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Search results for: ENTANGLEMENT DISTILLATION
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Multipartite secret key distillation and bound entanglement
PublicationRecently 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...
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Fidelity thresholds in single copy entanglement distillation
PublicationRozważono różne aspekty destylacji zaszumionego splątania oraz pewne stowarzyszone efekty w kwantowej korekcji błędów. W szczególności pokazano, że w przypadku gdy dozwolona jest komunikacja klasyczna w jedną stronę oraz współdzielony stan kwantowy dxd nie jest czysty, to istnieje próg dla optymalnego ułamka F stanu, który może być otrzymany w procesie destylacji na jednej kopii. Wynika z tego, że aby otrzymać (probabilistycznie)...
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On entaglement distillation and quantum error correction of unknown states and channels.
PublicationBadano niezmienniczości splątania kwantowego oraz pojemności kwantowego kanału ze względu na ewentualną utratę informacji o pojedynczej kopii kwantowego stanu. Pokazano, że jeżeli dany kwantowy kanał ma pewne pojemności niezerowe, to odpowiadające mu stany posiadają niezerowe destylowalne splątanie. Postawiono pewne otwarte problemy dotyczące destylowalności splątania.
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Quantum entanglement
PublicationAll our former experience with application of quantum theory seems to say that what is predicted by quantum formalism must occur in the laboratory. But the essence of quantum formalism-entanglement, recognized by Einstein, Podolsky, Rosen, and Schrödinger-waited over 70 years to enter laboratories as a new resource as real as energy. This holistic property of compound quantum systems, which involves nonclassical correlations between...
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Entanglement-redistribution boxes
PublicationWe establish a framework to study the classical-communication properties of primitive local operations assisted by classical communication which realize various redistributions of entanglement, like, e.g., entanglement swapping. On the one hand, we analyze what local operations and how much classical communication are needed to perform them. On the other hand, we investigate whether and to what extent such primitives can help to...
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Quantum entanglement in time
PublicationIn this paper we present a concept of quantum entanglement in time in a context of entangled consistent histories. These considerations are supported by presentation of necessary tools closely related to those acting on a space of spatial multipartite quantum states. We show that in similarity to monogamy of quantum entanglement in space, quantum entanglement in time is also endowed with this property for a particular history....
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Dynamics of quantum entanglement
PublicationA model of discrete dynamics of entanglement of a bipartite quantum state is considered. It involves a global unitary dynamics of the system and periodic actions of local bistochastic or decaying channel. For initially pure states the decay of entanglement is accompanied by an increase of von Neumann entropy of the system. We observe and discuss revivals of entanglement due to unitary interaction of subsystems. For some mixed states...
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Squashed entanglement for multipartite states and entanglement measures based on the mixed convex roof
PublicationNew measures of multipartite entanglement are constructedbased on two definitions of multipartite information anddifferent methods of optimizing over extensions of the states. Oneis a generalization of the squashed entanglement where one takesthe mutual information of parties conditioned on the state's extensionand takes the infimum over such extensions. Additivity ofthe multipartite squashed entanglement is proved for both versionsof...
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12 [Chapter]. Bound entanglement
PublicationKwantowe splątanie jest jednym z podstawowych elementów kwantowej teorii informacji. Jak wiadomo niskowymiarowe (2otimes 2 i 2otimes 3) splątane stany kwantowe są zawsze destylowalne. W wyższych wymiarach jednak istnieją stany, które mimo, że są splątane nie pozwalają na destylację. Ten rodzaj splątania, nazywany związanym, jest często trudny do wykrycia i pozornie bezużyteczny. Jak pokazują jednak liczne badania splątanie związane...
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Sudden death of effective entanglement
PublicationSudden death of entanglement is a well-known effect resulting from the finite volume of separable states. We study the case when the observer has a limited measurement capability and analyze the effective entanglement (i.e., entanglement minimized over the output data). We show that in the well-defined system of two quantum dots monitored by single-electron transistors, one may observe a sudden death of effective entanglement when...
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Direct detection of quantum entanglement
PublicationPoddano dyskusji teorię splątania w kontekście historycznym. Omówiono detekcję splątania przy użyciu sieci złożonej z bramek kwantowych.
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Locking entanglement with a single qubit
PublicationBadamy utratę plątania dwuczęściowego stanu narażanego na odrzucenie lub pomiar jednego kubitu.
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Direct detection of quantum entanglement
PublicationBasing on positive maps separability criterion we propose the experimentally viable, direct detection of quantum entanglement. It is efficient and does not require any a priori knowledge about the state. For two qubits it provides a sharp (i.e., “if and only if”) separability test and estimation of amount of entanglement. We view this method as a new form of quantum computation, namely, as a decision problem with quantum data structure.
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Collective Uncertainty Entanglement Test
PublicationFor a given pure state of a composite quantum system we analyze the product of its projections onto aset of locally orthogonal separable pure states. We derive a bound for this product analogous to theentropic uncertainty relations. For bipartite systems the bound is saturated for maximally entangled statesand it allows us to construct a family of entanglement measures, we shall call collectibility. As thesequantities are experimentally...
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Bound entanglement maximally violating Bell inequalities: quantum entanglement is not fully equivalent to cryptographic security
PublicationW pracy pokazano, że czterokubitowy stan o splątaniu związanym może maksymalnie łamać prostą nierówność Bella podobną do standardowej nierówności CHSH. Prostota rozważanego układu oraz odporność splątania sprawiają, że łamanie to jest obiecujące dla współczesnej technologii eksperymentalnej. Z drugiej strony, splątanie tego stanu nie pozwala na destylację bezpiecznego klucza kryptograficznego, zatem ani splątanie, ani maksymalne...
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Degree of entaglement as a physically ill-posted problem: The case of entaglement with vacuum
PublicationAnalizujemy przypadek fotonu w superpozycji różnych modów i zadajemy pytanie o stopień ich splątania z próżnią. Problem okazuje się być źle postawiony, gdyż nie wiemy którą reprezentację algebry CCR wybrać dla kwantowania pola. Gdy dokonamy wyboru jednoznacznie możemy rozwiązać zagadnienie splątania. Tak więc trudność nie leży w matematyce lecz w fizyce problemu.
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Entanglement-swapping boxes and their communication properties
PublicationWe pose the fundamental question of communication properties of primitives irrespectively of their implementation. To illustrate the idea we introduce the concept of entanglement-swapping boxes, i.e., we consider any quantum operations which perform entanglement swapping, not necessarily via simple quantum teleportation. We ask a question about the properties of such boxes, i.e., what local operations and how much classical communication...
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Separability in terms of a single entanglement witness
PublicationThe separability problem is formulated in terms of a characterization of a single entanglement witness. More specifically, we show that any (in general multipartite) state rho is separable if and only if a specially constructed entanglement witness W-rho is weakly optimal, i.e., its expectation value vanishes on at least one product vector. Interestingly, the witness can always be chosen to be decomposable. Our result changes the...
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Secure key from bound entanglement
PublicationScharakteryzowaliśmy zestaw dzielonych kwantowych stanów, który zawiera kryptograficznie prywatny klucz. Pozwala nam to przerobić teorię prywatności jako paradygmat blisko związany z tą, która jest używana w manipulacjach splątania.
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Wastewater treatment by membrane distillation
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Membrane distillation with laminar flow
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Rotationally invariant bipartite states and bound entanglement
PublicationW pracy rozważano stany kwantowe niezmiennicze na działanie grupy SO(3). Pokazano, że w przypadku, gdy pierwszy podukład ma parzysty wymiar większy lub równy cztery oraz drugi podukład ma wymiar dowolny, większy niż pierwszy to pośród takich stanów zawsze istnieje splątanie związane.
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Entanglement in helium atom confined in an impenetrable cavity
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Constructive entanglement test from triangle inequality
PublicationWe derive a simple lower bound on the geometric measure of entanglement for mixed quantum states in the case of a general multipartite system. The main ingredient of the presented derivation is the triangle inequality applied to the root infidelity distance in the space of density matrices. The obtained bound leads to entanglement criteria with a straightforward interpretation. The proposed criteria provide an experimentally accessible,...
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Experimental generation of complex noisy photonic entanglement
PublicationWe 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...
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Completely entangled subspaces of entanglement depth k
PublicationWe introduce a class of entangled subspaces: completely entangled subspaces of entanglement depth k (k-CESs). These are subspaces of multipartite Hilbert spaces containing only pure states with an entanglement depth of at least k. We present an efficient construction of k-CESs of any achievable dimensionality in any multipartite scenario. Further, we discuss the relation between these subspaces and unextendible product bases (UPBs)....
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Bound entanglement for continuous variables is a rare phenomenon
PublicationWykazano, że splątanie związane w przypadku zmiennych ciągłych jest rzadkimfenomenem. W szczególności pokazano, że zbiór stanów niedestylowalnych jestnigdzie gęsty w zbiorze wszystkich stanów kwantowych. Poddano dyskusji splą-tanie związane w kontekście liczby Schmidta.
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On direct detection of entanglement properties of unknown states
PublicationPrzystępnie omówiono detekcję własności splątania kwantowych stanów. Uwzględniono zarówno detekcje o charakterze jakościowym jak i ilościowym.
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On structural physical approximations and entanglement breaking maps
PublicationVery recently, a conjecture saying that the so-called structural physical approximations (SPAs) to optimal positive maps (optimal entanglement witnesses) give entanglement breaking (EB) maps (separable states) has been posed (Korbicz et al 2008 Phys. Rev. A 78 062105). The main purpose of this contribution is to explore this subject. First, we extend the set of entanglement witnesses supporting the conjecture. Then, we ask whether...
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Quantum metrology: Heisenberg limit with bound entanglement
PublicationQuantum entanglement may provide a huge boost in the precision of parameter estimation. However, quantum metrology seems to be extremely sensitive to noise in the probe state. There is an important still open question: What type of entanglement is useful as a resource in quantum metrology? Here we raise this question in relation to entanglement distillation. We provide a counterintuitive example of a family of bound entangled states...
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Entanglement and Nonlocality are Inequivalent for Any Number of Parties
PublicationUnderstanding the relation between nonlocality and entanglement is one of the fundamental problems in quantum physics. In the bipartite case, it is known that these two phenomena are inequivalent, as there exist entangled states of two parties that do not violate any Bell inequality. However, except for a single example of an entangled three-qubit state that has a local model, almost nothing is known about such a relation in multipartite...
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Progress towards a unified approach to entanglement distribution
PublicationEntanglement distribution is key to the success of secure communication schemes based on quantum mechanics, and there is a strong need for an ultimate architecture able to overcome the limitations of recent proposals such as those based on entanglement percolation or quantum repeaters. In this work we provide a broad theoretical background for the development of such technologies. In particular, we investigate the question of whether...
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Unifying classical and quantum key distillation
PublicationPrzypuśćmy, że dwie oddalone od siebie osoby, Alicja i Bob, oraz osoba z nimi niewspółpracująca, Ewa, mają dostęp do systemów kwantowych przygotowanych w stanie rho_ABE. Ponadto Alicja i Bob mogą używać lokalnych operacji i uwiarygodnionej komunikacji publicznej. Celem Alicji i Boba jest ustanowienie klucza, który nie będzie znany Ewie. Nasze badania inicjują podejście do wspomnianego zagadnienia oparte na unifikacji dwóch standardowych...
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Progress in module design for membrane distillation
PublicationThere have been tremendous advances in membrane distillation (MD) since the concept was introduced in 1961: new membrane designs and process configurations have emerged, and its commercial viability has been evaluated in several pilot-scale studies. However, its high energy consumption has hindered its commercialization. One of the most promising ways to overcome this obstacle is to develop more energy-efficient membrane modules....
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Desalination of geothermal water by membrane distillation
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Water Purification by Membrane Distillation Process
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The fermentation process integrated with membrane distillation
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Capillary Polypropylene Membranes for Membrane Distillation
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Ethanol production in membrane distillation bioreactor
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Heat transport in the membrane distillation process
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The Application of Submerged Modules for Membrane Distillation
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Bilge water separation by membrane distillation
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Study on the concentration of acids by membrane distillation
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Alkaline scaling in the membrane distillation process
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Two-electron entanglement in elliptically deformed quantum dots
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Entanglement Entropies in the Ground States of Helium-Like Atoms
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Entanglement in Hooke’s Law Atoms: an Effect of the Dimensionality of the Space
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Entanglement of Two Charged Bosons in Strongly Anisotropic Traps
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Quantum Entanglement of Two Harmonically Trapped Dipolar Particles
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A few steps more towards NPT bound entanglement
PublicationIn this paper, existence of bound entangled states with nonpositive partial transpose (NPT) is considered. As one knows, existence of such states would in particular imply nonadditivity of distillable entanglement. Moreover, it would rule out a simple mathematical description of the set of distillable states. The particular state, known to be 1-copy nondistillable and supposed to be bound entangled, is considered. The problem of...