. This relativistic effect is called the Wigner rotation. The Wigner rotation has to been taken into account when we observe spin-correlation of moving particles in a different coordinate frame. In this paper, first, we explain quantum entanglement and its modification due to the Wigner rotation. After that, we introduce an extended model instead of one pair state model. In the extended model, quantum entanglement state is prepared as a superposition state of various pair states. We have computed the von Neumann entropy and the Shannon entropy to see the global behavior of variation for the spin correlation due to the relativistic effect. We also discuss distinguishability between the two particles of the pair. (author)

Energy entanglement relation for quantum energy teleportation

Energy Technology Data Exchange (ETDEWEB)

Hotta, Masahiro, E-mail: hotta@tuhep.phys.tohoku.ac.j [Department of Physics, Faculty of Science, Tohoku University, Sendai 980-8578 (Japan)

2010-07-26

Protocols of quantum energy teleportation (QET), while retaining causality and local energy conservation, enable the transportation of energy from a subsystem of a many-body quantum system to a distant subsystem by local operations and classical communication through ground-state entanglement. We prove two energy-entanglement inequalities for a minimal QET model. These relations help us to gain a profound understanding of entanglement itself as a physical resource by relating entanglement to energy as an evident physical resource.

Entanglement Equilibrium and the Einstein Equation.

Science.gov (United States)

Jacobson, Ted

2016-05-20

A link between the semiclassical Einstein equation and a maximal vacuum entanglement hypothesis is established. The hypothesis asserts that entanglement entropy in small geodesic balls is maximized at fixed volume in a locally maximally symmetric vacuum state of geometry and quantum fields. A qualitative argument suggests that the Einstein equation implies the validity of the hypothesis. A more precise argument shows that, for first-order variations of the local vacuum state of conformal quantum fields, the vacuum entanglement is stationary if and only if the Einstein equation holds. For nonconformal fields, the same conclusion follows modulo a conjecture about the variation of entanglement entropy.

Quantum key distribution with entangled photon sources

International Nuclear Information System (INIS)

Ma Xiongfeng; Fung, Chi-Hang Fred; Lo, H.-K.

2007-01-01

A parametric down-conversion (PDC) source can be used as either a triggered single-photon source or an entangled-photon source in quantum key distribution (QKD). The triggering PDC QKD has already been studied in the literature. On the other hand, a model and a post-processing protocol for the entanglement PDC QKD are still missing. We fill in this important gap by proposing such a model and a post-processing protocol for the entanglement PDC QKD. Although the PDC model is proposed to study the entanglement-based QKD, we emphasize that our generic model may also be useful for other non-QKD experiments involving a PDC source. Since an entangled PDC source is a basis-independent source, we apply Koashi and Preskill's security analysis to the entanglement PDC QKD. We also investigate the entanglement PDC QKD with two-way classical communications. We find that the recurrence scheme increases the key rate and the Gottesman-Lo protocol helps tolerate higher channel losses. By simulating a recent 144-km open-air PDC experiment, we compare three implementations: entanglement PDC QKD, triggering PDC QKD, and coherent-state QKD. The simulation result suggests that the entanglement PDC QKD can tolerate higher channel losses than the coherent-state QKD. The coherent-state QKD with decoy states is able to achieve highest key rate in the low- and medium-loss regions. By applying the Gottesman-Lo two-way post-processing protocol, the entanglement PDC QKD can tolerate up to 70 dB combined channel losses (35 dB for each channel) provided that the PDC source is placed in between Alice and Bob. After considering statistical fluctuations, the PDC setup can tolerate up to 53 dB channel losses

Zero modes and entanglement entropy

Energy Technology Data Exchange (ETDEWEB)

Yazdi, Yasaman K. [Perimeter Institute for Theoretical Physics,31 Caroline St. N., Waterloo, ON, N2L 2Y5 (Canada); Department of Physics and Astronomy, University of Waterloo,200 University Avenue West, Waterloo, ON, N2L 3G1 (Canada)

2017-04-26

Ultraviolet divergences are widely discussed in studies of entanglement entropy. Also present, but much less understood, are infrared divergences due to zero modes in the field theory. In this note, we discuss the importance of carefully handling zero modes in entanglement entropy. We give an explicit example for a chain of harmonic oscillators in 1D, where a mass regulator is necessary to avoid an infrared divergence due to a zero mode. We also comment on a surprising contribution of the zero mode to the UV-scaling of the entanglement entropy.

Slow Images and Entangled Photons

International Nuclear Information System (INIS)

Swordy, Simon

2007-01-01

I will discuss some recent experiments using slow light and entangled photons. We recently showed that it was possible to map a two dimensional image onto very low light level signals, slow them down in a hot atomic vapor while preserving the amplitude and phase of the images. If time remains, I will discuss some of our recent work with time-energy entangled photons for quantum cryptography. We were able to show that we could have a measurable state space of over 1000 states for a single pair of entangled photons in fiber.

Generic entangling through quantum indistinguishability

Indian Academy of Sciences (India)

quantum systems (methods such as entanglement swapping [5] fall in this ... continued till the particles anti-bunch, in which case they are entangled. 2. .... in the context of the scattering of ballistic electrons from a magnetic impurity in a semi-.

Entanglement model of homeopathy as an example of generalized entanglement predicted by weak quantum theory.

Science.gov (United States)

Walach, H

2003-08-01

Homeopathy is scientifically banned, both for lack of consistent empirical findings, but more so for lack of a sound theoretical model to explain its purported effects. This paper makes an attempt to introduce an explanatory idea based on a generalized version of quantum mechanics (QM), the weak quantum theory (WQT). WQT uses the algebraic formalism of QM proper, but drops some restrictions and definitions typical for QM. This results in a general axiomatic framework similar to QM, but more generalized and applicable to all possible systems. Most notably, WQT predicts entanglement, which in QM is known as Einstein-Podolsky-Rosen (EPR) correlatedness within quantum systems. According to WQT, this entanglement is not only tied to quantum systems, but is to be expected whenever a global and a local variable describing a system are complementary. This idea is used here to reconstruct homeopathy as an exemplification of generalized entanglement as predicted by WQT. It transpires that homeopathy uses two instances of generalized entanglement: one between the remedy and the original substance (potentiation principle) and one between the individual symptoms of a patient and the general symptoms of a remedy picture (similarity principle). By bringing these two elements together, double entanglement ensues, which is reminiscent of cryptographic and teleportation applications of entanglement in QM proper. Homeopathy could be a macroscopic analogue to quantum teleportation. This model is exemplified and some predictions are derived, which make it possible to test the model. Copyright 2003 S. Karger GmbH, Freiburg

Thermal entanglement in an orthogonal dimer-plaquette chain with alternating Ising–Heisenberg coupling

International Nuclear Information System (INIS)

Paulinelli, H G; De Souza, S M; Rojas, Onofre

2013-01-01

In this paper we explore the entanglement in an orthogonal dimer-plaquette Ising–Heisenberg chain, assembled between plaquette edges, also known as orthogonal dimer plaquettes. The quantum entanglement properties involving an infinite chain structure are quite important, not only because the mathematical calculation is cumbersome but also because real materials are well represented by infinite chains. Using the local gauge symmetry of this model, we are able to map onto a simple spin-1 like Ising and spin-1/2 Heisenberg dimer model with single effective ion anisotropy. Thereafter this model can be solved using the decoration transformation and transfer matrix approach. First, we discuss the phase diagram at zero temperature of this model, where we find five ground states, one ferromagnetic, one antiferromagnetic, one triplet–triplet disordered and one triplet–singlet disordered phase, beside a dimer ferromagnetic–antiferromagnetic phase. In addition, we discuss the thermodynamic properties such as entropy, where we display the residual entropy. Furthermore, using the nearest site correlation function it is possible also to analyze the pairwise thermal entanglement for both orthogonal dimers. Additionally, we discuss the threshold temperature of the entangled region as a function of Hamiltonian parameters. We find a quite interesting thin reentrance threshold temperature for one of the dimers, and we also discuss the differences and similarities for both dimers. (paper)

Statistical bounds on the dynamical production of entanglement

International Nuclear Information System (INIS)

Abreu, Romulo F.; Vallejos, Raul O.

2007-01-01

We present a random-matrix analysis of the entangling power of a unitary operator as a function of the number of times it is iterated. We consider unitaries belonging to the circular ensembles of random matrices [the circular unitary (CUE) or circular orthogonal ensemble] applied to random (real or complex) nonentangled states. We verify numerically that the average entangling power is a monotonically decreasing function of time. The same behavior is observed for the 'operator entanglement' - an alternative measure of the entangling strength of a unitary operator. On the analytical side we calculate the CUE operator entanglement and asymptotic values for the entangling power. We also provide a theoretical explanation of the time dependence in the CUE cases

Experimental observation of entanglement duality for identical particles

International Nuclear Information System (INIS)

Ma, J-J; Yuan, X-X; Zu, C; Chang, X-Y; Hou, P-Y; Duan, L-M

2014-01-01

It was shown recently that entanglement of identical particles has a feature called dualism (Bose and Home 2013 Phys. Rev. Lett. 110 140404), which is fundamentally connected with quantum indistinguishability. Here we report an experiment that observes the entanglement duality for the first time with two identical photons, which manifest polarization entanglement when labeled by different paths or path entanglement when labeled by polarization states. By adjusting the mismatch in frequency or arrival time of the entangled photons, we tune the photon indistinguishability from the quantum to the classical limit and observe that the entanglement duality disappears under the emergence of classical distinguishability, confirming it as a characteristic feature of quantum indistinguishable particles. (paper)

The geometry of entanglement and Grover's algorithm

International Nuclear Information System (INIS)

Iwai, Toshihiro; Hayashi, Naoki; Mizobe, Kimitake

2008-01-01

A measure of entanglement with respect to a bipartite partition of n-qubit has been defined and studied from the viewpoint of Riemannian geometry (Iwai 2007 J. Phys. A: Math. Theor. 40 12161). This paper has two aims. One is to study further the geometry of entanglement, and the other is to investigate Grover's search algorithms, both the original and the fixed-point ones, in reference with entanglement. As the distance between the maximally entangled states and the separable states is known already in the previous paper, this paper determines the set of maximally entangled states nearest to a typical separable state which is used as an initial state in Grover's search algorithms, and to find geodesic segments which realize the above-mentioned distance. As for Grover's algorithms, it is already known that while the initial and the target states are separable, the algorithms generate sequences of entangled states. This fact is confirmed also in the entanglement measure proposed in the previous paper, and then a split Grover algorithm is proposed which generates sequences of separable states only with respect to the bipartite partition

Optomechanical entanglement via non-degenerate parametric interactions

Science.gov (United States)

Ahmed, Rizwan; Qamar, Shahid

2017-10-01

We present a scheme for the optomechanical entanglement between a micro-mechanical mirror and the field inside a bimodal cavity system using a non-degenerate optical parametric amplifier (NOPA). Our results show that the introduction of NOPA makes the entanglement stronger or more robust against the mean number of average thermal phonons and cavity decay. Interestingly, macroscopic entanglement depends upon the choice of the phase associated with classical field driving NOPA. We also consider the effects of input laser power on optomechanical entanglement.

Quantum Entanglement: Separability, Measure, Fidelity of Teleportation, and Distillation

Directory of Open Access Journals (Sweden)

Ming Li

2010-01-01

Full Text Available Quantum entanglement plays crucial roles in quantum information processing. Quantum entangled states have become the key ingredient in the rapidly expanding field of quantum information science. Although the nonclassical nature of entanglement has been recognized for many years, considerable efforts have been taken to understand and characterize its properties recently. In this review, we introduce some recent results in the theory of quantum entanglement. In particular separability criteria based on the Bloch representation, covariance matrix, normal form and entanglement witness, lower bounds, subadditivity property of concurrence and tangle, fully entangled fraction related to the optimal fidelity of quantum teleportation, and entanglement distillation will be discussed in detail.

Probabilistic Teleportation of a Four-Particle Entangled State

Institute of Scientific and Technical Information of China (English)

ZHAN You-Bang; FU Hao; DONG Zheng-Chao

2005-01-01

A Scheme for teleporting an unknown four-particle entangled state is proposed via entangled swapping. In this scheme, four pairs of entangled particles are used as quantum channel. It is shown that, if the four pairs of particles are nonmaximally entangled, the teleportation can be successfully realized with certain probability if a receiver adopts some appropriate unitary transformations.

Entangled photons from single atoms and molecules

Science.gov (United States)

Nordén, Bengt

2018-05-01

The first two-photon entanglement experiment performed 50 years ago by Kocher and Commins (KC) provided isolated pairs of entangled photons from an atomic three-state fluorescence cascade. In view of questioning of Bell's theorem, data from these experiments are re-analyzed and shown sufficiently precise to confirm quantum mechanical and dismiss semi-classical theory without need for Bell's inequalities. Polarization photon correlation anisotropy (A) is useful: A is near unity as predicted quantum mechanically and well above the semi-classic range, 0 ⩽ A ⩽ 1 / 2 . Although yet to be found, one may envisage a three-state molecule emitting entangled photon pairs, in analogy with the KC atomic system. Antibunching in fluorescence from single molecules in matrix and entangled photons from quantum dots promise it be possible. Molecules can have advantages to parametric down-conversion as the latter photon distribution is Poissonian and unsuitable for producing isolated pairs of entangled photons. Analytical molecular applications of entangled light are also envisaged.

Maximal Entanglement in High Energy Physics

Directory of Open Access Journals (Sweden)

Alba Cervera-Lierta, José I. Latorre, Juan Rojo, Luca Rottoli

2017-11-01

Full Text Available We analyze how maximal entanglement is generated at the fundamental level in QED by studying correlations between helicity states in tree-level scattering processes at high energy. We demonstrate that two mechanisms for the generation of maximal entanglement are at work: i $s$-channel processes where the virtual photon carries equal overlaps of the helicities of the final state particles, and ii the indistinguishable superposition between $t$- and $u$-channels. We then study whether requiring maximal entanglement constrains the coupling structure of QED and the weak interactions. In the case of photon-electron interactions unconstrained by gauge symmetry, we show how this requirement allows reproducing QED. For $Z$-mediated weak scattering, the maximal entanglement principle leads to non-trivial predictions for the value of the weak mixing angle $\\theta_W$. Our results are a first step towards understanding the connections between maximal entanglement and the fundamental symmetries of high-energy physics.

Initial conditions and entanglement sudden death

International Nuclear Information System (INIS)

Qian, Xiao-Feng; Eberly, J.H.

2012-01-01

We report results bearing on the behavior of non-local decoherence and its potential for being managed or even controlled. The decoherence process known as entanglement sudden death (ESD) can drive prepared entanglement to zero at the same time that local coherences and fidelity remain non-zero. For a generic ESD-susceptible Bell superposition state, we provide rules restricting the occurrence and timing of ESD, amounting to management tools over a continuous variation of initial conditions. These depend on only three parameters: initial purity, entanglement and excitation. Knowledge or control of initial phases is not needed. -- Highlights: ► We study the possibility of managing disentanglement through initial conditions. ► The initial parameters are the amount of entanglement, excitation, and purity. ► Entanglement sudden death (ESD) free and ESD susceptible phases are identified. ► ESD onset time is also presented in the ESD susceptible phase. ► Our results may guide experiments to prepare ESD free or delayed ESD states.

Real-time imaging of quantum entanglement.

Science.gov (United States)

Fickler, Robert; Krenn, Mario; Lapkiewicz, Radek; Ramelow, Sven; Zeilinger, Anton

2013-01-01

Quantum Entanglement is widely regarded as one of the most prominent features of quantum mechanics and quantum information science. Although, photonic entanglement is routinely studied in many experiments nowadays, its signature has been out of the grasp for real-time imaging. Here we show that modern technology, namely triggered intensified charge coupled device (ICCD) cameras are fast and sensitive enough to image in real-time the effect of the measurement of one photon on its entangled partner. To quantitatively verify the non-classicality of the measurements we determine the detected photon number and error margin from the registered intensity image within a certain region. Additionally, the use of the ICCD camera allows us to demonstrate the high flexibility of the setup in creating any desired spatial-mode entanglement, which suggests as well that visual imaging in quantum optics not only provides a better intuitive understanding of entanglement but will improve applications of quantum science.

Entanglement of purification: from spin chains to holography

Science.gov (United States)

Nguyen, Phuc; Devakul, Trithep; Halbasch, Matthew G.; Zaletel, Michael P.; Swingle, Brian

2018-01-01

Purification is a powerful technique in quantum physics whereby a mixed quantum state is extended to a pure state on a larger system. This process is not unique, and in systems composed of many degrees of freedom, one natural purification is the one with minimal entanglement. Here we study the entropy of the minimally entangled purification, called the entanglement of purification, in three model systems: an Ising spin chain, conformal field theories holographically dual to Einstein gravity, and random stabilizer tensor networks. We conjecture values for the entanglement of purification in all these models, and we support our conjectures with a variety of numerical and analytical results. We find that such minimally entangled purifications have a number of applications, from enhancing entanglement-based tensor network methods for describing mixed states to elucidating novel aspects of the emergence of geometry from entanglement in the AdS/CFT correspondence.

Controlling bi-partite entanglement in multi-qubit systems

International Nuclear Information System (INIS)

Plesch, Martin; Novotny, Jaroslav; Dzurakova, Zuzana; Buzek, VladimIr

2004-01-01

Bi-partite entanglement in multi-qubit systems cannot be shared freely. The rules of quantum mechanics impose bounds on how multi-qubit systems can be correlated. In this paper, we utilize a concept of entangled graphs with weighted edges in order to analyse pure quantum states of multi-qubit systems. Here qubits are represented by vertexes of the graph, while the presence of bi-partite entanglement is represented by an edge between corresponding vertexes. The weight of each edge is defined to be the entanglement between the two qubits connected by the edge, as measured by the concurrence. We prove that each entangled graph with entanglement bounded by a specific value of the concurrence can be represented by a pure multi-qubit state. In addition, we present a logic network with O(N 2 ) elementary gates that can be used for preparation of the weighted entangled graphs of N qubits

Controlling bi-partite entanglement in multi-qubit systems

Science.gov (United States)

Plesch, Martin; Novotný, Jaroslav; Dzuráková, Zuzana; Buzek, Vladimír

2004-02-01

Bi-partite entanglement in multi-qubit systems cannot be shared freely. The rules of quantum mechanics impose bounds on how multi-qubit systems can be correlated. In this paper, we utilize a concept of entangled graphs with weighted edges in order to analyse pure quantum states of multi-qubit systems. Here qubits are represented by vertexes of the graph, while the presence of bi-partite entanglement is represented by an edge between corresponding vertexes. The weight of each edge is defined to be the entanglement between the two qubits connected by the edge, as measured by the concurrence. We prove that each entangled graph with entanglement bounded by a specific value of the concurrence can be represented by a pure multi-qubit state. In addition, we present a logic network with O(N2) elementary gates that can be used for preparation of the weighted entangled graphs of N qubits.

Hybrid Long-Distance Entanglement Distribution Protocol

DEFF Research Database (Denmark)

Brask, J.B.; Rigas, I.; Polzik, E.S.

2010-01-01

We propose a hybrid (continuous-discrete variable) quantum repeater protocol for long-distance entanglement distribution. Starting from states created by single-photon detection, we show how entangled coherent state superpositions can be generated by means of homodyne detection. We show that near......-deterministic entanglement swapping with such states is possible using only linear optics and homodyne detectors, and we evaluate the performance of our protocol combining these elements....

Multi-Photon Entanglement and Quantum Teleportation

National Research Council Canada - National Science Library

Shih, Yanhua

1999-01-01

The project 'Multi-Photon Entanglement and Quantum Teleportation' concerns a series of experimental and theoretical investigations on multi-photon entangled states and the applications, for example...

Entanglement-assisted quantum feedback control

Science.gov (United States)

Yamamoto, Naoki; Mikami, Tomoaki

2017-07-01

The main advantage of quantum metrology relies on the effective use of entanglement, which indeed allows us to achieve strictly better estimation performance over the standard quantum limit. In this paper, we propose an analogous method utilizing entanglement for the purpose of feedback control. The system considered is a general linear dynamical quantum system, where the control goal can be systematically formulated as a linear quadratic Gaussian control problem based on the quantum Kalman filtering method; in this setting, an entangled input probe field is effectively used to reduce the estimation error and accordingly the control cost function. In particular, we show that, in the problem of cooling an opto-mechanical oscillator, the entanglement-assisted feedback control can lower the stationary occupation number of the oscillator below the limit attainable by the controller with a coherent probe field and furthermore beats the controller with an optimized squeezed probe field.

Gaussian entanglement distribution via satellite

Science.gov (United States)

Hosseinidehaj, Nedasadat; Malaney, Robert

2015-02-01

In this work we analyze three quantum communication schemes for the generation of Gaussian entanglement between two ground stations. Communication occurs via a satellite over two independent atmospheric fading channels dominated by turbulence-induced beam wander. In our first scheme, the engineering complexity remains largely on the ground transceivers, with the satellite acting simply as a reflector. Although the channel state information of the two atmospheric channels remains unknown in this scheme, the Gaussian entanglement generation between the ground stations can still be determined. On the ground, distillation and Gaussification procedures can be applied, leading to a refined Gaussian entanglement generation rate between the ground stations. We compare the rates produced by this first scheme with two competing schemes in which quantum complexity is added to the satellite, thereby illustrating the tradeoff between space-based engineering complexity and the rate of ground-station entanglement generation.

Optomechanical entanglement via non-degenerate parametric interactions

International Nuclear Information System (INIS)

Ahmed, Rizwan; Qamar, Shahid

2017-01-01

We present a scheme for the optomechanical entanglement between a micro-mechanical mirror and the field inside a bimodal cavity system using a non-degenerate optical parametric amplifier (NOPA). Our results show that the introduction of NOPA makes the entanglement stronger or more robust against the mean number of average thermal phonons and cavity decay. Interestingly, macroscopic entanglement depends upon the choice of the phase associated with classical field driving NOPA. We also consider the effects of input laser power on optomechanical entanglement. (paper)

Multipartite entanglement via the Mayer-Vietoris theorem

Science.gov (United States)

Patrascu, Andrei T.

2017-10-01

The connection between entanglement and topology manifests itself in the form of the ER-EPR duality. This statement however refers to the maximally entangled states only. In this article I study the multipartite entanglement and the way in which it relates to the topological interpretation of the ER-EPR duality. The 2 dimensional genus 1 torus will be generalised to a n-dimensional general torus, where the information about the multipartite entanglement will be encoded in the higher inclusion maps of the Mayer-Vietorist sequence.

Continuous-variable entanglement sharing in noninertial frames

International Nuclear Information System (INIS)

Adesso, Gerardo; Fuentes-Schuller, Ivette; Ericsson, Marie

2007-01-01

We study the distribution of entanglement between modes of a free scalar field from the perspective of observers in uniform acceleration. We consider a two-mode squeezed state of the field from an inertial perspective, and analytically study the degradation of entanglement due to the Unruh effect, in the cases of either one or both observers undergoing uniform acceleration. We find that, for two observers undergoing finite acceleration, the entanglement vanishes between the lowest-frequency modes. The loss of entanglement is precisely explained as a redistribution of the inertial entanglement into multipartite quantum correlations among accessible and inaccessible modes from a noninertial perspective. We show that classical correlations are also lost from the perspective of two accelerated observers but conserved if one of the observers remains inertial

Wormholes and entanglement

International Nuclear Information System (INIS)

John C Baez; Vicary, Jamie

2014-01-01

Maldacena and Susskind have proposed a correspondence between wormholes and entanglement, dubbed ER=EPR. We study this in the context of three-dimensional topological quantum field theory (TQFT), where we show that the formation of a wormhole is the same process as creating a particle–antiparticle pair. A key feature of the ER=EPR proposal is that certain apparently entangled degrees of freedom turn out to be the same. We name this phenomenon ‘fake entanglement’, and show how it arises in our TQFT model. (paper)

Quantum separability and entanglement detection via entanglement-witness search and global optimization

International Nuclear Information System (INIS)

Ioannou, Lawrence M.; Travaglione, Benjamin C.

2006-01-01

We focus on determining the separability of an unknown bipartite quantum state ρ by invoking a sufficiently large subset of all possible entanglement witnesses given the expected value of each element of a set of mutually orthogonal observables. We review the concept of an entanglement witness from the geometrical point of view and use this geometry to show that the set of separable states is not a polytope and to characterize the class of entanglement witnesses (observables) that detect entangled states on opposite sides of the set of separable states. All this serves to motivate a classical algorithm which, given the expected values of a subset of an orthogonal basis of observables of an otherwise unknown quantum state, searches for an entanglement witness in the span of the subset of observables. The idea of such an algorithm, which is an efficient reduction of the quantum separability problem to a global optimization problem, was introduced by [Ioannou et al., Phys. Rev. A 70, 060303(R)], where it was shown to be an improvement on the naive approach for the quantum separability problem (exhaustive search for a decomposition of the given state into a convex combination of separable states). The last section of the paper discusses in more generality such algorithms, which, in our case, assume a subroutine that computes the global maximum of a real function of several variables. Despite this, we anticipate that such algorithms will perform sufficiently well on small instances that they will render a feasible test for separability in some cases of interest (e.g., in 3x3 dimensional systems)

Two-point entanglement near a quantum phase transition

International Nuclear Information System (INIS)

Chen, Han-Dong

2007-01-01

In this work, we study the two-point entanglement S(i, j), which measures the entanglement between two separated degrees of freedom (ij) and the rest of system, near a quantum phase transition. Away from the critical point, S(i, j) saturates with a characteristic length scale ξ E , as the distance |i - j| increases. The entanglement length ξ E agrees with the correlation length. The universality and finite size scaling of entanglement are demonstrated in a class of exactly solvable one-dimensional spin model. By connecting the two-point entanglement to correlation functions in the long range limit, we argue that the prediction power of a two-point entanglement is universal as long as the two involved points are separated far enough

Entanglement dynamics in itinerant fermionic and bosonic systems

Science.gov (United States)

Pillarishetty, Durganandini

2017-04-01

The concept of quantum entanglement of identical particles is fundamental in a wide variety of quantum information contexts involving composite quantum systems. However, the role played by particle indistinguishabilty in entanglement determination is being still debated. In this work, we study, theoretically, the entanglement dynamics in some itinerant bosonic and fermionic systems. We show that the dynamical behaviour of particle entanglement and spatial or mode entanglement are in general different. We also discuss the effect of fermionic and bosonic statistics on the dynamical behaviour. We suggest that the different dynamical behaviour can be used to distinguish between particle and mode entanglement in identical particle systems and discuss possible experimental realizations for such studies. I acknowledge financial support from DST, India through research Grant.

Optimal use of multipartite entanglement for continuous variable teleportation

International Nuclear Information System (INIS)

Adesso, G.; Illuminati, F.

2005-01-01

Full text: In this work we discuss how continuous variable teleportation takes advantage of the quadrature entanglement in different ways, depending on the preparation of the entangled state. For a given amount of the entanglement resource, we describe the best production scheme for a two-mode Gaussian state, which enables quantum teleportation with optimal fidelity. We extend this study to multiparty entangled Gaussian states and define an operative measure of multipartite entanglement related to the optimal fidelity in a quantum teleportation network experiment. This optimal fidelity is shown to be equivalent to the entanglement of formation for the standard two-user protocol, and to the multipartite localizable entanglement for the multiuser protocol. (author)

Probability-density-function characterization of multipartite entanglement

International Nuclear Information System (INIS)

Facchi, P.; Florio, G.; Pascazio, S.

2006-01-01

We propose a method to characterize and quantify multipartite entanglement for pure states. The method hinges upon the study of the probability density function of bipartite entanglement and is tested on an ensemble of qubits in a variety of situations. This characterization is also compared to several measures of multipartite entanglement

Experimental determination of entanglement with a single measurement.

Science.gov (United States)

Walborn, S P; Souto Ribeiro, P H; Davidovich, L; Mintert, F; Buchleitner, A

2006-04-20

Nearly all protocols requiring shared quantum information--such as quantum teleportation or key distribution--rely on entanglement between distant parties. However, entanglement is difficult to characterize experimentally. All existing techniques for doing so, including entanglement witnesses or Bell inequalities, disclose the entanglement of some quantum states but fail for other states; therefore, they cannot provide satisfactory results in general. Such methods are fundamentally different from entanglement measures that, by definition, quantify the amount of entanglement in any state. However, these measures suffer from the severe disadvantage that they typically are not directly accessible in laboratory experiments. Here we report a linear optics experiment in which we directly observe a pure-state entanglement measure, namely concurrence. Our measurement set-up includes two copies of a quantum state: these 'twin' states are prepared in the polarization and momentum degrees of freedom of two photons, and concurrence is measured with a single, local measurement on just one of the photons.

Dynamics of entanglement under decoherence in noninertial frames

International Nuclear Information System (INIS)

Shi Jia-Dong; Wu Tao; Song Xue-Ke; Ye Liu

2014-01-01

In this paper, we investigate the entanglement dynamics of a two-qubit entangled state coupled with its noisy environment, and plan to utilize weak measurement and quantum reversal measurement to study the entanglement dynamics under different decoherence channels in noninertial frames. Through the calculations and analyses, it is shown that the weak measurement can prevent entanglement from coupling to the amplitude damping channel, while the system is under the phase damping and flip channels. This protection protocol cannot prevent entanglement but will accelerate the death of entanglement. In addition, if the system is in the noninertial reference frame, then the effect of weak measurement will be weakened for the amplitude damping channel. Nevertheless, for other decoherence channels, the Unruh effect does not affect the quantum weak measurement, the only exception is that the maximum value of entanglement is reduced to √2/2 of the original value in the inertial frames. (general)

Task-oriented maximally entangled states

International Nuclear Information System (INIS)

Agrawal, Pankaj; Pradhan, B

2010-01-01

We introduce the notion of a task-oriented maximally entangled state (TMES). This notion depends on the task for which a quantum state is used as the resource. TMESs are the states that can be used to carry out the task maximally. This concept may be more useful than that of a general maximally entangled state in the case of a multipartite system. We illustrate this idea by giving an operational definition of maximally entangled states on the basis of communication tasks of teleportation and superdense coding. We also give examples and a procedure to obtain such TMESs for n-qubit systems.

Attack-Induced Entanglement of Noninteracting Fermi Gas

International Nuclear Information System (INIS)

Ren Jie; Zhu Shiqun

2008-01-01

The bipartite entanglement in Fermi gas without interaction is investigated when there are three fermions in the system. The negativity and the von Neumann entropy are employed to measure the entanglement of the system. The position of the third fermion can affect the entanglement between the first and the second fermions. The entanglement can be enhanced or suppressed when the third fermion changes its position. When the two fermions are at the same position or when their distance is more than 2.0/k F , the third fermion cannot affect them

Quantum communication using a multiqubit entangled channel

Energy Technology Data Exchange (ETDEWEB)

Ghose, Shohini, E-mail: sghose@wlu.ca [Department of Physics and Computer Science, Wilfrid Laurier University, Waterloo, Ontario (Canada); Institute for Quantum Computing, University of Waterloo, Ontario (Canada); Hamel, Angele [Department of Physics and Computer Science, Wilfrid Laurier University, Waterloo, Ontario (Canada)

2015-12-31

We describe a protocol in which two senders each teleport a qubit to a receiver using a multiqubit entangled state. The multiqubit channel used for teleportation is genuinely 4-qubit entangled and is not equivalent to a product of maximally entangled Bell pairs under local unitary operations. We discuss a scenario in which both senders must participate for the qubits to be successfully teleported. Such an all-or-nothing scheme cannot be implemented with standard two-qubit entangled Bell pairs and can be useful for different communication and computing tasks.

Anomalies of the entanglement entropy in chiral theories

Energy Technology Data Exchange (ETDEWEB)

Iqbal, Nabil [Institute for Theoretical Physics, University of Amsterdam,Science Park 904, Postbus 94485, 1090 GL Amsterdam (Netherlands); Wall, Aron C. [School of Natural Sciences, Institute for Advanced Study,Princeton, New Jersey 08540 (United States)

2016-10-20

We study entanglement entropy in theories with gravitational or mixed U(1) gauge-gravitational anomalies in two, four and six dimensions. In such theories there is an anomaly in the entanglement entropy: it depends on the choice of reference frame in which the theory is regulated. We discuss subtleties regarding regulators and entanglement entropies in anomalous theories. We then study the entanglement entropy of free chiral fermions and self-dual bosons and show that in sufficiently symmetric situations this entanglement anomaly comes from an imbalance in the flux of modes flowing through the boundary, controlled by familiar index theorems. In two and four dimensions we use anomalous Ward identities to find general expressions for the transformation of the entanglement entropy under a diffeomorphism. (In the case of a mixed anomaly there is an alternative presentation of the theory in which the entanglement entropy is not invariant under a U(1) gauge transformation. The free-field manifestation of this phenomenon involves a novel kind of fermion zero mode on a gravitational background with a twist in the normal bundle to the entangling surface.) We also study d-dimensional anomalous systems as the boundaries of d+1 dimensional gapped Hall phases. Here the full system is non-anomalous, but the boundary anomaly manifests itself in a change in the entanglement entropy when the boundary metric is sheared relative to the bulk.

Quantum-entanglement storage and extraction in quantum network node

Science.gov (United States)

Shan, Zhuoyu; Zhang, Yong

Quantum computing and quantum communication have become the most popular research topic. Nitrogen-vacancy (NV) centers in diamond have been shown the great advantage of implementing quantum information processing. The generation of entanglement between NV centers represents a fundamental prerequisite for all quantum information technologies. In this paper, we propose a scheme to realize the high-fidelity storage and extraction of quantum entanglement information based on the NV centers at room temperature. We store the entangled information of a pair of entangled photons in the Bell state into the nuclear spins of two NV centers, which can make these two NV centers entangled. And then we illuminate how to extract the entangled information from NV centers to prepare on-demand entangled states for optical quantum information processing. The strategy of engineering entanglement demonstrated here maybe pave the way towards a NV center-based quantum network.

Sudden entanglement death, and ways to avoid it

International Nuclear Information System (INIS)

Eberly, J.H.; Ting Yu

2005-01-01

We report that non-communicating but entangled qubit pairs are almost universally liable to sudden entanglement death. In the presence of minor and purely local environmental noises their mixed-state entanglement may abruptly become zero long before the noises are able to destroy the local qubit coherence. Despite the inability of unitary transformations to alter entanglement, for example of Werner states, unitary transformations have been found to delay or defeat the sudden death event. These results upset the conventional understanding that entanglement lifetime can be estimated from qubit lifetime. This is not even approximately or qualitatively true. (author)

Detecting nonlocal Cooper pair entanglement by optical Bell inequality violation

OpenAIRE

Nigg, Simon E.; Tiwari, Rakesh P.; Walter, Stefan; Schmidt, Thomas L.

2014-01-01

Based on the Bardeen Cooper Schrieffer (BCS) theory of superconductivity, the coherent splitting of Cooper pairs from a superconductor to two spatially separated quantum dots has been predicted to generate nonlocal pairs of entangled electrons. In order to test this hypothesis, we propose a scheme to transfer the spin state of a split Cooper pair onto the polarization state of a pair of optical photons. We show that the produced photon pairs can be used to violate a Bell inequality, unambiguo...

Entanglement scaling in lattice systems

Energy Technology Data Exchange (ETDEWEB)

Audenaert, K M R [Institute for Mathematical Sciences, Imperial College London, 53 Prince' s Gate, Exhibition Road, London SW7 2PG (United Kingdom); Cramer, M [QOLS, Blackett Laboratory, Imperial College London, Prince Consort Road, London SW7 2BW (United Kingdom); Eisert, J [Institute for Mathematical Sciences, Imperial College London, 53 Prince' s Gate, Exhibition Road, London SW7 2PG (United Kingdom); Plenio, M B [Institute for Mathematical Sciences, Imperial College London, 53 Prince' s Gate, Exhibition Road, London SW7 2PG (United Kingdom)

2007-05-15

We review some recent rigorous results on scaling laws of entanglement properties in quantum many body systems. More specifically, we study the entanglement of a region with its surrounding and determine its scaling behaviour with its size for systems in the ground and thermal states of bosonic and fermionic lattice systems. A theorem connecting entanglement between a region and the rest of the lattice with the surface area of the boundary between the two regions is presented for non-critical systems in arbitrary spatial dimensions. The entanglement scaling in the field limit exhibits a peculiar difference between fermionic and bosonic systems. In one-spatial dimension a logarithmic divergence is recovered for both bosonic and fermionic systems. In two spatial dimensions in the setting of half-spaces however we observe strict area scaling for bosonic systems and a multiplicative logarithmic correction to such an area scaling in fermionic systems. Similar questions may be posed and answered in classical systems.

Basic logic and quantum entanglement

International Nuclear Information System (INIS)

Zizzi, P A

2007-01-01

As it is well known, quantum entanglement is one of the most important features of quantum computing, as it leads to massive quantum parallelism, hence to exponential computational speed-up. In a sense, quantum entanglement is considered as an implicit property of quantum computation itself. But... can it be made explicit? In other words, is it possible to find the connective 'entanglement' in a logical sequent calculus for the machine language? And also, is it possible to 'teach' the quantum computer to 'mimic' the EPR 'paradox'? The answer is in the affirmative, if the logical sequent calculus is that of the weakest possible logic, namely Basic logic. - A weak logic has few structural rules. But in logic, a weak structure leaves more room for connectives (for example the connective 'entanglement'). Furthermore, the absence in Basic logic of the two structural rules of contraction and weakening corresponds to the validity of the no-cloning and no-erase theorems, respectively, in quantum computing

Standard forms and entanglement engineering of multimode Gaussian states under local operations

International Nuclear Information System (INIS)

Serafini, Alessio; Adesso, Gerardo

2007-01-01

We investigate the action of local unitary operations on multimode (pure or mixed) Gaussian states and single out the minimal number of locally invariant parameters which completely characterize the covariance matrix of such states. For pure Gaussian states, central resources for continuous-variable quantum information, we investigate separately the parameter reduction due to the additional constraint of global purity, and the one following by the local-unitary freedom. Counting arguments and insights from the phase-space Schmidt decomposition and in general from the framework of symplectic analysis, accompany our description of the standard form of pure n-mode Gaussian states. In particular, we clarify why only in pure states with n ≤ 3 modes all the direct correlations between position and momentum operators can be set to zero by local unitary operations. For any n, the emerging minimal set of parameters contains complete information about all forms of entanglement in the corresponding states. An efficient state engineering scheme (able to encode direct correlations between position and momentum operators as well) is proposed to produce entangled multimode Gaussian resources, its number of optical elements matching the minimal number of locally invariant degrees of freedom of general pure n-mode Gaussian states. Finally, we demonstrate that so-called 'block-diagonal' Gaussian states, without direct correlations between position and momentum, are systematically less entangled, on average, than arbitrary pure Gaussian states

Entangled biphoton source - property and preparation

International Nuclear Information System (INIS)

Shih, Yanhua

2003-01-01

One of the most surprising consequences of quantum mechanics is the entanglement of two or more distance particles. Even though there are still questions regarding the fundamental issues of quantum theory, quantum entanglement has started to play important roles in practical engineering applications such as quantum information processing, quantum metrology, quantum imaging and quantum lithography. Two-photon states have been the most popular entangled states in fundamental and applied research. Using spontaneous parametric down conversion as an example, this review introduces the concept of biphoton wavepacket and emphasizes the very different physics associated with the entangled two-photon system (pure state) and with the 'individual' subsystems (statistical mixture). Experimental approaches for Bell state preparation, pumped by continuous wave and ultrashort pulse are discussed

Entangled biphoton source - property and preparation

CERN Document Server

Shih, Y

2003-01-01

One of the most surprising consequences of quantum mechanics is the entanglement of two or more distance particles. Even though there are still questions regarding the fundamental issues of quantum theory, quantum entanglement has started to play important roles in practical engineering applications such as quantum information processing, quantum metrology, quantum imaging and quantum lithography. Two-photon states have been the most popular entangled states in fundamental and applied research. Using spontaneous parametric down conversion as an example, this review introduces the concept of biphoton wavepacket and emphasizes the very different physics associated with the entangled two-photon system (pure state) and with the 'individual' subsystems (statistical mixture). Experimental approaches for Bell state preparation, pumped by continuous wave and ultrashort pulse are discussed.

Maximally Entangled Multipartite States: A Brief Survey

International Nuclear Information System (INIS)

Enríquez, M; Wintrowicz, I; Życzkowski, K

2016-01-01

The problem of identifying maximally entangled quantum states of a composite quantum systems is analyzed. We review some states of multipartite systems distinguished with respect to certain measures of quantum entanglement. Numerical results obtained for 4-qubit pure states illustrate the fact that the notion of maximally entangled state depends on the measure used. (paper)

Entanglement-assisted quantum MDS codes constructed from negacyclic codes

Science.gov (United States)

Chen, Jianzhang; Huang, Yuanyuan; Feng, Chunhui; Chen, Riqing

2017-12-01

Recently, entanglement-assisted quantum codes have been constructed from cyclic codes by some scholars. However, how to determine the number of shared pairs required to construct entanglement-assisted quantum codes is not an easy work. In this paper, we propose a decomposition of the defining set of negacyclic codes. Based on this method, four families of entanglement-assisted quantum codes constructed in this paper satisfy the entanglement-assisted quantum Singleton bound, where the minimum distance satisfies q+1 ≤ d≤ n+2/2. Furthermore, we construct two families of entanglement-assisted quantum codes with maximal entanglement.

Collapse–revival of quantum discord and entanglement

International Nuclear Information System (INIS)

Yan, Xue-Qun; Zhang, Bo-Ying

2014-01-01

In this paper the correlations dynamics of two atoms in the case of a micromaser-type system is investigated. Our results predict certain quasi-periodic collapse and revival phenomena for quantum discord and entanglement when the field is in Fock state and the two atoms are initially in maximally mixed state, which is a special separable state. Our calculations also show that the oscillations of the time evolution of both quantum discord and entanglement are almost in phase and they both have similar evolution behavior in some time range. The fact reveals the consistency of quantum discord and entanglement in some dynamical aspects. - Highlights: • The correlations dynamics of two atoms in the case of a micromaser-type system is investigated. • A quasi-periodic collapse and revival phenomenon for quantum discord and entanglement is reported. • A phenomenon of correlations revivals different from that of non-Markovian dynamics is revealed. • The oscillations of time evolution of both quantum discord and entanglement are almost in phase in our system. • Quantum discord and entanglement have similar evolution behavior in some time range

First law of entanglement rates from holography

Science.gov (United States)

O'Bannon, Andy; Probst, Jonas; Rodgers, Ronnie; Uhlemann, Christoph F.

2017-09-01

For a perturbation of the state of a conformal field theory (CFT), the response of the entanglement entropy is governed by the so-called "first law" of entanglement entropy, in which the change in entanglement entropy is proportional to the change in energy. Whether such a first law holds for other types of perturbations, such as a change to the CFT Lagrangian, remains an open question. We use holography to study the evolution in time t of entanglement entropy for a CFT driven by a t -linear source for a conserved U (1 ) current or marginal scalar operator. We find that although the usual first law of entanglement entropy may be violated, a first law for the rates of change of entanglement entropy and energy still holds. More generally, we prove that this first law for rates holds in holography for any asymptotically (d +1 )-dimensional anti-de Sitter metric perturbation whose t dependence first appears at order zd in the Fefferman-Graham expansion about the boundary at z =0 .

Entanglement in a simple quantum phase transition

International Nuclear Information System (INIS)

Osborne, Tobias J.; Nielsen, Michael A.

2002-01-01

What entanglement is present in naturally occurring physical systems at thermal equilibrium? Most such systems are intractable and it is desirable to study simple but realistic systems that can be solved. An example of such a system is the one-dimensional infinite-lattice anisotropic XY model. This model is exactly solvable using the Jordan-Wigner transform, and it is possible to calculate the two-site reduced density matrix for all pairs of sites. Using the two-site density matrix, the entanglement of formation between any two sites is calculated for all parameter values and temperatures. We also study the entanglement in the transverse Ising model, a special case of the XY model, which exhibits a quantum phase transition. It is found that the next-nearest-neighbor entanglement (though not the nearest-neighbor entanglement) is a maximum at the critical point. Furthermore, we show that the critical point in the transverse Ising model corresponds to a transition in the behavior of the entanglement between a single site and the remainder of the lattice

Entanglement Swapping in the Presence of White and Color Noise

Science.gov (United States)

Dotsenko, Ivan S.; Korobka, R.

2018-02-01

The influence of white and color noise on the outcome of the entanglement swapping process is investigated in a four-qubit system. Critical degree of noise in initial state, that could destroy entanglement in a result state is presented. The entanglement characteristics, such as concurrence, tangle, etc. are compared. Results could be helpful for experiments regarding entanglement swapping as conditions for initial quantum entangled states, to obtain entangled result state.

Breakdown of entanglement during the teleportation

International Nuclear Information System (INIS)

Wang Jinfeng; Wang Yuming; Li Xueqian

2005-01-01

The teleportation may become an important means for remote distance communications in the future, and the mechanism is based on entanglement of quantum states. But the entanglement is fragile. As the state is disturbed by the environment the entanglement may be broken down. In this work, authors choose the electron-positron pair in an entangled state of spin 0 as an example to investigate the rate of breaking down of the entanglement by the Compton scattering with the background radiation photons or Bremsstrahlung with strong magnetic fields of some astronomical objects which the electron or positron passes by. Since the spin projection of single electron (positron) is not physically measurable and the electron beams cannot keep its shape for long because of the Coulomb repulsion among the charged particles in the beam, the only way is to shoot one electron-positron pair each time and continuously repeat the processes. With all the restraints this study has only pedagogic meaning, but may shed light on further studies where other information messages are chosen. (authors)

Entanglement evolution for quantum trajectories

International Nuclear Information System (INIS)

Vogelsberger, S; Spehner, D

2011-01-01

Entanglement is a key resource in quantum information. It can be destroyed or sometimes created by interactions with a reservoir. In recent years, much attention has been devoted to the phenomena of entanglement sudden death and sudden birth, i.e., the sudden disappearance or revival of entanglement at finite times resulting from a coupling of the quantum system to its environment. We investigate the evolution of the entanglement of noninteracting qubits coupled to reservoirs under monitoring of the reservoirs by means of continuous measurements. Because of these measurements, the qubits remain at all times in a pure state, which evolves randomly. To each measurement result (or 'realization') corresponds a quantum trajectory in the Hilbert space of the qubits. We show that for two qubits coupled to independent baths subjected to local measurements, the average of the qubits' concurrence over all quantum trajectories is either constant or decays exponentially. The corresponding decay rate depends on the measurement scheme only. This result contrasts with the entanglement sudden death phenomenon exhibited by the qubits' density matrix in the absence of measurements. Our analysis applies to arbitrary quantum jump dynamics (photon counting) as well as to quantum state diffusion (homodyne or heterodyne detections) in the Markov limit. We discuss the best measurement schemes to protect the entanglement of the qubits. We also analyze the case of two qubits coupled to a common bath. Then, the average concurrence can vanish at discrete times and may coincide with the concurrence of the density matrix. The results explained in this article have been presented during the 'Fifth International Workshop DICE2010' by the first author and have been the subject of a prior publication.

Entanglement dynamics of a pure bipartite system in dissipative environments

Energy Technology Data Exchange (ETDEWEB)

Tahira, Rabia; Ikram, Manzoor; Azim, Tasnim; Suhail Zubairy, M [Centre for Quantum Physics, COMSATS Institute of Information Technology, Islamabad (Pakistan)

2008-10-28

We investigate the phenomenon of sudden death of entanglement in a bipartite system subjected to dissipative environments with arbitrary initial pure entangled state between two atoms. We find that in a vacuum reservoir the presence of the state where both atoms are in excited states is a necessary condition for the sudden death of entanglement. Otherwise entanglement remains for an infinite time and decays asymptotically with the decay of individual qubits. For pure 2-qubit entangled states in a thermal environment, we observe that the sudden death of entanglement always happens. The sudden death time of the entangled states is related to the temperature of the reservoir and the initial preparation of the entangled states.

Entanglement dynamics of a pure bipartite system in dissipative environments

International Nuclear Information System (INIS)

Tahira, Rabia; Ikram, Manzoor; Azim, Tasnim; Suhail Zubairy, M

2008-01-01

We investigate the phenomenon of sudden death of entanglement in a bipartite system subjected to dissipative environments with arbitrary initial pure entangled state between two atoms. We find that in a vacuum reservoir the presence of the state where both atoms are in excited states is a necessary condition for the sudden death of entanglement. Otherwise entanglement remains for an infinite time and decays asymptotically with the decay of individual qubits. For pure 2-qubit entangled states in a thermal environment, we observe that the sudden death of entanglement always happens. The sudden death time of the entangled states is related to the temperature of the reservoir and the initial preparation of the entangled states.

Quantum teleportation of entangled squeezed vacuum states

Institute of Scientific and Technical Information of China (English)

蔡新华

2003-01-01

An optical scheme for probabilistic teleporting entangled squeezed vacuum states (SVS) is proposed. In this scheme,the teleported state is a bipartite entangled SVS,and the quantum channel is a tripartite entangled SVS.The process of the teleportation is achieved by using a 50/50 symmetric beamsplitter and photon detectors with the help of classical information.

Entangling two transportable neutral atoms via local spin exchange.

Science.gov (United States)

Kaufman, A M; Lester, B J; Foss-Feig, M; Wall, M L; Rey, A M; Regal, C A

2015-11-12

To advance quantum information science, physical systems are sought that meet the stringent requirements for creating and preserving quantum entanglement. In atomic physics, robust two-qubit entanglement is typically achieved by strong, long-range interactions in the form of either Coulomb interactions between ions or dipolar interactions between Rydberg atoms. Although such interactions allow fast quantum gates, the interacting atoms must overcome the associated coupling to the environment and cross-talk among qubits. Local interactions, such as those requiring substantial wavefunction overlap, can alleviate these detrimental effects; however, such interactions present a new challenge: to distribute entanglement, qubits must be transported, merged for interaction, and then isolated for storage and subsequent operations. Here we show how, using a mobile optical tweezer, it is possible to prepare and locally entangle two ultracold neutral atoms, and then separate them while preserving their entanglement. Ground-state neutral atom experiments have measured dynamics consistent with spin entanglement, and have detected entanglement with macroscopic observables; we are now able to demonstrate position-resolved two-particle coherence via application of a local gradient and parity measurements. This new entanglement-verification protocol could be applied to arbitrary spin-entangled states of spatially separated atoms. The local entangling operation is achieved via spin-exchange interactions, and quantum tunnelling is used to combine and separate atoms. These techniques provide a framework for dynamically entangling remote qubits via local operations within a large-scale quantum register.

Bounds on absolutely maximally entangled states from shadow inequalities, and the quantum MacWilliams identity

Science.gov (United States)

Huber, Felix; Eltschka, Christopher; Siewert, Jens; Gühne, Otfried

2018-04-01

A pure multipartite quantum state is called absolutely maximally entangled (AME), if all reductions obtained by tracing out at least half of its parties are maximally mixed. Maximal entanglement is then present across every bipartition. The existence of such states is in many cases unclear. With the help of the weight enumerator machinery known from quantum error correction and the shadow inequalities, we obtain new bounds on the existence of AME states in dimensions larger than two. To complete the treatment on the weight enumerator machinery, the quantum MacWilliams identity is derived in the Bloch representation. Finally, we consider AME states whose subsystems have different local dimensions, and present an example for a 2×3×3×3 system that shows maximal entanglement across every bipartition.

Entanglement entropy after selective measurements in quantum chains

Energy Technology Data Exchange (ETDEWEB)

Najafi, Khadijeh [Department of Physics, Georgetown University,37th and O Sts. NW, Washington, DC 20057 (United States); Rajabpour, M.A. [Instituto de Física, Universidade Federal Fluminense,Av. Gal. Milton Tavares de Souza s/n, Gragoatá, 24210-346, Niterói, RJ (Brazil)

2016-12-22

We study bipartite post measurement entanglement entropy after selective measurements in quantum chains. We first study the quantity for the critical systems that can be described by conformal field theories. We find a connection between post measurement entanglement entropy and the Casimir energy of floating objects. Then we provide formulas for the post measurement entanglement entropy for open and finite temperature systems. We also comment on the Affleck-Ludwig boundary entropy in the context of the post measurement entanglement entropy. Finally, we also provide some formulas regarding modular hamiltonians and entanglement spectrum in the after measurement systems. After through discussion regarding CFT systems we also provide some predictions regarding massive field theories. We then discuss a generic method to calculate the post measurement entanglement entropy in the free fermion systems. Using the method we study the post measurement entanglement entropy in the XY spin chain. We check numerically the CFT and the massive field theory results in the transverse field Ising chain and the XX model. In particular, we study the post meaurement entanglement entropy in the infinite, periodic and open critical transverse field Ising chain and the critical XX model. The effect of the temperature and the gap is also discussed in these models.

Entanglement entropy after selective measurements in quantum chains

International Nuclear Information System (INIS)

Najafi, Khadijeh; Rajabpour, M.A.

2016-01-01

We study bipartite post measurement entanglement entropy after selective measurements in quantum chains. We first study the quantity for the critical systems that can be described by conformal field theories. We find a connection between post measurement entanglement entropy and the Casimir energy of floating objects. Then we provide formulas for the post measurement entanglement entropy for open and finite temperature systems. We also comment on the Affleck-Ludwig boundary entropy in the context of the post measurement entanglement entropy. Finally, we also provide some formulas regarding modular hamiltonians and entanglement spectrum in the after measurement systems. After through discussion regarding CFT systems we also provide some predictions regarding massive field theories. We then discuss a generic method to calculate the post measurement entanglement entropy in the free fermion systems. Using the method we study the post measurement entanglement entropy in the XY spin chain. We check numerically the CFT and the massive field theory results in the transverse field Ising chain and the XX model. In particular, we study the post meaurement entanglement entropy in the infinite, periodic and open critical transverse field Ising chain and the critical XX model. The effect of the temperature and the gap is also discussed in these models.

Entanglement between noncomplementary parts of many-body systems

International Nuclear Information System (INIS)

Wichterich, Hannu Christian

2011-01-01

This thesis investigates the structure and behaviour of entanglement, the purely quantum mechanical part of correlations, in many-body systems, employing both numerical and analytical techniques at the interface of condensed matter theory and quantum information theory. Entanglement can be seen as a precious resource which, for example, enables the noiseless and instant transmission of quantum information, provided the communicating parties share a sufficient ''amount'' of it. Furthermore, measures of entanglement of a quantum mechanical state are perceived as useful probes of collective properties of many-body systems. For instance, certain measures are capable of detecting and classifying ground-state phases and, particularly, transition (or critical) points separating such phases. Chapters 2 and 3 focus on entanglement in many-body systems and its use as a potential resource for communication protocols. They address the questions of how a substantial amount of entanglement can be established between distant subsystems, and how efficiently this entanglement could be ''harvested'' by way of measurements. The subsequent chapters 4 and 5 are devoted to universality of entanglement between large collections of particles undergoing a quantum phase transition, where, despite the enormous complexity of these systems, collective properties including entanglement no longer depend crucially on the microscopic details. (orig.)

Quantum entanglement: theory and applications

Energy Technology Data Exchange (ETDEWEB)

Schuch, N.

2007-10-10

This thesis deals with various questions concerning the quantification, the creation, and the application of quantum entanglement. Entanglement arises due to the restriction to local operations and classical communication. We investigate how the notion of entanglement changes if additional restrictions in form of a superselection rule are imposed and show that they give rise to a new resource. We characterize this resource and demonstrate that it can be used to overcome the restrictions, very much as entanglement can overcome the restriction to local operations by teleportation. We next turn towards the optimal generation of resources. We show how squeezing can be generated as efficiently as possible from noisy squeezing operations supplemented by noiseless passive operations, and discuss the implications of this result to the optimal generation of entanglement. The difficulty in describing the behaviour of correlated quantum many-body systems is ultimately due to the complicated entanglement structure of multipartite states. Using quantum information techniques, we investigate the ground state properties of lattices of harmonic oscillators. We derive an exponential decay of correlations for gapped systems, compute the dependence of correlation length and gap, and investigate the notion of criticality by relating a vanishing energy gap to an algebraic decay of correlations. Recently, ideas from entanglement theory have been applied to the description of many-body systems. Matrix Product States (MPS), which have a particularly simple interpretation from the point of quantum information, perform extremely well in approximating the ground states of local Hamiltonians. It is generally believed that this is due to the fact that both ground states and MPS obey an entropic area law. We clarify the relation between entropy scaling laws and approximability by MPS, and in particular find that an area law does not necessarily imply approximability. Using the quantum

Quantum entanglement: theory and applications

International Nuclear Information System (INIS)

Schuch, N.

2007-01-01

This thesis deals with various questions concerning the quantification, the creation, and the application of quantum entanglement. Entanglement arises due to the restriction to local operations and classical communication. We investigate how the notion of entanglement changes if additional restrictions in form of a superselection rule are imposed and show that they give rise to a new resource. We characterize this resource and demonstrate that it can be used to overcome the restrictions, very much as entanglement can overcome the restriction to local operations by teleportation. We next turn towards the optimal generation of resources. We show how squeezing can be generated as efficiently as possible from noisy squeezing operations supplemented by noiseless passive operations, and discuss the implications of this result to the optimal generation of entanglement. The difficulty in describing the behaviour of correlated quantum many-body systems is ultimately due to the complicated entanglement structure of multipartite states. Using quantum information techniques, we investigate the ground state properties of lattices of harmonic oscillators. We derive an exponential decay of correlations for gapped systems, compute the dependence of correlation length and gap, and investigate the notion of criticality by relating a vanishing energy gap to an algebraic decay of correlations. Recently, ideas from entanglement theory have been applied to the description of many-body systems. Matrix Product States (MPS), which have a particularly simple interpretation from the point of quantum information, perform extremely well in approximating the ground states of local Hamiltonians. It is generally believed that this is due to the fact that both ground states and MPS obey an entropic area law. We clarify the relation between entropy scaling laws and approximability by MPS, and in particular find that an area law does not necessarily imply approximability. Using the quantum

Entanglement entropy evolution under double-trace deformation

Energy Technology Data Exchange (ETDEWEB)

Song, Yushu [College of Physical Science and Technology, Hebei University, Baoding (China)

2017-12-15

In this paper, we study the bulk entanglement entropy evolution in conical BTZ black bole background using the heat kernel method. This is motivated by exploring the new examples where the quantum correction of the entanglement entropy gives the leading contribution. We find that in the large black hole limit the bulk entanglement entropy decreases under the double-trace deformation which is consistent with the holographic c theorem and in the small black hole limit the bulk entanglement entropy increases under the deformation. We also discuss the minimal area correction. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Entanglement entropy and differential entropy for massive flavors

International Nuclear Information System (INIS)

Jones, Peter A.R.; Taylor, Marika

2015-01-01

In this paper we compute the holographic entanglement entropy for massive flavors in the D3-D7 system, for arbitrary mass and various entangling region geometries. We show that the universal terms in the entanglement entropy exactly match those computed in the dual theory using conformal perturbation theory. We derive holographically the universal terms in the entanglement entropy for a CFT perturbed by a relevant operator, up to second order in the coupling; our results are valid for any entangling region geometry. We present a new method for computing the entanglement entropy of any top-down brane probe system using Kaluza-Klein holography and illustrate our results with massive flavors at finite density. Finally we discuss the differential entropy for brane probe systems, emphasising that the differential entropy captures only the effective lower-dimensional Einstein metric rather than the ten-dimensional geometry.

Statistical mechanics of multipartite entanglement

Science.gov (United States)

Facchi, P.; Florio, G.; Marzolino, U.; Parisi, G.; Pascazio, S.

2009-02-01

We characterize the multipartite entanglement of a system of n qubits in terms of the distribution function of the bipartite purity over all balanced bipartitions. We search for those (maximally multipartite entangled) states whose purity is minimum for all bipartitions and recast this optimization problem into a problem of statistical mechanics.

Statistical mechanics of multipartite entanglement

Energy Technology Data Exchange (ETDEWEB)

Facchi, P [Dipartimento di Matematica, Universita di Bari, I-70125 Bari (Italy); Florio, G; Pascazio, S [Istituto Nazionale di Fisica Nucleare, Sezione di Bari, I-70126 Bari (Italy); Marzolino, U [Dipartimento di Fisica Teorica, Universita di Trieste, Strada Costiera 11, 34014 Trieste (Italy); Parisi, G [Dipartimento di Fisica, Universita di Roma ' La Sapienza' , Piazzale Aldo Moro 2, 00185 Roma, Italy, Centre for Statistical Mechanics and Complexity (SMC), CNR-INFM, 00185 Roma (Italy)

2009-02-06

We characterize the multipartite entanglement of a system of n qubits in terms of the distribution function of the bipartite purity over all balanced bipartitions. We search for those (maximally multipartite entangled) states whose purity is minimum for all bipartitions and recast this optimization problem into a problem of statistical mechanics.

Statistical mechanics of multipartite entanglement

International Nuclear Information System (INIS)

Facchi, P; Florio, G; Pascazio, S; Marzolino, U; Parisi, G

2009-01-01

We characterize the multipartite entanglement of a system of n qubits in terms of the distribution function of the bipartite purity over all balanced bipartitions. We search for those (maximally multipartite entangled) states whose purity is minimum for all bipartitions and recast this optimization problem into a problem of statistical mechanics

Separability criteria and method of measurement for entanglement

Science.gov (United States)

Mohd, Siti Munirah; Idrus, Bahari; Mukhtar, Muriati

2014-06-01

Quantum computers have the potentials to solve certain problems faster than classical computers. In quantum computer, entanglement is one of the elements beside superposition. Recently, with the advent of quantum information theory, entanglement has become an important resource for Quantum Information and Computation. The purpose of this paper is to discuss the separability criteria and method of measurement for entanglement. This paper is aimed at viewing the method that has been proposed in previous works in bipartite and multipartite entanglement. The outcome of this paper is to classify the different method that used to measure entanglement for bipartite and multipartite cases including the advantage and disadvantage of each method.

Separability criteria and method of measurement for entanglement

Energy Technology Data Exchange (ETDEWEB)

Mohd, Siti Munirah; Idrus, Bahari; Mukhtar, Muriati [Industrial Computing Research Group, Faculty of Information Science and Technology, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor (Malaysia)

2014-06-19

Quantum computers have the potentials to solve certain problems faster than classical computers. In quantum computer, entanglement is one of the elements beside superposition. Recently, with the advent of quantum information theory, entanglement has become an important resource for Quantum Information and Computation. The purpose of this paper is to discuss the separability criteria and method of measurement for entanglement. This paper is aimed at viewing the method that has been proposed in previous works in bipartite and multipartite entanglement. The outcome of this paper is to classify the different method that used to measure entanglement for bipartite and multipartite cases including the advantage and disadvantage of each method.

Non-Markovian dynamics of entanglement for multipartite systems

Energy Technology Data Exchange (ETDEWEB)

Zhou Jiang; Wu Chengjun; Zhu Mingyi; Guo Hong, E-mail: hongguo@pku.edu.c [CREAM Group, State Key Laboratory of Advanced Optical Communication Systems and Networks (Peking University) and Institute of Quantum Electronics, School of Electronics Engineering and Computer Science, and Center for Computational Science and Engineering (CCSE), Peking University, Beijing 100871 (China)

2009-11-14

Entanglement dynamics for a couple of two-level atoms interacting with independent structured reservoirs is studied using a non-perturbative approach. It is shown that the revival of atom entanglement is not necessarily accompanied by the sudden death of reservoir entanglement, and vice versa. In fact, atom entanglement can revive before, simultaneously or even after the disentanglement of reservoirs. Using a novel method based on the population analysis for the excited atomic state, we present the quantitative criteria for the revival and death phenomena. To give a more physically intuitive insight, the quasimode Hamiltonian method is applied. Our quantitative analysis is helpful for the practical engineering of entanglement.

Characterizing entanglement with global and marginal entropic measures

International Nuclear Information System (INIS)

Adesso, Gerardo; Illuminati, Fabrizio; De Siena, Silvio

2003-01-01

We qualify the entanglement of arbitrary mixed states of bipartite quantum systems by comparing global and marginal mixednesses quantified by different entropic measures. For systems of two qubits we discriminate the class of maximally entangled states with fixed marginal mixednesses, and determine an analytical upper bound relating the entanglement of formation to the marginal linear entropies. This result partially generalizes to mixed states the quantification of entanglement with marginal mixednesses holding for pure states. We identify a class of entangled states that, for fixed marginals, are globally more mixed than product states when measured by the linear entropy. Such states cannot be discriminated by the majorization criterion

Entanglement-assisted quantum MDS codes from negacyclic codes

Science.gov (United States)

Lu, Liangdong; Li, Ruihu; Guo, Luobin; Ma, Yuena; Liu, Yang

2018-03-01

The entanglement-assisted formalism generalizes the standard stabilizer formalism, which can transform arbitrary classical linear codes into entanglement-assisted quantum error-correcting codes (EAQECCs) by using pre-shared entanglement between the sender and the receiver. In this work, we construct six classes of q-ary entanglement-assisted quantum MDS (EAQMDS) codes based on classical negacyclic MDS codes by exploiting two or more pre-shared maximally entangled states. We show that two of these six classes q-ary EAQMDS have minimum distance more larger than q+1. Most of these q-ary EAQMDS codes are new in the sense that their parameters are not covered by the codes available in the literature.

Separability criteria and method of measurement for entanglement

International Nuclear Information System (INIS)

Mohd, Siti Munirah; Idrus, Bahari; Mukhtar, Muriati

2014-01-01

Quantum computers have the potentials to solve certain problems faster than classical computers. In quantum computer, entanglement is one of the elements beside superposition. Recently, with the advent of quantum information theory, entanglement has become an important resource for Quantum Information and Computation. The purpose of this paper is to discuss the separability criteria and method of measurement for entanglement. This paper is aimed at viewing the method that has been proposed in previous works in bipartite and multipartite entanglement. The outcome of this paper is to classify the different method that used to measure entanglement for bipartite and multipartite cases including the advantage and disadvantage of each method

Quantifying entanglement in two-mode Gaussian states

Science.gov (United States)

Tserkis, Spyros; Ralph, Timothy C.

2017-12-01

Entangled two-mode Gaussian states are a key resource for quantum information technologies such as teleportation, quantum cryptography, and quantum computation, so quantification of Gaussian entanglement is an important problem. Entanglement of formation is unanimously considered a proper measure of quantum correlations, but for arbitrary two-mode Gaussian states no analytical form is currently known. In contrast, logarithmic negativity is a measure that is straightforward to calculate and so has been adopted by most researchers, even though it is a less faithful quantifier. In this work, we derive an analytical lower bound for entanglement of formation of generic two-mode Gaussian states, which becomes tight for symmetric states and for states with balanced correlations. We define simple expressions for entanglement of formation in physically relevant situations and use these to illustrate the problematic behavior of logarithmic negativity, which can lead to spurious conclusions.

Entanglement of identical particles and the detection process

DEFF Research Database (Denmark)

Tichy, Malte C.; de Melo, Fernando; Kus, Marek

2013-01-01

We introduce detector-level entanglement, a unified entanglement concept for identical particles that takes into account the possible deletion of many-particle which-way information through the detection process. The concept implies a measure for the effective indistinguishability of the particles...... statistical behavior depends on their initial entanglement. Our results show that entanglement cannot be attributed to a state of identical particles alone, but that the detection process has to be incorporated in the analysis....

Communication cost of entanglement transformations

International Nuclear Information System (INIS)

Hayden, Patrick; Winter, Andreas

2003-01-01

We study the amount of communication needed for two parties to transform some given joint pure state into another one, either exactly or with some fidelity. Specifically, we present a method to lower bound this communication cost even when the amount of entanglement does not increase. Moreover, the bound applies even if the initial state is supplemented with unlimited entanglement in the form of EPR (Einstein-Podolsky-Rosen) pairs and the communication is allowed to be quantum mechanical. We then apply the method to the determination of the communication cost of asymptotic entanglement concentration and dilution. While concentration is known to require no communication whatsoever, the best known protocol for dilution, discovered by H.-K. Lo and S. Popescu [Phys. Rev. Lett. 83, 1459 (1999)], requires exchange of a number of bits that is of the order of the square root of the number of EPR pairs. Here we prove a matching lower bound of the same asymptotic order, demonstrating the optimality of the Lo-Popescu protocol up to a constant factor and establishing the existence of a fundamental asymmetry between the concentration and dilution tasks. We also discuss states for which the minimal communication cost is proportional to their entanglement, such as the states recently introduced in the context of 'embezzling entanglement' (W. van Dam and P. Hayden, e-print quant-ph/0201041)

Distillable entanglement in d circle times d dimensions

NARCIS (Netherlands)

Hamieh, S; Zaraket, H

2003-01-01

Distillable entanglement (E-d) is one of the acceptable measures of entanglement of mixed states. On the basis of discrimination through local operation and classical communication, this letter gives E-d for two classes of orthogonal multipartite maximally entangled states.

Effect of Bound Entanglement on the Convertibility of Pure States

International Nuclear Information System (INIS)

Ishizaka, Satoshi

2004-01-01

I show that bound entanglement strongly influences the quantum entanglement processing of pure states: If N distant parties share appropriate bound entangled states with positive partial transpose, all N-partite pure entangled states become inter-convertible by stochastic local operations and classical communication (SLOCC) at the single copy level. This implies that the Schmidt rank of a bipartite pure entangled state can be increased, and that two incomparable tripartite entanglement of the GHZ and W type can be inter-converted by the assistance of bound entanglement. Further, I propose the simplest experimental scheme for the demonstration of the corresponding bound-entanglement-assisted SLOCC. This scheme does not need quantum gates and is feasible for the current experimental technology of linear optics

Transfer of d-level quantum states through spin chains by random swapping

International Nuclear Information System (INIS)

Bayat, A.; Karimipour, V.

2007-01-01

We generalize an already proposed protocol for quantum state transfer to spin chains of arbitrary spin. An arbitrary unknown d-level state is transferred through a chain with rather good fidelity by the natural dynamics of the chain. We compare the performance of this protocol for various values of d. A by-product of our study is a much simpler method for picking up the state at the destination as compared with the one proposed previously. We also discuss entanglement distribution through such chains and show that the quality of entanglement transition increases with the number of levels d

Entanglement sharing via qudit channels: Nonmaximally entangled states may be necessary for one-shot optimal singlet fraction and negativity

Science.gov (United States)

Pal, Rajarshi; Bandyopadhyay, Somshubhro

2018-03-01

We consider the problem of establishing entangled states of optimal singlet fraction and negativity between two remote parties for every use of a noisy quantum channel and trace-preserving local operations and classical communication (LOCC) under the assumption that the parties do not share prior correlations. We show that for a family of quantum channels in every finite dimension d ≥3 , one-shot optimal singlet fraction and entanglement negativity are attained only with appropriate nonmaximally entangled states. A consequence of our results is that the ordering of entangled states in all finite dimensions may not be preserved under trace-preserving LOCC.

HMSRP Hawaiian Monk Seal Entanglement data

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The data set contains records of all entanglements of Hawaiian monk seals in marine debris. The data set comprises records of seals entangled by derelict fishing...

Direct method for measuring and witnessing quantum entanglement of arbitrary two-qubit states through Hong-Ou-Mandel interference

Science.gov (United States)

Bartkiewicz, Karol; Chimczak, Grzegorz; Lemr, Karel

2017-02-01

We describe a direct method for experimental determination of the negativity of an arbitrary two-qubit state with 11 measurements performed on multiple copies of the two-qubit system. Our method is based on the experimentally accessible sequences of singlet projections performed on up to four qubit pairs. In particular, our method permits the application of the Peres-Horodecki separability criterion to an arbitrary two-qubit state. We explicitly demonstrate that measuring entanglement in terms of negativity requires three measurements more than detecting two-qubit entanglement. The reported minimal set of interferometric measurements provides a complete description of bipartite quantum entanglement in terms of two-photon interference. This set is smaller than the set of 15 measurements needed to perform a complete quantum state tomography of an arbitrary two-qubit system. Finally, we demonstrate that the set of nine Makhlin's invariants needed to express the negativity can be measured by performing 13 multicopy projections. We demonstrate both that these invariants are a useful theoretical concept for designing specialized quantum interferometers and that their direct measurement within the framework of linear optics does not require performing complete quantum state tomography.

Dynamics of pairwise entanglement between two Tavis-Cummings atoms

International Nuclear Information System (INIS)

Guo Jinliang; Song Heshan

2008-01-01

We investigate the time evolution of pairwise entanglement between two Tavis-Cummings atoms for various entangled initial states, including pure and mixed states. We find that the phenomenon of entanglement sudden death behaviors is distinct in the evolution of entanglement for different initial states. What deserves mentioning here is that the initial portion of the excited state in the initial state is responsible for the sudden death of entanglement, and the degree of this effect also depends on the initial states

Effect of mode–mode competition on atom–atom entanglement

International Nuclear Information System (INIS)

Qin, Wu; Mao-Fa, Fang; Jian-Wu, Cai

2010-01-01

A system consisting of two atoms interacting with a two-mode vacuum is considered, where each atom is resonant with the two cavity modes through two different competing transitions. The effect of mode–mode competition on the atom–atom entanglement is investigated. We find that the entanglement between the two atoms can be induced by the mode–mode competition. For the initial atomic state |Ψ(0)}, whether the atoms are initially separated or entangled, a large or even maximal entanglement between them can be obtained periodically by introducing the mode–mode competition. For the initial atomic state |Φ(0)}, the strong mode–mode competition can prevent the two atoms entangled initially from suffering entanglement sudden death; besides, it makes them in a more stable and longer-lived entanglement than in the non-competition case. (classical areas of phenomenology)

Entanglement detection in hybrid optomechanical systems

International Nuclear Information System (INIS)

De Chiara, Gabriele; Paternostro, Mauro; Palma, G. Massimo

2011-01-01

We study a device formed by a Bose-Einstein condensate (BEC) coupled to the field of a cavity with a moving end mirror and find a working point such that the mirror-light entanglement is reproduced by the BEC-light quantum correlations. This provides an experimentally viable tool for inferring mirror-light entanglement with only a limited set of assumptions. We prove the existence of tripartite entanglement in the hybrid device, persisting up to temperatures of a few milli-Kelvin, and discuss a scheme to detect it.

Continuous-variable entanglement distillation of non-Gaussian mixed states

International Nuclear Information System (INIS)

Dong Ruifang; Lassen, Mikael; Heersink, Joel; Marquardt, Christoph; Leuchs, Gerd; Filip, Radim; Andersen, Ulrik L.

2010-01-01

Many different quantum-information communication protocols such as teleportation, dense coding, and entanglement-based quantum key distribution are based on the faithful transmission of entanglement between distant location in an optical network. The distribution of entanglement in such a network is, however, hampered by loss and noise that is inherent in all practical quantum channels. Thus, to enable faithful transmission one must resort to the protocol of entanglement distillation. In this paper we present a detailed theoretical analysis and an experimental realization of continuous variable entanglement distillation in a channel that is inflicted by different kinds of non-Gaussian noise. The continuous variable entangled states are generated by exploiting the third order nonlinearity in optical fibers, and the states are sent through a free-space laboratory channel in which the losses are altered to simulate a free-space atmospheric channel with varying losses. We use linear optical components, homodyne measurements, and classical communication to distill the entanglement, and we find that by using this method the entanglement can be probabilistically increased for some specific non-Gaussian noise channels.

Bound entangled states violate a nonsymmetric local uncertainty relation

International Nuclear Information System (INIS)

Hofmann, Holger F.

2003-01-01

As a consequence of having a positive partial transpose, bound entangled states lack many of the properties otherwise associated with entanglement. It is therefore interesting to identify properties that distinguish bound entangled states from separable states. In this paper, it is shown that some bound entangled states violate a nonsymmetric class of local uncertainty relations [H. F. Hofmann and S. Takeuchi, Phys. Rev. A 68, 032103 (2003)]. This result indicates that the asymmetry of nonclassical correlations may be a characteristic feature of bound entanglement

Basic logic and quantum entanglement

Energy Technology Data Exchange (ETDEWEB)

Zizzi, P A [Dipartimento di Matematica Pura ed Applicata, Via Trieste 63, 35121 Padova (Italy)

2007-05-15

As it is well known, quantum entanglement is one of the most important features of quantum computing, as it leads to massive quantum parallelism, hence to exponential computational speed-up. In a sense, quantum entanglement is considered as an implicit property of quantum computation itself. But... can it be made explicit? In other words, is it possible to find the connective 'entanglement' in a logical sequent calculus for the machine language? And also, is it possible to 'teach' the quantum computer to 'mimic' the EPR 'paradox'? The answer is in the affirmative, if the logical sequent calculus is that of the weakest possible logic, namely Basic logic. - A weak logic has few structural rules. But in logic, a weak structure leaves more room for connectives (for example the connective 'entanglement'). Furthermore, the absence in Basic logic of the two structural rules of contraction and weakening corresponds to the validity of the no-cloning and no-erase theorems, respectively, in quantum computing.

Experimental generation of complex noisy photonic entanglement

International Nuclear Information System (INIS)

Dobek, K; Banaszek, K; Karpiński, M; Demkowicz-Dobrzański, R; Horodecki, P

2013-01-01

We present an experimental scheme based on spontaneous parametric down-conversion to produce multiple-photon pairs in maximally entangled polarization states using an arrangement of two type-I nonlinear crystals. By introducing correlated polarization noise in the paths of the generated photons we prepare mixed-entangled states whose properties illustrate fundamental results obtained recently in quantum information theory, in particular those concerning bound entanglement and privacy. (paper)

Perfect controlled joint remote state preparation independent of entanglement degree of the quantum channel

International Nuclear Information System (INIS)

An, Nguyen Ba; Bich, Cao Thi

2014-01-01

We construct a quantum circuit to produce a task-oriented partially entangled state and use it as the quantum channel for controlled joint remote state preparation. Unlike most previous works, where the parameters of the quantum channel are given to the receiver who can accomplish the task only probabilistically by consuming auxiliary resource, operation and measurement, here we give them to the supervisor. Thanks to the knowledge of the task-oriented quantum channel parameters, the supervisor can carry out proper complete projective measurement, which, combined with the feed-forward technique adapted by the preparers, not only much economizes (simplifies) the receiver's resource (operation) but also yields unit total success probability. Notably, such apparent perfection does not depend on the entanglement degree of the shared quantum channel. Our protocol is within the reach of current quantum technologies. - Highlights: • Controlled joint remote state preparation is considered. • Quantum circuit is proposed to produce task-oriented partially entangled channel. • The quantum channel parameter is given to the supervisor (not to the receiver). • Unit success probability without additional resource/operations/measurement. • Perfection is achieved regardless of the shared entanglement degree

Fiber transport of spatially entangled photons

Science.gov (United States)

Löffler, W.; Eliel, E. R.; Woerdman, J. P.; Euser, T. G.; Scharrer, M.; Russell, P.

2012-03-01

High-dimensional entangled photons pairs are interesting for quantum information and cryptography: Compared to the well-known 2D polarization case, the stronger non-local quantum correlations could improve noise resistance or security, and the larger amount of information per photon increases the available bandwidth. One implementation is to use entanglement in the spatial degree of freedom of twin photons created by spontaneous parametric down-conversion, which is equivalent to orbital angular momentum entanglement, this has been proven to be an excellent model system. The use of optical fiber technology for distribution of such photons has only very recently been practically demonstrated and is of fundamental and applied interest. It poses a big challenge compared to the established time and frequency domain methods: For spatially entangled photons, fiber transport requires the use of multimode fibers, and mode coupling and intermodal dispersion therein must be minimized not to destroy the spatial quantum correlations. We demonstrate that these shortcomings of conventional multimode fibers can be overcome by using a hollow-core photonic crystal fiber, which follows the paradigm to mimic free-space transport as good as possible, and are able to confirm entanglement of the fiber-transported photons. Fiber transport of spatially entangled photons is largely unexplored yet, therefore we discuss the main complications, the interplay of intermodal dispersion and mode mixing, the influence of external stress and core deformations, and consider the pros and cons of various fiber types.

Mode entanglement of Gaussian fermionic states

Science.gov (United States)

Spee, C.; Schwaiger, K.; Giedke, G.; Kraus, B.

2018-04-01

We investigate the entanglement of n -mode n -partite Gaussian fermionic states (GFS). First, we identify a reasonable definition of separability for GFS and derive a standard form for mixed states, to which any state can be mapped via Gaussian local unitaries (GLU). As the standard form is unique, two GFS are equivalent under GLU if and only if their standard forms coincide. Then, we investigate the important class of local operations assisted by classical communication (LOCC). These are central in entanglement theory as they allow one to partially order the entanglement contained in states. We show, however, that there are no nontrivial Gaussian LOCC (GLOCC) among pure n -partite (fully entangled) states. That is, any such GLOCC transformation can also be accomplished via GLU. To obtain further insight into the entanglement properties of such GFS, we investigate the richer class of Gaussian stochastic local operations assisted by classical communication (SLOCC). We characterize Gaussian SLOCC classes of pure n -mode n -partite states and derive them explicitly for few-mode states. Furthermore, we consider certain fermionic LOCC and show how to identify the maximally entangled set of pure n -mode n -partite GFS, i.e., the minimal set of states having the property that any other state can be obtained from one state inside this set via fermionic LOCC. We generalize these findings also to the pure m -mode n -partite (for m >n ) case.

Global entanglement in XXZ chains

International Nuclear Information System (INIS)

Canosa, N.; Rossignoli, R.

2006-01-01

We examine the thermal entanglement of XXZ-type Heisenberg chains in the presence of a uniform magnetic field along the z axes through the evaluation of the negativity associated with bipartitions of the whole system and subsystems. Limit temperatures for nonzero global negativities are shown to depend on the asymmetry Δ, but not on the uniform field, and can be much higher than those limiting pairwise entanglement. It is also shown that global bipartite entanglement may exist for T>0 even for Δ≥1, i.e., when the system is fully aligned (and hence separable) at T=0, and that the bipartition leading to the highest limit temperature depends on Δ

Time evolution of the Wigner function in the entangled-state representation

International Nuclear Information System (INIS)

Fan Hongyi

2002-01-01

For quantum-mechanical entangled states we introduce the entangled Wigner operator in the entangled-state representation. We derive the time evolution equation of the entangled Wigner operator . The trace product rule for entangled Wigner functions is also obtained

Computational complexity in entanglement transformations

Science.gov (United States)

Chitambar, Eric A.

In physics, systems having three parts are typically much more difficult to analyze than those having just two. Even in classical mechanics, predicting the motion of three interacting celestial bodies remains an insurmountable challenge while the analogous two-body problem has an elementary solution. It is as if just by adding a third party, a fundamental change occurs in the structure of the problem that renders it unsolvable. In this thesis, we demonstrate how such an effect is likewise present in the theory of quantum entanglement. In fact, the complexity differences between two-party and three-party entanglement become quite conspicuous when comparing the difficulty in deciding what state changes are possible for these systems when no additional entanglement is consumed in the transformation process. We examine this entanglement transformation question and its variants in the language of computational complexity theory, a powerful subject that formalizes the concept of problem difficulty. Since deciding feasibility of a specified bipartite transformation is relatively easy, this task belongs to the complexity class P. On the other hand, for tripartite systems, we find the problem to be NP-Hard, meaning that its solution is at least as hard as the solution to some of the most difficult problems humans have encountered. One can then rigorously defend the assertion that a fundamental complexity difference exists between bipartite and tripartite entanglement since unlike the former, the full range of forms realizable by the latter is incalculable (assuming P≠NP). However, similar to the three-body celestial problem, when one examines a special subclass of the problem---invertible transformations on systems having at least one qubit subsystem---we prove that the problem can be solved efficiently. As a hybrid of the two questions, we find that the question of tripartite to bipartite transformations can be solved by an efficient randomized algorithm. Our results are

Evolution of entanglement under echo dynamics

International Nuclear Information System (INIS)

Prosen, Tomaz; Znidaric, Marko; Seligman, Thomas H.

2003-01-01

Echo dynamics and fidelity are often used to discuss stability in quantum-information processing and quantum chaos. Yet fidelity yields no information about entanglement, the characteristic property of quantum mechanics. We study the evolution of entanglement in echo dynamics. We find qualitatively different behavior between integrable and chaotic systems on one hand and between random and coherent initial states for integrable systems on the other. For the latter the evolution of entanglement is given by a classical time scale. Analytic results are illustrated numerically in a Jaynes-Cummings model

Teleportation of Multi-qudit Entangled States

Institute of Scientific and Technical Information of China (English)

ZHAN Xiao-Gui; LI Hong-Mei; ZENG Hao-Sheng

2006-01-01

@@ We propose a method to realize the teleportation of an unknown entangled state that consists of many qudits through a partially entangled-qudit quantum channel with the help of 2 log2 d-bit classical communication. The operations used in the teleportation process include a generalized Bell-state measurement and a series of singlequdit π-measurements performed by Alice, a series of generalized qudit-Pauli gates and two-level unitary gates,as well as a qubit measurement performed by Bob. For a maximally entangled quantum channel, the successful probability of the teleportation becomes unit.

Entangled Light Emission From a Diode

International Nuclear Information System (INIS)

Stevenson, R. M.; Shields, A. J.; Salter, C. L.; Farrer, I.; Nicoll, C. A.; Ritchie, D. A.

2011-01-01

Electrically-driven entangled photon generation is demonstrated for the first time using a single semiconductor quantum dot embedded in a light emitting diode structure. The entanglement fidelity is shown to be of sufficient quality for applications such as quantum key distribution.

A Criterion to Identify Maximally Entangled Four-Qubit State

International Nuclear Information System (INIS)

Zha Xinwei; Song Haiyang; Feng Feng

2011-01-01

Paolo Facchi, et al. [Phys. Rev. A 77 (2008) 060304(R)] presented a maximally multipartite entangled state (MMES). Here, we give a criterion for the identification of maximally entangled four-qubit states. Using this criterion, we not only identify some existing maximally entangled four-qubit states in the literature, but also find several new maximally entangled four-qubit states as well. (general)

Quantum key distribution with an entangled light emitting diode

Energy Technology Data Exchange (ETDEWEB)

Dzurnak, B.; Stevenson, R. M.; Nilsson, J.; Dynes, J. F.; Yuan, Z. L.; Skiba-Szymanska, J.; Shields, A. J. [Toshiba Research Europe Limited, 208 Science Park, Milton Road, Cambridge CB4 0GZ (United Kingdom); Farrer, I.; Ritchie, D. A. [Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE (United Kingdom)

2015-12-28

Measurements performed on entangled photon pairs shared between two parties can allow unique quantum cryptographic keys to be formed, creating secure links between users. An advantage of using such entangled photon links is that they can be adapted to propagate entanglement to end users of quantum networks with only untrusted nodes. However, demonstrations of quantum key distribution with entangled photons have so far relied on sources optically excited with lasers. Here, we realize a quantum cryptography system based on an electrically driven entangled-light-emitting diode. Measurement bases are passively chosen and we show formation of an error-free quantum key. Our measurements also simultaneously reveal Bell's parameter for the detected light, which exceeds the threshold for quantum entanglement.

Entanglement in Quantum Field Theory: particle mixing and oscillations

International Nuclear Information System (INIS)

Blasone, M; Dell'Anno, F; De Siena, S; Illuminati, F

2013-01-01

The phenomena of particle mixing and flavor oscillations in elementary particle physics are associated with multi-mode entanglement of single-particle states. We show that, in the framework of quantum field theory, these phenomena exhibit a fine structure of quantum correlations, as multi-mode multi-particle entanglement appears. Indeed, the presence of anti-particles adds further degrees of freedom, thus providing nontrivial contributions both to flavor entanglement and, more generally, to multi-partite entanglement. By using the global entanglement measure, based on the linear entropies associated with all the possible bipartitions, we analyze the entanglement in the multiparticle states of two-flavor neutrinos and anti-neutrinos. A direct comparison with the instance of the quantum mechanical Pontecorvo single-particle states is also performed.

Deterministic dense coding with partially entangled states

Science.gov (United States)

Mozes, Shay; Oppenheim, Jonathan; Reznik, Benni

2005-01-01

The utilization of a d -level partially entangled state, shared by two parties wishing to communicate classical information without errors over a noiseless quantum channel, is discussed. We analytically construct deterministic dense coding schemes for certain classes of nonmaximally entangled states, and numerically obtain schemes in the general case. We study the dependency of the maximal alphabet size of such schemes on the partially entangled state shared by the two parties. Surprisingly, for d>2 it is possible to have deterministic dense coding with less than one ebit. In this case the number of alphabet letters that can be communicated by a single particle is between d and 2d . In general, we numerically find that the maximal alphabet size is any integer in the range [d,d2] with the possible exception of d2-1 . We also find that states with less entanglement can have a greater deterministic communication capacity than other more entangled states.

Tractable Quantification of Entanglement for Multipartite Pure States

International Nuclear Information System (INIS)

Nian-Quan, Jiang; Yu-Jian, Wang; Yi-Zhuang, Zheng; Gen-Chang, Cai

2008-01-01

We present kth-order entanglement measure and global kth-order entanglement measure for multipartite pure states, and extend Bennett's measure of partial entropy for bipartite pure states to a multipartite case. These measures are computable and can effectively classify and quantify the entanglement of multipartite pure states. (general)

Entanglement in a QFT Model of Neutrino Oscillations

International Nuclear Information System (INIS)

Illuminati, F.; Blasone, M.; Dell’Anno, F.; De Siena, S.

2014-01-01

Tools of quantum information theory can be exploited to provide a convenient description of the phenomena of particle mixing and flavor oscillations in terms of entanglement, a fundamental quantum resource. We extend such a picture to the domain of quantum field theory where, due to the nontrivial nature of flavor neutrino states, the presence of antiparticles provides additional contributions to flavor entanglement. We use a suitable entanglement measure, the concurrence, that allows extracting the two-mode (flavor) entanglement from the full multimode, multiparticle flavor neutrino states

Entanglement in continuous-variable systems: recent advances and current perspectives

International Nuclear Information System (INIS)

Adesso, Gerardo; Illuminati, Fabrizio

2007-01-01

We review the theory of continuous-variable entanglement with special emphasis on foundational aspects, conceptual structures and mathematical methods. Much attention is devoted to the discussion of separability criteria and entanglement properties of Gaussian states, for their great practical relevance in applications to quantum optics and quantum information, as well as for the very clean framework that they allow for the study of the structure of nonlocal correlations. We give a self-contained introduction to phase-space and symplectic methods in the study of Gaussian states of infinite-dimensional bosonic systems. We review the most important results on the separability and distillability of Gaussian states and discuss the main properties of bipartite entanglement. These include the extremal entanglement, minimal and maximal, of two-mode mixed Gaussian states, the ordering of two-mode Gaussian states according to different measures of entanglement, the unitary (reversible) localization and the scaling of bipartite entanglement in multimode Gaussian states. We then discuss recent advances in the understanding of entanglement sharing in multimode Gaussian states, including the proof of the monogamy inequality of distributed entanglement for all Gaussian states. Multipartite entanglement of Gaussian states is reviewed by discussing its qualification by different classes of separability, and the main consequences of the monogamy inequality, such as the quantification of genuine tripartite entanglement in three-mode Gaussian states, the promiscuous nature of entanglement sharing in symmetric Gaussian states and the possible coexistence of unlimited bipartite and multipartite entanglement. We finally review recent advances and discuss possible perspectives on the qualification and quantification of entanglement in non-Gaussian states, a field of research that is to a large extent yet to be explored

Entanglement in continuous-variable systems: recent advances and current perspectives

Energy Technology Data Exchange (ETDEWEB)

Adesso, Gerardo [Dipartimento di Fisica, Universita degli Studi di Roma ' La Sapienza' , Piazzale Aldo Moro 5, I-00185 Rome (Italy); Illuminati, Fabrizio [Dipartimento di Matematica e Informatica, Universita degli Studi di Salerno, Via Ponte don Melillo, I-84084 Fisciano (Italy)

2007-07-13

We review the theory of continuous-variable entanglement with special emphasis on foundational aspects, conceptual structures and mathematical methods. Much attention is devoted to the discussion of separability criteria and entanglement properties of Gaussian states, for their great practical relevance in applications to quantum optics and quantum information, as well as for the very clean framework that they allow for the study of the structure of nonlocal correlations. We give a self-contained introduction to phase-space and symplectic methods in the study of Gaussian states of infinite-dimensional bosonic systems. We review the most important results on the separability and distillability of Gaussian states and discuss the main properties of bipartite entanglement. These include the extremal entanglement, minimal and maximal, of two-mode mixed Gaussian states, the ordering of two-mode Gaussian states according to different measures of entanglement, the unitary (reversible) localization and the scaling of bipartite entanglement in multimode Gaussian states. We then discuss recent advances in the understanding of entanglement sharing in multimode Gaussian states, including the proof of the monogamy inequality of distributed entanglement for all Gaussian states. Multipartite entanglement of Gaussian states is reviewed by discussing its qualification by different classes of separability, and the main consequences of the monogamy inequality, such as the quantification of genuine tripartite entanglement in three-mode Gaussian states, the promiscuous nature of entanglement sharing in symmetric Gaussian states and the possible coexistence of unlimited bipartite and multipartite entanglement. We finally review recent advances and discuss possible perspectives on the qualification and quantification of entanglement in non-Gaussian states, a field of research that is to a large extent yet to be explored.

A quantitative witness for Greenberger-Horne-Zeilinger entanglement.

Science.gov (United States)

Eltschka, Christopher; Siewert, Jens

2012-01-01

Along with the vast progress in experimental quantum technologies there is an increasing demand for the quantification of entanglement between three or more quantum systems. Theory still does not provide adequate tools for this purpose. The objective is, besides the quest for exact results, to develop operational methods that allow for efficient entanglement quantification. Here we put forward an analytical approach that serves both these goals. We provide a simple procedure to quantify Greenberger-Horne-Zeilinger-type multipartite entanglement in arbitrary three-qubit states. For two qubits this method is equivalent to Wootters' seminal result for the concurrence. It establishes a close link between entanglement quantification and entanglement detection by witnesses, and can be generalised both to higher dimensions and to more than three parties.

Effects of cavity-cavity interaction on the entanglement dynamics of a generalized double Jaynes-Cummings model

Science.gov (United States)

Pandit, Mahasweta; Das, Sreetama; Singha Roy, Sudipto; Shekhar Dhar, Himadri; Sen, Ujjwal

2018-02-01

We consider a generalized double Jaynes-Cummings model consisting of two isolated two-level atoms, each contained in a lossless cavity that interact with each other through a controlled photon-hopping mechanism. We analytically show that at low values of such a mediated cavity-cavity interaction, the temporal evolution of entanglement between the atoms, under the effects of cavity perturbation, exhibits the well-known phenomenon of entanglement sudden death (ESD). Interestingly, for moderately large interaction values, a complete preclusion of ESD is achieved, irrespective of its value in the initial atomic state. Our results provide a model to sustain entanglement between two atomic qubits, under the adverse effect of cavity induced perturbation, by introducing a non-intrusive inter-cavity photon exchange that can be physically realized through cavity-QED setups in contemporary experiments.

Entanglement of two distant qubits driven by thermal environments

International Nuclear Information System (INIS)

Montenegro, Víctor; Eremeev, Vitalie; Orszag, Miguel

2012-01-01

A model of entanglement generation of two initially disentangled qubits, each coupled to a separate cavity with the cavities connected by a fiber, is considered. The creation and evolution of the atomic entanglement are studied in the framework of the microscopic master equation capable of describing an open quantum system. The cavities and fiber are coupled to their own thermal environment. In these conditions, we compute the concurrence as a measure of the atomic entanglement and study the contribution of the environments at finite temperature to the dynamics of entanglement. As a result, one finds interesting effects where the thermal baths stimulate the generation of the entanglement in a given range of temperatures and the effect could be seen especially at some stage of the entanglement evolution. The range of temperatures at which entanglement increases is limited by some optimal values, depending on the physical characteristics of the system, such as operating cavity/fiber frequencies, atom-field detuning and couplings, and loss rates.

Criticality and entanglement in random quantum systems

International Nuclear Information System (INIS)

Refael, G; Moore, J E

2009-01-01

We review studies of entanglement entropy in systems with quenched randomness, concentrating on universal behavior at strongly random quantum critical points. The disorder-averaged entanglement entropy provides insight into the quantum criticality of these systems and an understanding of their relationship to non-random ('pure') quantum criticality. The entanglement near many such critical points in one dimension shows a logarithmic divergence in subsystem size, similar to that in the pure case but with a different universal coefficient. Such universal coefficients are examples of universal critical amplitudes in a random system. Possible measurements are reviewed along with the one-particle entanglement scaling at certain Anderson localization transitions. We also comment briefly on higher dimensions and challenges for the future.

On the entanglement entropy for gauge theories

International Nuclear Information System (INIS)

Ghosh, Sudip; Soni, Ronak M; Trivedi, Sandip P.

2015-01-01

We propose a definition for the entanglement entropy of a gauge theory on a spatial lattice. Our definition applies to any subset of links in the lattice, and is valid for both Abelian and Non-Abelian gauge theories. For ℤ_N and U(1) theories, without matter, our definition agrees with a particular case of the definition given by Casini, Huerta and Rosabal. We also argue that in general, both for Abelian and Non-Abelian theories, our definition agrees with the entanglement entropy calculated using a definition of the replica trick. Our definition, however, does not agree with some standard ways to measure entanglement, like the number of Bell pairs which can be produced by entanglement distillation.

Entanglement Entropy of AdS Black Holes

Directory of Open Access Journals (Sweden)

Maurizio Melis

2010-11-01

Full Text Available We review recent progress in understanding the entanglement entropy of gravitational configurations for anti-de Sitter gravity in two and three spacetime dimensions using the AdS/CFT correspondence. We derive simple expressions for the entanglement entropy of two- and three-dimensional black holes. In both cases, the leading term of the entanglement entropy in the large black hole mass expansion reproduces exactly the Bekenstein-Hawking entropy, whereas the subleading term behaves logarithmically. In particular, for the BTZ black hole the leading term of the entanglement entropy can be obtained from the large temperature expansion of the partition function of a broad class of 2D CFTs on the torus.

Developments in entanglement theory and applications to relevant physical systems

OpenAIRE

Lamata Manuel, Lucas

2007-01-01

This Thesis is devoted to the analysis of entanglement in relevant physical systems. Entanglement is the conducting theme of this research, though I do not dedicate to a single topic, but consider a wide scope of physical situations. I have followed mainly three lines of research for this Thesis, with a series of different works each, which are, Entanglement and Relativistic Quantum Theory, Continuous-variable entanglement, and Multipartite entanglement.

Bipartite entanglement in continuous variable cluster states

Energy Technology Data Exchange (ETDEWEB)

Cable, Hugo; Browne, Daniel E, E-mail: cqthvc@nus.edu.s, E-mail: d.browne@ucl.ac.u [Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, Singapore 117543 (Singapore)

2010-11-15

A study of the entanglement properties of Gaussian cluster states, proposed as a universal resource for continuous variable (CV) quantum computing is presented in this paper. The central aim is to compare mathematically idealized cluster states defined using quadrature eigenstates, which have infinite squeezing and cannot exist in nature, with Gaussian approximations that are experimentally accessible. Adopting widely used definitions, we first review the key concepts, by analysing a process of teleportation along a CV quantum wire in the language of matrix product states. Next we consider the bipartite entanglement properties of the wire, providing analytic results. We proceed to grid cluster states, which are universal for the qubit case. To extend our analysis of the bipartite entanglement, we adopt the entropic-entanglement width, a specialized entanglement measure introduced recently by Van den Nest et al (2006 Phys. Rev. Lett. 97 150504), adapting their definition to the CV context. Finally, we consider the effects of photonic loss, extending our arguments to mixed states. Cumulatively our results point to key differences in the properties of idealized and Gaussian cluster states. Even modest loss rates are found to strongly limit the amount of entanglement. We discuss the implications for the potential of CV analogues for measurement-based quantum computation.

Remarks on entanglement entropy in string theory

Science.gov (United States)

Balasubramanian, Vijay; Parrikar, Onkar

2018-03-01

Entanglement entropy for spatial subregions is difficult to define in string theory because of the extended nature of strings. Here we propose a definition for bosonic open strings using the framework of string field theory. The key difference (compared to ordinary quantum field theory) is that the subregion is chosen inside a Cauchy surface in the "space of open string configurations." We first present a simple calculation of this entanglement entropy in free light-cone string field theory, ignoring subtleties related to the factorization of the Hilbert space. We reproduce the answer expected from an effective field theory point of view, namely a sum over the one-loop entanglement entropies corresponding to all the particle-excitations of the string, and further show that the full string theory regulates ultraviolet divergences in the entanglement entropy. We then revisit the question of factorization of the Hilbert space by analyzing the covariant phase-space associated with a subregion in Witten's covariant string field theory. We show that the pure gauge (i.e., BRST exact) modes in the string field become dynamical at the entanglement cut. Thus, a proper definition of the entropy must involve an extended Hilbert space, with new stringy edge modes localized at the entanglement cut.

The emergence of typical entanglement in two-party random processes

International Nuclear Information System (INIS)

Dahlsten, O C O; Oliveira, R; Plenio, M B

2007-01-01

We investigate the entanglement within a system undergoing a random, local process. We find that there is initially a phase of very fast generation and spread of entanglement. At the end of this phase the entanglement is typically maximal. In Oliveira et al (2007 Phys. Rev. Lett. 98 130502) we proved that the maximal entanglement is reached to a fixed arbitrary accuracy within O(N 3 ) steps, where N is the total number of qubits. Here we provide a detailed and more pedagogical proof. We demonstrate that one can use the so-called stabilizer gates to simulate this process efficiently on a classical computer. Furthermore, we discuss three ways of identifying the transition from the phase of rapid spread of entanglement to the stationary phase: (i) the time when saturation of the maximal entanglement is achieved, (ii) the cutoff moment, when the entanglement probability distribution is practically stationary, and (iii) the moment block entanglement exhibits volume scaling. We furthermore investigate the mixed state and multipartite setting. Numerically, we find that the mutual information appears to behave similarly to the quantum correlations and that there is a well-behaved phase-space flow of entanglement properties towards an equilibrium. We describe how the emergence of typical entanglement can be used to create a much simpler tripartite entanglement description. The results form a bridge between certain abstract results concerning typical (also known as generic) entanglement relative to an unbiased distribution on pure states and the more physical picture of distributions emerging from random local interactions

Emergence of Symmetries from Entanglement

CERN Multimedia

CERN. Geneva

2016-01-01

Maximal Entanglement appears to be a key ingredient for the emergence of symmetries. We first illustrate this phenomenon using two examples: the emergence of conformal symmetry in condensed matter systems and  the relation of tensor networks to holography. We further present a Principle of Maximal Entanglement that seems to dictate to a large extend the structure of gauge symmetry.

Delayed-Choice Experiments and the Metaphysics of Entanglement

Science.gov (United States)

Egg, Matthias

2013-09-01

Delayed-choice experiments in quantum mechanics are often taken to undermine a realistic interpretation of the quantum state. More specifically, Healey has recently argued that the phenomenon of delayed-choice entanglement swapping is incompatible with the view that entanglement is a physical relation between quantum systems. This paper argues against these claims. It first reviews two paradigmatic delayed-choice experiments and analyzes their metaphysical implications. It then applies the results of this analysis to the case of entanglement swapping, showing that such experiments pose no threat to realism about entanglement.

All pure bipartite entangled states can be self-tested

Science.gov (United States)

Coladangelo, Andrea; Goh, Koon Tong; Scarani, Valerio

2017-05-01

Quantum technologies promise advantages over their classical counterparts in the fields of computation, security and sensing. It is thus desirable that classical users are able to obtain guarantees on quantum devices, even without any knowledge of their inner workings. That such classical certification is possible at all is remarkable: it is a consequence of the violation of Bell inequalities by entangled quantum systems. Device-independent self-testing refers to the most complete such certification: it enables a classical user to uniquely identify the quantum state shared by uncharacterized devices by simply inspecting the correlations of measurement outcomes. Self-testing was first demonstrated for the singlet state and a few other examples of self-testable states were reported in recent years. Here, we address the long-standing open question of whether every pure bipartite entangled state is self-testable. We answer it affirmatively by providing explicit self-testing correlations for all such states.

Teleportation of continuous variable multimode Greeberger-Horne-Zeilinger entangled states

International Nuclear Information System (INIS)

He Guangqiang; Zhang Jingtao; Zeng Guihua

2008-01-01

Quantum teleportation protocols of continuous variable (CV) Greeberger-Horne-Zeilinger (GHZ) and Einstein-Podolsky-Rosen (EPR) entangled states are proposed, and are generalized to teleportation of arbitrary multimode GHZ entangled states described by Van Loock and Braunstein (2000 Phys. Rev. Lett. 84 3482). Each mode of a multimode entangled state is teleported using a CV EPR entangled pair and classical communication. The analytical expression of fidelity for the multimode Gaussian states which evaluates the teleportation quality is presented. The analytical results show that the fidelity is a function of both the squeezing parameter r, which characterizes the multimode entangled state to be teleported, and the channel parameter p, which characterizes the EPR pairs shared by Alice and Bob. The fidelity increases with increasing p, but decreases with increasing r, i.e., it is more difficult to teleport the more perfect multimode entangled states. The entanglement degree of the teleported multimode entangled states increases with increasing both r and p. In addition, the fact is proved that our teleportation protocol of EPR entangled states using parallel EPR pairs as quantum channels is the best case of the protocol using four-mode entangled states (Adhikari et al 2008 Phys. Rev. A 77 012337).

Renormalization group flow of entanglement entropy on spheres

Energy Technology Data Exchange (ETDEWEB)

Ben-Ami, Omer; Carmi, Dean [Raymond and Beverly Sackler Faculty of Exact Sciences School of Physics and Astronomy,Tel-Aviv University, Ramat-Aviv 69978 (Israel); Smolkin, Michael [Center for Theoretical Physics and Department of Physics,University of California, Berkeley, CA 94720 (United States)

2015-08-12

We explore entanglement entropy of a cap-like region for a generic quantum field theory residing in the Bunch-Davies vacuum on de Sitter space. Entanglement entropy in our setup is identical with the thermal entropy in the static patch of de Sitter, and we derive a simple relation between the vacuum expectation value of the energy-momentum tensor trace and the RG flow of entanglement entropy. In particular, renormalization of the bare couplings and logarithmic divergence of the entanglement entropy are interrelated in our setup. We confirm our findings by recovering known universal contributions for a free field theory deformed by a mass operator as well as obtain correct universal behaviour at the fixed points. Simple examples of entanglement entropy flows are elaborated in d=2,3,4. In three dimensions we find that while the renormalized entanglement entropy is stationary at the fixed points, it is not monotonic. We provide a computational evidence that the universal ‘area law’ for a conformally coupled scalar is different from the known result in the literature, and argue that this difference survives in the limit of flat space. Finally, we carry out the spectral decomposition of entanglement entropy flow and discuss its application to the F-theorem.

Determination of continuous variable entanglement by purity measurements.

Science.gov (United States)

Adesso, Gerardo; Serafini, Alessio; Illuminati, Fabrizio

2004-02-27

We classify the entanglement of two-mode Gaussian states according to their degree of total and partial mixedness. We derive exact bounds that determine maximally and minimally entangled states for fixed global and marginal purities. This characterization allows for an experimentally reliable estimate of continuous variable entanglement based on measurements of purity.

Variation of entanglement entropy in scattering process

Energy Technology Data Exchange (ETDEWEB)

Seki, Shigenori, E-mail: sigenori@hanyang.ac.kr [Research Institute for Natural Science, Hanyang University, Seoul 133-791 (Korea, Republic of); Park, I.Y., E-mail: inyongpark05@gmail.com [Department of Applied Mathematics, Philander Smith College, Little Rock, AR 72223 (United States); Sin, Sang-Jin, E-mail: sjsin@hanyang.ac.kr [Department of Physics, Hanyang University, Seoul 133-791 (Korea, Republic of)

2015-04-09

In a scattering process, the final state is determined by an initial state and an S-matrix. We focus on two-particle scattering processes and consider the entanglement between these particles. For two types initial states, i.e., an unentangled state and an entangled one, we calculate perturbatively the change of entanglement entropy from the initial state to the final one. Then we show a few examples in a field theory and in quantum mechanics.

Genuine multipartite entanglement of symmetric Gaussian states: Strong monogamy, unitary localization, scaling behavior, and molecular sharing structure

Science.gov (United States)

Adesso, Gerardo; Illuminati, Fabrizio

2008-10-01

We investigate the structural aspects of genuine multipartite entanglement in Gaussian states of continuous variable systems. Generalizing the results of Adesso and Illuminati [Phys. Rev. Lett. 99, 150501 (2007)], we analyze whether the entanglement shared by blocks of modes distributes according to a strong monogamy law. This property, once established, allows us to quantify the genuine N -partite entanglement not encoded into 2,…,K,…,(N-1) -partite quantum correlations. Strong monogamy is numerically verified, and the explicit expression of the measure of residual genuine multipartite entanglement is analytically derived, by a recursive formula, for a subclass of Gaussian states. These are fully symmetric (permutation-invariant) states that are multipartitioned into blocks, each consisting of an arbitrarily assigned number of modes. We compute the genuine multipartite entanglement shared by the blocks of modes and investigate its scaling properties with the number and size of the blocks, the total number of modes, the global mixedness of the state, and the squeezed resources needed for state engineering. To achieve the exact computation of the block entanglement, we introduce and prove a general result of symplectic analysis: Correlations among K blocks in N -mode multisymmetric and multipartite Gaussian states, which are locally invariant under permutation of modes within each block, can be transformed by a local (with respect to the partition) unitary operation into correlations shared by K single modes, one per block, in effective nonsymmetric states where N-K modes are completely uncorrelated. Due to this theorem, the above results, such as the derivation of the explicit expression for the residual multipartite entanglement, its nonnegativity, and its scaling properties, extend to the subclass of non-symmetric Gaussian states that are obtained by the unitary localization of the multipartite entanglement of symmetric states. These findings provide strong

Deriving covariant holographic entanglement

Energy Technology Data Exchange (ETDEWEB)

Dong, Xi [School of Natural Sciences, Institute for Advanced Study, Princeton, NJ 08540 (United States); Lewkowycz, Aitor [Jadwin Hall, Princeton University, Princeton, NJ 08544 (United States); Rangamani, Mukund [Center for Quantum Mathematics and Physics (QMAP), Department of Physics, University of California, Davis, CA 95616 (United States)

2016-11-07

We provide a gravitational argument in favour of the covariant holographic entanglement entropy proposal. In general time-dependent states, the proposal asserts that the entanglement entropy of a region in the boundary field theory is given by a quarter of the area of a bulk extremal surface in Planck units. The main element of our discussion is an implementation of an appropriate Schwinger-Keldysh contour to obtain the reduced density matrix (and its powers) of a given region, as is relevant for the replica construction. We map this contour into the bulk gravitational theory, and argue that the saddle point solutions of these replica geometries lead to a consistent prescription for computing the field theory Rényi entropies. In the limiting case where the replica index is taken to unity, a local analysis suffices to show that these saddles lead to the extremal surfaces of interest. We also comment on various properties of holographic entanglement that follow from this construction.

Quantum entanglement in polarization and space

NARCIS (Netherlands)

Lee, Peter Sing Kin

2006-01-01

One of the most intriguing concepts of quantum mechanics is quantum entanglement. Two physical systems are said to be entangled with respect to a certain variable, if their individual outcomes of the variable are undetermined before measurement, but strictly correlated. Measurement of the variable

Entanglement-assisted quantum low-density parity-check codes

International Nuclear Information System (INIS)

Fujiwara, Yuichiro; Clark, David; Tonchev, Vladimir D.; Vandendriessche, Peter; De Boeck, Maarten

2010-01-01

This article develops a general method for constructing entanglement-assisted quantum low-density parity-check (LDPC) codes, which is based on combinatorial design theory. Explicit constructions are given for entanglement-assisted quantum error-correcting codes with many desirable properties. These properties include the requirement of only one initial entanglement bit, high error-correction performance, high rates, and low decoding complexity. The proposed method produces several infinite families of codes with a wide variety of parameters and entanglement requirements. Our framework encompasses the previously known entanglement-assisted quantum LDPC codes having the best error-correction performance and many other codes with better block error rates in simulations over the depolarizing channel. We also determine important parameters of several well-known classes of quantum and classical LDPC codes for previously unsettled cases.

Quantum entanglement and fixed-point bifurcations

International Nuclear Information System (INIS)

Hines, Andrew P.; McKenzie, Ross H.; Milburn, G.J.

2005-01-01

How does the classical phase-space structure for a composite system relate to the entanglement characteristics of the corresponding quantum system? We demonstrate how the entanglement in nonlinear bipartite systems can be associated with a fixed-point bifurcation in the classical dynamics. Using the example of coupled giant spins we show that when a fixed point undergoes a supercritical pitchfork bifurcation, the corresponding quantum state--the ground state--achieves its maximum amount of entanglement near the critical point. We conjecture that this will be a generic feature of systems whose classical limit exhibits such a bifurcation

Detecting Kondo Entanglement by Electron Conductance

Science.gov (United States)

Yoo, Gwangsu; Lee, S.-S. B.; Sim, H.-S.

2018-04-01

Quantum entanglement between an impurity spin and electrons nearby is a key property of the single-channel Kondo effects. We show that the entanglement can be detected by measuring electron conductance through a double quantum dot in an orbital Kondo regime. We derive a relation between the entanglement and the conductance, when the SU(2) spin symmetry of the regime is weakly broken. The relation reflects the universal form of many-body states near the Kondo fixed point. Using it, the spatial distribution of the entanglement—hence, the Kondo cloud—can be detected, with breaking of the symmetry spatially nonuniformly by electrical means.

Multipartite entangled states in particle mixing

International Nuclear Information System (INIS)

Blasone, M.; Dell'Anno, F.; De Siena, S.; Di Mauro, M.; Illuminati, F.

2008-01-01

In the physics of flavor mixing, the flavor states are given by superpositions of mass eigenstates. By using the occupation number to define a multiqubit space, the flavor states can be interpreted as multipartite mode-entangled states. By exploiting a suitable global measure of entanglement, based on the entropies related to all possible bipartitions of the system, we analyze the correlation properties of such states in the instances of three- and four-flavor mixing. Depending on the mixing parameters, and, in particular, on the values taken by the free phases, responsible for the CP-violation, entanglement concentrates in certain bipartitions. We quantify in detail the amount and the distribution of entanglement in the physically relevant cases of flavor mixing in quark and neutrino systems. By using the wave packet description for localized particles, we use the global measure of entanglement, suitably adapted for the instance of multipartite mixed states, to analyze the decoherence, induced by the free evolution dynamics, on the quantum correlations of stationary neutrino beams. We define a decoherence length as the distance associated with the vanishing of the coherent interference effects among massive neutrino states. We investigate the role of the CP-violating phase in the decoherence process.

Entangled states that cannot reproduce original classical games in their quantum version

International Nuclear Information System (INIS)

Shimamura, Junichi; Oezdemir, S.K.; Morikoshi, Fumiaki; Imoto, Nobuyuki

2004-01-01

A model of a quantum version of classical games should reproduce the original classical games in order to be able to make a comparative analysis of quantum and classical effects. We analyze a class of symmetric multipartite entangled states and their effect on the reproducibility of the classical games. We present the necessary and sufficient condition for the reproducibility of the original classical games. Satisfying this condition means that complete orthogonal bases can be constructed from a given multipartite entangled state provided that each party is restricted to two local unitary operators. We prove that most of the states belonging to the class of symmetric states with respect to permutations, including the N-qubit W state, do not satisfy this condition

Entanglement between electronic states in silicene and photons

Energy Technology Data Exchange (ETDEWEB)

Rastgoo, S. [Physics Department, College of Sciences, Shiraz University, Shiraz 71454 (Iran, Islamic Republic of); Shirkani, H. [Physics Department, Persian Gulf University, Bushehr 75169 (Iran, Islamic Republic of); Golshan, M.M., E-mail: golshan@susc.ac.ir [Physics Department, College of Sciences, Shiraz University, Shiraz 71454 (Iran, Islamic Republic of)

2015-06-12

Temporal behavior of entanglement between electrons in silicene and single mode radiations is reported. We show that the corresponding total Hamiltonian and time evolution operators are block diagonal. Initial states are divided into two categories for which buckling and the intrinsic spin–orbit effects are either of opposite or the same signs. Negativity shows that π-electrons and photons periodically become entangled for both categories. The entanglement spontaneously shows abrupt variations when buckling and the spin–orbit effects are equal but opposite in sign, leading to quantum phase transitions. As photonic excitations increase, the entanglement exhibits plateaus of constant durations for such initial states. - Highlights: • Time evolution of entanglement between π-electrons and photons in silicene is reported. • Intrinsic spin–orbit coupling (ISOC) and buckling effect (BE) are taken into account. • Initial states with ISOC and BE of opposite signs show quantum phase transitions. • Quantum phase transitions spontaneously occur when ISOC is equal to BE. • Periodic plateaus of maximal entanglement are observed for high photonic excitations.

Increasing Entanglement between Gaussian States by Coherent Photon Subtraction

DEFF Research Database (Denmark)

Ourjoumtsev, Alexei; Dantan, Aurelien Romain; Tualle Brouri, Rosa

2007-01-01

We experimentally demonstrate that the entanglement between Gaussian entangled states can be increased by non-Gaussian operations. Coherent subtraction of single photons from Gaussian quadrature-entangled light pulses, created by a nondegenerate parametric amplifier, produces delocalized states...

Entanglement entropy from the holographic stress tensor

International Nuclear Information System (INIS)

Bhattacharyya, Arpan; Sinha, Aninda

2013-01-01

We consider entanglement entropy in the context of gauge/gravity duality for conformal field theories in even dimensions. The holographic prescription due to Ryu and Takayanagi (RT) leads to an equation describing how the entangling surface extends into the bulk geometry. We show that setting to zero, the time–time component of the Brown–York stress tensor evaluated on the co-dimension 1 entangling surface, leads to the same equation. By considering a spherical entangling surface as an example, we observe that the Euclidean action methods in AdS/CFT will lead to the RT area functional arising as a counterterm needed to regularize the stress tensor. We present arguments leading to a justification for the minimal area prescription. (paper)

Measurement-Based Entanglement of Noninteracting Bosonic Atoms.

Science.gov (United States)

Lester, Brian J; Lin, Yiheng; Brown, Mark O; Kaufman, Adam M; Ball, Randall J; Knill, Emanuel; Rey, Ana M; Regal, Cindy A

2018-05-11

We demonstrate the ability to extract a spin-entangled state of two neutral atoms via postselection based on a measurement of their spatial configuration. Typically, entangled states of neutral atoms are engineered via atom-atom interactions. In contrast, in our Letter, we use Hong-Ou-Mandel interference to postselect a spin-singlet state after overlapping two atoms in distinct spin states on an effective beam splitter. We verify the presence of entanglement and determine a bound on the postselected fidelity of a spin-singlet state of (0.62±0.03). The experiment has direct analogy to creating polarization entanglement with single photons and hence demonstrates the potential to use protocols developed for photons to create complex quantum states with noninteracting atoms.

Testing for entanglement with periodic coarse graining

Science.gov (United States)

Tasca, D. S.; Rudnicki, Łukasz; Aspden, R. S.; Padgett, M. J.; Souto Ribeiro, P. H.; Walborn, S. P.

2018-04-01

Continuous-variable systems find valuable applications in quantum information processing. To deal with an infinite-dimensional Hilbert space, one in general has to handle large numbers of discretized measurements in tasks such as entanglement detection. Here we employ the continuous transverse spatial variables of photon pairs to experimentally demonstrate entanglement criteria based on a periodic structure of coarse-grained measurements. The periodization of the measurements allows an efficient evaluation of entanglement using spatial masks acting as mode analyzers over the entire transverse field distribution of the photons and without the need to reconstruct the probability densities of the conjugate continuous variables. Our experimental results demonstrate the utility of the derived criteria with a success rate in entanglement detection of ˜60 % relative to 7344 studied cases.

Multipartite entanglement and frustration

International Nuclear Information System (INIS)

Facchi, P; Florio, G; Pascazio, S; Marzolino, U; Parisi, G

2010-01-01

Some features of the global entanglement of a composed quantum system can be quantified in terms of the purity of a balanced bipartition, made up of half of its subsystems. For the given bipartition, purity can always be minimized by taking a suitable (pure) state. When many bipartitions are considered, the requirement that purity be minimal for all bipartitions can engender conflicts and frustration will arise. This unearths an interesting link between frustration and multipartite entanglement, defined as the average purity over all (balanced) bipartitions.

Multipartite entanglement and frustration

Science.gov (United States)

Facchi, P.; Florio, G.; Marzolino, U.; Parisi, G.; Pascazio, S.

2010-02-01

Some features of the global entanglement of a composed quantum system can be quantified in terms of the purity of a balanced bipartition, made up of half of its subsystems. For the given bipartition, purity can always be minimized by taking a suitable (pure) state. When many bipartitions are considered, the requirement that purity be minimal for all bipartitions can engender conflicts and frustration will arise. This unearths an interesting link between frustration and multipartite entanglement, defined as the average purity over all (balanced) bipartitions.

Multipartite entanglement and frustration

Energy Technology Data Exchange (ETDEWEB)

Facchi, P [Dipartimento di Matematica, Universita di Bari, I-70125 Bari (Italy); Florio, G; Pascazio, S [Istituto Nazionale di Fisica Nucleare, Sezione di Bari, I-70126 Bari (Italy); Marzolino, U [Dipartimento di Fisica, Universita di Trieste, and Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I-34014 Trieste (Italy); Parisi, G [Dipartimento di Fisica, Universita di Roma ' La Sapienza' , Piazzale Aldo Moro 2, Centre for Statistical Mechanics and Complexity (SMC), CNR-INFM, and Istituto Nazionale di Fisica Nucleare, Sezione di Roma, 00185 Roma (Italy)], E-mail: paolo.facchi@ba.infn.it

2010-02-15

Some features of the global entanglement of a composed quantum system can be quantified in terms of the purity of a balanced bipartition, made up of half of its subsystems. For the given bipartition, purity can always be minimized by taking a suitable (pure) state. When many bipartitions are considered, the requirement that purity be minimal for all bipartitions can engender conflicts and frustration will arise. This unearths an interesting link between frustration and multipartite entanglement, defined as the average purity over all (balanced) bipartitions.

Effect of weak measurement on entanglement distribution over noisy channels.

Science.gov (United States)

Wang, Xin-Wen; Yu, Sixia; Zhang, Deng-Yu; Oh, C H

2016-03-03

Being able to implement effective entanglement distribution in noisy environments is a key step towards practical quantum communication, and long-term efforts have been made on the development of it. Recently, it has been found that the null-result weak measurement (NRWM) can be used to enhance probabilistically the entanglement of a single copy of amplitude-damped entangled state. This paper investigates remote distributions of bipartite and multipartite entangled states in the amplitudedamping environment by combining NRWMs and entanglement distillation protocols (EDPs). We show that the NRWM has no positive effect on the distribution of bipartite maximally entangled states and multipartite Greenberger-Horne-Zeilinger states, although it is able to increase the amount of entanglement of each source state (noisy entangled state) of EDPs with a certain probability. However, we find that the NRWM would contribute to remote distributions of multipartite W states. We demonstrate that the NRWM can not only reduce the fidelity thresholds for distillability of decohered W states, but also raise the distillation efficiencies of W states. Our results suggest a new idea for quantifying the ability of a local filtering operation in protecting entanglement from decoherence.

Holographic entanglement entropy in Lovelock gravities

NARCIS (Netherlands)

de Boer, J.; Kulaxizi, M.; Parnachev, A.

2011-01-01

We study entanglement entropies of simply connected surfaces in field theories dual to Lovelock gravities. We consider Gauss-Bonnet and cubic Lovelock gravities in detail. In the conformal case the logarithmic terms in the entanglement entropy are governed by the conformal anomalies of the CFT; we

Spin entanglement, decoherence and Bohm's EPR paradox

OpenAIRE

Cavalcanti, E. G.; Drummond, P. D.; Bachor, H. A.; Reid, M. D.

2007-01-01

We obtain criteria for entanglement and the EPR paradox for spin-entangled particles and analyse the effects of decoherence caused by absorption and state purity errors. For a two qubit photonic state, entanglement can occur for all transmission efficiencies. In this case, the state preparation purity must be above a threshold value. However, Bohm's spin EPR paradox can be achieved only above a critical level of loss. We calculate a required efficiency of 58%, which appears achievable with cu...

Non-binary Entanglement-assisted Stabilizer Quantum Codes

OpenAIRE

Riguang, Leng; Zhi, Ma

2011-01-01

In this paper, we show how to construct non-binary entanglement-assisted stabilizer quantum codes by using pre-shared entanglement between the sender and receiver. We also give an algorithm to determine the circuit for non-binary entanglement-assisted stabilizer quantum codes and some illustrated examples. The codes we constructed do not require the dual-containing constraint, and many non-binary classical codes, like non-binary LDPC codes, which do not satisfy the condition, can be used to c...

Controllable entanglement sudden birth of Heisenberg spins

International Nuclear Information System (INIS)

Zheng Qiang; Zhi Qijun; Zhang Xiaoping; Ren Zhongzhou

2011-01-01

We investigate the Entanglement Sudden Birth (ESB) of two Heisenberg spins A and B. The third controller, qutrit C is introduced, which only has the Dzyaloshinskii-Moriya (DM) spin-orbit interaction with qubit B. We find that the DM interaction is necessary to induce the Entanglement Sudden Birth of the system qubits A and B, and the initial states of the system qubits and the qutrit C are also important to control its Entanglement Sudden Birth. (authors)

Universal quantum entanglement between an oscillator and continuous fields

International Nuclear Information System (INIS)

Miao Haixing; Danilishin, Stefan; Chen Yanbei

2010-01-01

Quantum entanglement has been actively sought in optomechanical and electromechanical systems. The simplest system is a mechanical oscillator interacting with a coherent optical field, while the oscillator also suffers from thermal decoherence. With a rigorous functional analysis, we develop a mathematical framework for treating quantum entanglement that involves infinite degrees of freedom. We show that the quantum entanglement is always present between the oscillator and continuous optical field--even when the environmental temperature is high and the oscillator is highly classical. Such a universal entanglement is also shown to be able to survive more than one mechanical oscillation period if the characteristic frequency of the optomechanical interaction is larger than that of the thermal noise. In addition, we introduce effective optical modes that are ordered by the entanglement strength to better understand the entanglement structure, analogously to the energy spectrum of an atomic system. In particular, we derive the optical mode that is maximally entangled with the mechanical oscillator, which will be useful for future quantum computing and encoding information into mechanical degrees of freedom.

Reduction of entanglement degradation in Einstein-Gauss-Bonnet gravity

International Nuclear Information System (INIS)

Nasr Esfahani, B.; Shamirzaie, M.; Soltani, M.

2011-01-01

Bipartite entanglement for states of a noninteracting bosonic or fermionic field in the spacetime of a spherically symmetric black hole of Einstein-Gauss-Bonnet gravity is investigated. Although the initial state is chosen to be maximally entangled as the Bell states, the Hawking-Unruh effect causes the state to be mixed and the entanglement degrades, but with different asymptotic behaviors for the fermionic and bosonic fields. The Gauss-Bonnet term with positive α can play an antigravitation role and so this causes a decrease in the Hawking-Unruh effect and consequently reduces the entanglement degradation. On the other hand, the suggested higher dimensions for the spacetime lead to increased entanglement degradation by increasing the dimension. There is a dramatic difference between the behaviors of the entanglement in terms of the radius of the horizon for a five-dimensional black hole and that for higher dimensional black holes. Both bosonic and fermionic fields entanglements are treated beyond the single-mode approximation. Also, the cases where the accelerating observers located at regions near and far from the event horizon of black hole are studied separately.

Polarization entanglement purification for concatenated Greenberger-Horne-Zeilinger state

Science.gov (United States)

Zhou, Lan; Sheng, Yu-Bo

2017-10-01

Entanglement purification plays a fundamental role in long-distance quantum communication. In the paper, we put forward the first polarization entanglement purification protocol (EPP) for one type of nonlocal logic-qubit entanglement, i.e., concatenated Greenberger-Horne-Zeilinger (C-GHZ) state, resorting to the photon-atom interaction in low-quality (Q) cavity. In contrast to existing EPPs, this protocol can purify the bit-flip error and phase-flip error in both physic and logic level. Instead of measuring the photons directly, this protocol only requires to measure the atom states to judge whether the protocol is successful. In this way, the purified logic entangled states can be preserved for further application. Moreover, it makes this EPP repeatable so as to obtain a higher fidelity of logic entangled states. As the logic-qubit entanglement utilizes the quantum error correction (QEC) codes, which has an inherent stability against noise and decoherence, this EPP combined with the QEC codes may provide a double protection for the entanglement from the channel noise and may have potential applications in long-distance quantum communication.

An entanglement concentration protocol for cluster states using ...

Indian Academy of Sciences (India)

It may be noted that these protocols are not the only approaches of gener- ating maximally entangled states. There are several other protocols such as entanglement purification [8–12], quantum entanglement distillation [13,14], etc., to this effect. The history of ECP starts in the work of Bennett et al [8] in 1996 in which he ...

Persistent entanglement in the classical limit

Energy Technology Data Exchange (ETDEWEB)

Everitt, M J [Centre for Physical Electronics and Quantum Technology, School of Science and Technology, University of Sussex, Falmer, Brighton BN1 9QT (United Kingdom); Clark, T D [Centre for Physical Electronics and Quantum Technology, School of Science and Technology, University of Sussex, Falmer, Brighton BN1 9QT (United Kingdom); Stiffell, P B [Centre for Physical Electronics and Quantum Technology, School of Science and Technology, University of Sussex, Falmer, Brighton BN1 9QT (United Kingdom); Ralph, J F [Department of Electrical and Electronic Engineering, Liverpool University, Brownlow Hill, Liverpool L69 3GJ (United Kingdom); Bulsara, A R [Space and Naval Warfare Systems Center, Code 2363, 53560 Hull Street, San Diego, CA 92152-5001 (United States); Harland, C J [Centre for Physical Electronics and Quantum Technology, School of Science and Technology, University of Sussex, Falmer, Brighton BN1 9QT (United Kingdom)

2005-02-01

The apparent difficulty in recovering classical nonlinear dynamics and chaos from standard quantum mechanics has been the subject of a great deal of interest over the last 20 years. For open quantum systems-those coupled to a dissipative environment and/or a measurement device-it has been demonstrated that chaotic-like behaviour can be recovered in the appropriate classical limit. In this paper, we investigate the entanglement generated between two nonlinear oscillators, coupled to each other and to their environment. Entanglement-the inability to factorize coupled quantum systems into their constituent parts-is one of the defining features of quantum mechanics. Indeed, it underpins many of the recent developments in quantum technologies. Here, we show that the entanglement characteristics of two 'classical' states (chaotic and periodic solutions) differ significantly in the classical limit. In particular, we show that significant levels of entanglement are preserved only in the chaotic-like solutions.

Entanglement probabilities of polymers: a white noise functional approach

International Nuclear Information System (INIS)

Bernido, Christopher C; Carpio-Bernido, M Victoria

2003-01-01

The entanglement probabilities for a highly flexible polymer to wind n times around a straight polymer are evaluated using white noise analysis. To introduce the white noise functional approach, the one-dimensional random walk problem is taken as an example. The polymer entanglement scenario, viewed as a random walk on a plane, is then treated and the entanglement probabilities are obtained for a magnetic flux confined along the straight polymer, and a case where an entangled polymer is subjected to the potential V = f-dot(s)θ. In the absence of the magnetic flux and the potential V, the entanglement probabilities reduce to a result obtained by Wiegel

Geometric entanglement in topologically ordered states

International Nuclear Information System (INIS)

Orús, Román; Wei, Tzu-Chieh; Buerschaper, Oliver; Nest, Maarten Van den

2014-01-01

Here we investigate the connection between topological order and the geometric entanglement, as measured by the logarithm of the overlap between a given state and its closest product state of blocks. We do this for a variety of topologically ordered systems such as the toric code, double semion, colour code and quantum double models. As happens for the entanglement entropy, we find that for sufficiently large block sizes the geometric entanglement is, up to possible sub-leading corrections, the sum of two contributions: a bulk contribution obeying a boundary law times the number of blocks and a contribution quantifying the underlying pattern of long-range entanglement of the topologically ordered state. This topological contribution is also present in the case of single-spin blocks in most cases, and constitutes an alternative characterization of topological order for these quantum states based on a multipartite entanglement measure. In particular, we see that the topological term for the two-dimensional colour code is twice as much as the one for the toric code, in accordance with recent renormalization group arguments (Bombin et al 2012 New J. Phys. 14 073048). Motivated by these results, we also derive a general formalism to obtain upper- and lower-bounds to the geometric entanglement of states with a non-Abelian group symmetry, and which we explicitly use to analyse quantum double models. Furthermore, we also provide an analysis of the robustness of the topological contribution in terms of renormalization and perturbation theory arguments, as well as a numerical estimation for small systems. Some of the results in this paper rely on the ability to disentangle single sites from the quantum state, which is always possible for the systems that we consider. Additionally we relate our results to the behaviour of the relative entropy of entanglement in topologically ordered systems, and discuss a number of numerical approaches based on tensor networks that could be

Entanglement entropy and duality in AdS4

Directory of Open Access Journals (Sweden)

Ioannis Bakas

2015-07-01

Full Text Available Small variations of the entanglement entropy δS and the expectation value of the modular Hamiltonian δE are computed holographically for circular entangling curves in the boundary of AdS4, using gravitational perturbations with general boundary conditions in spherical coordinates. Agreement with the first law of thermodynamics, δS=δE, requires that the line element of the entangling curve remains constant. In this context, we also find a manifestation of electric–magnetic duality for the entanglement entropy and the corresponding modular Hamiltonian, following from the holographic energy–momentum/Cotton tensor duality.