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Search results for: quantum entanglement
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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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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...
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All Nonclassical Correlations Can Be Activated into Distillable Entanglement
PublicationWe devise a protocol in which general nonclassical multipartite correlations produce a physically relevant effect, leading to the creation of bipartite entanglement. In particular, we show that the relative entropy of quantumness, which measures all nonclassical correlations among subsystems of a quantum system, is equivalent to and can be operationally interpreted as the minimum distillable entanglement generated between the system...
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Method for universal detection of two-photon polarization entanglement
PublicationDetecting 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...
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Inequivalence of entanglement, steering, and Bell nonlocality for general measurements
PublicationEinstein-Podolsky-Rosen steering is a form of inseparability in quantum theory commonly acknowledged to be intermediate between entanglement and Bell nonlocality. However, this statement has so far only been proven for a restricted class of measurements, namely, projective measurements. Here we prove that entanglement, one-way steering, two-way steering, and nonlocality are genuinely different considering general measurements,...
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Are quantum correlations symmetric?
PublicationWe provide operational definition of symmetry of entanglement: An entangled state contains symmetric entanglement if its subsystems can be exchanged (swapped) by means of local operations and classical communication. We show that in general states have asymmetric entanglement. This allows to construct nonsymmetric measure of entanglement, and a parameter that reports asymmetry of entanglement contents of quantum state. We propose...
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Quantum origins of objectivity
PublicationIn spite of all of its successes, quantum mechanics leaves us with a central problem: How does nature create a bridge from fragile quanta to the objective world of everyday experience? Here we find that a basic structure within quantum mechanics that leads to the perceived objectivity is a so-called spectrum broadcast structure. We uncover this based on minimal assumptions, without referring to any dynamical details or a concrete...
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Quantum privacy witness
PublicationWhile it is usually known that the mean value of a single observable is enough to detect entanglement or its distillability, the counterpart of such an approach in the case of quantum privacy has been missing. Here we develop the concept of a privacy witness, i.e., a single observable that may detect the presence of the secure key even in the case of bound entanglement. Then we develop the notion of secret-key estimation based...
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Quantum Coherence as a Resource
PublicationThe coherent superposition of states, in combination with the quantization of observables, represents one of the most fundamental features that mark the departure of quantum mechanics from the classical realm. Quantum coherence in many-body systems embodies the essence of entanglement and is an essential ingredient for a plethora of physical phenomena in quantum optics, quantum information, solid state physics, and nanoscale thermodynamics....
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Correlated electrons and transport in a quantum point contact and in a double-quantum-dot system
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Advances in Quantum Chemistry
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EPJ Quantum Technology
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Quantum Science and Technology
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Quantum Beam Science
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Advanced Quantum Technologies
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QUANTUM INFORMATION & COMPUTATION
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PROGRESS IN QUANTUM ELECTRONICS
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AVS Quantum Science
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IET Quantum Communication
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Radiophysics and Quantum Electronics
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Quantum Machine Intelligence
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Can Communication Power of Separable Correlations Exceed That of Entanglement Resource?
PublicationThe scenario of remote state preparation with a shared correlated quantum state and one bit of forward communication [B. Dakić et al., Nat. Phys. 8, 666 (2012)] is considered. Optimization of the transmission efficiency is extended to include general encoding and decoding strategies. The importance of the use of linear fidelity is recognized. It is shown that separable states cannot exceed the efficiency of entangled states by...
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A macroscopic device for quantum computation
PublicationPrzeanalizowano mechaniczny model kwantowego układu 2-bitowego. Model jest zilustrowany algorytmem Deutscha i Arvinda.
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Quantum security and theory of decoherence
PublicationWe sketch a relation between two crucial, yet independent, fields in quantum information research, viz. quantum decoherence and quantum cryptography. We investigate here how the standard cryptographic assumption of shielded laboratory, stating that data generated by a secure quantum device remain private unless explicitly published, is disturbed by the einselection mechanism of quantum Darwinism explaining the measurement process...
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Hybrid no-signaling-quantum correlations
PublicationFundamental investigations in non-locality have shown that while the no-signaling principle alone is not sufficient to single out the set of quantum non-local correlations, local quantum mechanics and no-signaling together exactly reproduce the set of quantum correlations in the two-party Bell scenario. Here, we introduce and study an intermediate hybrid no-signaling quantum set of non-local correlations that we term HNSQ in the...
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The symmetric extendibility of quantum states
PublicationStudies on the symmetric extendibility of quantum states have become particularly important in the context of the analysis of one-way quantum measures of entanglement, and the distillability and security of quantum protocols. In this paper we analyze composite systems containing a symmetric extendible part, with particular attention devoted to the one-way security of such systems. Further, we introduce a new one-way entanglement...
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Probing the structure of quantum mechanics
PublicationWstęp do problemów dotyczących struktury mechaniki kwantowej, a w szczegółności związanych z jej nieliniowością, nielokalnością, a także problemami aks-jomatyzacji i wykorzystaniem zjawisk kwantowych do budowy komuterów.
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Long-distance quantum communication over noisy networks without long-time quantum memory
PublicationThe problem of sharing entanglement over large distances is crucial for implementations of quantum cryptography. A possible scheme for long-distance entanglement sharing and quantum communication exploits networks whose nodes share Einstein-Podolsky-Rosen (EPR) pairs. In Perseguers et al. [Phys. Rev. A 78, 062324 (2008)] the authors put forward an important isomorphism between storing quantum information in a dimension D and transmission...
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INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY
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Ground-State Entanglement Properties of Helium Atom in a Finite Spherical Cavity
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Note on the Harmonic Approximation in the Treatment of Entanglement: N Cold Trapped Ions
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General construction of noiseless networks detecting entanglement with the help of linear maps
PublicationW pracy zaprezentowano ogólny schemat konstrukcji bezszumowych sieci pozwalających wykrywać splątanie przy pomocy odwzorowań liniowych. Pokazano jak zastosować metodę do detekcji splątania nieznanego stanu bez jego wcześniejszej rekonstrukcji. W szczególności pokazano, że zawsze istnieje bezszumowa sieć pozwalająca wykrywać splątanie przy użyciu dodatnich, ale nie kompletnie dodatnich odwzorowań. Zaprezentowano także uogólnienie...
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Low-dimensional bound entanglement with one-way distillable cryptographic key
PublicationIn this paper, we provide a class of bound entangled states that have positive distillable secure key rate. The smallest state of this kind is 4 circle times 4, which shows that peculiar security contained in bound entangled states does not need high-dimensional systems. We show that for these states a positive key rate can be obtained by one-way Devetak-Winter (DW) protocol. Subsequently, the volume of bound entangled key-distillable...
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Entanglement of genuinely entangled subspaces and states: Exact, approximate, and numerical results
PublicationGenuinely entangled subspaces (GESs) are those subspaces of multipartite Hilbert spaces that consist only of genuinely multiparty entangled pure states. They are natural generalizations of the well-known notion of completely entangled subspaces, which by definition are void of fully product vectors. Entangled subspaces are an important tool of quantum information theory as they directly lead to constructions of entangled states,...
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The decay of quantum correlations between quantum dot spin qubits and the characteristics of its magnetic-field dependence
PublicationWe address the question of the role of quantum correlations beyond entanglement in the context of quantum magnetometry. We study the evolution of the rescaled variant of the geometric quantum discord of two electron-spin qubits interacting with an environment of nuclear spins via the hyperfine interaction. We have found that quantum correlations display a strong magnetic-field sensitivity which can be utilized for decoherence-driven...
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Bipartite correlations in quantum resonance states
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Quantum channel capacities: multiparty communication
PublicationAnalizowane są różne aspekty wieloużytkownikowej komunikacji kwantowymi kanałami bez pamięci. Uogólnione zostały pewne znane rezultaty dotyczące komunikacji kwantowej w układzie jeden nadawca -jeden odbiorca. W szczególności pokazana została bezużyteczność komunikacji klasycznej ''w przód'' w procesie transmisji informacji kwantowej oraz równoważność definicji regionów pojemności opartych na różnych miarach wierności transmisji:...
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Macroscopic models for quantum systems and computers
PublicationOpisano układy makroskopowe realizujące dwubitowe operacje kwantowe.
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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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Aspects of multistation quantum information broadcasting
PublicationWe study quantum information transmission over multiparty quantum channel. In particular, we show an equivalence of different capacity notions and provide a multiletter characterization of a capacity region for a general quantum channel with k senders and m receivers. We point out natural generalizations to the case of two-way classical communication capacity. (C) 2010 Elsevier B.V. All rights reserved.
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Quantum dots in gas sensing a review
PublicationAir pollution becomes an increasing problem in the recent years. There is a need to develop more sensitive gas sensors. Much effort has been performed to develop different types of gas sensors, such as electrochemical sensors or polymer sensors. One of the most promising approaches to improve sensors performance is the application of the nanostructures as sensing materials. State of the art of quantum...
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Two examples of Quantum Dynamical Semigroups
PublicationThe Hamiltonians of the considered bi-partite systems are of the form $$ H_{S,R} = H_S /times 1_R + Q_{S} /times M_R + 1_S /times H_R $$ Subindex $S$ corresponds to the observed system and $R$ to the reservoir (the enviroment of $S$). Two classes of systems are distinguished: the discrete-continuous...
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Dynamical objectivity in quantum Brownian motion
PublicationClassical objectivity as a property of quantum states —a view proposed to explain the observer-independent character of our world from quantum theory, is an important step in bridging the quantum-classical gap. It was recently derived in terms of spectrum broadcast structures for small objects embedded in noisy photon-like environments. However, two fundamental problems have arisen: a description of objective motion and applicability...
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Quantum structure in competing lizard communities
PublicationAlmost two decades of research on applications of the mathematical formalism of quantum theory as a modeling tool in domains different from the micro-world has given rise to many successful applications in situations related to human behavior and thought, more specifically in cognitive processes of decision-making and the ways concepts are combined into sentences. In this article, we extend this approach to animal behavior, showing...
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A simple test for quantum channel capacity
PublicationBased on state and channel isomorphism we point out that semidefiniteprogramming can be used as a quick test for nonzero one-way quantum channelcapacity. This can be achieved by searching for symmetric extensions of statesisomorphic to a given quantum channel. With this method we provide examplesof quantum channels that can lead to high entanglement transmission but stillhave zero one-way capacity, in particular, regions of symmetric...
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Superadditivity of two quantum information resources
PublicationEntanglement is one of the most puzzling features of quantum theory and a principal resource for quantum information processing. It is well known that in classical information theory, the addition of two classical information resources will not lead to any extra advantages. On the contrary, in quantum information, a spectacular phenomenon of the superadditivity of two quantum information resources emerges. It shows that quantum...
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No Quantum Realization of Extremal No-Signaling Boxes
PublicationThe study of quantum correlations is important for fundamental reasons as well as for quantum communication and information processing tasks. On the one hand, it is of tremendous interest to derive the correlations produced by measurements on separated composite quantum systems from within the set of all correlations obeying the no-signaling principle of relativity, by means of information-theoretic principles. On the other hand,...
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Semi-definite programming and quantum information
PublicationThis paper presents a comprehensive exploration of semi-definite programming (SDP) techniques within the context of quantum information. It examines the mathematical foundations of convex optimization, duality, and SDP formulations, providing a solid theoretical framework for addressing optimization challenges in quantum systems. By leveraging these tools, researchers and practitioners can characterize classical and quantum correlations,...