Optimization of entanglement witnesses
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.
Minimal tomography with entanglement witnesses
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
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.
Witnessing entanglement by proxy
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)
Minimal Entanglement Witness from Electrical Current Correlations.
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.
Minimal Entanglement Witness from Electrical Current Correlations
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.
Minimal tomography with entanglement witnesses
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...
Minimal Entanglement Witness From Electrical Current Correlations
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 ...
From entanglement witness to generalized Catalan numbers
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.
Detecting quantum entanglement. Entanglement witnesses and uncertainty relations
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
Optimal entanglement witnesses for qubits and qutrits
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
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
Optimal Entanglement Witnesses for Qubits and Qutrits
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)
Entangled entanglement: A construction procedure
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.
Optimized entanglement witnesses for Dicke states
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 witnesses arising from exposed positive linear maps
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...
Estimating localizable entanglement from witnesses
Amaro, David; Müller, Markus; Pal, Amit Kumar
2018-01-01
Computing localizable entanglement for noisy many-particle quantum states is difficult due to the optimization over all possible sets of local projection measurements. Therefore, it is crucial to develop lower bounds, which can provide useful information about the behaviour of localizable entanglement, and which can be determined by measuring a limited number of operators, or by performing least number of measurements on the state, preferably without performing a full state tomography. In thi...
Witnessing Multipartite Entanglement by Detecting Asymmetry
Davide Girolami
2017-03-01
Full Text Available The characterization of quantum coherence in the context of quantum information theory and its interplay with quantum correlations is currently subject of intense study. Coherence in a Hamiltonian eigenbasis yields asymmetry, the ability of a quantum system to break a dynamical symmetry generated by the Hamiltonian. We here propose an experimental strategy to witness multipartite entanglement in many-body systems by evaluating the asymmetry with respect to an additive Hamiltonian. We test our scheme by simulating asymmetry and entanglement detection in a three-qubit Greenberger–Horne–Zeilinger (GHZ diagonal state.
Spin Entanglement Witness for Quantum Gravity.
Bose, Sougato; Mazumdar, Anupam; Morley, Gavin W; Ulbricht, Hendrik; Toroš, Marko; Paternostro, Mauro; Geraci, Andrew A; Barker, Peter F; Kim, M S; Milburn, Gerard
2017-12-15
Understanding gravity in the framework of quantum mechanics is one of the great challenges in modern physics. However, the lack of empirical evidence has lead to a debate on whether gravity is a quantum entity. Despite varied proposed probes for quantum gravity, it is fair to say that there are no feasible ideas yet to test its quantum coherent behavior directly in a laboratory experiment. Here, we introduce an idea for such a test based on the principle that two objects cannot be entangled without a quantum mediator. We show that despite the weakness of gravity, the phase evolution induced by the gravitational interaction of two micron size test masses in adjacent matter-wave interferometers can detectably entangle them even when they are placed far apart enough to keep Casimir-Polder forces at bay. We provide a prescription for witnessing this entanglement, which certifies gravity as a quantum coherent mediator, through simple spin correlation measurements.
Entanglement witness via quantum-memory-assisted entropic uncertainty relation
Shi, Jiadong; Ding, Zhiyong; Wu, Tao; He, Juan; Yu, Lizhi; Sun, Wenyang; Wang, Dong; Ye, Liu
2017-12-01
By virtue of the quantum-memory-assisted entropic uncertainty relation (EUR), we analyze entanglement witness via the efficiencies of the estimates proposed by Berta (2010 Nat. Phys. 6 659) and Pati (2012 Phys. Rev. A 86 042105). The results show that, without a structured reservoir, the entanglement regions witnessed by these EUR estimates are only determined by the chosen estimated setup, and have no correlation with the explicit form of the initial state. On the other hand, with the structured reservoirs, the time regions during which the entanglement can be witnessed, and the corresponding entanglement regions closely depend on the choice of the estimated setup, the initial state and the state purity p . Concretely, for a pure state with p=1 , the entanglement can be witnessed by both estimates, while for mixed states with p=0.78 , it can only be witnessed using the Pati estimate. What is more, we find that the time regions incorporating the Pati estimate become discontinuous for the initial state with ≤ft| {{φ }\\prime } \\right> ={≤ft(≤ft| 01 \\right> +≤ft| 10 \\right> \\right)}/{\\sqrt{2}} , and the corresponding entanglement regions remain the same; however the entanglement can only be witnessed once by utilizing the Berta estimate.
Entanglement witnessing and quantum cryptography with nonideal ferromagnetic detectors
Kłobus, Waldemar; Grudka, Andrzej; Baumgartner, Andreas; Tomaszewski, Damian; Schönenberger, Christian; Martinek, Jan
2014-01-01
We investigate theoretically the use of non-ideal ferromagnetic contacts as a mean to detect quantum entanglement of electron spins in transport experiments. We use a designated entanglement witness and find a minimal spin polarization of $\\eta > 1/\\sqrt{3} \\approx 58 %$ required to demonstrate spin entanglement. This is significantly less stringent than the ubiquitous tests of Bell's inequality with $\\eta > 1/\\sqrt[4]{2}\\approx 84%$. In addition, we discuss the impact of decoherence and nois...
Entanglement witnessing and quantum cryptography with nonideal ferromagnetic detectors
Kłobus, Waldemar; Grudka, Andrzej; Baumgartner, Andreas; Tomaszewski, Damian; Schönenberger, Christian; Martinek, Jan
2014-03-01
We investigate theoretically the use of nonideal ferromagnetic contacts as a means to detect quantum entanglement of electron spins in transport experiments. We use a designated entanglement witness and find a minimal spin polarization of η >1/√3 ≈58% required to demonstrate spin entanglement. This is significantly less stringent than the ubiquitous tests of Bell's inequality with η >1/√24 >≈84%. In addition, we discuss the impact of decoherence and noise on entanglement detection and apply the presented framework to a simple quantum cryptography protocol. Our results are directly applicable to a large variety of experiments.
A quantitative witness for Greenberger-Horne-Zeilinger entanglement.
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.
Nonlinear entanglement witnesses, covariance matrices and the geometry of separable states
Guehne, Otfried [Institut fuer Quantenoptik und Quanteninformation, Oesterreichische Akademie der Wissenschaften, A-6020 Innsbruck (Austria); Luetkenhaus, Norbert [Institute for Quantum Computing and Department of Physics and Astronomy, University of Waterloo, 200 University Avenue West, Waterloo, Ontario N2L 3G1 (Canada)
2007-05-15
Entanglement witnesses provide a standard tool for the analysis of entanglement in experiments. We investigate possible nonlinear entanglement witnesses from several perspectives. First, we demonstrate that they can be used to show that the set of separable states has no facets. Second, we give a new derivation of nonlinear witnesses based on covariance matrices. Finally, we investigate extensions to the multipartite case.
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.
Greenberger-Horne-Zeilinger and W entanglement witnesses for the noninteracting Fermi gas
Habibian, Hessam; Clark, John W.; Behbood, Naeimeh; Hingerl, Kurt
2010-01-01
The existence and nature of tripartite entanglement of a noninteracting Fermi gas (NIFG) is investigated. Three classes of parametrized entanglement witnesses (EWs) are introduced with the aim of detecting genuine tripartite entanglement in the three-body reduced density matrix and discriminating between the presence of the two types of genuine tripartite entanglement, W/B and GHZ/W (the convex set of B states is comprised of mixed states of product and biseparable states; that of W states is comprised of mixed states of B states and W-type pure entangled states; and the GHZ (Greenberger-Horne-Zeilinger) set contains generic mixtures of any kind for a tripartite system). By choosing appropriate EW operators, the problem of finding GHZ and W EWs is reduced to linear programming. Specifically, we devise W EWs based on a spin-chain model with periodic boundary conditions, and we construct a class of parametrized GHZ EWs by linearly combining projection operators corresponding to all the different state-vector types arising for a three-fermion system. A third class of EWs is provided by a GHZ stabilizer operator capable of distinguishing W/B from GHZ/B entanglement, which is not possible with W EWs. Implementing these classes of EWs, it is found that all states containing genuine tripartite entanglement are of W type, and hence states containing GHZ/W genuine tripartite entanglement do not arise. Some genuine tripartite entangled states that have a positive partial transpose (PPT) with respect to some bipartition are detected. Finally, it is demonstrated that a NIFG does not exhibit 'pure'W/B genuine tripartite entanglement: three-party entanglement without any separable or biseparable admixture does not occur.
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)
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...
A quantitative witness for Greenberger-Horne-Zeilinger entanglement
Eltschka, Christopher [Institut fuer Theoretische Physik, Universitaet Regensburg, D-93040 Regensburg (Germany); Siewert, Jens [Departamento de Quimica Fisica, Universidad del Pais Vasco UPV/EHU, 48080 Bilbao (Spain); IKERBASQUE, Basque Foundation for Science, 48011 Bilbao (Spain)
2013-07-01
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. We provide a simple procedure to quantify Greenberger-Horne-Zeilinger-type multipartite entanglement in arbitrary three-qubit states. The method is based on the recently introduced GHZ symmetry and exact results for the states which are invariant under this symmetry, and generally gives a good lower bound to the three-tangle. A generalization both to more parties and to higher-dimensional systems is possible.
Hybrid methods for witnessing entanglement in a microscopic-macroscopic system
Spagnolo, Nicolo; Vitelli, Chiara; Paternostro, Mauro; De Martini, Francesco; Sciarrino, Fabio
2011-01-01
We propose a hybrid approach to the experimental assessment of the genuine quantum features of a general system consisting of microscopic and macroscopic parts. We infer entanglement by combining dichotomic measurements on a bidimensional system and phase-space inference through the Wigner distribution associated with the macroscopic component of the state. As a benchmark, we investigate the feasibility of our proposal in a bipartite-entangled state composed of a single-photon and a multiphoton field. Our analysis shows that, under ideal conditions, maximal violation of a Clauser-Horne-Shimony-Holt-based inequality is achievable regardless of the number of photons in the macroscopic part of the state. The difficulty in observing entanglement when losses and detection inefficiency are included can be overcome by using a hybrid entanglement witness that allows efficient correction for losses in the few-photon regime.
Hybrid methods for witnessing entanglement in a microscopic-macroscopic system
Spagnolo, Nicolo [Dipartimento di Fisica, Sapienza Universita di Roma, Piazzale Aldo Moro 5, I-00185 Roma (Italy); Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia, Piazzale Aldo Moro 5, I-00185 Roma (Italy); Vitelli, Chiara [Dipartimento di Fisica, Sapienza Universita di Roma, Piazzale Aldo Moro 5, I-00185 Roma (Italy); Paternostro, Mauro [School of Mathematics and Physics, Queen' s University, BT 7 1NN Belfast (United Kingdom); De Martini, Francesco [Dipartimento di Fisica, Sapienza Universita di Roma, Piazzale Aldo Moro 5, I-00185 Roma (Italy); Accademia Nazionale dei Lincei, via della Lungara 10, I-00165 Roma (Italy); Sciarrino, Fabio [Dipartimento di Fisica, Sapienza Universita di Roma, Piazzale Aldo Moro 5, I-00185 Roma (Italy); Istituto Nazionale di Ottica, Consiglio Nazionale delle Ricerche (INO-CNR), largo E. Fermi 6, I-50125 Firenze (Italy)
2011-09-15
We propose a hybrid approach to the experimental assessment of the genuine quantum features of a general system consisting of microscopic and macroscopic parts. We infer entanglement by combining dichotomic measurements on a bidimensional system and phase-space inference through the Wigner distribution associated with the macroscopic component of the state. As a benchmark, we investigate the feasibility of our proposal in a bipartite-entangled state composed of a single-photon and a multiphoton field. Our analysis shows that, under ideal conditions, maximal violation of a Clauser-Horne-Shimony-Holt-based inequality is achievable regardless of the number of photons in the macroscopic part of the state. The difficulty in observing entanglement when losses and detection inefficiency are included can be overcome by using a hybrid entanglement witness that allows efficient correction for losses in the few-photon regime.
Entanglement-assisted quantum MDS codes constructed from negacyclic codes
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.
Towards New Membrane Flow from de Wit-Nicolai Construction
Ahn, Changhyun; Paeng, Jinsub; Woo, Kyungsung
2011-01-01
The internal 4-form field strengths with 7-dimensional indices have been constructed by de Wit and Nicolai in 1986. They are determined by the following six quantities: the 56-bein of 4-dimensional N=8 gauged supergravity, the Killing vectors on the round seven-sphere, the covariant derivative acting on these Killing vectors, the warp factor, the field strengths with 4-dimensional indices and the 7-dimensional metric. In this paper, by projecting out the remaining mixed 4-form field strengths...
Zou, Hong-Mei; Fang, Mao-Fa; Yang, Bai-Yuan; Guo, You-Neng; He, Wei; Zhang, Shi-Yang
2014-01-01
The quantum entropic uncertainty relation and entanglement witness in the two-atom system coupling with the non-Markovian environments are studied using the time-convolutionless master-equation approach. The influence of the non-Markovian effect and detuning on the lower bound of the quantum entropic uncertainty relation and entanglement witness is discussed in detail. The results show that, only if the two non-Markovian reservoirs are identical, increasing detuning and non-Markovian effect can reduce the lower bound of the entropic uncertainty relation, lengthen the time region during which the entanglement can be witnessed, and effectively protect the entanglement region witnessed by the lower bound of the entropic uncertainty relation. The results can be applied in quantum measurement, quantum cryptography tasks and quantum information processing. (paper)
Device-independent entanglement certification of all entangled states
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...
Towards New Membrane Flow from de Wit-Nicolai Construction
Ahn, Changhyun; Paeng, Jinsub; Woo, Kyungsung
The internal 4-form field strengths with 7-dimensional indices have been constructed by de Wit and Nicolai in 1986. They are determined by the following six quantities: the 56-bein of 4-dimensional ${\\mathcal N} = 8$ gauged supergravity, the Killing vectors on the round seven-sphere, the covariant derivative acting on these Killing vectors, the warp factor, the field strengths with 4-dimensional indices and the 7-dimensional metric. In this paper, by projecting out the remaining mixed 4-form field strengths in an SU(8) tensor that appears in the variation of spin-½ fermionic sector, we also write down them explicitly in terms of some of the above quantities. For the known critical points, the ${\\mathcal N} = 8$ $SO(8)$ point and the nonsupersymmetric SO(7)+ point, we reproduce the corresponding 11-dimensional uplifts by computing the full nonlinear expressions. Moreover, we find out the 11-dimensional lift of the nonsupersymmetric SO(7)+ invariant flow. We decode their implicit formula for the first time and the present work will provide how to obtain the new supersymmetric or nonsupersymmetric membrane flows in 11 dimensions.
Sen, Aditi; Sen, Ujjwal; Zukowski, Marek
2002-01-01
We consider a Bell inequality for a continuous range of settings of the apparatus at each site. This 'functional' Bell inequality gives a better range of violation for generalized Greenberger, Horne, and Zeilinger states. Also a family of N-qubit bound entangled states violate this inequality for N>5
Witnessing in the New Memory Ecology : Memory Construction of the Syrian Conflict on YouTube
Smit, Pieter Hendrik; Broersma, Marcel; Heinrich, Ansgard
2017-01-01
With the pervasiveness of mobile technologies, witnesses have the opportunity to mediate up-close and seemingly truthful recordings of events. As such, “witness videos” have become prominent in news reports and serve as authoritative resources in the construction of memory. However, once they are
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.
Higher dimensional unitary braid matrices: Construction, associated structures and entanglements
Abdesselam, B.; Chakrabarti, A.; Dobrev, V.K.; Mihov, S.G.
2007-03-01
We construct (2n) 2 x (2n) 2 unitary braid matrices R-circumflex for n ≥ 2 generalizing the class known for n = 1. A set of (2n) x (2n) matrices (I, J,K,L) are defined. R-circumflex is expressed in terms of their tensor products (such as K x J), leading to a canonical formulation for all n. Complex projectors P ± provide a basis for our real, unitary R-circumflex. Baxterization is obtained. Diagonalizations and block- diagonalizations are presented. The loss of braid property when R-circumflex (n > 1) is block-diagonalized in terms of R-circumflex (n = 1) is pointed out and explained. For odd dimension (2n + 1) 2 x (2n + 1) 2 , a previously constructed braid matrix is complexified to obtain unitarity. R-circumflexLL- and R-circumflexTT- algebras, chain Hamiltonians, potentials for factorizable S-matrices, complex non-commutative spaces are all studied briefly in the context of our unitary braid matrices. Turaev construction of link invariants is formulated for our case. We conclude with comments concerning entanglements. (author)
Heo, Jino; Kang, Min-Sung; Hong, Chang-Ho; Choi, Seong-Gon; Hong, Jong-Phil
2017-08-01
We propose quantum information processing schemes to generate and swap entangled states based on the interactions between flying photons and quantum dots (QDs) confined within optical cavities for quantum communication. To produce and distribute entangled states (Bell and Greenberger-Horne-Zeilinger [GHZ] states) between the photonic qubits of flying photons of consumers (Alice and Bob) and electron-spin qubits of a provider (trust center, or TC), the TC employs the interactions of the QD-cavity system, which is composed of a charged QD (negatively charged exciton) inside a single-sided cavity. Subsequently, the TC constructs an entanglement channel (Bell state and 4-qubit GHZ state) to link one consumer with another through entanglement swapping, which can be realized to exploit a probe photon with interactions of the QD-cavity systems and single-qubit measurements without Bell state measurement, for quantum communication between consumers. Consequently, the TC, which has quantum nodes (QD-cavity systems), can accomplish constructing the entanglement channel (authenticated channel) between two separated consumers from the distributions of entangled states and entanglement swapping. Furthermore, our schemes using QD-cavity systems, which are feasible with a certain probability of success and high fidelity, can be experimentally implemented with technology currently in use.
Construction of Hamiltonians by supervised learning of energy and entanglement spectra
Fujita, Hiroyuki; Nakagawa, Yuya O.; Sugiura, Sho; Oshikawa, Masaki
2018-02-01
Correlated many-body problems ubiquitously appear in various fields of physics such as condensed matter, nuclear, and statistical physics. However, due to the interplay of the large number of degrees of freedom, it is generically impossible to treat these problems from first principles. Thus the construction of a proper model, namely, effective Hamiltonian, is essential. Here, we propose a simple supervised learning algorithm for constructing Hamiltonians from given energy or entanglement spectra. We apply the proposed scheme to the Hubbard model at the half-filling, and compare the obtained effective low-energy spin model with several analytic results based on the high-order perturbation theory, which have been inconsistent with each other. We also show that our approach can be used to construct the entanglement Hamiltonian of a quantum many-body state from its entanglement spectrum as well. We exemplify this using the ground states of the S =1 /2 two-leg Heisenberg ladders. We observe a qualitative difference between the entanglement Hamiltonians of the two phases (the Haldane and the rung singlet phase) of the model due to the different origin of the entanglement. In the Haldane phase, we find that the entanglement Hamiltonian is nonlocal by nature, and the locality can be restored by introducing the anisotropy and turning the ground state into the large-D phase. Possible applications to the model construction from experimental data and to various problems of strongly correlated systems are discussed.
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.
Multipartite Entanglement Detection with Minimal Effort
Knips, Lukas; Schwemmer, Christian; Klein, Nico; Wieśniak, Marcin; Weinfurter, Harald
2016-11-01
Certifying entanglement of a multipartite state is generally considered a demanding task. Since an N qubit state is parametrized by 4N-1 real numbers, one might naively expect that the measurement effort of generic entanglement detection also scales exponentially with N . Here, we introduce a general scheme to construct efficient witnesses requiring a constant number of measurements independent of the number of qubits for states like, e.g., Greenberger-Horne-Zeilinger states, cluster states, and Dicke states. For four qubits, we apply this novel method to experimental realizations of the aforementioned states and prove genuine four-partite entanglement with two measurement settings only.
Deckert, Sharon K.
2010-01-01
This article examines how the interrelated identities of witness, victim, and perpetrator are co-constructed in forensic interviews occurring after allegations of child sexual abuse are made. Work related to issues of power in the area of forensic interviews with children tends to focus on coerciveness, and interviewers have power relative to…
Complete hierarchies of efficient approximations to problems in entanglement theory
Eisert, Jens; Hyllus, Philipp; Guehne, Otfried; Curty, Marcos
2004-01-01
We investigate several problems in entanglement theory from the perspective of convex optimization. This list of problems comprises (A) the decision whether a state is multiparty entangled, (B) the minimization of expectation values of entanglement witnesses with respect to pure product states, (C) the closely related evaluation of the geometric measure of entanglement to quantify pure multiparty entanglement, (D) the test whether states are multiparty entangled on the basis of witnesses based on second moments and on the basis of linear entropic criteria, and (E) the evaluation of instances of maximal output purities of quantum channels. We show that these problems can be formulated as certain optimization problems: as polynomially constrained problems employing polynomials of degree 3 or less. We then apply very recently established known methods from the theory of semidefinite relaxations to the formulated optimization problems. By this construction we arrive at a hierarchy of efficiently solvable approximations to the solution, approximating the exact solution as closely as desired, in a way that is asymptotically complete. For example, this results in a hierarchy of efficiently decidable sufficient criteria for multiparticle entanglement, such that every entangled state will necessarily be detected in some step of the hierarchy. Finally, we present numerical examples to demonstrate the practical accessibility of this approach
Ou, Bao-Quan; Liu, Chang; Sun, Yuan; Chen, Ping-Xing
2018-02-01
Inspired by the recent developments of the research on the atom-photon quantum interface and energy-time entanglement between single-photon pulses, we are motivated to study the deterministic protocol for the frequency-bin entanglement of the atom-photon hybrid system, which is analogous to the frequency-bin entanglement between single-photon pulses. We show that such entanglement arises naturally in considering the interaction between a frequency-bin entangled single-photon pulse pair and a single atom coupled to an optical cavity, via straightforward atom-photon phase gate operations. Its anticipated properties and preliminary examples of its potential application in quantum networking are also demonstrated. Moreover, we construct a specific quantum entanglement witness tool to detect such extended frequency-bin entanglement from a reasonably general set of separable states, and prove its capability theoretically. We focus on the energy-time considerations throughout the analysis.
Spatially distributed multipartite entanglement enables EPR steering of atomic clouds
Kunkel, Philipp; Prüfer, Maximilian; Strobel, Helmut; Linnemann, Daniel; Frölian, Anika; Gasenzer, Thomas; Gärttner, Martin; Oberthaler, Markus K.
2018-04-01
A key resource for distributed quantum-enhanced protocols is entanglement between spatially separated modes. However, the robust generation and detection of entanglement between spatially separated regions of an ultracold atomic system remain a challenge. We used spin mixing in a tightly confined Bose-Einstein condensate to generate an entangled state of indistinguishable particles in a single spatial mode. We show experimentally that this entanglement can be spatially distributed by self-similar expansion of the atomic cloud. We used spatially resolved spin read-out to reveal a particularly strong form of quantum correlations known as Einstein-Podolsky-Rosen (EPR) steering between distinct parts of the expanded cloud. Based on the strength of EPR steering, we constructed a witness, which confirmed genuine 5-partite entanglement.
Mishra, Utkarsh; Rakshit, Debraj; Prabhu, R; Sen, Aditi; Sen, Ujjwal
2016-01-01
Disordered systems form one of the centrestages of research in many body sciences and lead to a plethora of interesting phenomena and applications. A paradigmatic disordered system consists of a one-dimensional array of quantum spin-1/2 particles, governed by the Heisenberg spin glass Hamiltonian with natural or engineered quenched disordered couplings in an external magnetic field. These systems allow disorder-induced enhancement for bipartite and multipartite observables. Here we show that simultaneous application of independent quenched disorders results in disorder-induced enhancement, while the same is absent with individual application of the same disorders. We term the phenomenon as constructive interference and the corresponding parameter stretches as the Venus regions. Interestingly, it has only been observed for multiparty entanglement and is absent for the single- and two-party physical quantities. (paper)
Entanglement in a Dimerized Antiferromagnetic Heisenberg Chain
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...
Adele
formal rules of evidence apply) to help it understand the issues of a case and ... statements on medical expert witness by professional representative bodies in .... determining the size of the financial settlement that may have to be made to the.
Aniello, Paolo; Chruściński, Dariusz
2017-07-01
A symmetry witness is a suitable subset of the space of selfadjoint trace class operators that allows one to determine whether a linear map is a symmetry transformation, in the sense of Wigner. More precisely, such a set is invariant with respect to an injective densely defined linear operator in the Banach space of selfadjoint trace class operators (if and) only if this operator is a symmetry transformation. According to a linear version of Wigner’s theorem, the set of pure states—the rank-one projections—is a symmetry witness. We show that an analogous result holds for the set of projections with a fixed rank (with some mild constraint on this rank, in the finite-dimensional case). It turns out that this result provides a complete classification of the sets of projections with a fixed rank that are symmetry witnesses. These particular symmetry witnesses are projectable; i.e. reasoning in terms of quantum states, the sets of ‘uniform’ density operators of corresponding fixed rank are symmetry witnesses too.
Geometric multipartite entanglement measures
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
Christiansen, Lene Bull; Frello, Birgitta
2016-01-01
This article deals with emotional address in the narrative modality of celebrity witnessing in the marketing of development aid. We analyse Danish celebrity narratives of global caring, drawing on Luc Boltanski’s work on a ‘politics of pity’, Lilie Chouliaraki’s notion of the ‘aspirational discou...
Nonlocality, Entanglement Witnesses and Supra-correlations
2012-04-01
quantum non-locality, non-signaling theories, Popescu-Rohrlich boxes, EPR 1. INTRODUCTION Physics imposes limits on the correlations that can be...References [1] J.S. Bell, “On the Einstein Podolsky Rosen paradox ,” Physics 1, 195 (1964). [2] B. Tsirelson, “Quantum Generalizations of Bell’s
Spin Entanglement Witness for Quantum Gravity
Bose, Sougato; Mazumdar, Anupam; Morley, Gavin W.; Ulbricht, Hendrik; Toros, Marko; Paternostro, Mauro; Geraci, Andrew A.; Barker, Peter F.; Kim, M. S.; Milburn, Gerard
2017-01-01
Understanding gravity in the framework of quantum mechanics is one of the great challenges in modern physics. However, the lack of empirical evidence has lead to a debate on whether gravity is a quantum entity. Despite varied proposed probes for quantum gravity, it is fair to say that there are no
Quantum Entanglement: Separability, Measure, Fidelity of Teleportation, and Distillation
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.
Characterizing quantum correlations. Entanglement, uncertainty relations and exponential families
Niekamp, Soenke
2012-04-20
This thesis is concerned with different characterizations of multi-particle quantum correlations and with entropic uncertainty relations. The effect of statistical errors on the detection of entanglement is investigated. First, general results on the statistical significance of entanglement witnesses are obtained. Then, using an error model for experiments with polarization-entangled photons, it is demonstrated that Bell inequalities with lower violation can have higher significance. The question for the best observables to discriminate between a state and the equivalence class of another state is addressed. Two measures for the discrimination strength of an observable are defined, and optimal families of observables are constructed for several examples. A property of stabilizer bases is shown which is a natural generalization of mutual unbiasedness. For sets of several dichotomic, pairwise anticommuting observables, uncertainty relations using different entropies are constructed in a systematic way. Exponential families provide a classification of states according to their correlations. In this classification scheme, a state is considered as k-correlated if it can be written as thermal state of a k-body Hamiltonian. Witness operators for the detection of higher-order interactions are constructed, and an algorithm for the computation of the nearest k-correlated state is developed.
Characterizing quantum correlations. Entanglement, uncertainty relations and exponential families
Niekamp, Soenke
2012-01-01
This thesis is concerned with different characterizations of multi-particle quantum correlations and with entropic uncertainty relations. The effect of statistical errors on the detection of entanglement is investigated. First, general results on the statistical significance of entanglement witnesses are obtained. Then, using an error model for experiments with polarization-entangled photons, it is demonstrated that Bell inequalities with lower violation can have higher significance. The question for the best observables to discriminate between a state and the equivalence class of another state is addressed. Two measures for the discrimination strength of an observable are defined, and optimal families of observables are constructed for several examples. A property of stabilizer bases is shown which is a natural generalization of mutual unbiasedness. For sets of several dichotomic, pairwise anticommuting observables, uncertainty relations using different entropies are constructed in a systematic way. Exponential families provide a classification of states according to their correlations. In this classification scheme, a state is considered as k-correlated if it can be written as thermal state of a k-body Hamiltonian. Witness operators for the detection of higher-order interactions are constructed, and an algorithm for the computation of the nearest k-correlated state is developed.
Optimal detection of entanglement in Greenberger-Horne-Zeilinger states
Kay, Alastair
2011-01-01
We present a broad class of N-qubit Greenberger-Horne-Zeilinger (GHZ)-diagonal states such that nonpositivity under the partial transpose operation is necessary and sufficient for the presence of entanglement, including many naturally arising instances such as dephased GHZ states. Furthermore, our proof directly leads to an entanglement witness which saturates this bound. The witness is applied to thermal GHZ states to prove that the entanglement can be extremely robust to system imperfections.
Bipartite entangled stabilizer mutually unbiased bases as maximum cliques of Cayley graphs
van Dam, Wim; Howard, Mark
2011-07-01
We examine the existence and structure of particular sets of mutually unbiased bases (MUBs) in bipartite qudit systems. In contrast to well-known power-of-prime MUB constructions, we restrict ourselves to using maximally entangled stabilizer states as MUB vectors. Consequently, these bipartite entangled stabilizer MUBs (BES MUBs) provide no local information, but are sufficient and minimal for decomposing a wide variety of interesting operators including (mixtures of) Jamiołkowski states, entanglement witnesses, and more. The problem of finding such BES MUBs can be mapped, in a natural way, to that of finding maximum cliques in a family of Cayley graphs. Some relationships with known power-of-prime MUB constructions are discussed, and observables for BES MUBs are given explicitly in terms of Pauli operators.
Bipartite entangled stabilizer mutually unbiased bases as maximum cliques of Cayley graphs
Dam, Wim van; Howard, Mark
2011-01-01
We examine the existence and structure of particular sets of mutually unbiased bases (MUBs) in bipartite qudit systems. In contrast to well-known power-of-prime MUB constructions, we restrict ourselves to using maximally entangled stabilizer states as MUB vectors. Consequently, these bipartite entangled stabilizer MUBs (BES MUBs) provide no local information, but are sufficient and minimal for decomposing a wide variety of interesting operators including (mixtures of) Jamiolkowski states, entanglement witnesses, and more. The problem of finding such BES MUBs can be mapped, in a natural way, to that of finding maximum cliques in a family of Cayley graphs. Some relationships with known power-of-prime MUB constructions are discussed, and observables for BES MUBs are given explicitly in terms of Pauli operators.
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.
Entanglement and decoherence in high energy physics
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)
General entanglement-assisted transformation for bipartite pure quantum states
Song, Wei; Huang, Yan; Nai-LeLiu; Chen, Zeng-Bing
2007-01-01
We introduce the general catalysts for pure entanglement transformations under local operations and classical communications in such a way that we disregard the profit and loss of entanglement of the catalysts per se. As such, the possibilities of pure entanglement transformations are greatly expanded. We also design an efficient algorithm to detect whether a k × k general catalyst exists for a given entanglement transformation. This algorithm can also be exploited to witness the existence of standard catalysts.
Positive maps, majorization, entropic inequalities and detection of entanglement
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.
Braiding transformation, entanglement swapping, and Berry phase in entanglement space
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
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.
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 reactivation in separable environments
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)
Quantum entanglement via nilpotent polynomials
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
Multipartite entanglement and firewalls
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.
Detection of entanglement with few local measurements
Guehne, O.; Hyllus, P.; Bruss, D.; Lewenstein, M.; Sanpera, A.; Ekert, A.; Macchiavello, C.
2002-01-01
We introduce a general method for the experimental detection of entanglement by performing only few local measurements, assuming some prior knowledge of the density matrix. The idea is based on the minimal decomposition of witness operators into a pseudomixture of local operators. We discuss an experimentally relevant case of two qubits, and show an example how bound entanglement can be detected with few local measurements
Detection of entanglement with few local measurements
Guehne, O.; Hyllus, P.; Bruss, D.; Ekert, A.; Lewenstein, M.; Macchiavello, C.; Sanpera, A.
2002-01-01
We introduce a general method for the experimental detection of entanglement by performing only few local measurements, assuming some prior knowledge of the density matrix. The idea is based on the minimal decomposition of witness operators into a pseudo-mixture of local operators. We discuss an experimentally relevant case of two qubits, and show an example how bound entanglement can be detected with few local measurements.
Detection of entanglement with few local measurements
Gühne, O.; Hyllus, P.; Bruß, D.; Ekert, A.; Lewenstein, M.; Macchiavello, C.; Sanpera, A.
2002-12-01
We introduce a general method for the experimental detection of entanglement by performing only few local measurements, assuming some prior knowledge of the density matrix. The idea is based on the minimal decomposition of witness operators into a pseudomixture of local operators. We discuss an experimentally relevant case of two qubits, and show an example how bound entanglement can be detected with few local measurements.
Deriving covariant holographic entanglement
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.
Non-existence of bipartite bound entanglement with negative partial transposition
Sperling, J.; Vogel, W.
2009-01-01
Bound entanglement with a nonpositive partial transposition (NPT) does not exist. For any NPT entangled state a distillation procedure can be based on a certain number of copies. This number is the minimal Schmidt rank of a pure state needed to witness the NPT entanglement under study.
Experimental Measurement-Device-Independent Entanglement Detection
Nawareg, Mohamed; Muhammad, Sadiq; Amselem, Elias; Bourennane, Mohamed
2015-02-01
Entanglement is one of the most puzzling features of quantum theory and of great importance for the new field of quantum information. The determination whether a given state is entangled or not is one of the most challenging open problems of the field. Here we report on the experimental demonstration of measurement-device-independent (MDI) entanglement detection using witness method for general two qubits photon polarization systems. In the MDI settings, there is no requirement to assume perfect implementations or neither to trust the measurement devices. This experimental demonstration can be generalized for the investigation of properties of quantum systems and for the realization of cryptography and communication protocols.
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
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
Experimental determination of entanglement with a single measurement.
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.
Teleportation of entanglement over 143 km.
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.
PROTECTION OF THREATENED WITNESSES
Nadia Claudia CANTEMIR-STOICA
2016-05-01
Full Text Available First, I wish to make a presentation of historically institution and subsequently parallels between past and current regulators to expose whether the legislature has reached desire - namely ensuring effective protection of witnesses threatened and vulnerable. Also, I decided to analyze the topic from the perspective of the criminal procedural provisions of Law 682/2002 and witness protection, which are republished to expose the conditions and criteria by which to ensure this status. I also want to present besides theoretical and practical ways in which the National Office for Witness Protection gives effective legal provisions. Not least, I will bring criticism of current regulation and not by law ferenda proposals.
The entanglement evolution between two entangled atoms
... 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 ...
Elgaard Jensen, Torben
2007-01-01
and the problematic work life elsewhere. Finally, it notes that the manager's strategy enacts a timeworld characterised by dramatic epochal changes, which is radically different from the more stable and knowable time-world that is enacted in ordinary scientific discourses. Key words: actor-network theory, witnessing......Abstract: The paper explores the phenomenon of witnessing the future through a case study of how a Scandinavian new economy firm managed to persuade a number of business journalists that it was "the future". It describes the procedures and rhetorical strategies that the manager deployed to turn...... the journalists into witnesses. It compares the manager's strategy to other cases of effective witnessing in courtrooms and in science. It concludes that the manager's persuasiveness is derived from his ability to articulate a series of pointed contrasts between the attractive working life within the firm...
Studying entanglement-assisted entanglement transformation
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
Dynamics of Quantum Entanglement in Reservoir with Memory Effects
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)
Waste Inspection Tomography (WIT)
Bernardi, R.T.
1995-01-01
Waste Inspection Tomography (WIT) provides mobile semi-trailer mounted nondestructive examination (NDE) and assay (NDA) for nuclear waste drum characterization. WIT uses various computed tomography (CT) methods for both NDE and NDA of nuclear waste drums. Low level waste (LLW), transuranic (TRU), and mixed radioactive waste can be inspected and characterized without opening the drums. With externally transmitted x-ray NDE techniques, WIT has the ability to identify high density waste materials like heavy metals, define drum contents in two- and three-dimensional space, quantify free liquid volumes through density and x-ray attenuation coefficient discrimination, and measure drum wall thickness. With waste emitting gamma-ray NDA techniques, WIT can locate gamma emitting radioactive sources in two- and three-dimensional space, identify gamma emitting isotopic species, identify the external activity levels of emitting gamma-ray sources, correct for waste matrix attenuation, provide internal activity approximations, and provide the data needed for waste classification as LLW or TRU. The mobile feature of WIT allows inspection technologies to be brought to the nuclear waste drum storage site without the need to relocate drums for safe, rapid, and cost-effective characterization of regulated nuclear waste. The combination of these WIT characterization modalities provides the inspector with an unprecedented ability to non-invasively characterize the regulated contents of waste drums as large as 110 gallons, weighing up to 1,600 pounds. Any objects that fit within these size and weight restrictions can also be inspected on WIT, such as smaller waste bags and drums that are five and thirty-five gallons
Superadditivity of distillable entanglement from quantum teleportation
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
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
Local copying of orthogonal entangled quantum states
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
Multipartite bound entanglement and three-setting Bell inequalities
Kaszlikowski, Dagomir; Chen Jingling; Oh, C.H.; Kwek, L.C.
2002-01-01
It was shown by Dur [Phys. Rev. Lett. 87, 230402 (2001)] that N (N≥4) qubits described by a certain one-parameter family F of bound entangled states violate the Mermin-Klyshko inequality for N≥8. In this paper we prove that the states from the family F violate Bell inequalities derived by Zukowski and Kaszlikowski [Phys. Rev. A 56, R1682 (1997)], in which each observer measures three noncommuting sets of orthogonal projectors, for N≥7. We also derive a simple one-parameter family of entanglement witnesses that detect entanglement for all the states belonging to F. It is possible that these entanglement witnesses could be generated by some Bell inequalities
The entanglement evolution between two entangled atoms
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 ...
Charcterization of multipartite entanglement
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.)
Charcterization of multipartite entanglement
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.)
Entangled states in quantum mechanics
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.
Waste inspection tomography (WIT)
Bernardi, R.T. [Bio-Imaging Research, Inc., Lincolnshire, IL (United States)
1995-10-01
Waste Inspection Tomography (WIT) provides mobile semi-trailer mounted nondestructive examination (NDE) and assay (NDA) for nuclear waste drum characterization. WIT uses various computed tomography (CT) methods for both NDE and NDA of nuclear waste drums. Low level waste (LLW), transuranic (TRU), and mixed radioactive waste can be inspected and characterized without opening the drums. With externally transmitted x-ray NDE techniques, WIT has the ability to identify high density waste materials like heavy metals, define drum contents in two- and three-dimensional space, quantify free liquid volumes through density and x-ray attenuation coefficient discrimination, and measure drum wall thickness. With waste emitting gamma-ray NDA techniques, WIT can locate gamma emitting radioactive sources in two- and three-dimensional space, identify gamma emitting, isotopic species, identify the external activity levels of emitting gamma-ray sources, correct for waste matrix attenuation, provide internal activity approximations, and provide the data needed for waste classification as LLW or TRU.
Waste inspection tomography (WIT)
Bernardi, R.T.
1995-01-01
Waste Inspection Tomography (WIT) provides mobile semi-trailer mounted nondestructive examination (NDE) and assay (NDA) for nuclear waste drum characterization. WIT uses various computed tomography (CT) methods for both NDE and NDA of nuclear waste drums. Low level waste (LLW), transuranic (TRU), and mixed radioactive waste can be inspected and characterized without opening the drums. With externally transmitted x-ray NDE techniques, WIT has the ability to identify high density waste materials like heavy metals, define drum contents in two- and three-dimensional space, quantify free liquid volumes through density and x-ray attenuation coefficient discrimination, and measure drum wall thickness. With waste emitting gamma-ray NDA techniques, WIT can locate gamma emitting radioactive sources in two- and three-dimensional space, identify gamma emitting, isotopic species, identify the external activity levels of emitting gamma-ray sources, correct for waste matrix attenuation, provide internal activity approximations, and provide the data needed for waste classification as LLW or TRU
Entanglement in mutually unbiased bases
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.
Deelan Cunden, Fabio; Facchi, Paolo; Florio, Giuseppe; Pascazio, Saverio
2013-05-01
Let a pure state | ψ> be chosen randomly in an NM-dimensional Hilbert space, and consider the reduced density matrix ρ A of an N-dimensional subsystem. The bipartite entanglement properties of | ψ> are encoded in the spectrum of ρ A . By means of a saddle point method and using a "Coulomb gas" model for the eigenvalues, we obtain the typical spectrum of reduced density matrices. We consider the cases of an unbiased ensemble of pure states and of a fixed value of the purity. We finally obtain the eigenvalue distribution by using a statistical mechanics approach based on the introduction of a partition function.
Allahverdyan, A.E.; Khrennikov, A.; Nieuwenhuizen, Th.M.
2005-01-01
For two classical Brownian particles an analog of continuous-variable quantum entanglement is presented: The common probability distribution of the two coordinates and the corresponding coarse-grained velocities cannot always be prepared via mixing of any factorized distributions referring to the two particles separately. This is possible for particles which have interacted in the past, but do not interact at present. Three factors are crucial for the effect: (1) separation of time scales of coordinate and momentum which motivates the definition of coarse-grained velocities; (2) the resulting uncertainty relations between the coordinate of the Brownian particle and the change of its coarse-grained velocity; (3) the fact that the coarse-grained velocity, though pertaining to a single Brownian particle, is defined on a common context of two particles. The Brownian entanglement is a consequence of a coarse-grained description and disappears for a finer resolution of the Brownian motion. Analogies with the quantum situation are discussed, as well as possibilities of experimental realization of the effect in examples of macroscopic Brownian motion
Hadjiivanov, L.; Todorov, I.
2015-01-01
Expository paper providing a historical survey of the gradual transformation of the 'philosophical discussions' between Bohr, Einstein and Schrödinger on foundational issues in quantum mechanics into a quantitative prediction of a new quantum effect, its experimental verification and its proposed (and loudly advertised) applications. The basic idea of the 1935 paper of Einstein-Podolsky-Rosen (EPR) was reformulated by David Bohm for a finite dimensional spin system. This allowed John Bell to derive his inequalities that separate the prediction of quantum entanglement from its possible classical interpretation. We reproduce here their later (1971) version, reviewing on the way the generalization (and mathematical derivation) of Heisenberg's uncertainty relations (due to Weyl and Schrödinger) needed for the passage from EPR to Bell. We also provide an improved derivation of the quantum theoretic violation of Bell's inequalities. Soon after the experimental confirmation of the quantum entanglement (culminating with the work of Alain Aspect) it was Feynman who made public the idea of a quantum computer based on the observed effect
Transitivity of an entangled choice
Makowski, Marcin; Piotrowski, Edward W
2011-01-01
We describe a quantum model of a simple choice game (constructed upon the entangled state of two qubits), which involves the fundamental problem of transitive-intransitive preferences. We compare attainability of optimal intransitive strategies in both classical and quantum models with the use of geometrical interpretation.
Fast entanglement detection for unknown states of two spatial qutrits
Lima, G.; Gomez, E. S.; Saavedra, C.; Vargas, A.; Vianna, R. O.
2010-01-01
We investigate the practicality of the method proposed by Maciel et al. [Phys. Rev. A. 80, 032325 (2009).] for detecting the entanglement of two spatial qutrits (three-dimensional quantum systems), which are encoded in the discrete transverse momentum of single photons transmitted through a multislit aperture. The method is based on the acquisition of partial information of the quantum state through projective measurements, and a data processing analysis done with semidefinite programs. This analysis relies on generating gradually an optimal entanglement witness operator, and numerical investigations have shown that it allows for the entanglement detection of unknown states with a cost much lower than full state tomography.
Direct Characterization of Ultrafast Energy-Time Entangled Photon Pairs.
MacLean, Jean-Philippe W; Donohue, John M; Resch, Kevin J
2018-02-02
Energy-time entangled photons are critical in many quantum optical phenomena and have emerged as important elements in quantum information protocols. Entanglement in this degree of freedom often manifests itself on ultrafast time scales, making it very difficult to detect, whether one employs direct or interferometric techniques, as photon-counting detectors have insufficient time resolution. Here, we implement ultrafast photon counters based on nonlinear interactions and strong femtosecond laser pulses to probe energy-time entanglement in this important regime. Using this technique and single-photon spectrometers, we characterize all the spectral and temporal correlations of two entangled photons with femtosecond resolution. This enables the witnessing of energy-time entanglement using uncertainty relations and the direct observation of nonlocal dispersion cancellation on ultrafast time scales. These techniques are essential to understand and control the energy-time degree of freedom of light for ultrafast quantum optics.
ETHIOPIAN WITNESS PROTECTION SYSTEM: COMPARATIVE ...
witness protection involves social cohesion of the protected person. Scholars ..... interests' need to balance an accused right to know and confront prosecution ..... was reduced to 2.5 years through the fast tracking of witness protection cases.
Remote entanglement distribution
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
Deterministic dense coding with partially entangled 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.
Strong monotonicity in mixed-state entanglement manipulation
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
Renormalizing Entanglement Distillation
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 branching operator
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.
Entanglement without nonlocality
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
Entanglement in SU(2)-invariant quantum systems: The positive partial transpose criterion and others
Schliemann, John
2005-01-01
We study entanglement in mixed bipartite quantum states which are invariant under simultaneous SU(2) transformations in both subsystems. Previous results on the behavior of such states under partial transposition are substantially extended. The spectrum of the partial transpose of a given SU(2)-invariant density matrix ρ is entirely determined by the diagonal elements of ρ in a basis of tensor-product states of both spins with respect to a common quantization axis. We construct a set of operators which act as entanglement witnesses on SU(2)-invariant states. A sufficient criterion for ρ having a negative partial transpose is derived in terms of a simple spin correlator. The same condition is a necessary criterion for the partial transpose to have the maximum number of negative eigenvalues. Moreover, we derive a series of sum rules which uniquely determine the eigenvalues of the partial transpose in terms of a system of linear equations. Finally we compare our findings with other entanglement criteria including the reduction criterion, the majorization criterion, and the recently proposed local uncertainty relations
Mutually Unbiased Maximally Entangled Bases for the Bipartite System Cd⊗ C^{dk}
Nan, Hua; Tao, Yuan-Hong; Wang, Tian-Jiao; Zhang, Jun
2016-10-01
The construction of maximally entangled bases for the bipartite system Cd⊗ Cd is discussed firstly, and some mutually unbiased bases with maximally entangled bases are given, where 2≤ d≤5. Moreover, we study a systematic way of constructing mutually unbiased maximally entangled bases for the bipartite system Cd⊗ C^{dk}.
Entanglement quantification by local unitary operations
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
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.
Multipartite secret key distillation and bound entanglement
Augusiak, Remigiusz; Horodecki, Pawel
2009-01-01
Recently it has been shown that quantum cryptography beyond pure entanglement distillation is possible and a paradigm for the associated protocols has been established. Here we systematically generalize the whole paradigm to the multipartite scenario. We provide constructions of new classes of multipartite bound entangled states, i.e., those with underlying twisted Greenberger-Horne-Zeilinger (GHZ) structure and nonzero distillable cryptographic key. We quantitatively estimate the key from below with the help of the privacy squeezing technique.
Gauge field entanglement in Kitaev's honeycomb model
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.
Testing the structure of multipartite entanglement with Bell inequalities.
Brunner, Nicolas; Sharam, James; Vértesi, Tamás
2012-03-16
We show that the rich structure of multipartite entanglement can be tested following a device-independent approach. Specifically we present Bell inequalities for distinguishing between different types of multipartite entanglement, without placing any assumptions on the measurement devices used in the protocol, in contrast with usual entanglement witnesses. We first address the case of three qubits and present Bell inequalities that can be violated by W states but not by Greenberger-Horne-Zeilinger states, and vice versa. Next, we devise 'subcorrelation Bell inequalities' for any number of parties, which can provably not be violated by a broad class of multipartite entangled states (generalizations of Greenberger-Horne-Zeilinger states), but for which violations can be obtained for W states. Our results give insight into the nonlocality of W states. The simplicity and robustness of our tests make them appealing for experiments.
Increasing the statistical significance of entanglement detection in experiments.
Jungnitsch, Bastian; Niekamp, Sönke; Kleinmann, Matthias; Gühne, Otfried; Lu, He; Gao, Wei-Bo; Chen, Yu-Ao; Chen, Zeng-Bing; Pan, Jian-Wei
2010-05-28
Entanglement is often verified by a violation of an inequality like a Bell inequality or an entanglement witness. Considerable effort has been devoted to the optimization of such inequalities in order to obtain a high violation. We demonstrate theoretically and experimentally that such an optimization does not necessarily lead to a better entanglement test, if the statistical error is taken into account. Theoretically, we show for different error models that reducing the violation of an inequality can improve the significance. Experimentally, we observe this phenomenon in a four-photon experiment, testing the Mermin and Ardehali inequality for different levels of noise. Furthermore, we provide a way to develop entanglement tests with high statistical significance.
Wang, Jun [Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education, College of Chemistry and Materials Science, Northwest University, Xi' an 710127 (China); College of Chemistry and Environmental Engineering, Sichuan University of Science & Engineering, Zigong 643000 (China); Bai, Chao [Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education, College of Chemistry and Materials Science, Northwest University, Xi' an 710127 (China); Hu, Huai-Ming, E-mail: ChemHu1@NWU.EDU.CN [Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education, College of Chemistry and Materials Science, Northwest University, Xi' an 710127 (China); Yuan, Fei; Xue, Gang-Lin [Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education, College of Chemistry and Materials Science, Northwest University, Xi' an 710127 (China)
2017-05-15
Eight Zn(II)-based coordination polymers, namely, [Zn{sub 2}L{sub 2}(2,2’-bipy)]{sub n}·nH{sub 2}O (1), [Zn{sub 2}L{sub 2}(phen)]{sub n}·nH{sub 2}O (2), [ZnL(phen)(H{sub 2}O)]{sub n} (3), [Zn{sub 3}L{sub 3}(4,4’-bipy)]{sub n} (4), [Zn{sub 2}L{sub 2}(4,4’-bipy){sub 2}]{sub n} [Zn{sub 2}L{sub 2}(H{sub 2}O){sub 2}]{sub n}·2nH{sub 2}O (5), [Zn{sub 4}L{sub 4}(bpp){sub 2}]{sub n} (6), [ZnL(bbi){sub 0.5}]{sub n} (7), [ZnL(bpz)]{sub n} (8) (H{sub 2}L=4,4’-([1,2-phenylenebis-(methylene)]bis(oxy))dibenzoic acid, 2,2’-bipy =2,2’-bipyridine, phen =1,10-phenanthroline, 4,4’-bpy=4,4’-bipyridine, bpp =1,3-bis(4-pyridyl)propane, bbi=1,4-bis(imidazol-1-yl)butane, bpz=3,3′,5,5′-tetramethyl-4,4′-bipyrazole), have been hydrothermally synthesized and structurally characterized. 1–8 display various coordination motifs with different entangled forms and conformations due to the effect of the assistant N-donor ligands. The photoluminescent properties of compounds 1–8 in solid state were studied. Interestingly, 3 exhibits highly efficient luminescent sensing for Cu{sup 2+} cations and CrO{sub 4}{sup 2-} anions, as well as detection ability for the different organic solvents and nitro explosives. These results indicated that it could be utilized as a multi-responsive luminescent sensor. Furthermore, compound 3 also shows good chemical resistance to both acidity and alkalinity solutions with pH ranging from 2 to 13. Thus, multi-photofunctionality and fluorescent response to pH have been combined in the 3, which is the first example in the Zn-based hybrid materials. - Graphical abstract: Eight new Zn(II)-based coordination polymers constructed from a flexible V-shaped long bicarboxylic acid and different N-donor ligands have been hydrothermally synthesized through fixing the metal salts and the solvent systems. The photoluminescent properties of complexes 1−8 in solid state were studied. Interestingly, 3 exhibits highly efficient luminescent sensing for Cu{sup 2
Wang, Jun; Bai, Chao; Hu, Huai-Ming; Yuan, Fei; Xue, Gang-Lin
2017-01-01
Eight Zn(II)-based coordination polymers, namely, [Zn 2 L 2 (2,2’-bipy)] n ·nH 2 O (1), [Zn 2 L 2 (phen)] n ·nH 2 O (2), [ZnL(phen)(H 2 O)] n (3), [Zn 3 L 3 (4,4’-bipy)] n (4), [Zn 2 L 2 (4,4’-bipy) 2 ] n [Zn 2 L 2 (H 2 O) 2 ] n ·2nH 2 O (5), [Zn 4 L 4 (bpp) 2 ] n (6), [ZnL(bbi) 0.5 ] n (7), [ZnL(bpz)] n (8) (H 2 L=4,4’-([1,2-phenylenebis-(methylene)]bis(oxy))dibenzoic acid, 2,2’-bipy =2,2’-bipyridine, phen =1,10-phenanthroline, 4,4’-bpy=4,4’-bipyridine, bpp =1,3-bis(4-pyridyl)propane, bbi=1,4-bis(imidazol-1-yl)butane, bpz=3,3′,5,5′-tetramethyl-4,4′-bipyrazole), have been hydrothermally synthesized and structurally characterized. 1–8 display various coordination motifs with different entangled forms and conformations due to the effect of the assistant N-donor ligands. The photoluminescent properties of compounds 1–8 in solid state were studied. Interestingly, 3 exhibits highly efficient luminescent sensing for Cu 2+ cations and CrO 4 2- anions, as well as detection ability for the different organic solvents and nitro explosives. These results indicated that it could be utilized as a multi-responsive luminescent sensor. Furthermore, compound 3 also shows good chemical resistance to both acidity and alkalinity solutions with pH ranging from 2 to 13. Thus, multi-photofunctionality and fluorescent response to pH have been combined in the 3, which is the first example in the Zn-based hybrid materials. - Graphical abstract: Eight new Zn(II)-based coordination polymers constructed from a flexible V-shaped long bicarboxylic acid and different N-donor ligands have been hydrothermally synthesized through fixing the metal salts and the solvent systems. The photoluminescent properties of complexes 1−8 in solid state were studied. Interestingly, 3 exhibits highly efficient luminescent sensing for Cu 2+ cations and CrO 4 2- anions, as well as detection ability for the different organic solvents and nitro explosives, in which indicates it could be
Fibonacci - Protagonist or Witness?
Høyrup, Jens
2014-01-01
Leonardo Fibonacci (ca. 1170 - after 1240) during his boyhood went to Bejaïa, learned about the Hindu-Arabic numerals there, and continued to collect information about their use during travels to the Arabic world. He then wrote the Liber abbaci, which with half a century’s delay inspired the crea......Leonardo Fibonacci (ca. 1170 - after 1240) during his boyhood went to Bejaïa, learned about the Hindu-Arabic numerals there, and continued to collect information about their use during travels to the Arabic world. He then wrote the Liber abbaci, which with half a century’s delay inspired......, of course, that Fibonacci learned about Arabic (and Byzantine) commercial arithmetic, and that he presented it in his book. He is thus a witness (with a degree of reliability which has to be determined) of the commercial mathematics thriving in the commercially developed parts of the Mediterranean world...... with Arabic non-scholarly traditions, at least until ca. 1350 within an open space, apparently concentrated around the Iberian region....
Entanglement quantification by local unitary operations
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.
Machine learning spatial geometry from entanglement features
You, Yi-Zhuang; Yang, Zhao; Qi, Xiao-Liang
2018-02-01
Motivated by the close relations of the renormalization group with both the holography duality and the deep learning, we propose that the holographic geometry can emerge from deep learning the entanglement feature of a quantum many-body state. We develop a concrete algorithm, call the entanglement feature learning (EFL), based on the random tensor network (RTN) model for the tensor network holography. We show that each RTN can be mapped to a Boltzmann machine, trained by the entanglement entropies over all subregions of a given quantum many-body state. The goal is to construct the optimal RTN that best reproduce the entanglement feature. The RTN geometry can then be interpreted as the emergent holographic geometry. We demonstrate the EFL algorithm on a 1D free fermion system and observe the emergence of the hyperbolic geometry (AdS3 spatial geometry) as we tune the fermion system towards the gapless critical point (CFT2 point).
Quantum Entanglement and Reduced Density Matrices
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.
Relating Out-of-Time-Order Correlations to Entanglement via Multiple-Quantum Coherences.
Gärttner, Martin; Hauke, Philipp; Rey, Ana Maria
2018-01-26
Out-of-time-order correlations (OTOCs) characterize the scrambling, or delocalization, of quantum information over all the degrees of freedom of a system and thus have been proposed as a proxy for chaos in quantum systems. Recent experimental progress in measuring OTOCs calls for a more thorough understanding of how these quantities characterize complex quantum systems, most importantly in terms of the buildup of entanglement. Although a connection between OTOCs and entanglement entropy has been derived, the latter only quantifies entanglement in pure systems and is hard to access experimentally. In this work, we formally demonstrate that the multiple-quantum coherence spectra, a specific family of OTOCs well known in NMR, can be used as an entanglement witness and as a direct probe of multiparticle entanglement. Our results open a path to experimentally testing the fascinating idea that entanglement is the underlying glue that links thermodynamics, statistical mechanics, and quantum gravity.
Relating Out-of-Time-Order Correlations to Entanglement via Multiple-Quantum Coherences
Gärttner, Martin; Hauke, Philipp; Rey, Ana Maria
2018-01-01
Out-of-time-order correlations (OTOCs) characterize the scrambling, or delocalization, of quantum information over all the degrees of freedom of a system and thus have been proposed as a proxy for chaos in quantum systems. Recent experimental progress in measuring OTOCs calls for a more thorough understanding of how these quantities characterize complex quantum systems, most importantly in terms of the buildup of entanglement. Although a connection between OTOCs and entanglement entropy has been derived, the latter only quantifies entanglement in pure systems and is hard to access experimentally. In this work, we formally demonstrate that the multiple-quantum coherence spectra, a specific family of OTOCs well known in NMR, can be used as an entanglement witness and as a direct probe of multiparticle entanglement. Our results open a path to experimentally testing the fascinating idea that entanglement is the underlying glue that links thermodynamics, statistical mechanics, and quantum gravity.
Entanglement of three-qubit Greenberger-Horne-Zeilinger-symmetric 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.
Salberger, Olof; Korepin, Vladimir
We introduce a new model of interacting spin 1/2. It describes interactions of three nearest neighbors. The Hamiltonian can be expressed in terms of Fredkin gates. The Fredkin gate (also known as the controlled swap gate) is a computational circuit suitable for reversible computing. Our construction generalizes the model presented by Peter Shor and Ramis Movassagh to half-integer spins. Our model can be solved by means of Catalan combinatorics in the form of random walks on the upper half plane of a square lattice (Dyck walks). Each Dyck path can be mapped on a wave function of spins. The ground state is an equally weighted superposition of Dyck walks (instead of Motzkin walks). We can also express it as a matrix product state. We further construct a model of interacting spins 3/2 and greater half-integer spins. The models with higher spins require coloring of Dyck walks. We construct a SU(k) symmetric model (where k is the number of colors). The leading term of the entanglement entropy is then proportional to the square root of the length of the lattice (like in the Shor-Movassagh model). The gap closes as a high power of the length of the lattice [5, 11].
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.
Measurement-Device-Independent Approach to Entanglement Measures
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.
Cotler, Jordan; Wilczek, Frank
2016-01-01
We introduce quantum history states and their mathematical framework, thereby reinterpreting and extending the consistent histories approach to quantum theory. Through thought experiments, we demonstrate that our formalism allows us to analyze a quantum version of history in which we reconstruct the past by observations. In particular, we can pass from measurements to inferences about ‘what happened’ in a way that is sensible and free of paradox. Our framework allows for a richer understanding of the temporal structure of quantum theory, and we construct history states that embody peculiar, non-classical correlations in time. (paper)
Semi-device-independent random-number expansion without entanglement
Li Hongwei; Yin Zhenqiang; Wu Yuchun; Zou Xubo; Wang Shuang; Chen Wei; Guo Guangcan; Han Zhengfu
2011-01-01
By testing the classical correlation violation between two systems, true random numbers can be generated and certified without applying classical statistical method. In this work, we propose a true random-number expansion protocol without entanglement, where the randomness can be guaranteed only by the two-dimensional quantum witness violation. Furthermore, we only assume that the dimensionality of the system used in the protocol has a tight bound, and the whole protocol can be regarded as a semi-device-independent black-box scenario. Compared with the device-independent random-number expansion protocol based on entanglement, our protocol is much easier to implement and test.
Remarks on entanglement swapping
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)
Quantum entanglement and geometry of determinantal varieties
Chen Hao
2006-01-01
Quantum entanglement was first recognized as a feature of quantum mechanics in the famous paper of Einstein, Podolsky, and Rosen. Recently it has been realized that quantum entanglement is a key ingredient in quantum computation, quantum communication, and quantum cryptography. In this paper, we introduce algebraic sets, which are determinantal varieties in the complex projective spaces or the products of complex projective spaces, for the mixed states on bipartite or multipartite quantum systems as their invariants under local unitary transformations. These invariants are naturally arised from the physical consideration of measuring mixed states by separable pure states. Our construction has applications in the following important topics in quantum information theory: (1) separability criterion, it is proved that the algebraic sets must be a union of the linear subspaces if the mixed states are separable; (2) simulation of Hamiltonians, it is proved that the simulation of semipositive Hamiltonians of the same rank implies the projective isomorphisms of the corresponding algebraic sets; (3) construction of bound entangled mixed states, examples of the entangled mixed states which are invariant under partial transpositions (thus PPT bound entanglement) are constructed systematically from our new separability criterion
A class of symmetric Bell diagonal entanglement witnesses—a geometric perspective
Chruściński, Dariusz
2014-01-01
We provide a class of Bell diagonal entanglement witnesses displaying an additional local symmetry—a maximal commutative subgroup of the unitary group U(n). Remarkably, this class of witnesses is parameterized by a torus being a maximal commutative subgroup of an orthogonal group SO(n−1). It is shown that a generic element from the class defines an indecomposable entanglement witness. The paper provides a geometric perspective for some aspects of the entanglement theory and an interesting interplay between group theory and block-positive operators in C n ⊗C n . This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical devoted to ‘50 years of Bell’s theorem’. (paper)
A new device-independent dimension witness and its experimental implementation
Cai, Yu; Bancal, Jean-Daniel; Romero, Jacquiline; Scarani, Valerio
2016-07-01
A dimension witness is a criterion that sets a lower bound on the dimension needed to reproduce the observed data. Three types of dimension witnesses can be found in the literature: device-dependent ones, in which the bound is obtained assuming some knowledge on the state and the measurements; device-independent prepare-and-measure ones, that can be applied to any system including classical ones; and device-independent Bell-based ones, that certify the minimal dimension of some entangled systems. Here we consider the Collins-Gisin-Linden-Massar-Popescu Bell-type inequality for four outcomes. We show that a sufficiently high violation of this inequality witnesses d≥slant 4 and present a proof-of-principle experimental observation of such a violation. This presents a first experimental violation of the third type of dimension witness beyond qutrits.
Probabilistic teleportation scheme of two-mode entangled photon states by using linear optic element
XIANG Shao-hua
2003-01-01
A scheme for teleporting two-mode entangled photon states with the successful probability 33.3% is proposed. In the scheme, the teleporte d qubit is two-mode photon entangled states, and two pairs of EPR pair are used as quantum channel between a sender and a receiver. This procedure is achieved by using two 50/50 symmetric beam splitters and four photon number detectors wit h the help of classical information.
Maximally multipartite entangled 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.
Entanglement, holography and causal diamonds
Boer, Jan de [Institute of Physics, Universiteit van Amsterdam,Science Park 904, 1090 GL Amsterdam (Netherlands); Haehl, Felix M. [Centre for Particle Theory & Department of Mathematical Sciences, Durham University,South Road, Durham DH1 3LE (United Kingdom); Heller, Michal P.; Myers, Robert C. [Perimeter Institute for Theoretical Physics,31 Caroline Street North, Waterloo, Ontario N2L 2Y5 (Canada)
2016-08-29
We argue that the degrees of freedom in a d-dimensional CFT can be re-organized in an insightful way by studying observables on the moduli space of causal diamonds (or equivalently, the space of pairs of timelike separated points). This 2d-dimensional space naturally captures some of the fundamental nonlocality and causal structure inherent in the entanglement of CFT states. For any primary CFT operator, we construct an observable on this space, which is defined by smearing the associated one-point function over causal diamonds. Known examples of such quantities are the entanglement entropy of vacuum excitations and its higher spin generalizations. We show that in holographic CFTs, these observables are given by suitably defined integrals of dual bulk fields over the corresponding Ryu-Takayanagi minimal surfaces. Furthermore, we explain connections to the operator product expansion and the first law of entanglement entropy from this unifying point of view. We demonstrate that for small perturbations of the vacuum, our observables obey linear two-derivative equations of motion on the space of causal diamonds. In two dimensions, the latter is given by a product of two copies of a two-dimensional de Sitter space. For a class of universal states, we show that the entanglement entropy and its spin-three generalization obey nonlinear equations of motion with local interactions on this moduli space, which can be identified with Liouville and Toda equations, respectively. This suggests the possibility of extending the definition of our new observables beyond the linear level more generally and in such a way that they give rise to new dynamically interacting theories on the moduli space of causal diamonds. Various challenges one has to face in order to implement this idea are discussed.
Daniell, M.L.
2000-09-01
The motivation of this thesis was to create higher-order entanglements. The first experimental observation of a four-photon entanglement was presented in the experiment of this thesis. And the visibility of this entanglement was 0.79+-0.06, which is sufficient to make claims of the nonlocality of quantum mechanics. This therefore lays a foundation for experiments showing the nonlocality of teleportation, and the purification of entanglement. The work of this thesis brings together a lot of earlier work done by the Zeilinger Group, and lays a foundation for future experiments. Earlier experiments such as teleportation together with entanglement swapping, which are 'complete teleportation' in as much as the state teleported is entirely undefined, can be combined and re-done with this four-photon entanglement. This result would be the first demonstration of complete, nonlocal teleportation. Also this experiment can be slightly modified and used to perform the first experimental quantum purification of entanglement, which is of vital importance to the fields of quantum information, and also is interesting for fundamental experiments on entanglement. Another direct application of this experiment is to perform the first 'event-ready' testing of Bell's Inequality. Here the four-photon entanglement can be used as a source of entangled photons, whereby the photons have no common source. This would enable an even more stringent testing of Bells theorem. Finally this experiment can be used for the demonstration and investigation of many practical, directly applicable quantum information schemes. For instance quantum cryptography, error correction, and computing. (author)
Non-binary Entanglement-assisted Stabilizer Quantum Codes
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...
Entanglement negativity in the multiverse
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
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
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.
Multisetting Bell-type inequalities for detecting genuine multipartite entanglement
Pal, Karoly F.; Vertesi, Tamas
2011-01-01
In a recent paper, Bancal et al.[Phys. Rev. Lett. 106, 250404 (2011)] put forward the concept of device-independent witnesses of genuine multipartite entanglement. These witnesses are capable of verifying genuine multipartite entanglement produced in a laboratory without resorting to any knowledge of the dimension of the state space or of the specific form of the measurement operators. As a by-product they found a multiparty three-setting Bell inequality which makes it possible to detect genuine n-partite entanglement in a noisy n-qubit Greenberger-Horne-Zeilinger (GHZ) state for visibilities as low as 2/3 in a device-independent way. In this paper, we generalize this inequality to an arbitrary number of settings, demonstrating a threshold visibility of 2/π∼0.6366 for number of settings going to infinity. We also present a pseudotelepathy Bell inequality achieving the same threshold value. We argue that our device-independent witnesses are optimal in the sense that for n odd the above value cannot be beaten with n-party-correlation Bell inequalities.
Quantum Entanglement in Neural Network States
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
Mutual preservation of entanglement
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.
Entanglement for multipartite systems of indistinguishable particles
Grabowski, Janusz [Polish Academy of Sciences, Institute of Mathematics, Sniadeckich 8, PO Box 21, 00-956 Warsaw (Poland); Kus, Marek [Center for Theoretical Physics, Polish Academy of Sciences, Aleja Lotnikow 32/46, 02-668 Warszawa (Poland); Marmo, Giuseppe, E-mail: jagrab@impan.pl, E-mail: marek.kus@cft.edu.pl, E-mail: marmo@na.infn.it [Dipartimento di Scienze Fisiche, Universita ' Federico II' di Napoli and Istituto Nazionale di Fisica Nucleare, Sezione di Napoli, Complesso Universitario di Monte Sant Angelo, Via Cintia, I-80126 Napoli (Italy)
2011-04-29
We analyze the concept of entanglement for a multipartite system with bosonic and fermionic constituents and its generalization to systems with arbitrary parastatistics. We use the representation theory of symmetry groups to formulate a unified approach to this problem in terms of simple tensors with an appropriate symmetry. For an arbitrary parastatistics, we define the S-rank generalizing the notion of the Schmidt rank. The S-rank, defined for all types of tensors, serves for distinguishing entanglement of pure states. In addition, for Bose and Fermi statistics, we construct an analog of the Jamiolkowski isomorphism.
Multiple-copy entanglement transformation and entanglement catalysis
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
A heralded two-qutrit entangled state
Joo, Jaewoo; Sanders, Barry C; Rudolph, Terry
2009-01-01
We propose a scheme for building a heralded two-qutrit entangled state from polarized photons. An optical circuit is presented to build the maximally entangled two-qutrit state from two heralded Bell pairs and ideal threshold detectors. Several schemes are discussed for constructing the two Bell pairs. We also show how one can produce an unbalanced two-qutrit state that could be of general purpose use in some protocols. In terms of the applications of the maximally entangled qutrit state, we mainly focus on how to use the state to demonstrate a violation of the Collins-Gisin-Linden-Massar-Popescu inequality under the restriction of measurements which can be performed using linear optical elements and photon counting. Other possible applications of the state, such as for higher dimensional quantum cryptography, teleportation and generation of heralded two-qudit states, are also briefly discussed.
Entanglement-assisted quantum MDS codes from negacyclic codes
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.
Holographic Entanglement Entropy
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...
Entanglement in neutrino oscillations
Blasone, M.; Dell' Anno, F.; De Siena, S.; Illuminati, F. [Universita degli Studi di Salerno Via Ponte don Melillon, Dipt. di Matematica e Informatica, Fisciano SA (Italy); INFN Sezione di Napoli, Gruppo collegato di Salerno - Baronissi SA (Italy); Dell' Anno, F.; De Siena, S.; Illuminati, F. [CNR-INFM Coherentia - Napoli (Italy); Blasone, M. [ISI Foundation for Scientific Interchange, Torino (Italy)
2009-03-15
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)
Entanglement in neutrino oscillations
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)
Transplanckian entanglement entropy
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
Method for universal detection of two-photon polarization entanglement
Bartkiewicz, Karol; Horodecki, Paweł; Lemr, Karel; Miranowicz, Adam; Życzkowski, Karol
2015-03-01
Detecting and quantifying quantum entanglement of a given unknown state poses problems that are fundamentally important for quantum information processing. Surprisingly, no direct (i.e., without quantum tomography) universal experimental implementation of a necessary and sufficient test of entanglement has been designed even for a general two-qubit state. Here we propose an experimental method for detecting a collective universal witness, which is a necessary and sufficient test of two-photon polarization entanglement. It allows us to detect entanglement for any two-qubit mixed state and to establish tight upper and lower bounds on its amount. A different element of this method is the sequential character of its main components, which allows us to obtain relatively complicated information about quantum correlations with the help of simple linear-optical elements. As such, this proposal realizes a universal two-qubit entanglement test within the present state of the art of quantum optics. We show the optimality of our setup with respect to the minimal number of measured quantities.
Deterministic dense coding and entanglement entropy
Bourdon, P. S.; Gerjuoy, E.; McDonald, J. P.; Williams, H. T.
2008-01-01
We present an analytical study of the standard two-party deterministic dense-coding protocol, under which communication of perfectly distinguishable messages takes place via a qudit from a pair of nonmaximally entangled qudits in a pure state |ψ>. Our results include the following: (i) We prove that it is possible for a state |ψ> with lower entanglement entropy to support the sending of a greater number of perfectly distinguishable messages than one with higher entanglement entropy, confirming a result suggested via numerical analysis in Mozes et al. [Phys. Rev. A 71, 012311 (2005)]. (ii) By explicit construction of families of local unitary operators, we verify, for dimensions d=3 and d=4, a conjecture of Mozes et al. about the minimum entanglement entropy that supports the sending of d+j messages, 2≤j≤d-1; moreover, we show that the j=2 and j=d-1 cases of the conjecture are valid in all dimensions. (iii) Given that |ψ> allows the sending of K messages and has √(λ 0 ) as its largest Schmidt coefficient, we show that the inequality λ 0 ≤d/K, established by Wu et al. [Phys. Rev. A 73, 042311 (2006)], must actually take the form λ 0 < d/K if K=d+1, while our constructions of local unitaries show that equality can be realized if K=d+2 or K=2d-1
Healthcare system simulation using Witness
Khakdaman, Masoud; Zeinahvazi, Milad; Zohoori, Bahareh; Nasiri, Fardokht; Wong, Kuan Yew
2013-01-01
Simulation techniques have a proven track record in manufacturing industry as well as other areas such as healthcare system improvement. In this study, simulation model of a health center in Malaysia is developed through the application of WITNESS simulation software which has shown its flexibility and capability in manufacturing industry. Modelling procedure is started through process mapping and data collection and continued with model development, verification, validation and experimentation. At the end, final results and possible future improvements are demonstrated.
Entanglement diversion and quantum teleportation of entangled coherent states
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.
Entanglement, holography and causal diamonds
de Boer, Jan; Haehl, Felix M.; Heller, Michal P.; Myers, Robert C.
2016-08-01
We argue that the degrees of freedom in a d-dimensional CFT can be reorganized in an insightful way by studying observables on the moduli space of causal diamonds (or equivalently, the space of pairs of timelike separated points). This 2 d-dimensional space naturally captures some of the fundamental nonlocality and causal structure inherent in the entanglement of CFT states. For any primary CFT operator, we construct an observable on this space, which is defined by smearing the associated one-point function over causal diamonds. Known examples of such quantities are the entanglement entropy of vacuum excitations and its higher spin generalizations. We show that in holographic CFTs, these observables are given by suitably defined integrals of dual bulk fields over the corresponding Ryu-Takayanagi minimal surfaces. Furthermore, we explain connections to the operator product expansion and the first law of entanglemententropy from this unifying point of view. We demonstrate that for small perturbations of the vacuum, our observables obey linear two-derivative equations of motion on the space of causal diamonds. In two dimensions, the latter is given by a product of two copies of a two-dimensional de Sitter space. For a class of universal states, we show that the entanglement entropy and its spin-three generalization obey nonlinear equations of motion with local interactions on this moduli space, which can be identified with Liouville and Toda equations, respectively. This suggests the possibility of extending the definition of our new observables beyond the linear level more generally and in such a way that they give rise to new dynamically interacting theories on the moduli space of causal diamonds. Various challenges one has to face in order to implement this idea are discussed.
Expert witness and Jungian archetypes.
Lallave, Juan Antonio; Gutheil, Thomas Gordon
2012-01-01
Jung's theories of archetype, shadow, and the personal and collective unconscious provide a postmodern framework in which to consider the role of the expert witness in judicial proceedings. Archetypal themes, motifs, and influences help to illuminate the shadow of the judicial system and projections and behaviors among the cast of the court in pursuing justice. This article speaks to archetypal influences and dialectical tensions encountered by the expert witness in this judicial drama. The archetype of Justice is born from the human need for order and relational fairness in a world of chaos. The persona of justice is the promise of truth in the drama. The shadow of justice is untruth, the need to win by any means. The dynamics of the trickster archetype serve and promote injustice. These influences are examined by means of a case example. This approach will deepen understanding of court proceedings and the role of the expert witness in the heroic quest for justice. Copyright © 2012 Elsevier Ltd. All rights reserved.
Signature of quantum entanglement in NH{sub 4}CuPO{sub 4}·H{sub 2}O
Chakraborty, Tanmoy, E-mail: tanmoy@iiserkol.ac.in; Singh, Harkirat; Mitra, Chiranjib, E-mail: chiranjib@iiserkol.ac.in [Indian Institute of Science Education and Research (IISER) Kolkata, Mohanpur Campus, PO: BCKV Campus Main Office, Mohanpur 741252, Nadia, West Bengal (India)
2014-01-21
Entangled solid state systems have gained a great deal of attention due to their fruitful applications in modern quantum technologies. Herein, detection of entanglement content from experimental magnetic susceptibility and specific heat data is reported for NH{sub 4}CuPO{sub 4}·H{sub 2}O in its solid state crystalline form. NH{sub 4}CuPO{sub 4}·H{sub 2}O is a prototype of Heisenberg spin 1/2 dimer system. Temperature dependent magnetic susceptibility and specific data are fitted to an isolated dimer model and the exchange coupling constant is determined. Field dependent magnetization isotherms taken at different temperatures are plotted in a three dimensional plot. Subsequently, entanglement is detected both from susceptibility and specific heat through two different entanglement measures; entanglement witness and entanglement of formation. The temperature evolution of entanglement is studied and the critical temperature is determined up to which entanglement exists. Temperature dependent nature of entanglement extracted from susceptibility and specific heat shows good consistency with each other. Moreover, the field dependent entanglement is also investigated.
Three qubit entanglement within graphical Z/X-calculus
Bob Coecke
2011-03-01
Full Text Available The compositional techniques of categorical quantum mechanics are applied to analyse 3-qubit quantum entanglement. In particular the graphical calculus of complementary observables and corresponding phases due to Duncan and one of the authors is used to construct representative members of the two genuinely tripartite SLOCC classes of 3-qubit entangled states, GHZ and W. This nicely illustrates the respectively pairwise and global tripartite entanglement found in the W- and GHZ-class states. A new concept of supplementarity allows us to characterise inhabitants of the W class within the abstract diagrammatic calculus; these method extends to more general multipartite qubit states.
Manipulating continuous variable photonic entanglement
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)
41 CFR 105-70.033 - Witnesses.
2010-07-01
... 41 Public Contracts and Property Management 3 2010-07-01 2010-07-01 false Witnesses. 105-70.033 Section 105-70.033 Public Contracts and Property Management Federal Property Management Regulations System... may proceed by leading questions only if the witness is a hostile witness, an adverse party, or a...
2010-10-01
... 47 Telecommunication 1 2010-10-01 2010-10-01 false Witness fees. 1.339 Section 1.339....339 Witness fees. Witnesses who are subpenaed and respond thereto are entitled to the same fees, including mileage, as are paid for like service in the courts of the United States. Fees shall be paid by...
Cosmological quantum entanglement
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)
Multipartite entanglement in neutrino oscillations
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
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.
Quantum secret sharing protocol using modulated doubly entangled photons
Chuan, Wang; Yong, Zhang
2009-01-01
In this paper, we propose a quantum secret sharing protocol utilizing polarization modulated doubly entangled photon pairs. The measurement devices are constructed. By modulating the polarizations of entangled photons, the boss could encode secret information on the initial state and share the photons with different members to realize the secret sharing process. This protocol shows the security against intercept-resend attack and dishonest member cheating. The generalized quantum secret sharing protocol is also discussed. (general)
Universal entanglement transformations without communication
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
Quantum Statistics and Entanglement Problems
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.
Images in quantum entanglement
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.
Images in quantum entanglement
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.
Entanglement entropy from tensor network states for stabilizer codes
He, Huan; Zheng, Yunqin; Bernevig, B. Andrei; Regnault, Nicolas
2018-03-01
In this paper, we present the construction of tensor network states (TNS) for some of the degenerate ground states of three-dimensional (3D) stabilizer codes. We then use the TNS formalism to obtain the entanglement spectrum and entropy of these ground states for some special cuts. In particular, we work out examples of the 3D toric code, the X-cube model, and the Haah code. The latter two models belong to the category of "fracton" models proposed recently, while the first one belongs to the conventional topological phases. We mention the cases for which the entanglement entropy and spectrum can be calculated exactly: For these, the constructed TNS is a singular value decomposition (SVD) of the ground states with respect to particular entanglement cuts. Apart from the area law, the entanglement entropies also have constant and linear corrections for the fracton models, while the entanglement entropies for the toric code models only have constant corrections. For the cuts we consider, the entanglement spectra of these three models are completely flat. We also conjecture that the negative linear correction to the area law is a signature of extensive ground-state degeneracy. Moreover, the transfer matrices of these TNSs can be constructed. We show that the transfer matrices are projectors whose eigenvalues are either 1 or 0. The number of nonzero eigenvalues is tightly related to the ground-state degeneracy.
Multipartite entanglement and frustration
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
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
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.
Entanglement in miscible blends
Watanabe, Hiroshi
2010-03-01
The entanglement length Le of polymer chains (corresponding to the entanglement molecular weight Me) is not an intrinsic material parameter but changes with the interaction with surrounding chains. For miscible blends of cis-polyisoprene (PI) and poly(tert-butyl styrene) (PtBS), changes of Le on blending was examined. It turned out that the Le averaged over the number fractions of the Kuhn segments of the components (PI and PtBS) satisfactorily describes the viscoelastic behavior of pseudo-monodisperse blends in which the terminal relaxation time is the same for PI and PtBS.
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)
Multi-particle entanglement via two-party entanglement
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.
[Evaluation of Wits appraisal with superimposition method].
Xu, T; Ahn, J; Baumrind, S
1999-07-01
To compare the conventional Wits appraisal with superimposed Wits appraisal in evaluation of sagittal jaw relationship change between pre and post orthodontic treatment. The sample consists of 48-case pre and post treatment lateral head films. Computerized digitizing is used to get the cephalometric landmarks and measure conventional Wits value, superimposed Wits value and ANB angle. The correlation analysis among these three measures was done by SAS statistical package. The change of ANB angle has higher correlation with the change of superimposed Wits than that of the conventional Wits. The r-value is as high as 0.849 (P < 0.001). The superimposed Wits appraisal reflects the change of sagittal jaw relationship more objectively than the conventional one.
Correcting quantum errors with entanglement.
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.
Entanglement in the Bogoliubov vacuum
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...
Microscopic wormholes and the geometry of entanglement
Lobo, Francisco S.N. [Centro de Astronomia e Astrofisica da Universidade de Lisboa, Lisbon (Portugal); Olmo, Gonzalo J. [Centro Mixto Universidad de Valencia-CSIC, Universidad de Valencia, Departamento de Fisica Teorica y IFIC, Valencia (Spain); Rubiera-Garcia, D. [Universidade Federal da Paraiba, Departamento de Fisica, Joao Pessoa, Paraiba (Brazil)
2014-06-15
It has recently been suggested that Einstein-Rosen (ER) bridges can be interpreted as maximally entangled states of two black holes that form a complex Einstein-Podolsky-Rosen (EPR) pair. This relationship has been dubbed as the ER = EPR correlation. In this work, we consider the latter conjecture in the context of quadratic Palatini theory. An important result, which stems from the underlying assumptions as regards the geometry on which the theory is constructed, is the fact that all the charged solutions of the quadratic Palatini theory possess a wormhole structure. Our results show that spacetime may have a foam like microstructure with wormholes generated by fluctuations of the quantum vacuum. This involves the spontaneous creation/annihilation of entangled particle-antiparticle pairs, existing in a maximally entangled state connected by a nontraversable wormhole. Since the particles are produced from the vacuum and therefore exist in a singlet state, they are necessarily entangled with one another. This gives further support to the ER = EPR claim. (orig.)
Spatial entanglement patterns and Einstein-Podolsky-Rosen steering in Bose-Einstein condensates
Fadel, Matteo; Zibold, Tilman; Décamps, Boris; Treutlein, Philipp
2018-04-01
Many-particle entanglement is a fundamental concept of quantum physics that still presents conceptual challenges. Although nonclassical states of atomic ensembles were used to enhance measurement precision in quantum metrology, the notion of entanglement in these systems was debated because the correlations among the indistinguishable atoms were witnessed by collective measurements only. Here, we use high-resolution imaging to directly measure the spin correlations between spatially separated parts of a spin-squeezed Bose-Einstein condensate. We observe entanglement that is strong enough for Einstein-Podolsky-Rosen steering: We can predict measurement outcomes for noncommuting observables in one spatial region on the basis of corresponding measurements in another region with an inferred uncertainty product below the Heisenberg uncertainty bound. This method could be exploited for entanglement-enhanced imaging of electromagnetic field distributions and quantum information tasks.
Photon Entanglement Through Brain Tissue.
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.
Experimental test of entangled histories
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.
Blasone, Massimo [Dipartimento di Fisica, Università degli Studi di Salerno, Via Ponte don Melillo, I-84084 Fisciano (Italy); INFN Sezione di Napoli, Gruppo collegato di Salerno (Italy); Dell' Anno, Fabio; De Siena, Silvio; Illuminati, Fabrizio [Dipartimento di Ingegneria Industriale, Università degli Studi di Salerno, Via Ponte don Melillo, I-84084 Fisciano (Italy)
2013-04-15
Neutrino oscillations can be equivalently described in terms of (dynamical) entanglement of neutrino flavor modes. We review previous results derived in the context of quantum mechanics and extend them to the quantum field theory framework, were a rich structure of quantum correlations appears.
Blasone, Massimo; Dell'Anno, Fabio; De Siena, Silvio; Illuminati, Fabrizio
2013-01-01
Neutrino oscillations can be equivalently described in terms of (dynamical) entanglement of neutrino flavor modes. We review previous results derived in the context of quantum mechanics and extend them to the quantum field theory framework, were a rich structure of quantum correlations appears
Facets of tripartite entanglement
Quantum mechanical correlations between results of measurments on entangled ..... It is interesting that motivation underpinning Einstein locality is not the relativistic re- quirement of no faster-than-light signalling but rather a consideration related .... of the relevant studies see, for instance, D Home, Conceptual foundations.
Multipartite entangled quantum states: Transformation, Entanglement monotones and Application
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
Operational classification and quantification of multipartite entangled states
Rigolin, Gustavo; Oliveira, Thiago R. de; Oliveira, Marcos C. de
2006-01-01
We formalize and extend an operational multipartite entanglement measure introduced by T. R. Oliveira, G. Rigolin, and M. C. de Oliveira, Phys. Rev. A 73, 010305(R) (2006), through the generalization of global entanglement (GE) [D. A. Meyer and N. R. Wallach, J. Math. Phys. 43, 4273 (2002)]. Contrarily to GE the main feature of this measure lies in the fact that we study the mean linear entropy of all possible partitions of a multipartite system. This allows the construction of an operational multipartite entanglement measure which is able to distinguish among different multipartite entangled states that GE failed to discriminate. Furthermore, it is also maximum at the critical point of the Ising chain in a transverse magnetic field, being thus able to detect a quantum phase transition
Time evolution as refining, coarse graining and entangling
Dittrich, Bianca; Steinhaus, Sebastian
2014-01-01
We argue that refining, coarse graining and entangling operators can be obtained from time evolution operators. This applies in particular to geometric theories, such as spin foams. We point out that this provides a construction principle for the physical vacuum in quantum gravity theories and more generally allows construction of a (cylindrically) consistent continuum limit of the theory. (paper)
Time evolution as refining, coarse graining and entangling
Dittrich, Bianca; Steinhaus, Sebastian
2014-12-01
We argue that refining, coarse graining and entangling operators can be obtained from time evolution operators. This applies in particular to geometric theories, such as spin foams. We point out that this provides a construction principle for the physical vacuum in quantum gravity theories and more generally allows construction of a (cylindrically) consistent continuum limit of the theory.
Kenfack, Lionel Tenemeza; Tchoffo, Martin; Fouokeng, Georges Collince; Fai, Lukong Cornelius
2018-04-01
The effects of 1/f^{α } (α =1,2) noise stemming from one or a collection of random bistable fluctuators (RBFs), on the evolution of entanglement, of three non-interacting qubits are investigated. Three different initial configurations of the qubits are analyzed in detail: the Greenberger-Horne-Zeilinger (GHZ)-type states, W-type states and mixed states composed of a GHZ state and a W state (GHZ-W). For each initial configuration, the evolution of entanglement is investigated for three different qubit-environment (Q-E) coupling setups, namely independent environments, mixed environments and common environment coupling. With the help of tripartite negativity and suitable entanglement witnesses, we show that the evolution of entanglement is extremely influenced not only by the initial configuration of the qubits, the spectrum of the environment and the Q-E coupling setup considered, but also by the number of RBF modeling the environment. Indeed, we find that the decay of entanglement is accelerated when the number of fluctuators modeling the environment is increased. Furthermore, we find that entanglement can survive indefinitely to the detrimental effects of noise even for increasingly larger numbers of RBFs. On the other hand, we find that the proficiency of the tripartite entanglement witnesses to detect entanglement is weaker than that of the tripartite negativity and that the symmetry of the initial states is broken when the qubits are coupled to the noise in mixed environments. Finally, we find that the 1 / f noise is more harmful to the survival of entanglement than the 1/f2 noise and that the mixed GHZ-W states followed by the GHZ-type states preserve better entanglement than the W-type ones.
Experimental Determination of Multipartite Entanglement with Incomplete Information
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.
Probabilistic Teleportation of the Three-Particle Entangled State viaEntanglement Swapping
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.
Racial entanglements and sociological confusions: repudiating the rehabilitation of integration.
Valluvan, Sivamohan
2018-06-01
In line with the broader nationalist advances currently remaking the Western political landscape, the concept of integration has witnessed a marked rehabilitation. Whilst many influential critiques of the sociology of integration are already available, this article contests the concept's renewed purchase through addressing its own internal incoherence. Based on research in Stockholm, this critique concerns the relationship between ethnic identity and cultural integration. It will be argued that integration and the production of difference are intertwined, entangled dualities, and far from being a benign entanglement, this duality is premised on the force and reach of everyday civic racisms. Of pivotal and unique analytical significance here is the observation that racism should not only be considered an exogenous process that impedes integration, but as a multifaceted phenomenon folded into integration. © London School of Economics and Political Science 2017.
The entanglement purification for entangled multi-particle states
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 between two interacting CFTs and generalized holographic entanglement entropy
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
Entanglement and quantum teleportation via decohered tripartite entangled states
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.
Bond dimension witnesses and the structure of homogeneous matrix product states
Miguel Navascues
2018-01-01
Full Text Available For the past twenty years, Matrix Product States (MPS have been widely used in solid state physics to approximate the ground state of one-dimensional spin chains. In this paper, we study homogeneous MPS (hMPS, or MPS constructed via site-independent tensors and a boundary condition. Exploiting a connection with the theory of matrix algebras, we derive two structural properties shared by all hMPS, namely: a there exist local operators which annihilate all hMPS of a given bond dimension; and b there exist local operators which, when applied over any hMPS of a given bond dimension, decouple (cut the particles where they act from the spin chain while at the same time join (glue the two loose ends back again into a hMPS. Armed with these tools, we show how to systematically derive `bond dimension witnesses', or 2-local operators whose expectation value allows us to lower bound the bond dimension of the underlying hMPS. We extend some of these results to the ansatz of Projected Entangled Pairs States (PEPS. As a bonus, we use our insight on the structure of hMPS to: a derive some theoretical limitations on the use of hMPS and hPEPS for ground state energy computations; b show how to decrease the complexity and boost the speed of convergence of the semidefinite programming hierarchies described in [Phys. Rev. Lett. 115, 020501 (2015] for the characterization of finite-dimensional quantum correlations.
Solvent-free porous framework resulted from 3D entanglement of 1D zigzag coordination polymer
Kole, Goutam Kumar Umar
2010-01-01
A solvent-free porous metal organic framework is constructed by the 3D entanglement of 1D zigzag coordination polymeric chains. The role of solvents and the effect of reaction conditions on such unique entanglement are addressed. © 2010 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
Entropy of entangled states and SU(1,1) and SU(2) symmetries
Santana, A.E.; Khanna, F.C.; Revzen, M.
2002-01-01
Based on a recent definition of a measure for entanglement [Plenio and Vedral, Contemp. Phys. 39, 431 (1998)], examples of maximum entangled states are presented. The construction of such states, which have symmetry SU(1,1) and SU(2), follows the guidance of thermofield dynamics formalism
Solvent-free porous framework resulted from 3D entanglement of 1D zigzag coordination polymer
Kole, Goutam Kumar Umar; Cairns, Amy J.; Eddaoudi, Mohamed; Vittal, Jagadese J.
2010-01-01
A solvent-free porous metal organic framework is constructed by the 3D entanglement of 1D zigzag coordination polymeric chains. The role of solvents and the effect of reaction conditions on such unique entanglement are addressed. © 2010 The Royal
Entanglement Classification of extended Greenberger-Horne-Zeilinger-Symmetric States
Jung, Eylee; Park, DaeKil
2013-01-01
In this paper we analyze entanglement classification of extended Greenberger-Horne-Zeilinger-symmetric states $\\rho^{ES}$, which is parametrized by four real parameters $x$, $y_1$, $y_2$ and $y_3$. The condition for separable states of $\\rho^{ES}$ is analytically derived. The higher classes such as bi-separable, W, and Greenberger-Horne-Zeilinger classes are roughly classified by making use of the class-specific optimal witnesses or map from the extended Greenberger-Horne-Zeilinger symmetry t...
Entangled network and quantum communication
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.
Photonic simulation of entanglement growth and engineering after a spin chain quench.
Pitsios, Ioannis; Banchi, Leonardo; Rab, Adil S; Bentivegna, Marco; Caprara, Debora; Crespi, Andrea; Spagnolo, Nicolò; Bose, Sougato; Mataloni, Paolo; Osellame, Roberto; Sciarrino, Fabio
2017-11-17
The time evolution of quantum many-body systems is one of the most important processes for benchmarking quantum simulators. The most curious feature of such dynamics is the growth of quantum entanglement to an amount proportional to the system size (volume law) even when interactions are local. This phenomenon has great ramifications for fundamental aspects, while its optimisation clearly has an impact on technology (e.g., for on-chip quantum networking). Here we use an integrated photonic chip with a circuit-based approach to simulate the dynamics of a spin chain and maximise the entanglement generation. The resulting entanglement is certified by constructing a second chip, which measures the entanglement between multiple distant pairs of simulated spins, as well as the block entanglement entropy. This is the first photonic simulation and optimisation of the extensive growth of entanglement in a spin chain, and opens up the use of photonic circuits for optimising quantum devices.
Hyperspherical entanglement entropy
Dowker, J S
2010-01-01
The coefficient of the log term in the entanglement entropy associated with hyperspherical surfaces in flat spacetime is shown to equal the conformal anomaly by conformally transforming Euclideanized spacetime to a sphere and using already existing formulae for the relevant heat-kernel coefficients after cyclic factoring. The result follows from the fact that the conformal anomaly on this lune has an extremum at the ordinary sphere limit. A proof is given. Agreement with a recent evaluation of the coefficient is found.
Hyperspherical entanglement entropy
Dowker, J S, E-mail: dowker@man.ac.u [Theory Group, School of Physics and Astronomy, University of Manchester, Manchester (United Kingdom)
2010-11-05
The coefficient of the log term in the entanglement entropy associated with hyperspherical surfaces in flat spacetime is shown to equal the conformal anomaly by conformally transforming Euclideanized spacetime to a sphere and using already existing formulae for the relevant heat-kernel coefficients after cyclic factoring. The result follows from the fact that the conformal anomaly on this lune has an extremum at the ordinary sphere limit. A proof is given. Agreement with a recent evaluation of the coefficient is found.
Inter-Universal Quantum Entanglement
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.
Global entanglement in multiparticle systems
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
Gravity as Quantum Entanglement Force
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...
Configuration of separability and tests for multipartite entanglement in bell-type experiments.
Nagata, Koji; Koashi, Masato; Imoto, Nobuyuki
2002-12-23
We derive tight quadratic inequalities for all kinds of hybrid separable-inseparable n-particle density operators on an arbitrary dimensional space. This methodology enables us to derive a tight quadratic inequality as tests for full n-partite entanglement in various Bell-type correlation experiments on the systems that may not be identified as a collection of qubits, e.g., those involving photons measured by incomplete detectors. It is also proved that when the two measured observables are assumed to precisely anticommute, a stronger quadratic inequality can be used as a witness of full n-partite entanglement.
Experimental Entanglement Distribution by Separable 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.
Error exponents for entanglement concentration
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
Entanglement in a parametric converter
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.
Evolving and Combining Facial Composites: Between-Witness and Within-Witness Morphs Compared
Valentine, Tim; Davis, Josh P.; Thorner, Kate; Solomon, Chris; Gibson, Stuart
2010-01-01
Student participant-witnesses produced 4 composites of unfamiliar faces with a system that uses a genetic algorithm to evolve appearance of artificial faces. Morphs of 4 composites produced by different witnesses (between-witness morphs) were judged better likenesses (Experiment 1) and were more frequently named (Experiment 2) by participants who…
2010-04-01
... 20 Employees' Benefits 1 2010-04-01 2010-04-01 false Witnesses. 258.2 Section 258.2 Employees' Benefits RAILROAD RETIREMENT BOARD REGULATIONS UNDER THE RAILROAD RETIREMENT ACT HEARINGS BEFORE THE BOARD... a delegation of authority to such examiner to require and compel the attendance of witnesses and the...
Children's Witnessing of Adult Domestic Violence.
Edleson, Jeffrey L.
1999-01-01
Expands common definitions of how children witness adult domestic violence through a review of 31 research articles. A variety of behavioral, emotional, and cognitive-functioning problems among children were found to be associated with exposure to domestic violence. Factors that appear to moderate the impact of witnessing violence (child abuse,…
2010-01-01
... 6 Domestic Security 1 2010-01-01 2010-01-01 false Witnesses. 13.33 Section 13.33 Domestic Security DEPARTMENT OF HOMELAND SECURITY, OFFICE OF THE SECRETARY PROGRAM FRAUD CIVIL REMEDIES § 13.33 Witnesses. (a) Except as provided in paragraph (b) of this section, testimony at the hearing will be given orally by...
Safety Tips from the Expert Witness.
Gray, Gary R.
1995-01-01
Many physical educators and coaches use the potential for liability to guide their decisions about conducting activities. By understanding expert witnesses' roles in negligence actions, surer planning, teaching, and coaching are possible. The paper describes issues that expert witnesses examine in negligence actions against physical educators,…
Ethiopian witness protection system: comparative analysis with ...
Witnesses are the eyes and the ears of justice.” They assist the court in deciding the guilt or otherwise of the accused person. They are crucial in a criminal proceeding; from reporting of crime to its trial. The evidence by a witness is crucial for the ...
Neurosurgical Procedures in Jehovah's Witnesses: The Tema ...
BACKGROUND: On account of religious reasons, Jehovah Witnesses do not accept blood or blood products; occasionally, they accept reinfusion of autologous blood via a cell saver during surgery. OBJECTIVE: The aim of this study was to document the demographics of Jehovah Witnesses undergoing neurosurgical ...
14 CFR 406.161 - Witness fees.
2010-01-01
... 14 Aeronautics and Space 4 2010-01-01 2010-01-01 false Witness fees. 406.161 Section 406.161 Aeronautics and Space COMMERCIAL SPACE TRANSPORTATION, FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF... the same fees and mileage expenses as are paid to a witness in a court of the United States in...
Multi-Photon Entanglement and Quantum Teleportation
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...
Gerck, Ed
We present a new, comprehensive framework to qualitatively improve election outcome trustworthiness, where voting is modeled as an information transfer process. Although voting is deterministic (all ballots are counted), information is treated stochastically using Information Theory. Error considerations, including faults, attacks, and threats by adversaries, are explicitly included. The influence of errors may be corrected to achieve an election outcome error as close to zero as desired (error-free), with a provably optimal design that is applicable to any type of voting, with or without ballots. Sixteen voting system requirements, including functional, performance, environmental and non-functional considerations, are derived and rated, meeting or exceeding current public-election requirements. The voter and the vote are unlinkable (secret ballot) although each is identifiable. The Witness-Voting System (Gerck, 2001) is extended as a conforming implementation of the provably optimal design that is error-free, transparent, simple, scalable, robust, receipt-free, universally-verifiable, 100% voter-verified, and end-to-end audited.
Partial recovery of entanglement in bipartite-entanglement transformations
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-assisted quantum low-density parity-check codes
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.
Statistical mechanics of multipartite entanglement
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
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
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
Entanglement transfer between bipartite systems
Bougouffa, Smail; Ficek, Zbigniew
2012-01-01
The problem of a controlled transfer of an entanglement initially encoded into two two-level atoms that are successively sent through two single-mode cavities is investigated. The atoms and the cavity modes form a four-qubit system and we demonstrate the conditions under which the initial entanglement encoded into the atoms can be completely transferred to other pairs of qubits. We find that in the case of non-zero detuning between the atomic transition frequencies and the cavity mode frequencies, no complete transfer of the initial entanglement is possible to any of the other pairs of qubits. In the case of exact resonance and equal coupling strengths of the atoms to the cavity modes, an initial maximally entangled state of the atoms can be completely transferred to the cavity modes. Complete transfer of the entanglement is restricted to the cavity modes, with transfer to the other pairs being limited to 50%. We find that complete transfer of an initial entanglement to other pairs of qubits may take place if the initial state is not the maximally entangled state and the atoms couple to the cavity modes with unequal strengths. Depending on the ratio between the coupling strengths, optimal entanglement can be created between the atoms and one of the cavity modes.
Generic entangling through quantum indistinguishability
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-.
Emergence of Symmetries from Entanglement
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.
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...
32 CFR 516.54 - Witnesses for the United States.
2010-07-01
... 32 National Defense 3 2010-07-01 2010-07-01 true Witnesses for the United States. 516.54 Section..., Travel, and Expenses of Witnesses § 516.54 Witnesses for the United States. (a) Status of witness. A military member authorized to appear as a witness for the United States, including those authorized to...
Caring for the Jehovah's Witness Parturient.
Mason, C LaToya; Tran, Connie K
2015-12-01
Caring for the Jehovah's Witness parturient is a complex task that presents a number of ethical, medical, and legal concerns because many Jehovah's Witnesses refuse allogeneic blood transfusion. Childbirth and its surrounding events may be associated with significant blood loss. Given their significant role in the intraoperative administration of blood products, anesthesia providers should be familiar with factors that must be considered in the perioperative care of Jehovah's Witness parturients. Several pharmacologic therapies, anesthetic techniques, and operative interventions aimed at blood conservation may be useful in the care of such patients. Aside from their refusal of transfusion, each Witness makes a personal decision on the acceptability of derivatives of plasma or cellular blood components and autologous blood management. Therefore, the patient-physician relationship must ensure that the individual patient's desires are accurately communicated, respected, and documented in the patient's medical record. The Perioperative Surgical Home model is appropriate for use in caring for Jehovah's Witness patients because it allows for the early and continuing coordination of care and communication between the patient and a multidisciplinary team. In this article, we present a focused review of concepts important to the provision of anesthetic care of parturients who are Jehovah's Witnesses and introduce an algorithmic perioperative approach that may be applied to the care of the Jehovah's Witness parturient undergoing an operative procedure.
Entangled cloning of stabilizer codes and free fermions
Hsieh, Timothy H.
2016-10-01
Though the no-cloning theorem [Wooters and Zurek, Nature (London) 299, 802 (1982), 10.1038/299802a0] prohibits exact replication of arbitrary quantum states, there are many instances in quantum information processing and entanglement measurement in which a weaker form of cloning may be useful. Here, I provide a construction for generating an "entangled clone" for a particular but rather expansive and rich class of states. Given a stabilizer code or free fermion Hamiltonian, this construction generates an exact entangled clone of the original ground state, in the sense that the entanglement between the original and the exact copy can be tuned to be arbitrarily small but finite, or large, and the relation between the original and the copy can also be modified to some extent. For example, this Rapid Communication focuses on generating time-reversed copies of stabilizer codes and particle-hole transformed ground states of free fermion systems, although untransformed clones can also be generated. The protocol leverages entanglement to simulate a transformed copy of the Hamiltonian without having to physically implement it and can potentially be realized in superconducting qubits or ultracold atomic systems.
Bearing witness: an existential position in caring.
Arman, Maria
2007-12-01
A basic assumption for the study is that perceiving a person's deepest needs and desires to be on hand for another person, and their attempt to do so, have, in an ontological sense, the power to bear witness of goodness and eternity. The study was based on a theoretical basis of a caring science view of suffering, as well as the ethics of the philosopher Lévinas. The aim was to explore and clinically validate nuances of witnessing as a caring act.A Socratic dialogue was performed and an interpretive (hermeneutic) method was employed in this study. The Socratic dialogue with four nurses in palliative care focused on and analysed one clinical example of witnessing in palliative care. As basis for the findings are the participating nurses jointly formulated assumptions on the subject: To be a witness you have to be with the patient and refer back to him or her what you have seen; but also to act in accordance with what you have perceived. In the moment you witness, a window is opened onto the unknown; you become vulnerable as a caregiver and require courage. Being a witness encompasses existential and spiritual aspects; being a fellow human being, having a heart to heart relationship is a wilful act on the part of the nurse. Our theoretical discussion focuses on the language of the body, courage as a bridge to an existential encounter and the alleviation of patients' suffering through caregivers' witnessing. A conclusive aspect is that being a witness may bring a new understanding of life in the face of death and suffering. The existential position of being a witness requires the caregiver to be courageous because of its transformative prospect, but may utterly enrich both parties' inner life of shared meaning.
Entanglement entropy and duality
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.
Mc
2012-07-01
Full Text Available stream_source_info McLaren_2012.pdf.txt stream_content_type text/plain stream_size 2190 Content-Encoding ISO-8859-1 stream_name McLaren_2012.pdf.txt Content-Type text/plain; charset=ISO-8859-1 High dimensional... entanglement M. McLAREN1,2, F.S. ROUX1 & A. FORBES1,2,3 1. CSIR National Laser Centre, PO Box 395, Pretoria 0001 2. School of Physics, University of the Stellenbosch, Private Bag X1, 7602, Matieland 3. School of Physics, University of Kwazulu...
Nomura, Yasunori [Berkeley Center for Theoretical Physics, Department of Physics, University of California, Berkeley, CA 94720 (United States); Theoretical Physics Group, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo Institutes for Advanced Study, Kashiwa 277-8583 (Japan); Salzetta, Nico, E-mail: nsalzetta@berkeley.edu [Berkeley Center for Theoretical Physics, Department of Physics, University of California, Berkeley, CA 94720 (United States); Theoretical Physics Group, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Sanches, Fabio; Weinberg, Sean J. [Berkeley Center for Theoretical Physics, Department of Physics, University of California, Berkeley, CA 94720 (United States); Theoretical Physics Group, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States)
2016-12-10
We study the Hilbert space structure of classical spacetimes under the assumption that entanglement in holographic theories determines semiclassical geometry. We show that this simple assumption has profound implications; for example, a superposition of classical spacetimes may lead to another classical spacetime. Despite its unconventional nature, this picture admits the standard interpretation of superpositions of well-defined semiclassical spacetimes in the limit that the number of holographic degrees of freedom becomes large. We illustrate these ideas using a model for the holographic theory of cosmological spacetimes.
Entanglements in Conjugated Polymers
Xie, Renxuan; Lee, Youngmin; Aplan, Melissa; Caggiano, Nick; Gomez, Enrique; Colby, Ralph
Conjugated polymers, such as poly(3-hexylthiophene-2,5-diyl) (P3HT) and poly-((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(thiophen-5-yl)-2,1,3-benzothiadiazole]-2',2''-diyl) (PFTBT), are widely used as hole and electron transport materials in a variety of electronic devices. However, fundamental knowledge regarding chain entanglements and nematic-to-isotropic transition is still lacking and are crucial to maximize charge transport properties. A systematic melt rheology study on P3HT with various molecular weights and regio regularities was performed. We find that the entanglement molecular weight Me is 5.0 kg/mol for regiorandom P3HT, but the apparent Me for regioregular P3HT is significantly higher. The difference is postulated to arise from the presence of a nematic phase only in regioregular P3HT. Analogously, PFTBT shows a clear rheological signature of the nematic-to-isotropic transition as a reversible sharp transition at 278 C. Shearing of this nematic phase leads to anisotropic crystalline order in PFTBT. We postulate that aligning the microstructure will impact charge transport and thereby advance the field of conducting polymers. National Science Foundation.
Experimental entanglement distillation of mesoscopic quantum states
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...
Increasing the statistical significance of entanglement detection in experiments
Jungnitsch, Bastian; Niekamp, Soenke; Kleinmann, Matthias; Guehne, Otfried [Institut fuer Quantenoptik und Quanteninformation, Innsbruck (Austria); Lu, He; Gao, Wei-Bo; Chen, Zeng-Bing [Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei (China); Chen, Yu-Ao; Pan, Jian-Wei [Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei (China); Physikalisches Institut, Universitaet Heidelberg (Germany)
2010-07-01
Entanglement is often verified by a violation of an inequality like a Bell inequality or an entanglement witness. Considerable effort has been devoted to the optimization of such inequalities in order to obtain a high violation. We demonstrate theoretically and experimentally that such an optimization does not necessarily lead to a better entanglement test, if the statistical error is taken into account. Theoretically, we show for different error models that reducing the violation of an inequality can improve the significance. We show this to be the case for an error model in which the variance of an observable is interpreted as its error and for the standard error model in photonic experiments. Specifically, we demonstrate that the Mermin inequality yields a Bell test which is statistically more significant than the Ardehali inequality in the case of a photonic four-qubit state that is close to a GHZ state. Experimentally, we observe this phenomenon in a four-photon experiment, testing the above inequalities for different levels of noise.
Squashed entanglement in infinite dimensions
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.
Graphical Classification of Entangled Qutrits
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.
Local cloning of entangled states
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.
Impact of quantum entanglement on spectrum of cosmological fluctuations
Kanno, Sugumi, E-mail: sugumi.kanno@uct.ac.za [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)
2014-07-01
We investigate the effect of entanglement between two causally separated open charts in de Sitter space on the spectrum of vacuum fluctuations. We consider a free massive scalar field, and construct the reduced density matrix by tracing out the vacuum state for one of the open charts, as recently derived by Maldacena and Pimentel. We formulate the mean-square vacuum fluctuations by using the reduced density matrix and show that the scale invariant spectrum of massless scalar field is realized on small scales. On the other hand, we find that the quantum entanglement affects the shape of the spectrum on large scales comparable to or greater than the curvature radius.
Zero modes and entanglement entropy
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
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.
Teleportation of Squeezed Entangled State
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＞.
Bound entanglement and local realism
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
The Entangled Cosmos: an experiment in physical theopoetics
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 harmonic chain out of equilibrium
Eisler, Viktor; Zimborás, Zoltán
2014-01-01
We study the entanglement in a chain of harmonic oscillators driven out of equilibrium by preparing the two sides of the system at different temperatures, and subsequently joining them together. The steady state is constructed explicitly and the logarithmic negativity is calculated between two adjacent segments of the chain. We find that, for low temperatures, the steady-state entanglement is a sum of contributions pertaining to left- and right-moving excitations emitted from the two reservoirs. In turn, the steady-state entanglement is a simple average of the Gibbs-state values and thus its scaling can be obtained from conformal field theory. A similar averaging behaviour is observed during the entire time evolution. As a particular case, we also discuss a local quench where both sides of the chain are initialized in their respective ground states. (paper)
Theory of finite-entanglement scaling at one-dimensional quantum critical points.
Pollmann, Frank; Mukerjee, Subroto; Turner, Ari M; Moore, Joel E
2009-06-26
Studies of entanglement in many-particle systems suggest that most quantum critical ground states have infinitely more entanglement than noncritical states. Standard algorithms for one-dimensional systems construct model states with limited entanglement, which are a worse approximation to quantum critical states than to others. We give a quantitative theory of previously observed scaling behavior resulting from finite entanglement at quantum criticality. Finite-entanglement scaling in one-dimensional systems is governed not by the scaling dimension of an operator but by the "central charge" of the critical point. An important ingredient is the universal distribution of density-matrix eigenvalues at a critical point [P. Calabrese and A. Lefevre, Phys. Rev. A 78, 032329 (2008)10.1103/PhysRevA.78.032329]. The parameter-free theory is checked against numerical scaling at several quantum critical points.
Gaussian entanglement revisited
Lami, Ludovico; Serafini, Alessio; Adesso, Gerardo
2018-02-01
We present a novel approach to the separability problem for Gaussian quantum states of bosonic continuous variable systems. We derive a simplified necessary and sufficient separability criterion for arbitrary Gaussian states of m versus n modes, which relies on convex optimisation over marginal covariance matrices on one subsystem only. We further revisit the currently known results stating the equivalence between separability and positive partial transposition (PPT) for specific classes of Gaussian states. Using techniques based on matrix analysis, such as Schur complements and matrix means, we then provide a unified treatment and compact proofs of all these results. In particular, we recover the PPT-separability equivalence for: (i) Gaussian states of 1 versus n modes; and (ii) isotropic Gaussian states. In passing, we also retrieve (iii) the recently established equivalence between separability of a Gaussian state and and its complete Gaussian extendability. Our techniques are then applied to progress beyond the state of the art. We prove that: (iv) Gaussian states that are invariant under partial transposition are necessarily separable; (v) the PPT criterion is necessary and sufficient for separability for Gaussian states of m versus n modes that are symmetric under the exchange of any two modes belonging to one of the parties; and (vi) Gaussian states which remain PPT under passive optical operations can not be entangled by them either. This is not a foregone conclusion per se (since Gaussian bound entangled states do exist) and settles a question that had been left unanswered in the existing literature on the subject. This paper, enjoyable by both the quantum optics and the matrix analysis communities, overall delivers technical and conceptual advances which are likely to be useful for further applications in continuous variable quantum information theory, beyond the separability problem.
Entanglement of Grassmannian Coherent States for Multi-Partite n-Level Systems
Ghader Najarbashi
2011-01-01
Full Text Available In this paper, we investigate the entanglement of multi-partite Grassmannian coherent states (GCSs described by Grassmann numbers for n>2 degree of nilpotency. Choosing an appropriate weight function, we show that it is possible to construct some well-known entangled pure states, consisting of GHZ, W, Bell, cluster type and bi-separable states, which are obtained by integrating over tensor product of GCSs. It is shown that for three level systems, the Grassmann creation and annihilation operators b and b^† together with bz form a closed deformed algebra, i.e., SU_q(2 with q=e^{2πi/3}, which is useful to construct entangled qutrit-states. The same argument holds for three level squeezed states. Moreover combining the Grassmann and bosonic coherent states we construct maximal entangled super coherent states.
Entangled Bessel-Gaussian beams
McLaren, M
2012-10-01
Full Text Available by performing a Bell-type experiment and showing a violation of the Clauser-Horne-Shimony-Holt inequality. In addition, we use quantum state tomography to indicate higher-dimensional entanglement in terms of BG modes....
Gaussian entanglement distribution via satellite
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.
Continuous-Variable Entanglement Swapping
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.
Quantum entanglement and quantum teleportation
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.)
Entanglement scaling in lattice systems
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.
Transverse correlations in multiphoton entanglement
Wen Jianming; Rubin, Morton H.; Shih Yanhua
2007-01-01
We have analyzed the transverse correlation in multiphoton entanglement. The generalization of quantum ghost imaging is extended to the N-photon state. The Klyshko's two-photon advanced-wave picture is generalized to the N-photon case
Entanglement distribution in quantum networks
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
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 as a signature of quantum chaos.
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.
Pseudo-entanglement evaluated in noninertial frames
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.
Mixtures of maximally entangled pure states
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.
Quantum entanglement of identical particles
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
Thermodynamic entanglement of magnonic condensates
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.
Multipartite geometric entanglement in finite size XY model
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.
Compact 6 dB Two-Color Continuous Variable Entangled Source Based on a Single Ring Optical Resonator
Ning Wang
2018-02-01
Full Text Available Continuous-variable entangled optical beams at the degenerate wavelength of 0.8 μm or 1.5 μm have been investigated extensively, but separately. The two-color entangled states of these two useful wavelengths, with sufficiently high degrees of entanglement, still lag behind. In this work, we analyze the various limiting factors that affect the entanglement degree. On the basis of this, we successfully achieve 6 dB of two-color quadrature entangled light beams by improving the escape efficiency of the nondegenerate optical amplifier, the stability of the phase-locking servo system, and the detection efficiency. Our entangled source is constructed only from a single ring optical resonator, and thus is highly compact, which is suitable for applications in long-distance quantum communication networks.
29 CFR 18.701 - Opinion testimony by lay witnesses.
2010-07-01
... 29 Labor 1 2010-07-01 2010-07-01 true Opinion testimony by lay witnesses. 18.701 Section 18.701 Labor Office of the Secretary of Labor RULES OF PRACTICE AND PROCEDURE FOR ADMINISTRATIVE HEARINGS... Opinion testimony by lay witnesses. If the witness is not testifying as an expert, the witness' testimony...
Optimal simulation of a perfect entangler
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.
Exploring the sequential lineup advantage using WITNESS.
Goodsell, Charles A; Gronlund, Scott D; Carlson, Curt A
2010-12-01
Advocates claim that the sequential lineup is an improvement over simultaneous lineup procedures, but no formal (quantitatively specified) explanation exists for why it is better. The computational model WITNESS (Clark, Appl Cogn Psychol 17:629-654, 2003) was used to develop theoretical explanations for the sequential lineup advantage. In its current form, WITNESS produced a sequential advantage only by pairing conservative sequential choosing with liberal simultaneous choosing. However, this combination failed to approximate four extant experiments that exhibited large sequential advantages. Two of these experiments became the focus of our efforts because the data were uncontaminated by likely suspect position effects. Decision-based and memory-based modifications to WITNESS approximated the data and produced a sequential advantage. The next step is to evaluate the proposed explanations and modify public policy recommendations accordingly.
Generalized Remote Preparation of Arbitrary m-qubit Entangled States via Genuine Entanglements
Dong Wang
2015-03-01
Full Text Available Herein, we present a feasible, general protocol for quantum communication within a network via generalized remote preparation of an arbitrary m-qubit entangled state designed with genuine tripartite Greenberger–Horne–Zeilinger-type entangled resources. During the implementations, we construct novel collective unitary operations; these operations are tasked with performing the necessary phase transfers during remote state preparations. We have distilled our implementation methods into a five-step procedure, which can be used to faithfully recover the desired state during transfer. Compared to previous existing schemes, our methodology features a greatly increased success probability. After the consumption of auxiliary qubits and the performance of collective unitary operations, the probability of successful state transfer is increased four-fold and eight-fold for arbitrary two- and three-qubit entanglements when compared to other methods within the literature, respectively. We conclude this paper with a discussion of the presented scheme for state preparation, including: success probabilities, reducibility and generalizability.
Entanglement distillation protocols and number theory
Bombin, H.; Martin-Delgado, M.A.
2005-01-01
We show that the analysis of entanglement distillation protocols for qudits of arbitrary dimension D benefits from applying basic concepts from number theory, since the set Z D n associated with Bell diagonal states is a module rather than a vector space. We find that a partition of Z D n into divisor classes characterizes the invariant properties of mixed Bell diagonal states under local permutations. We construct a very general class of recursion protocols by means of unitary operations implementing these local permutations. We study these distillation protocols depending on whether we use twirling operations in the intermediate steps or not, and we study them both analytically and numerically with Monte Carlo methods. In the absence of twirling operations, we construct extensions of the quantum privacy algorithms valid for secure communications with qudits of any dimension D. When D is a prime number, we show that distillation protocols are optimal both qualitatively and quantitatively
Liu, Cheng-Ji; Li, Zhi-Hui; Bai, Chen-Ming; Si, Meng-Meng
2018-02-01
The concept of judgment space was proposed by Wang et al. (Phys. Rev. A 95, 022320, 2017), which was used to study some important properties of quantum entangled states based on local distinguishability. In this study, we construct 15 kinds of seven-qudit quantum entangled states in the sense of permutation, calculate their judgment space and propose a distinguishability rule to make the judgment space more clearly. Based on this rule, we study the local distinguishability of the 15 kinds of seven-qudit quantum entangled states and then propose a ( k, n) threshold quantum secret sharing scheme. Finally, we analyze the security of the scheme.
Teleportation of N-particle entangled W state via entanglement swapping
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.
Protecting single-photon entanglement with practical entanglement source
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.
Experimental distribution of entanglement with separable carriers
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.
Separability criteria for genuine multiparticle entanglement
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
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
HMSRP Hawaiian Monk Seal Entanglement data
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...
Relay entanglement and clusters of correlated spins
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.
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)
2010-04-01
...' Benefits EMPLOYMENT STANDARDS ADMINISTRATION, DEPARTMENT OF LABOR FEDERAL COAL MINE HEALTH AND SAFETY ACT... days before the hearing. The failure to give notice of the appearance of an expert witness in... relevant to the physical condition of the miner, such physician must have prepared a medical report...
'Het gaat niet over zwart en wit'
Drs. Kennedy Aquilino Tielman; prof dr Douwe Beijaard; Dr. Perry den Brok; Dr. S. Bolhuis
2009-01-01
'Het gaat niet over zwart en wit' De meeste mbo-scholen hebben samenwerking tussen de leerlingen hoog in het vaandel. Kunnen samenwerken is belangrijk voor de latere beroepsuitoefening en het functioneren van de leerlingen in de samenleving. De grote culturele diversiteit binnen de leerlingpopulatie
Witness: The Movie. A Material Development Project.
Conlon, Susan Henderson
A teaching guide and series of exercises for high-intermediate or advanced English-as-a-Second-Language (ESL) instruction based on the movie "Witness" are presented. The materials are designed primarily to develop English listening and speaking skills and enhance awareness of American culture and the criminal justice system. The teaching…
Associations between witnessing parental violence and ...
information concerning witnessing parental violence as a child, symptoms of depression during the current academic year. Logistic regression procedures were used to estimate odds ratios (OR) and 95% confidence intervals (95% CI). Results: Approximately 22.7% female students and 27.1% of the male students reported ...
Bystanders' Reactions to Witnessing Repetitive Abuse Experiences
Janson, Gregory R.; Carney, JoLynn V.; Hazler, Richard J.; Oh, Insoo
2009-01-01
The Impact of Event Scale-Revised (D. S. Weiss & C. R. Marmar, 1997) was used to obtain self-reported trauma levels from 587 young adults recalling childhood or adolescence experiences as witnesses to common forms of repetitive abuse defined as bullying. Mean participant scores were in a range suggesting potential need for clinical assessment…
2010-04-01
... 21 Food and Drugs 1 2010-04-01 2010-04-01 false Witnesses. 17.37 Section 17.37 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES GENERAL CIVIL MONEY PENALTIES... pay for his or her travel to the hearing. The sponsoring party is responsible for producing the...
Quantum entanglement and special relativity
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)
Quantum walks with entangled coins
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
Communication cost of entanglement transformations
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)
Energy entanglement relation for quantum energy teleportation
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.
On entanglement-assisted quantum codes achieving the entanglement-assisted Griesmer bound
Li, Ruihu; Li, Xueliang; Guo, Luobin
2015-12-01
The theory of entanglement-assisted quantum error-correcting codes (EAQECCs) is a generalization of the standard stabilizer formalism. Any quaternary (or binary) linear code can be used to construct EAQECCs under the entanglement-assisted (EA) formalism. We derive an EA-Griesmer bound for linear EAQECCs, which is a quantum analog of the Griesmer bound for classical codes. This EA-Griesmer bound is tighter than known bounds for EAQECCs in the literature. For a given quaternary linear code {C}, we show that the parameters of the EAQECC that EA-stabilized by the dual of {C} can be determined by a zero radical quaternary code induced from {C}, and a necessary condition under which a linear EAQECC may achieve the EA-Griesmer bound is also presented. We construct four families of optimal EAQECCs and then show the necessary condition for existence of EAQECCs is also sufficient for some low-dimensional linear EAQECCs. The four families of optimal EAQECCs are degenerate codes and go beyond earlier constructions. What is more, except four codes, our [[n,k,d_{ea};c
Entropy-driven phase transitions of entanglement
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.
Maximally Entangled Multipartite States: A Brief Survey
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)
Quantum entanglement and quantum computational algorithms
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 ...
Universal distortion-free entanglement concentration
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
Quantum teleportation of entangled squeezed vacuum states
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.
Relationship between squeezing and entangled state transformations
Fan Hong Yi
2003-01-01
We show that c-number dilation transform in the Einstein-Podolsky-Rosen (EPR) entangled state, i.e. vertical bar eta sub 1 , eta sub 2) -> vertical bar eta sub 1 , eta sub 2 /mu) (or vertical bar eta sub 1 , eta sub 2) -> vertical bar eta sub 1 /mu, eta sub 2)), maps onto a kind of one-sided two-mode squeezing operator exp left brace i lambda/2(P sub 1 + P sub 2)(Q sub 1 + Q sub 2) - lambda/2 right brace, (or exp left brace i lambda/2(P sub 1 - P sub 2)(Q sub 1 - Q sub 2) - lambda/2 right brace). Using the IWOP technique, we derive their normally ordered form and construct the corresponding squeezed states. In doing so, some new relationship between squeezing and entangled state transformation is revealed. The dynamic Hamiltonian for such a kind of squeezing evolution is derived. The properties and application of the one-sided squeezed state are briefly discussed. These states can also be obtained with the use of a beam splitter.
Entanglement and optimal quantum information processing
Siomau, Michael
2011-01-01
Today we are standing on the verge of new enigmatic era of quantum technologies. In spite of the significant progress that has been achieved over the last three decades in experimental generation and manipulation as well as in theoretical description of evolution of single quantum systems, there are many open problems in understanding the behavior and properties of complex multiparticle quantum systems. In this thesis, we investigate theoretically a number of problems related to the description of entanglement - the nonlocal feature of complex quantum systems - of multiparticle states of finite-dimensional quantum systems. We also consider the optimal ways of manipulation of such systems. The focus is made, especially, on such optimal quantum transformations that provide a desired operation independently on the initial state of the given system. The first part of this thesis, in particular, is devoted to the detailed analysis of evolution of entanglement of complex quantum systems subjected to general non-unitary dynamics. In the second part of the thesis we construct several optimal state independent transformations, analyze their properties and suggest their applications in quantum communication and quantum computing. (orig.)
Structural entanglements in protein complexes
Zhao, Yani; Chwastyk, Mateusz; Cieplak, Marek
2017-06-01
We consider multi-chain protein native structures and propose a criterion that determines whether two chains in the system are entangled or not. The criterion is based on the behavior observed by pulling at both termini of each chain simultaneously in the two chains. We have identified about 900 entangled systems in the Protein Data Bank and provided a more detailed analysis for several of them. We argue that entanglement enhances the thermodynamic stability of the system but it may have other functions: burying the hydrophobic residues at the interface and increasing the DNA or RNA binding area. We also study the folding and stretching properties of the knotted dimeric proteins MJ0366, YibK, and bacteriophytochrome. These proteins have been studied theoretically in their monomeric versions so far. The dimers are seen to separate on stretching through the tensile mechanism and the characteristic unraveling force depends on the pulling direction.
Entanglement in open quantum systems
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
Global entanglement in XXZ chains
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
Measuring coherence with entanglement concurrence
Qi, Xianfei; Gao, Ting; Yan, Fengli
2017-07-01
Quantum coherence is a fundamental manifestation of the quantum superposition principle. Recently, Baumgratz et al (2014 Phys. Rev. Lett. 113 140401) presented a rigorous framework to quantify coherence from the view of theory of physical resource. Here we propose a new valid quantum coherence measure which is a convex roof measure, for a quantum system of arbitrary dimension, essentially using the generalized Gell-Mann matrices. Rigorous proof shows that the proposed coherence measure, coherence concurrence, fulfills all the requirements dictated by the resource theory of quantum coherence measures. Moreover, strong links between the resource frameworks of coherence concurrence and entanglement concurrence is derived, which shows that any degree of coherence with respect to some reference basis can be converted to entanglement via incoherent operations. Our work provides a clear quantitative and operational connection between coherence and entanglement based on two kinds of concurrence. This new coherence measure, coherence concurrence, may also be beneficial to the study of quantum coherence.
Berry phase in entangled systems
Bertlmann, R.A.; Hasegawa, Y.; Hiesmayr, B.C.; Durstberger, C.
2005-01-01
Full text: The influence of the geometric phase, in particular the Berry phase, on an entangled spin-1/2 system is studied. We discuss in detail the case, where the geometric phase is generated only by one part of the Hilbert space. We are able to cancel the effects of the dynamical phase by using the 'spin-echo' method. We analyze how the Berry phase affects the Bell angles and the maximal violation of a CHSH-Bell inequality. Furthermore, we suggest an experimental realization of our setup within neutron interferometry. It is possible to create entanglement between different degrees of freedom (spin and spatial degree of freedom) for a single neutron. The influence of the geometrical phase on the entangled neutron state is tested experimentally which is work in progress. (author)
Quantum Entanglements: Selected Papers
Giannetto, E
2005-01-01
This book is a sort of tribute to Rob Clifton (1964-2002), Associate Professor of Philosophy and Associate Director of the Center for Philosophy of Science at the University of Pittsburgh, philosopher of physics and editor of the journal Studies in the History and Philosophy of Modern Physics, who tragically died of cancer. It contains fourteen papers by Clifton, for the most part written in collaboration with other authors (Jeffrey Bub (2), Sheldon Goldstein, Michael Dickson, Hans Halvorson (6), Adrian Kent (2)), published between 1995 and 2002. The choice of papers made by the editors is very impressive. They concern the foundations of quantum mechanics and quantum field theory. Among the issues discussed are the modal interpretations of quantum mechanics, the problems of hidden variables theories, non-locality, Bell's inequality, the Einstein-Podolsky-Rosen paradox, Lorentz invariance, de-coherence, non-contextuality, complementarity, entanglement and quantum information. A consequence of such investigations is that non-separability is a more complex issue than violation of Bell's inequality. Apart from the perspective one can follow-whether one agrees or not with Clifton-these papers are effective contributions to an understanding of the problems involved in the foundations of quantum mechanics. The most interesting parts, in my opinion, are related to the extension of the discussion of foundational problems to quantum field theory: on the algebraic approach, and on the twin concepts of particle and vacuum. Non-locality appears to be 'worse' in relativistic quantum field theory than in non-relativistic quantum mechanics. All the papers deal with relevant epistemological and even historical aspects of quantum mechanics interpretations, but all the issues are discussed from a technical, logical and mathematical approach. A complete bibliography of Clifton's papers is given at the end of the volume. (book review)
Entanglement evolution for quantum trajectories
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.
Bosonic behavior of entangled fermions
C. Tichy, Malte; Alexander Bouvrie, Peter; Mølmer, Klaus
2012-01-01
Two bound, entangled fermions form a composite boson, which can be treated as an elementary boson as long as the Pauli principle does not affect the behavior of many such composite bosons. The departure of ideal bosonic behavior is quantified by the normalization ratio of multi-composite-boson st......Two bound, entangled fermions form a composite boson, which can be treated as an elementary boson as long as the Pauli principle does not affect the behavior of many such composite bosons. The departure of ideal bosonic behavior is quantified by the normalization ratio of multi...
Deterministic chaos in entangled eigenstates
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
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
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
Quantum entanglement: theory and applications
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
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
Benchmarks and statistics of entanglement dynamics
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
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.)
Marletto, C; Vedral, V
2017-12-15
All existing quantum-gravity proposals are extremely hard to test in practice. Quantum effects in the gravitational field are exceptionally small, unlike those in the electromagnetic field. The fundamental reason is that the gravitational coupling constant is about 43 orders of magnitude smaller than the fine structure constant, which governs light-matter interactions. For example, detecting gravitons-the hypothetical quanta of the gravitational field predicted by certain quantum-gravity proposals-is deemed to be practically impossible. Here we adopt a radically different, quantum-information-theoretic approach to testing quantum gravity. We propose witnessing quantumlike features in the gravitational field, by probing it with two masses each in a superposition of two locations. First, we prove that any system (e.g., a field) mediating entanglement between two quantum systems must be quantum. This argument is general and does not rely on any specific dynamics. Then, we propose an experiment to detect the entanglement generated between two masses via gravitational interaction. By our argument, the degree of entanglement between the masses is a witness of the field quantization. This experiment does not require any quantum control over gravity. It is also closer to realization than detecting gravitons or detecting quantum gravitational vacuum fluctuations.
Role of initial coherence on entanglement dynamics of two qubit X states
V, Namitha C.; Satyanarayana, S. V. M.
2018-02-01
Bipartite entanglement is a necessary resource in most processes in quantum information science. Decoherence resulting from the interaction of the bipartite system with environment not only degrades the entanglement, but can result in abrupt disentanglement, known as entanglement sudden death (ESD). In some cases, a subsequent revival of entanglement is also possible. ESD is an undesirable feature for the state to be used as a resource in applications. In order to delay or avoid ESD, it is necessary to understand its origin. In this work we investigate the role of initial coherence on entanglement dynamics of a spatially separated two qubit system in a common vacuum reservoir with dipolar interaction. We construct two classes of X states, namely, states with one photon coherence (X 1) and states with two photon coherence (X 2). Considering them as initial states, we study entanglement dynamics under Markov approximation. We find for states in X 1, ESD time, revival time and time over which the state remains disentangled increase with increase in coherence. On the other hand for states in X 2, with increase in coherence ESD time increases, revival time remains same and time of disentanglement decreases. Thus, states with two photon coherence are better resources for applications since their entanglement is robust against decoherence compared to states with one photon coherence.
Transverse entanglement migration in Hilbert space
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
Dynamics and entanglement in spherically symmetric quantum gravity
Husain, Viqar; Terno, Daniel R.
2010-01-01
The gravity-scalar field system in spherical symmetry provides a natural setting for exploring gravitational collapse and its aftermath in quantum gravity. In a canonical approach, we give constructions of the Hamiltonian operator, and of semiclassical states peaked on constraint-free data. Such states provide explicit examples of physical states. We also show that matter-gravity entanglement is an inherent feature of physical states, whether or not there is a black hole.
CHILD WITNESSES AND THE CONFRONTATION CLAUSE.
Lyon, Thomas D; Dente, Julia A
2012-01-01
After the Supreme Court's ruling in Crawford v. Washington that a criminal defendant's right to confront the witnesses against him is violated by the admission of testimonial hearsay that has not been cross-examined, lower courts have overturned convictions in which hearsay from children was admitted after child witnesses were either unwilling or unable to testify. A review of social scientific evidence regarding the dynamics of child sexual abuse suggests a means for facilitating the fair receipt of children's evidence. Courts should hold that defendants have forfeited their confrontation rights if they exploited a child's vulnerabilities such that they could reasonably anticipate that the child would be unavailable to testify. Exploitation includes choosing victims on the basis of their filial dependency, their vulnerability, or their immaturity, as well as taking actions that create or accentuate those vulnerabilities.
Will "no blood" kill Jehovah Witnesses?
Chua, R; Tham, K F
2006-11-01
A 46-year-old Indonesian woman presented with signs and symptoms suggestive of an ovarian tumour and was advised to have surgery with exploratory laparotomy and removal of the mass. She agreed but refused blood transfusion any time in the course of her treatment or procedure, as she was a Jehovah Witness. As there was a high risk of intraoperative haemorrhage, steps were taken to reduce any consequent complications due to the surgery. The ethical conflict is between respecting patient autonomy and compromising standards of care, arising from the refusal of a standard therapy. The latest developments in the blood transfusion doctrine policy for the Jehovah Witnesses are also discussed in this case study.
Continuous variable polarization entanglement, experiment and analysis
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
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 in Gaussian matrix-product states
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
Classical-driving-assisted entanglement dynamics control
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.
Former astronaut Armstrong witnesses STS-83 launch
1997-01-01
Apollo l1 Commander Neil A. Armstrong and his wife, Carol, were among the many special NASA STS-83 launch guests who witnessed the liftoff of the Space Shuttle Columbia April 4 at the Banana Creek VIP Viewing Site at KSC. Columbia took off from Launch Pad 39A at 2:20:32 p.m. EST to begin the 16-day Microgravity Science Laboratory-1 (MSL-1) mission.
Communication via an entangled coherent quantum network
El Allati, A; Hassouni, Y [Faculte des Sciences, Departement de Physique, Laboratoire de Physique Theorique URAC 13, Universite Mohammed V Agdal Rabat, Avenue Ibn Battouta, B.P. 1014, Rabat (Morocco); Metwally, N, E-mail: Nmetwally@gmail.com [Mathematics Department, College of Science, University of Bahrain, PO Box 32038 (Bahrain)
2011-06-01
A quantum network (QN) is constructed via maximum entangled coherent states. The possibility of using this network to achieve quantum communication between multi-participants is investigated. We showed that the probability of the successful teleportation of an unknown state depends on the size of the used network. As the number of participants increases, the success probability does not depend on the intensity of the field. Implementing a quantum teleportation protocol via a noisy QN is discussed. The unknown state can be teleported perfectly with small values of the field intensity and larger values of the noise strength. The success probability of this suggested protocol increases abruptly for larger values of the noise strength and gradually for small values. For small-size QNs, the fidelity of the teleported state decreases smoothly, whereas it decreases abruptly for larger-sized networks.
Bessel-Gaussian entanglement; presentation
Mclaren, M
2013-07-01
Full Text Available mode Hologram Page 9 Violation of Bell’s inequality demonstrates entanglement © CSIR 2013 www.csir.co.za P ro b ab il it y Classical Quantum mechanical M. McLaren et al.,2012, Opt. Express, 20, 23589 Page 10 Comparison...
Basic logic and quantum entanglement
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
Basic logic and quantum entanglement
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.
Entangling light in high dimensions
Pors, Jan Bardeus
2011-01-01
Quantum entanglement is a fundamental trait of quantum mechanics that causes the information about the properties of two (or more) objects to be inextricably linked. When a measurement on one of the objects is performed, the state of the other object is immediately altered, even when these objects
Computational complexity in entanglement transformations
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
Displacement-enhanced entanglement distillation of single-mode-squeezed entangled states
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...
29 CFR 1921.18 - Witnesses and fees.
2010-07-01
... 29 Labor 7 2010-07-01 2010-07-01 false Witnesses and fees. 1921.18 Section 1921.18 Labor Regulations Relating to Labor (Continued) OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR... WORKERS' COMPENSATION ACT Miscellaneous § 1921.18 Witnesses and fees. Witnesses subpoenaed by any party...
32 CFR 724.213 - Attendance of witnesses.
2010-07-01
... BOARD Authority/Policy for Departmental Discharge Review § 724.213 Attendance of witnesses. Arrangement for attendance of witnesses testifying in behalf of the applicant at discharge review hearings is the... 32 National Defense 5 2010-07-01 2010-07-01 false Attendance of witnesses. 724.213 Section 724.213...
41 CFR 50-203.20 - Examination of witnesses.
2010-07-01
... 41 Public Contracts and Property Management 1 2010-07-01 2010-07-01 true Examination of witnesses... Under the Walsh-Healey Public Contracts Act § 50-203.20 Examination of witnesses. The administrative law... such examination or cross-examination of any witness as may be required for a full and true disclosure...
12 CFR 512.5 - Rights of witnesses.
2010-01-01
... has given. During the taking of the testimony of a witness, such attorney may make summary notes... before, during, and after the taking of his testimony and may briefly question the witness, on the record... permitted to be present during the taking of testimony of any other witness called in such proceeding...
Steady-state entanglement and thermalization of coupled qubits in two common heat baths
Hu, Li-Zhen; Man, Zhong-Xiao; Xia, Yun-Jie
2018-03-01
In this work, we study the steady-state entanglement and thermalization of two coupled qubits embedded in two common baths with different temperatures. The common bath is relevant when the two qubits are difficult to be isolated to only contact with their local baths. With the quantum master equation constructed in the eigenstate representation of the coupled qubits, we have demonstrated the variations of steady-state entanglement with respect to various parameters of the qubits' system in both equilibrium and nonequilibrium cases of the baths. The coupling strength and energy detuning of the qubits as well as the temperature gradient of the baths are found to be beneficial to the enhancement of the entanglement. We note a dark state of the qubits that is free from time-evolution and its initial population can greatly influence the steady-state entanglement. By virtues of effective temperatures, we also study the thermalization of the coupled qubits and their variations with energy detuning.
Recyclable amplification for single-photon entanglement from photon loss and decoherence
Zhou, Lan; Chen, Ling-Quan; Zhong, Wei; Sheng, Yu-Bo
2018-01-01
We put forward a highly efficient recyclable single-photon assisted amplification protocol, which can protect single-photon entanglement (SPE) from photon loss and decoherence. Making use of quantum nondemolition detection gates constructed with the help of cross-Kerr nonlinearity, our protocol has some attractive advantages. First, the parties can recover less-entangled SPE to be maximally entangled SPE, and reduce photon loss simultaneously. Second, if the protocol fails, the parties can repeat the protocol to reuse some discarded items, which can increase the success probability. Third, when the protocol is successful, they can similarly repeat the protocol to further increase the fidelity of the SPE. Thereby, our protocol provides a possible way to obtain high entanglement, high fidelity and high success probability simultaneously. In particular, our protocol shows higher success probability in the practical high photon loss channel. Based on the above features, our amplification protocol has potential for future application in long-distance quantum communication.
Volume-law scaling for the entanglement entropy in spin-1/2 chains
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.
Spatial entanglement patterns and Einstein-Podolsky-Rosen steering in Bose-Einstein condensates.
Fadel, Matteo; Zibold, Tilman; Décamps, Boris; Treutlein, Philipp
2018-04-27
Many-particle entanglement is a fundamental concept of quantum physics that still presents conceptual challenges. Although nonclassical states of atomic ensembles were used to enhance measurement precision in quantum metrology, the notion of entanglement in these systems was debated because the correlations among the indistinguishable atoms were witnessed by collective measurements only. Here, we use high-resolution imaging to directly measure the spin correlations between spatially separated parts of a spin-squeezed Bose-Einstein condensate. We observe entanglement that is strong enough for Einstein-Podolsky-Rosen steering: We can predict measurement outcomes for noncommuting observables in one spatial region on the basis of corresponding measurements in another region with an inferred uncertainty product below the Heisenberg uncertainty bound. This method could be exploited for entanglement-enhanced imaging of electromagnetic field distributions and quantum information tasks. Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.
Báez-León, Carmen; Moreno-Jiménez, Bernardo; Aguirre-Camacho, Aldo; Olmos, Ricardo
2016-12-01
The role played by witnesses of bullying in nursing settings remains little studied, despite their potential relevance in explaining the onset and development of bullying. The objective of this study was to develop a model to account for witnesses' intention to help and helping behaviour in response to bullying in a nursing setting. Three hundred and thirty-seven witnesses completed self-report measures of variables predicting intention to help and helping behaviour. A full structural model was constructed using structural equation modelling. The intention to help victims was elicited by tension, group identity, support to peers' initiative to intervene and absence of fear of retaliation. However, engagement in helping behaviour was only predicted by the absence of fear of retaliation. This study shows that witnesses of bullying in nursing settings do not remain impassive, but their experienced discomfort and intention to help victims is not sufficient to predict helping behaviour. Fear of possible retaliation if intervening in favour of victims constitutes a crucial factor explaining witnesses' hesitation to help victims. Several implications for the implementation of policies directed at eradicating bullying in nursing settings are discussed. © 2016 John Wiley & Sons Ltd.
Entanglement dynamics in quantum information theory
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 dynamics in quantum information theory
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
Witness sample preparation for measuring antireflection coatings.
Willey, Ronald R
2014-02-01
Measurement of antireflection coating of witness samples from across the worldwide industry has been shown to have excess variability from a sampling taken for the OSA Topical Meeting on Optical Interference Coatings: Measurement Problem. Various sample preparation techniques have been discussed with their limitations, and a preferred technique is recommended with its justification, calibration procedures, and limitations. The common practice of grinding the second side to reduce its reflection is less than satisfactory. One recommended practice is to paint the polished second side, which reduces its reflection to almost zero. A method to evaluate the suitability of given paints is also described.
Characterizing quantum correlations. The genuine multiparticle negativity as entanglement monotone
Hofmann, Martin
2014-01-01
Multiparticle entanglement is a useful resource in quantum information processing. It is involved in some quantum key distribution protocols, quantum metrology and many other physical applications and phenomena and can be experimentally observed in various quantum systems. Having said this, its classification, detection and especially its quantification is quite challenging. To this day there exists no general mixed state measure for genuine multiparticle entanglement, which can be computed and analytically treated at the same time. In this thesis the analytical characterisation of genuine multiparticle entanglement in quantum systems using the computable genuine multiparticle negativity as entanglement measure is provided. Furthermore, the notion of stabiliser states, which are families of symmetric genuine multiparticle entangled states, is generalised and a useful method to exploit local symmetries to speed up the computation of the investigated entanglement measure is provided. In the first part, after a short introduction, the genuine multiparticle negativity, which is defined as an optimisation problem known as semidefinite programming problem, is investigated. It is discussed, how this entanglement measure can be characterised in an analytical way. First, it is shown that the genuine multiparticle negativity with an appropriate renormalisation can be considered as coming from a mixed convex roof construction. Using this result, its analytical value for generalised n-qubit Greenberger-Horne-Zeilingerdiagonal states and four-qubit cluster-diagonal states is determined. In the second part of this thesis, the genuine multiparticle negativity is used to study the scaling and spatial distribution of genuine multiparticle entanglement in three- and four-spin reduced states of a onedimensional spin model at its quantum phase transition. At the quantum phase transition of the one dimensional XY -model, which can be studied with analytic rigour, a logarithmic
Entanglement rules for holographic Fermi surfaces
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 between two spatially separated atomic modes
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 rules for holographic Fermi surfaces
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 criteria for microscopic-macroscopic systems
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.
Entangled photons and quantum communication
Yuan Zhensheng, E-mail: yuanzs@ustc.edu.c [Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Physikalisches Institut, Universitaet Heidelberg, Philosophenweg 12, 69120 Heidelberg (Germany); Bao Xiaohui [Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Physikalisches Institut, Universitaet Heidelberg, Philosophenweg 12, 69120 Heidelberg (Germany); Lu Chaoyang; Zhang Jun; Peng Chengzhi [Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Pan Jianwei, E-mail: pan@ustc.edu.c [Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Physikalisches Institut, Universitaet Heidelberg, Philosophenweg 12, 69120 Heidelberg (Germany)
2010-12-15
This article reviews the progress of quantum communication that utilizes photonic entanglement. We start with a survey of various methods for generating entangled photons, followed by an introduction of the theoretical principles and the experimental implementations of quantum key distribution. We then move on to a discussion of more involved quantum communication protocols including quantum dense coding, teleportation and quantum communication complexity. After that, we review the progress in free-space quantum communication, decoherence-free subspace, and quantum repeater protocols which are essential ingredients for long-distance quantum communication. Practical realizations of quantum repeaters, which require an interface between photons and quantum memories, are discussed briefly. Finally, we draw concluding remarks considering the technical challenges, and put forward an outlook on further developments of this field.
Quantum steganography using prior entanglement
Mihara, Takashi
2015-01-01
Steganography is the hiding of secret information within innocent-looking information (e.g., text, audio, image, video, etc.). A quantum version of steganography is a method based on quantum physics. In this paper, we propose quantum steganography by combining quantum error-correcting codes with prior entanglement. In many steganographic techniques, embedding secret messages in error-correcting codes may cause damage to them if the embedded part is corrupted. However, our proposed steganography can separately create secret messages and the content of cover messages. The intrinsic form of the cover message does not have to be modified for embedding secret messages. - Highlights: • Our steganography combines quantum error-correcting codes with prior entanglement. • Our steganography can separately create secret messages and the content of cover messages. • Errors in cover messages do not have affect the recovery of secret messages. • We embed a secret message in the Steane code as an example of our steganography
Quantum steganography using prior entanglement
Mihara, Takashi, E-mail: mihara@toyo.jp
2015-06-05
Steganography is the hiding of secret information within innocent-looking information (e.g., text, audio, image, video, etc.). A quantum version of steganography is a method based on quantum physics. In this paper, we propose quantum steganography by combining quantum error-correcting codes with prior entanglement. In many steganographic techniques, embedding secret messages in error-correcting codes may cause damage to them if the embedded part is corrupted. However, our proposed steganography can separately create secret messages and the content of cover messages. The intrinsic form of the cover message does not have to be modified for embedding secret messages. - Highlights: • Our steganography combines quantum error-correcting codes with prior entanglement. • Our steganography can separately create secret messages and the content of cover messages. • Errors in cover messages do not have affect the recovery of secret messages. • We embed a secret message in the Steane code as an example of our steganography.
Experimental quantum computing without entanglement.
Lanyon, B P; Barbieri, M; Almeida, M P; White, A G
2008-11-14
Deterministic quantum computation with one pure qubit (DQC1) is an efficient model of computation that uses highly mixed states. Unlike pure-state models, its power is not derived from the generation of a large amount of entanglement. Instead it has been proposed that other nonclassical correlations are responsible for the computational speedup, and that these can be captured by the quantum discord. In this Letter we implement DQC1 in an all-optical architecture, and experimentally observe the generated correlations. We find no entanglement, but large amounts of quantum discord-except in three cases where an efficient classical simulation is always possible. Our results show that even fully separable, highly mixed, states can contain intrinsically quantum mechanical correlations and that these could offer a valuable resource for quantum information technologies.
Entangled photons and quantum communication
Yuan Zhensheng; Bao Xiaohui; Lu Chaoyang; Zhang Jun; Peng Chengzhi; Pan Jianwei
2010-01-01
This article reviews the progress of quantum communication that utilizes photonic entanglement. We start with a survey of various methods for generating entangled photons, followed by an introduction of the theoretical principles and the experimental implementations of quantum key distribution. We then move on to a discussion of more involved quantum communication protocols including quantum dense coding, teleportation and quantum communication complexity. After that, we review the progress in free-space quantum communication, decoherence-free subspace, and quantum repeater protocols which are essential ingredients for long-distance quantum communication. Practical realizations of quantum repeaters, which require an interface between photons and quantum memories, are discussed briefly. Finally, we draw concluding remarks considering the technical challenges, and put forward an outlook on further developments of this field.
Quantum entanglement at negative temperature
Furman, G B; Meerovich, V M; Sokolovsky, V L
2013-01-01
An isolated spin system that is in internal thermodynamic equilibrium and that has an upper limit to its allowed energy states can possess a negative temperature. We calculate the thermodynamic characteristics and the concurrence in this system over the entire range of positive and negative temperatures. Our calculation was performed for different real structures, which can be used in experiments. It is found that the temperature dependence of the concurrence is substantially asymmetrical similarly to other thermodynamic characteristics. At a negative temperature the maximum concurrence and the absolute temperature of the entanglement appearance are significantly larger than those at a positive temperature. The concurrence can be characterized by two dimensionless parameters: the ratio between the Zeeman and dipolar energies and the ratio of the thermal and dipolar energies. It was shown that for all considered structures the dimensionless temperatures of the transition between entanglement and separability of the first and second spins are independent of spin structure and the number of spins. (paper)
Increasing Entanglement between Gaussian States by Coherent Photon Subtraction
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, non-Markovianity, and causal non-separability
Milz, Simon; Pollock, Felix A.; Le, Thao P.; Chiribella, Giulio; Modi, Kavan
2018-03-01
Quantum mechanics, in principle, allows for processes with indefinite causal order. However, most of these causal anomalies have not yet been detected experimentally. We show that every such process can be simulated experimentally by means of non-Markovian dynamics with a measurement on additional degrees of freedom. In detail, we provide an explicit construction to implement arbitrary a causal processes. Furthermore, we give necessary and sufficient conditions for open system dynamics with measurement to yield processes that respect causality locally, and find that tripartite entanglement and nonlocal unitary transformations are crucial requirements for the simulation of causally indefinite processes. These results show a direct connection between three counter-intuitive concepts: entanglement, non-Markovianity, and causal non-separability.
Holographic entanglement entropy for hollow cones and banana shaped regions
Dorn, Harald [Institut für Physik und IRIS Adlershof, Humboldt-Universität zu Berlin,Zum Großen Windkanal 6, D-12489 Berlin (Germany)
2016-06-09
We consider banana shaped regions as examples of compact regions, whose boundary has two conical singularities. Their regularised holographic entropy is calculated with all divergent as well as finite terms. The coefficient of the squared logarithmic divergence, also in such a case with internally curved boundary, agrees with that calculated in the literature for infinite circular cones with their internally flat boundary. For the otherwise conformally invariant coefficient of the ordinary logarithmic divergence an anomaly under exceptional conformal transformations is observed. The construction of minimal submanifolds, needed for the entanglement entropy of cones, requires fine-tuning of Cauchy data. Perturbations of such fine-tuning leads to solutions relevant for hollow cones. The divergent parts for the entanglement entropy of hollow cones are calculated. Increasing the difference between the opening angles of their outer and inner boundary, one finds a transition between connected solutions for small differences to disconnected solutions for larger ones.
Rigorous Free-Fermion Entanglement Renormalization from Wavelet Theory
Jutho Haegeman
2018-01-01
Full Text Available We construct entanglement renormalization schemes that provably approximate the ground states of noninteracting-fermion nearest-neighbor hopping Hamiltonians on the one-dimensional discrete line and the two-dimensional square lattice. These schemes give hierarchical quantum circuits that build up the states from unentangled degrees of freedom. The circuits are based on pairs of discrete wavelet transforms, which are approximately related by a “half-shift”: translation by half a unit cell. The presence of the Fermi surface in the two-dimensional model requires a special kind of circuit architecture to properly capture the entanglement in the ground state. We show how the error in the approximation can be controlled without ever performing a variational optimization.
Quantify entanglement by concurrence hierarchy
Fan, Heng; Matsumoto, Keiji; Imai, Hiroshi
2002-01-01
We define the concurrence hierarchy as d-1 independent invariants under local unitary transformations in d-level quantum system. The first one is the original concurrence defined by Wootters et al in 2-level quantum system and generalized to d-level pure quantum states case. We propose to use this concurrence hierarchy as measurement of entanglement. This measurement does not increase under local quantum operations and classical communication.
Entanglement and inhibited quantum evolution
Toschek, P E; Balzer, Chr; Hannemann, Th; Wunderlich, Ch; Neuhauser, W
2003-01-01
The evolution of a quantum system is impeded by the system's state being observed. A test on an ensemble neither proves the causal nexus nor discloses the nature of the inhibition. Two recent experiments that make use of sequential optical or microwave-optical double resonance on an individual trapped ion disprove a dynamical effect of back action by meter or environment. They rather indicate the ionic states involved in the evolution being entangled with the potentially recorded bivalued scattered-light signal
Spin entanglement, decoherence and Bohm's EPR paradox
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...
Gaussian maximally multipartite-entangled 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
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.
Variation of entanglement entropy in scattering process
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.
Hybrid Long-Distance Entanglement Distribution Protocol
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....
Controllable entanglement sudden birth of Heisenberg spins
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)
Experimental generation of complex noisy photonic entanglement
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)
Quantum dialogue using non-maximally entangled states based on entanglement swapping
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
Time evolution of the Wigner function in the entangled-state representation
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
Entanglement dynamics in random media
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.
Fidelity Witnesses for Fermionic Quantum Simulations
Gluza, M.; Kliesch, M.; Eisert, J.; Aolita, L.
2018-05-01
The experimental interest and developments in quantum spin-1 /2 chains has increased uninterruptedly over the past decade. In many instances, the target quantum simulation belongs to the broader class of noninteracting fermionic models, constituting an important benchmark. In spite of this class being analytically efficiently tractable, no direct certification tool has yet been reported for it. In fact, in experiments, certification has almost exclusively relied on notions of quantum state tomography scaling very unfavorably with the system size. Here, we develop experimentally friendly fidelity witnesses for all pure fermionic Gaussian target states. Their expectation value yields a tight lower bound to the fidelity and can be measured efficiently. We derive witnesses in full generality in the Majorana-fermion representation and apply them to experimentally relevant spin-1 /2 chains. Among others, we show how to efficiently certify strongly out-of-equilibrium dynamics in critical Ising chains. At the heart of the measurement scheme is a variant of importance sampling specially tailored to overlaps between covariance matrices. The method is shown to be robust against finite experimental-state infidelities.
Entanglement Swapping in the Presence of White and Color Noise
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.
Entanglement property in matrix product spin systems
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)
Quantum communication using a multiqubit entangled channel
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.
Entanglement polygon inequality in qubit systems
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 Equilibrium and the Einstein Equation.
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.
On Witnessed Models in Fuzzy Logic III - Witnessed Gödel Logics
Hájek, Petr
2010-01-01
Roč. 56, č. 2 (2010), s. 171-174 ISSN 0942-5616 R&D Projects: GA MŠk(CZ) 1M0545 Institutional research plan: CEZ:AV0Z10300504 Keywords : mathematical fuzzy logic * Gödel logic * witnessed models * arithmetical complexity Subject RIV: BA - General Mathematics Impact factor: 0.361, year: 2010
Two-Hierarchy Entanglement Swapping for a Linear Optical Quantum Repeater.
Xu, Ping; Yong, Hai-Lin; Chen, Luo-Kan; Liu, Chang; Xiang, Tong; Yao, Xing-Can; Lu, He; Li, Zheng-Da; Liu, Nai-Le; Li, Li; Yang, Tao; Peng, Cheng-Zhi; Zhao, Bo; Chen, Yu-Ao; Pan, Jian-Wei
2017-10-27
Quantum repeaters play a significant role in achieving long-distance quantum communication. In the past decades, tremendous effort has been devoted towards constructing a quantum repeater. As one of the crucial elements, entanglement has been created in different memory systems via entanglement swapping. The realization of j-hierarchy entanglement swapping, i.e., connecting quantum memory and further extending the communication distance, is important for implementing a practical quantum repeater. Here, we report the first demonstration of a fault-tolerant two-hierarchy entanglement swapping with linear optics using parametric down-conversion sources. In the experiment, the dominant or most probable noise terms in the one-hierarchy entanglement swapping, which is on the same order of magnitude as the desired state and prevents further entanglement connections, are automatically washed out by a proper design of the detection setting, and the communication distance can be extended. Given suitable quantum memory, our techniques can be directly applied to implementing an atomic ensemble based quantum repeater, and are of significant importance in the scalable quantum information processing.
Two-Hierarchy Entanglement Swapping for a Linear Optical Quantum Repeater
Xu, Ping; Yong, Hai-Lin; Chen, Luo-Kan; Liu, Chang; Xiang, Tong; Yao, Xing-Can; Lu, He; Li, Zheng-Da; Liu, Nai-Le; Li, Li; Yang, Tao; Peng, Cheng-Zhi; Zhao, Bo; Chen, Yu-Ao; Pan, Jian-Wei
2017-10-01
Quantum repeaters play a significant role in achieving long-distance quantum communication. In the past decades, tremendous effort has been devoted towards constructing a quantum repeater. As one of the crucial elements, entanglement has been created in different memory systems via entanglement swapping. The realization of j -hierarchy entanglement swapping, i.e., connecting quantum memory and further extending the communication distance, is important for implementing a practical quantum repeater. Here, we report the first demonstration of a fault-tolerant two-hierarchy entanglement swapping with linear optics using parametric down-conversion sources. In the experiment, the dominant or most probable noise terms in the one-hierarchy entanglement swapping, which is on the same order of magnitude as the desired state and prevents further entanglement connections, are automatically washed out by a proper design of the detection setting, and the communication distance can be extended. Given suitable quantum memory, our techniques can be directly applied to implementing an atomic ensemble based quantum repeater, and are of significant importance in the scalable quantum information processing.
On entanglement spreading from holography
Mezei, Márk [Princeton Center for Theoretical Science, Princeton University,Princeton, NJ 08544 (United States)
2017-05-11
A global quench is an interesting setting where we can study thermalization of subsystems in a pure state. We investigate entanglement entropy (EE) growth in global quenches in holographic field theories and relate some of its aspects to quantities characterizing chaos. More specifically we obtain four key results: We prove holographic bounds on the entanglement velocity v{sub E} and the butterfly effect speed v{sub B} that arises in the study of chaos. We obtain the EE as a function of time for large spherical entangling surfaces analytically. We show that the EE is insensitive to the details of the initial state or quenchÂ protocol. In a thermofield double state we determine analytically the two-sided mutual information between two large concentric spheres separated in time. We derive a bound on the rate of growth of EE for arbitrary shapes, and develop an expansion for EE at early times. In a companion paper https://arxiv.org/abs/1608.05101, these results are put in the broader context of EE growth in chaotic systems: we relate EE growth to the chaotic spreading of operators, derive bounds on EE at a given time, and compare the holographic results to spin chain numerics and toy models. In this paper, we perform holographic calculations that provide the basis of arguments presented in that paper. We prove holographic bounds on the entanglement velocity v{sub E} and the butterfly effect speed v{sub B} that arises in the study of chaos. We obtain the EE as a function of time for large spherical entangling surfaces analytically. We show that the EE is insensitive to the details of the initial state or quenchÂ protocol. In a thermofield double state we determine analytically the two-sided mutual information between two large concentric spheres separated in time. We derive a bound on the rate of growth of EE for arbitrary shapes, and develop an expansion for EE at early times.
Li, Rita Yi Man
2013-01-01
A close-to-ideal blend of suburb and city, speedy construction of towers of Babylon, the sparkling proportion of glass and steel buildings’ facade at night showcase the wisdom of humans. They also witness the footsteps, sweats and tears of architects and engineers. Unfortunately, these signatures of human civilizations are swathed in towering figures of construction accidents. Fretting about these on sites, different countries adopt different measures on sites. This book firstly sketches the construction accidents on sites, followed by a review on safety measures in some of the developing countries such as Bermuda, Egypt, Kuwait and China; as well as developed countries, for example, the United States, France and Singapore. It also highlights the enormous compensation costs with the courts’ experiences in the United Kingdom and Hong Kong.
Arm retraction dynamics of entangled star polymers: A forward flux sampling method study
Zhu, Jian; Likhtman, Alexei E.; Wang, Zuowei
2017-07-01
The study of dynamics and rheology of well-entangled branched polymers remains a challenge for computer simulations due to the exponentially growing terminal relaxation times of these polymers with increasing molecular weights. We present an efficient simulation algorithm for studying the arm retraction dynamics of entangled star polymers by combining the coarse-grained slip-spring (SS) model with the forward flux sampling (FFS) method. This algorithm is first applied to simulate symmetric star polymers in the absence of constraint release (CR). The reaction coordinate for the FFS method is determined by finding good agreement of the simulation results on the terminal relaxation times of mildly entangled stars with those obtained from direct shooting SS model simulations with the relative difference between them less than 5%. The FFS simulations are then carried out for strongly entangled stars with arm lengths up to 16 entanglements that are far beyond the accessibility of brute force simulations in the non-CR condition. Apart from the terminal relaxation times, the same method can also be applied to generate the relaxation spectra of all entanglements along the arms which are desired for the development of quantitative theories of entangled branched polymers. Furthermore, we propose a numerical route to construct the experimentally measurable relaxation correlation functions by effectively linking the data stored at each interface during the FFS runs. The obtained star arm end-to-end vector relaxation functions Φ (t ) and the stress relaxation function G(t) are found to be in reasonably good agreement with standard SS simulation results in the terminal regime. Finally, we demonstrate that this simulation method can be conveniently extended to study the arm-retraction problem in entangled star polymer melts with CR by modifying the definition of the reaction coordinate, while the computational efficiency will depend on the particular slip-spring or slip
Pakniat, R.; Soltani, M.; Tavassoly, M. K.
2018-03-01
Recently we studied the effect of photon addition in the initial coherent field on the entanglement swapping which causes some improvements in the process [Soltani et al., Int. J. Mod. Phys. B 31, 1750198 (2017)]. In this paper, we investigate the influence of multiphoton transitions in the atom-field interaction based on the cavity quantum electrodynamics on the entanglement swapping and show its considerable constructive effect on this process. The presented model consists of two two-level atoms namely A1 and A2 and two distinct cavity fields F1 and F2. Initially, the atoms are prepared in a maximally entangled state and the fields in the cavities are prepared in hybrid entangled state of number and coherent states, separately. Making the atom A2 to interact with the field F1 (via the generalized Jaynes-Cummings model which allows m-photon transitions between atomic levels in the emission and absorption processes) followed by their detection allows us to arrive at the entanglement swapping from the two atoms A1, A2 and the two fields F1, F2 to the atom-field A1-F2 system. Then, we pay our attention to the time evolution of success probability of detecting processes and fidelity. Also, to determine the amount of entanglement of the generated entangled state in the swapping process, the linear entropy is evaluated and the effect of parameter m concerning the multiphoton transitions on these quantities is investigated, numerically. It is observed that, by increasing the number of photons in the transition process, one may obtain considerable improvement in the relevant quantities of the entanglement swapping. In detail, the satisfactorily acceptable values 1 and 0.5 corresponding to success probability and fidelity are obtained for most of the times during observing of the above-mentioned procedure. We concluded that the presented formalism in this paper is much more advantageous than our presentation model in our earlier work mentioned above.
Feelings of children when witnessing parents' illness
Julia Wakiuchi
2016-12-01
Full Text Available This study aimed to learn the experiences of children who witness their parents' illness due to cancer. This is a descriptive, qualitative study, with six children between 10 and 12 years of age, children of cancer patients assisted by a support institution. The data were collected from July to August 2015, based on the guiding question: "How do you feel about your father/mother's illness?" From the analysis, two categories emerged: Recognizing the disease and the possibility of the parents 'death and, Growing as a child and living as an adult: the repercussions of parents with cancer in their children's lives, which reveal that children understand cancer and the possibility of death of their parents, being also affected by the disease. By experiencing the fears and repercussions of cancer, children need assistance by the family and health team during their parents' illness.
Two particle entanglement and its geometric duals
Wasay, Muhammad Abdul [University of Agriculture, Department of Physics, Faisalabad (Pakistan); Quaid-i-Azam University Campus, National Centre for Physics, Islamabad (Pakistan); Bashir, Asma [University of Agriculture, Department of Physics, Faisalabad (Pakistan)
2017-12-15
We show that for a system of two entangled particles, there is a dual description to the particle equations in terms of classical theory of conformally stretched spacetime. We also connect these entangled particle equations with Finsler geometry. We show that this duality translates strongly coupled quantum equations in the pilot-wave limit to weakly coupled geometric equations. (orig.)
Generating stationary entangled states in superconducting qubits
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.
Rank-dependant factorization of entanglement evolution
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.
On entanglement in neutrino mixing and oscillations
Blasone, Massimo; Dell'Anno, Fabio; De Siena, Silvio; Illuminati, Fabrizio
2010-01-01
We report on recent results about entanglement in the context of particle mixing and oscillations. We study in detail single-particle entanglement arising in two-flavor neutrino mixing. The analysis is performed first in the context of Quantum Mechanics, and then for the case of Quantum Field Theory.
On entanglement in neutrino mixing and oscillations
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)
2010-06-01
We report on recent results about entanglement in the context of particle mixing and oscillations. We study in detail single-particle entanglement arising in two-flavor neutrino mixing. The analysis is performed first in the context of Quantum Mechanics, and then for the case of Quantum Field Theory.
Two particle entanglement and its geometric duals
Wasay, Muhammad Abdul; Bashir, Asma
2017-01-01
We show that for a system of two entangled particles, there is a dual description to the particle equations in terms of classical theory of conformally stretched spacetime. We also connect these entangled particle equations with Finsler geometry. We show that this duality translates strongly coupled quantum equations in the pilot-wave limit to weakly coupled geometric equations. (orig.)
Entangled spins and ghost-spins
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.
Entangled Light Emission From a Diode
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.
Continuous variable tripartite entanglement from twin nonlinearities
Olsen, M K; Bradley, A S
2006-01-01
In this work, we analyse and compare the continuous variable tripartite entanglement available from the use of two concurrent or cascaded χ (2) nonlinearities. We examine both idealized travelling-wave models and more experimentally realistic intracavity models, showing that tripartite entangled outputs are readily producible. These may be a useful resource for applications such as quantum cryptography and teleportation
Quantum entanglement in polarization and space
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
Quantum entanglement and quantum computational algorithms
We demonstrate that the one- and the two-bit Deutsch-Jozsa algorithm does not require entanglement and can be mapped onto a classical optical scheme. It is only for three and more input bits that the DJ algorithm requires the implementation of entangling transformations and in these cases it is impossible to implement ...
Multiparticle entanglement under the influence of decoherence
Gühne, O.; Bodoky, F.; Blaauboer, M.
2008-01-01
We present a method to determine the decay of multiparticle quantum correlations as quantified by the geometric measure of entanglement under the influence of decoherence. With this, we compare the robustness of entanglement in Greenberger-Horne-Zeilinger (GHZ), cluster, W, and Dicke states of four
Holographic entanglement entropy in Lovelock gravities
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
Nonlocal hyperconcentration on entangled photons using photonic module system
Cao, Cong; Wang, Tie-Jun; Mi, Si-Chen [School of Science, Beijing University of Posts and Telecommunications, Beijing 100876 (China); State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Zhang, Ru [School of Science, Beijing University of Posts and Telecommunications, Beijing 100876 (China); State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876 (China); School of Ethnic Minority Education, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Wang, Chuan, E-mail: wangchuan@bupt.edu.cn [School of Science, Beijing University of Posts and Telecommunications, Beijing 100876 (China); State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876 (China)
2016-06-15
Entanglement distribution will inevitably be affected by the channel and environment noise. Thus distillation of maximal entanglement nonlocally becomes a crucial goal in quantum information. Here we illustrate that maximal hyperentanglement on nonlocal photons could be distilled using the photonic module and cavity quantum electrodynamics, where the photons are simultaneously entangled in polarization and spatial-mode degrees of freedom. The construction of the photonic module in a photonic band-gap structure is presented, and the operation of the module is utilized to implement the photonic nondestructive parity checks on the two degrees of freedom. We first propose a hyperconcentration protocol using two identical partially hyperentangled initial states with unknown coefficients to distill a maximally hyperentangled state probabilistically, and further propose a protocol by the assistance of an ancillary single photon prepared according to the known coefficients of the initial state. In the two protocols, the total success probability can be improved greatly by introducing the iteration mechanism, and only one of the remote parties is required to perform the parity checks in each round of iteration. Estimates on the system requirements and recent experimental results indicate that our proposal is realizable with existing or near-further technologies.
Nonlocal hyperconcentration on entangled photons using photonic module system
Cao, Cong; Wang, Tie-Jun; Mi, Si-Chen; Zhang, Ru; Wang, Chuan
2016-01-01
Entanglement distribution will inevitably be affected by the channel and environment noise. Thus distillation of maximal entanglement nonlocally becomes a crucial goal in quantum information. Here we illustrate that maximal hyperentanglement on nonlocal photons could be distilled using the photonic module and cavity quantum electrodynamics, where the photons are simultaneously entangled in polarization and spatial-mode degrees of freedom. The construction of the photonic module in a photonic band-gap structure is presented, and the operation of the module is utilized to implement the photonic nondestructive parity checks on the two degrees of freedom. We first propose a hyperconcentration protocol using two identical partially hyperentangled initial states with unknown coefficients to distill a maximally hyperentangled state probabilistically, and further propose a protocol by the assistance of an ancillary single photon prepared according to the known coefficients of the initial state. In the two protocols, the total success probability can be improved greatly by introducing the iteration mechanism, and only one of the remote parties is required to perform the parity checks in each round of iteration. Estimates on the system requirements and recent experimental results indicate that our proposal is realizable with existing or near-further technologies.
Crossover to entangled dynamics in polymer solutions and melts
Schweizer, K.S.; Szamel, G.
1995-01-01
A statistical dynamical theory of the crossover from unentangled Rouse dynamics to entangled behavior is constructed for chain polymer solutions and melts. Both time and spatial crossovers in long chain fluids, and the degree of polymerization crossover for short polymers, are treated. The analysis is based on a microscopic theory of the perturbative dynamical corrections to Rouse theory arising from chain connectivity and intermolecular excluded volume forces. The dependence of crossover properties such as the plateau shear modulus and entanglement time and length scale on solution density, solvent quality, and chain statistical segment length are derived by combining the dynamical theory with equilibrium liquid state integral equation methods. Scaling relations are obtained which appear to be in general accord with most experiments on both solutions and melts. The physical origin of the predicted scaling behaviors is the fractional power law temporal decay of the entanglement friction memory function on intermediate time scales, and power law reduced density dependence of the equilibrium force correlations. The theory is also applied to compute the dependence of the chain normal mode relaxation times on polymer density and chain length. Favorable qualitative comparisons with recent neutron spin echo experiments are made. copyright 1995 American Institute of Physics
Entanglement verification with detection efficiency mismatch
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, Bell inequality and all that
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, Bell inequality and all that
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-Gradient Routing for Quantum Networks.
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.
Maximal Entanglement in High Energy Physics
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.
Multipartite entanglement detection with nonsymmetric probing
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 temperature with Gauss–Bonnet term
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.
Entanglement entropy in top-down models
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
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.
Quantum entanglement of high angular momenta.
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.
Real-time imaging of quantum entanglement.
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 fidelity of quantum memories
Surmacz, K.; Nunn, J.; Waldermann, F. C.; Wang, Z.; Walmsley, I. A.; Jaksch, D.
2006-01-01
We introduce a figure of merit for a quantum memory which measures the preservation of entanglement between a qubit stored in and retrieved from the memory and an auxiliary qubit. We consider a general quantum memory system consisting of a medium of two level absorbers, with the qubit to be stored encoded in a single photon. We derive an analytic expression for our figure of merit taking into account Gaussian fluctuations in the Hamiltonian parameters, which, for example, model inhomogeneous broadening and storage time dephasing. Finally we specialize to the case of an atomic quantum memory where fluctuations arise predominantly from Doppler broadening and motional dephasing
Entanglement entropy of excited states
Alba, Vincenzo; Fagotti, Maurizio; Calabrese, Pasquale
2009-01-01
We study the entanglement entropy of a block of contiguous spins in excited states of spin chains. We consider the XY model in a transverse field and the XXZ Heisenberg spin chain. For the latter, we developed a numerical application of the algebraic Bethe ansatz. We find two main classes of states with logarithmic and extensive behavior in the dimension of the block, characterized by the properties of excitations of the state. This behavior can be related to the locality properties of the Hamiltonian having a given state as the ground state. We also provide several details of the finite size scaling
Secret sharing via quantum entanglement
Hillery, M.; Buzek, V.
1999-01-01
Secret sharing is a procedure for splitting a message into several parts so that no single part is sufficient to read the message, but the entire set is. This procedure can be implemented using either GHZ states or two-particle entangled states. In the quantum case the presence of an eavesdropper will introduce errors so that her presence can be detected. We also discuss how quantum information can be split into parts so that the message can be reconstructed from a sufficiently large subset of the parts. (Authors)
Entanglement and inhibited quantum evolution
Toschek, P E; Balzer, Chr; Hannemann, Th; Wunderlich, Ch; Neuhauser, W [Universitaet Hamburg, Institut fuer Laser-Physik, Jungiusstrasse 9, D-20355 Hamburg (Germany)
2003-03-14
The evolution of a quantum system is impeded by the system's state being observed. A test on an ensemble neither proves the causal nexus nor discloses the nature of the inhibition. Two recent experiments that make use of sequential optical or microwave-optical double resonance on an individual trapped ion disprove a dynamical effect of back action by meter or environment. They rather indicate the ionic states involved in the evolution being entangled with the potentially recorded bivalued scattered-light signal.
Quantum Entanglement Growth under Random Unitary Dynamics
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.
Quantum key distribution with entangled photon sources
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
Quantum Entanglement Growth under Random Unitary Dynamics
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.
Gain maximization in a probabilistic entanglement protocol
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.
Speaking to the yet unknowing world: Hamlet, Horatio and the problem of imperfect witness.
Phillips, Christine
2010-12-01
Every day doctors bear witness to others about the experiences, needs and feelings of their patients, drawing on what they have learnt from clinical consultations. This paper considers the medical task of bearing honourable and truthful witness through an examination of the role and actions of Horatio in Hamlet. Horatio is simultaneously located among the background machinery of the play, separate from the lives of the protagonists, and in the foreground, where his authoritative witness is repeatedly called upon by the play's characters. Horatio is invited to watch an unfolding disaster, his warnings are not heard, and at its conclusion he stands apart from the drama to give its account. The tensions between engagement and observation, and between partial and impartial accounting echo those faced by doctors in everyday clinical practice. The act of bearing witness, Shakespeare suggests, even for those who are tasked with being objective, is necessarily imperfect, and not dispassionate. Those people, including doctors, who are expected to construct authoritative accounts of the motives and actions of others may find in Hamlet a small lesson on the need to approach their summary narratives about others more humbly, aware of the narrowness and partiality of their perspective.
From expert witness to defendant: abolition of expert witness protection and its implications.
Mendelson, Danuta
2012-12-01
In Jones v Kaney [2011] 2 AC 398, the United Kingdom Supreme Court held that in England and Wales (but not in Scotland), clients can sue expert witnesses in negligence and/or contract for work performed under their retainer, whether in civil or criminal trials. The duties of expert witnesses in England are regulated by the Civil Procedure Rules and Protocols; the former also regulate the conduct of cases involving expert opinions. The legal context that led to the litigation is examined in the light of these rules, in particular, the nature of the allegations against Dr Kaney, a psychologist retained to provide psychiatric opinion. Jones v Kaney, as a decision of the United Kingdom Supreme Court, is not a binding precedent in Australia. However, unlike statutory enactments, common law judgments are retrospective in their operation, which means that health care practitioners who follow a generally accepted practice today may still be sued for damages by their patients or clients in the future. By definition, the future, including the refusal by the Australian High Court to follow Kaney's abolition of expert witnesses' immunity from suit for breach of duty to their clients, cannot be predicted with certainty. Consequently, health care practitioners in Australia and other countries should be aware of the case, its jurisprudential and practical ramifications.
Entanglement fidelity of the standard quantum teleportation channel
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.
Probabilistic Teleportation of a Four-Particle Entangled State
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.
Su, Zhaofeng; Guan, Ji; Li, Lvzhou
2018-01-01
Quantum entanglement is an indispensable resource for many significant quantum information processing tasks. However, in practice, it is difficult to distribute quantum entanglement over a long distance, due to the absorption and noise in quantum channels. A solution to this challenge is a quantum repeater, which can extend the distance of entanglement distribution. In this scheme, the time consumption of classical communication and local operations takes an important place with respect to time efficiency. Motivated by this observation, we consider a basic quantum repeater scheme that focuses on not only the optimal rate of entanglement concentration but also the complexity of local operations and classical communication. First, we consider the case where two different two-qubit pure states are initially distributed in the scenario. We construct a protocol with the optimal entanglement-concentration rate and less consumption of local operations and classical communication. We also find a criterion for the projective measurements to achieve the optimal probability of creating a maximally entangled state between the two ends. Second, we consider the case in which two general pure states are prepared and general measurements are allowed. We get an upper bound on the probability for a successful measurement operation to produce a maximally entangled state without any further local operations.
Quantum entanglement of baby universes
Aganagic, Mina; Okuda, Takuya; Ooguri, Hirosi
2007-01-01
We study quantum entanglements of baby universes which appear in non-perturbative corrections to the OSV formula for the entropy of extremal black holes in type IIA string theory compactified on the local Calabi-Yau manifold defined as a rank 2 vector bundle over an arbitrary genus G Riemann surface. This generalizes the result for G=1 in hep-th/0504221. Non-perturbative terms can be organized into a sum over contributions from baby universes, and the total wave-function is their coherent superposition in the third quantized Hilbert space. We find that half of the universes preserve one set of supercharges while the other half preserve a different set, making the total universe stable but non-BPS. The parent universe generates baby universes by brane/anti-brane pair creation, and baby universes are correlated by conservation of non-normalizable D-brane charges under the process. There are no other source of entanglement of baby universes, and all possible states are superposed with the equal weight
Quantum entanglement of baby universes
Essman, Eric P.; Aganagic, Mina; Okuda, Takuya; Ooguri, Hirosi
2006-01-01
We study quantum entanglements of baby universes which appear in non-perturbative corrections to the OSV formula for the entropy of extremal black holes in type IIA string theory compactified on the local Calabi-Yau manifold defined as a rank 2 vector bundle over an arbitrary genus G Riemann surface. This generalizes the result for G=1 in hep-th/0504221. Non-perturbative terms can be organized into a sum over contributions from baby universes, and the total wave-function is their coherent superposition in the third quantized Hilbert space. We find that half of the universes preserve one set of supercharges while the other half preserve a different set, making the total universe stable but non-BPS. The parent universe generates baby universes by brane/anti-brane pair creation, and baby universes are correlated by conservation of non-normalizable D-brane charges under the process. There are no other source of entanglement of baby universes, and all possible states are superposed with the equal weight
Linearity of holographic entanglement entropy
Almheiri, Ahmed [Stanford Institute for Theoretical Physics, Department of Physics,Stanford University, Stanford, CA 94305 (United States); Dong, Xi [School of Natural Sciences, Institute for Advanced Study,Princeton, NJ 08540 (United States); Swingle, Brian [Stanford Institute for Theoretical Physics, Department of Physics,Stanford University, Stanford, CA 94305 (United States)
2017-02-14
We consider the question of whether the leading contribution to the entanglement entropy in holographic CFTs is truly given by the expectation value of a linear operator as is suggested by the Ryu-Takayanagi formula. We investigate this property by computing the entanglement entropy, via the replica trick, in states dual to superpositions of macroscopically distinct geometries and find it consistent with evaluating the expectation value of the area operator within such states. However, we find that this fails once the number of semi-classical states in the superposition grows exponentially in the central charge of the CFT. Moreover, in certain such scenarios we find that the choice of surface on which to evaluate the area operator depends on the density matrix of the entire CFT. This nonlinearity is enforced in the bulk via the homology prescription of Ryu-Takayanagi. We thus conclude that the homology constraint is not a linear property in the CFT. We also discuss the existence of ‘entropy operators’ in general systems with a large number of degrees of freedom.
Gribling, Sander; de Laat, David; Laurent, Monique
2017-01-01
In this paper we study bipartite quantum correlations using techniques from tracial polynomial optimization. We construct a hierarchy of semidefinite programming lower bounds on the minimal entanglement dimension of a bipartite correlation. This hierarchy converges to a new parameter: the minimal
Resonating-valence-bond superconductors with fermionic projected entangled pair states
Poilblanc, D.; Corboz, P.; Schuch, N.; Cirac, J.I.
2014-01-01
We construct a family of simple fermionic projected entangled pair states (fPEPS) on the square lattice with bond dimension D=3 which are exactly hole-doped resonating valence bond (RVB) wave functions with short-range singlet bonds. Under doping the insulating RVB spin liquid evolves immediately
The Fermionic Projector, Entanglement, and the Collapse of the Wave Function
Finster, Felix
2010-01-01
After a brief introduction to the fermionic projector approach, we review how entanglement and second quantized bosonic and fermionic fields can be described in this framework. The constructions are discussed with regard to decoherence phenomena and the measurement problem. We propose a mechanism leading to the collapse of the wave function in the quantum mechanical measurement process.
The Fermionic Projector, entanglement and the collapse of the wave function
Finster, Felix, E-mail: Felix.Finster@mathematik.uni-r.de [Fakultaet fuer Mathematik, Universituet Regensburg, 93040 Regensburg (Germany)
2011-07-08
After a brief introduction to the fermionic projector approach, we review how entanglement and second quantized bosonic and fermionic fields can be described in this framework. The constructions are discussed with regard to decoherence phenomena and the measurement problem. We propose a mechanism leading to the collapse of the wave function in the quantum mechanical measurement process.
The Fermionic Projector, entanglement and the collapse of the wave function
Finster, Felix
2011-01-01
After a brief introduction to the fermionic projector approach, we review how entanglement and second quantized bosonic and fermionic fields can be described in this framework. The constructions are discussed with regard to decoherence phenomena and the measurement problem. We propose a mechanism leading to the collapse of the wave function in the quantum mechanical measurement process.
The Fermionic Projector, entanglement and the collapse of the wave function
Finster, Felix
2011-07-01
After a brief introduction to the fermionic projector approach, we review how entanglement and second quantized bosonic and fermionic fields can be described in this framework. The constructions are discussed with regard to decoherence phenomena and the measurement problem. We propose a mechanism leading to the collapse of the wave function in the quantum mechanical measurement process.
Cloning the entanglement of a pair of quantum bits
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
Analyzing Counsel/Witness Discourse in Nnewi, Anambra State ...
This paper analyzed counsel/witness discourse using the High Court in. Nnewi Municipal Council. Specifically, it described the structure and organization of counsel/witness discourse in the courtroom context highlighting some discourse features inherent in them, and observed the communication strategies and motivation ...
12 CFR 308.148 - Rights of witnesses.
2010-01-01
... meets the requirements of § 308.6 of the Uniform Rules. That counsel may be present and may: (1) Advise... conflict of interest arising out of an attorney's or law firm's representation of multiple witnesses, the... the Uniform Rules; and (e) Witness fees shall be paid in accordance with § 308.14 of the Uniform Rules...
Metallic witness packs for behind-armour debris characterization
Verolme, J.L.; Szymczak, M.; Broos, J.P.F.
1999-01-01
For the experimental characterization of behind-armour debris so-called metallic witness packs can be used. A metallic witness pack consists of an array of metallic plates interspaced by polystyrene foam sheets. To quantify the fragment mass and velocity from the corresponding hole area and position
Medicine, religion and faith: issues in Jehovah's Witnesses and ...
Background: Major surgical treatment in Jehovah's Witnesses (JW) presents complex ethical and legal issues to the physician. The Jehovah's Witness is willing to accept all medical treatment except blood transfusion; and so, the physician is often confronted with a difficult task especially in emergency settings and among ...
Residual entanglement and sudden death: A direct connection
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.
Breakdown of the equal area law for holographic entanglement entropy
McCarthy, Fiona; Kubizňák, David; Mann, Robert B.
2017-11-01
We investigate a holographic version of Maxwell's equal area law analogous to that for the phase transition in the black hole temperature/black hole entropy plane of a charged AdS black hole. We consider proposed area laws for both the black hole temperature/holographic entanglement entropy plane and the black hole temperature/2- point correlation function plane. Despite recent claims to the contrary, we demonstrate numerically that neither proposal is valid. We argue that there is no physical reason to expect such a construction in these planes.
Entanglement between smeared field operators in the Klein-Gordon vacuum
Zych, Magdalena; Costa, Fabio; Kofler, Johannes; Brukner, Caslav
2010-01-01
Quantum field theory is the application of quantum physics to fields. It provides a theoretical framework widely used in particle physics and condensed matter physics. One of the most distinct features of quantum physics with respect to classical physics is entanglement or the existence of strong correlations between subsystems that can even be spacelike separated. In quantum fields, observables restricted to a region of space define a subsystem. While there are proofs on the existence of local observables that would allow a violation of Bell's inequalities in the vacuum states of quantum fields as well as some explicit but technically demanding schemes requiring an extreme fine-tuning of the interaction between the fields and detectors, an experimentally accessible entanglement witness for quantum fields is still missing. Here we introduce smeared field operators which allow reducing the vacuum to a system of two effective bosonic modes. The introduction of such collective observables is motivated by the fact that no physical probe has access to fields in single spatial (mathematical) points but rather smeared over finite volumes. We first give explicit collective observables whose correlations reveal vacuum entanglement in the Klein-Gordon field. We then show that the critical distance between the two regions of space above which two effective bosonic modes become separable is of the order of the Compton wavelength of the particle corresponding to the massive Klein-Gordon field.
Cosmological perturbations in the entangled inflationary universe
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.
The geometry of entanglement and Grover's algorithm
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
Heralded entanglement of two remote atoms
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.
Moroder, Tobias
2009-01-01
In this thesis we address several different topics within the field of quantum information theory. These results can be classified to either enhance the applicability of certain conceptual ideas to be more suited for an actual experimental situation or to ease the analysis for further investigation of central problems. In detail, the present thesis contains the following achievements: We start our discussion with the question under which conditions a given set of expectation values is compatible with the first and second moments of the spin operators of a generic spin j state. We link this characterization of physical moments to the Bosesymmetric extension problem for a particular two qubit state that is completely determined by the given moments. Via this reformulation we can provide operational sub- and superset approximations in order to identify moments which are assured to be physical and others which are clearly incompatible with quantum mechanics. We show that this operational approximate solution becomes more accurate for increasing total spin numbers j and converges to the exact solution in the limiting case. Another part deals with the theoretical concept of entanglement witnesses. In particular, we concentrate how to improve the detection strength of a linear entanglement witness by nonlinear terms. We analyze two distinguished cases: Either we optimize the iteration method for a given target state or we try to improve the entanglement witness with respect to all entangled states equally. In the remaining parts we discuss different options in order to make already existing ideas more applicable for actual experiments, since most of the famous applications in quantum information theory have only been introduced on a very idealized level and hence are not directly valid for the real experiment. We investigate the theoretical concept of a squash model, that represents an elegant ''evaluation trick'' to directly apply for instance the security analysis of an
Moroder, Tobias
2009-07-31
In this thesis we address several different topics within the field of quantum information theory. These results can be classified to either enhance the applicability of certain conceptual ideas to be more suited for an actual experimental situation or to ease the analysis for further investigation of central problems. In detail, the present thesis contains the following achievements: We start our discussion with the question under which conditions a given set of expectation values is compatible with the first and second moments of the spin operators of a generic spin j state. We link this characterization of physical moments to the Bosesymmetric extension problem for a particular two qubit state that is completely determined by the given moments. Via this reformulation we can provide operational sub- and superset approximations in order to identify moments which are assured to be physical and others which are clearly incompatible with quantum mechanics. We show that this operational approximate solution becomes more accurate for increasing total spin numbers j and converges to the exact solution in the limiting case. Another part deals with the theoretical concept of entanglement witnesses. In particular, we concentrate how to improve the detection strength of a linear entanglement witness by nonlinear terms. We analyze two distinguished cases: Either we optimize the iteration method for a given target state or we try to improve the entanglement witness with respect to all entangled states equally. In the remaining parts we discuss different options in order to make already existing ideas more applicable for actual experiments, since most of the famous applications in quantum information theory have only been introduced on a very idealized level and hence are not directly valid for the real experiment. We investigate the theoretical concept of a squash model, that represents an elegant ''evaluation trick'' to directly apply for instance the
Developments in entanglement theory and applications to relevant physical systems
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.
Entanglement replication in driven dissipative many-body systems.
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.
Dynamics of pairwise entanglement between two Tavis-Cummings atoms
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
Guo, Rui; Zhou, Lan; Gu, Shi-Pu; Wang, Xing-Fu; Sheng, Yu-Bo
2017-03-01
The concatenated Greenberger-Horne-Zeilinger (C-GHZ) state is a new type of multipartite entangled state, which has potential application in future quantum information. In this paper, we propose a protocol of constructing arbitrary C-GHZ entangled state approximatively. Different from previous protocols, each logic qubit is encoded in the coherent state. This protocol is based on the linear optics, which is feasible in experimental technology. This protocol may be useful in quantum information based on the C-GHZ state.
Evolution of entanglement under echo dynamics
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
Detecting Kondo Entanglement by Electron Conductance
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.
Scattering effect on entanglement propagation in RCFTs
Numasawa, Tokiro [Yukawa Institute for Theoretical Physics, Kyoto University,Kitashirakawa Oiwakecho, Sakyo-ku, Kyoto, 606-8502 (Japan); Kavli Institute for Theoretical Physics, University of California Santa Barbara,Santa Barbara, CA, 93106 (United States)
2016-12-14
In this paper we discuss the scattering effect on entanglement propagation in RCFTs. In our setup, we consider the time evolution of excited states created by the insertion of many local operators. Our results show that because of the finiteness of quantum dimension, entanglement is not changed after the scattering in RCFTs. In this mean, entanglement is conserved after the scattering event in RCFTs, which reflects the integrability of the system. Our results are also consistent with the free quasiparticle picture after the global quenches.
Quantum entanglement and fixed-point bifurcations
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
Task-oriented maximally entangled states
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.
Teleportation of Multi-qudit Entangled States
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.
Entanglement detection in hybrid optomechanical systems
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.
Entanglement entropy with a time-dependent Hamiltonian
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.
Heralded noiseless amplification for single-photon entangled state with polarization feature
Wang, Dan-Dan; Jin, Yu-Yu; Qin, Sheng-Xian; Zu, Hao; Zhou, Lan; Zhong, Wei; Sheng, Yu-Bo
2018-03-01
Heralded noiseless amplification is a promising method to overcome the transmission photon loss in practical noisy quantum channel and can effectively lengthen the quantum communication distance. Single-photon entanglement is an important resource in current quantum communications. Here, we construct two single-photon-assisted heralded noiseless amplification protocols for the single-photon two-mode entangled state and single-photon three-mode W state, respectively, where the single-photon qubit has an arbitrary unknown polarization feature. After the amplification, the fidelity of the single-photon entangled state can be increased, while the polarization feature of the single-photon qubit can be well remained. Both the two protocols only require the linear optical elements, so that they can be realized under current experimental condition. Our protocols may be useful in current and future quantum information processing.
Seevinck, Michael; Uffink, Jos
2007-01-01
By introducing a quantitative 'degree of commutativity' in terms of the angle between spin observables we present two tight quantitative trade-off relations in the case of two qubits. First, for entangled states, between the degree of commutativity of local observables and the maximal amount of violation of the Bell inequality: if both local angles increase from zero to π/2 (i.e., the degree of local commutativity decreases), the maximum violation of the Bell inequality increases. Secondly, a converse trade-off relation holds for separable states: if both local angles approach π/2 the maximal value obtainable for the correlations in the Bell inequality decreases and thus the non-violation increases. As expected, the extremes of these relations are found in the case of anticommuting local observables where, respectively, the bounds of 2√(2) and √(2) hold for the expectation value of the Bell operator. The trade-off relations show that noncommmutativity gives ''a more than classical result'' for entangled states, whereas ''a less than classical result'' is obtained for separable states. The experimental relevance of the trade-off relation for separable states is that it provides an experimental test for two qubit entanglement. Its advantages are twofold: in comparison to violations of Bell inequalities it is a stronger criterion and in comparison to entanglement witnesses it needs to make less strong assumptions about the observables implemented in the experiment
Entangled de Sitter from stringy axionic Bell pair I. An analysis using Bunch-Davies vacuum
Choudhury, Sayantan; Panda, Sudhakar
2018-01-01
In this work, we study the quantum entanglement and compute entanglement entropy in de Sitter space for a bipartite quantum field theory driven by an axion originating from Type IIB string compactification on a Calabi-Yau three fold (CY 3 ) and in the presence of an NS5 brane. For this computation, we consider a spherical surface S 2 , which divides the spatial slice of de Sitter (dS 4 ) into exterior and interior sub-regions. We also consider the initial choice of vacuum to be Bunch-Davies state. First we derive the solution of the wave function of the axion in a hyperbolic open chart by constructing a suitable basis for Bunch-Davies vacuum state using Bogoliubov transformation. We then derive the expression for density matrix by tracing over the exterior region. This allows us to compute the entanglement entropy and Renyi entropy in 3 + 1 dimension. Furthermore, we quantify the UV-finite contribution of the entanglement entropy which contain the physics of long range quantum correlations of our expanding universe. Finally, our analysis complements the necessary condition for generating non-vanishing entanglement entropy in primordial cosmology due to the axion. (orig.)
On entanglement entropy in non-Abelian lattice gauge theory and 3D quantum gravity
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.
Entangled de Sitter from stringy axionic Bell pair I. An analysis using Bunch-Davies vacuum
Choudhury, Sayantan [Inter-University Centre for Astronomy and Astrophysics, Pune (India); Tata Institute of Fundamental Research, Department of Theoretical Physics, Mumbai (India); Panda, Sudhakar [Institute of Physics, Bhubaneswar, Odisha (India); National Institute of Science Education and Research, Bhubaneswar, Odisha (India); Homi Bhabha National Institute, Mumbai (India)
2018-01-15
In this work, we study the quantum entanglement and compute entanglement entropy in de Sitter space for a bipartite quantum field theory driven by an axion originating from Type IIB string compactification on a Calabi-Yau three fold (CY{sup 3}) and in the presence of an NS5 brane. For this computation, we consider a spherical surface S{sup 2}, which divides the spatial slice of de Sitter (dS{sub 4}) into exterior and interior sub-regions. We also consider the initial choice of vacuum to be Bunch-Davies state. First we derive the solution of the wave function of the axion in a hyperbolic open chart by constructing a suitable basis for Bunch-Davies vacuum state using Bogoliubov transformation. We then derive the expression for density matrix by tracing over the exterior region. This allows us to compute the entanglement entropy and Renyi entropy in 3 + 1 dimension. Furthermore, we quantify the UV-finite contribution of the entanglement entropy which contain the physics of long range quantum correlations of our expanding universe. Finally, our analysis complements the necessary condition for generating non-vanishing entanglement entropy in primordial cosmology due to the axion. (orig.)
Entanglement-continuous unitary transformations
Sahin, Serkan; Orus, Roman [Institute of Physics, Johannes Gutenberg University, 55099 Mainz (Germany)
2016-07-01
In this talk we present a new algorithm for quantum many-body systems using continuous unitary transformations (CUT) and tensor networks (TNs). With TNs we are able to approximate the solution to the flow equations that lie at the heart of continuous unitary transformations. We call this method Entanglement-Continuous Unitary Transformations (eCUT). It allows us to compute expectation values of local observables as well as tensor network representations of ground states and low-energy excited states. An implementation of the method is shown for 1d systems using matrix product operators. We show preliminary results for the 1d transverse-field Ising model to demonstrate the feasibility of the method.
Entropic Entanglement: Information Prison Break
Alexander Y. Yosifov
2017-01-01
Full Text Available We argue that certain nonviolent local quantum field theory (LQFT modification considered at the global horizon (r=2M of a static spherically symmetric black hole can lead to adiabatic leakage of quantum information in the form of Hawking particles. The source of the modification is (i smooth at r=2M and (ii rapidly vanishing at r≫2M. Furthermore, we restore the unitary evolution by introducing extra quanta which departs slightly from the generic Hawking emission without changing the experience of an infalling observer (no drama. Also, we suggest that a possible interpretation of the Bekenstein-Hawking bound as entanglement entropy may yield a nonsingular dynamical horizon behavior described by black hole thermodynamics. Hence, by treating gravity as a field theory and considering its coupling to the matter fields in the Minkowski vacuum, we derive the conjectured fluctuations of the background geometry of a black hole.
College students' behavioral reactions upon witnessing relational peer aggression.
You, Ji-In; Bellmore, Amy
2014-01-01
With a sample of 228 college students (82.5% females) from the Midwestern United States, individual factors that contribute to emerging adults' behavioral responses when witnessing relational aggression among their peers were explored. The experience of witnessing relational aggression was found to be systematically associated with college students' behavioral responses to relational aggression through two social cognitive processes: normative beliefs about relational aggression and susceptibility to peer influence. The experience of witnessing relational aggression was associated with defending behavior through normative beliefs about relational aggression and both assisting and reinforcing behavior through normative beliefs about relational aggression and susceptibility to peer influence. The experience of witnessing relational aggression was also associated with onlooking behavior through normative beliefs about relational aggression. The findings indicate that exposure to relational aggression as a witness may influence witness responses because of the way such exposure may shape specific social cognitions. The potential for using the study findings for promoting effective witness interventions among college students is discussed. © 2014 Wiley Periodicals, Inc.
Simulation and optimization of agricultural product supply chain system based on Witness
Jiandong Liu
2017-03-01
Full Text Available Researches on agricultural product supply chain have important implications for improving the efficiency of agricultural products circulation, strengthening the construction of agricultural market system, promoting agricultural modernization and solving the three rural issues. Agricultural product supply chain system has begun to be optimized through simulation technique. In this paper, agricultural product supply chain system is reasonably simplified and assumed. A simulation model was developed by using the simulation software Wit-ness to study agricultural product supply chain. Through the analysis of the simulation output data, improvement suggestions were also proposed as follows: improving the organization degree of agricultural products, improving the agricultural products processing, establishing strategic partnership and scientifically developing agricultural products logistics.
The method innovation in nuclear equipment quality witness tracing and management
Hao Guang
2012-01-01
The total construction cost of a nuclear power plant, equipment procurement cost accounts for about 47%-53%. Whether the quality of equipment can meet the technical requirements plays a significant role in the operation and maintenance of a nuclear power plant. Only if we adopt effective management can the equipment quality be ensured. As the most important method of quality control, the effective attendance and track of quality witness points has a crucial effect on contract smooth implementation as well. The essay mainly illustrates the method of quality witness point tracing and management and how to incorporate serious minded ideas and all take part in ways into quality management, hoping to offer some enlightenment on the innovation of nuclear power equipment quality management. (author)
Unfair Lineups Make Witnesses More Likely to Confuse Innocent and Guilty Suspects.
Colloff, Melissa F; Wade, Kimberley A; Strange, Deryn
2016-09-01
Eyewitness-identification studies have focused on the idea that unfair lineups (i.e., ones in which the police suspect stands out) make witnesses more willing to identify the police suspect. We examined whether unfair lineups also influence subjects' ability to distinguish between innocent and guilty suspects and their ability to judge the accuracy of their identification. In a single experiment (N = 8,925), we compared three fair-lineup techniques used by the police with unfair lineups in which we did nothing to prevent distinctive suspects from standing out. Compared with the fair lineups, doing nothing not only increased subjects' willingness to identify the suspect but also markedly impaired subjects' ability to distinguish between innocent and guilty suspects. Accuracy was also reduced at every level of confidence. These results advance theory on witnesses' identification performance and have important practical implications for how police should construct lineups when suspects have distinctive features. © The Author(s) 2016.
On the entanglement entropy for gauge theories
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.
From quantum entanglement to mirror neuron
Zak, Michail
2007-01-01
It is proposed that two fundamental phenomena: quantum entanglement in physics, and mirror neuron in biopsychology, can be described by using the same mathematical formalism, namely, the feedback from the Liouville equation to equation of motion
Entanglement-assisted quantum feedback control
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.
Entanglement entropy from the holographic stress tensor
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)
Spin entanglement, decoherence and Bohm's EPR paradox.
Cavalcanti, E G; Drummond, P D; Bachor, H A; Reid, M D
2009-10-12
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 current quantum optical technologies. For a macroscopic number of particles prepared in a correlated state, spin entanglement and the EPR paradox can be demonstrated using our criteria for efficiencies eta > 1/3 and eta > 2/3 respectively. This indicates a surprising insensitivity to loss decoherence, in a macroscopic system of ultra-cold atoms or photons.
Entangled biphoton source - property and preparation
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
Revisiting entanglement entropy of lattice gauge theories
Hung, Ling-Yan [Department of Physics and Center for Field Theory and Particle Physics, Fudan University,220 Handan Lu, Shanghai 200433 (China); Collaborative Innovation Center of Advanced Microstructures, Fudan University,220 Handan Lu, Shanghai 200433 (China); Wan, Yidun [Perimeter Institute for Theoretical Physics,31 Caroline Street, Waterloo, ON N2L 2Y5 (Canada)
2015-04-22
It is realized recently that the entanglement entropy in gauge theories is ambiguous because the Hilbert space cannot be expressed as a simple direct product of Hilbert spaces defined on the two regions; different ways of dividing the Hilbert spaces near the boundary leads to significantly different result, to the extreme that it could annihilate the otherwise finite topological entanglement entropy between two regions altogether. In this article, we first show that the topological entanglement entropy in the Kitaev model http://dx.doi.org/10.1016/S0003-4916(02)00018-0 which is not a true gauge theory, is free of ambiguity. Then, we give a physical interpretation, from the perspectives of what can be measured in an experiment, to the purported ambiguity of true gauge theories, where the topological entanglement arises as redundancy in counting the degrees of freedom along the boundary separating two regions. We generalize these discussions to non-Abelian gauge theories.
Persistent entanglement in the classical limit
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.
Criticality and entanglement in random quantum systems
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.
Converting multilevel nonclassicality into genuine multipartite entanglement
Regula, Bartosz; Piani, Marco; Cianciaruso, Marco; Bromley, Thomas R.; Streltsov, Alexander; Adesso, Gerardo
2018-03-01
Characterizing genuine quantum resources and determining operational rules for their manipulation are crucial steps to appraise possibilities and limitations of quantum technologies. Two such key resources are nonclassicality, manifested as quantum superposition between reference states of a single system, and entanglement, capturing quantum correlations among two or more subsystems. Here we present a general formalism for the conversion of nonclassicality into multipartite entanglement, showing that a faithful reversible transformation between the two resources is always possible within a precise resource-theoretic framework. Specializing to quantum coherence between the levels of a quantum system as an instance of nonclassicality, we introduce explicit protocols for such a mapping. We further show that the conversion relates multilevel coherence and multipartite entanglement not only qualitatively, but also quantitatively, restricting the amount of entanglement achievable in the process and in particular yielding an equality between the two resources when quantified by fidelity-based geometric measures.
Orbital-angular-momentum entanglement in turbulence
Hamadou Ibrahim, A
2013-06-01
Full Text Available The turbulence-induced decay of orbital-angular-momentum (OAM) entanglement between two photons is investigated numerically and experimentally. To compare our resultswith previouswork,we simulate the turbulent atmosphere with a single phase screen...
Entanglement degradation in depolarizing light scattering
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)
Projected entangled pair states: status and prospects
Verstraete, Frank [Universitaet Wien (Austria)
2008-07-01
We report on the progress made to extend the density matrix renormalization group to higher dimensions, discuss the underlying theory of projected entangled pair states (PEPS) and illustrate its potential on the hand of a few examples.
Testing for entanglement with periodic coarse graining
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.
Entangled biphoton source - property and preparation
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.
Classical statistical mechanics approach to multipartite entanglement
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 (Italy)
2010-06-04
We characterize the multipartite entanglement of a system of n qubits in terms of the distribution function of the bipartite purity over balanced bipartitions. We search for maximally multipartite entangled states, whose average purity is minimal, and recast this optimization problem into a problem of statistical mechanics, by introducing a cost function, a fictitious temperature and a partition function. By investigating the high-temperature expansion, we obtain the first three moments of the distribution. We find that the problem exhibits frustration.
Classical statistical mechanics approach to multipartite entanglement
Facchi, P.; Florio, G.; Marzolino, U.; Parisi, G.; Pascazio, S.
2010-06-01
We characterize the multipartite entanglement of a system of n qubits in terms of the distribution function of the bipartite purity over balanced bipartitions. We search for maximally multipartite entangled states, whose average purity is minimal, and recast this optimization problem into a problem of statistical mechanics, by introducing a cost function, a fictitious temperature and a partition function. By investigating the high-temperature expansion, we obtain the first three moments of the distribution. We find that the problem exhibits frustration.
Classical statistical mechanics approach to multipartite entanglement
Facchi, P; Florio, G; Pascazio, S; Marzolino, U; Parisi, G
2010-01-01
We characterize the multipartite entanglement of a system of n qubits in terms of the distribution function of the bipartite purity over balanced bipartitions. We search for maximally multipartite entangled states, whose average purity is minimal, and recast this optimization problem into a problem of statistical mechanics, by introducing a cost function, a fictitious temperature and a partition function. By investigating the high-temperature expansion, we obtain the first three moments of the distribution. We find that the problem exhibits frustration.
Entanglement detection via tighter local uncertainty relations
Zhang Chengjie; Zhang Yongsheng; Guo Guangcan; Nha, Hyunchul
2010-01-01
We propose an entanglement criterion based on local uncertainty relations (LURs) in a stronger form than the original LUR criterion introduced by Hofmann and Takeuchi [H. F. Hofmann and S. Takeuchi, Phys. Rev. A 68, 032103 (2003)]. Using arbitrarily chosen operators (A k ) and (B k ) of subsystems A and B, the tighter LUR criterion, which may be used not only for discrete variables but also for continuous variables, can detect more entangled states than the original criterion.
Monogamy inequality for distributed gaussian entanglement.
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.