Entanglement verification with realistic measurement devices via squashing operations (2009)
Moroder, Tobias, Gühne, Otfried, Beaudry, Normand J., Piani, Marco, Lütkenhaus, Norbert
Many protocols and experiments in quantum information science are described in terms of simple measurements on qubits. However, in a real implementation, the exact description is more difficult, and...
Separability criteria and entanglement witnesses for symmetric quantum states (2009)
We study the separability of symmetric bipartite quantum states and show that a single correlation measurement is sufficient to detect the entanglement of any bipartite symmetric state with a...
Experimental Test of Bell inequalities with Six-Qubit Graph States (2009)
Gao, Wei-Bo, Yao, Xing-Can, Xu, Ping, Gühne, Otfried, Cabello, Adán, Lu, Chao-Yang, ...
We report on the experimental realization of two different Bell inequality tests based on six-qubit linear-type and Y-shape graph states. For each of these states, the Bell inequalities tested are...
Experimental Realization of a Controlled-NOT Gate with Four-Photon Six-Qubit Cluster States (2009)
Gao, Wei-Bo, Xu, Ping, Yao, Xing-Can, Gühne, Otfried, Cabello, Adán, Lu, Chao-Yang, ...
We experimentally demonstrate an optical controlled-NOT (CNOT) gate with arbitrary single inputs based on a 4-photon 6-qubit cluster state entangled both in polarization and spatial modes. We first...
Separability criteria for genuine multiparticle entanglement (2009)
Gühne, Otfried, Seevinck, Michael
We present a method to derive separability criteria for the different classes of multiparticle entanglement, especially genuine multiparticle entanglement. The resulting criteria are necessary and...
Entanglement and permutational symmetry (2008)
We study the separability of permutationally symmetric quantum states. We show that for bipartite symmetric systems most of the relevant entanglement criteria coincide. However, we provide a method...
How can one prove that a given 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...
Experimental demonstration of a hyper-entangled ten-qubit Schr\"odinger cat state (2008)
Gao, Wei-Bo, Lu, Chao-Yang, Yao, Xing-Can, Xu, Ping, Gühne, Otfried, Goebel, Alexander, ...
Coherent manipulation of an increasing number of qubits for the generation of entangled states has been an important goal and benchmark in the emerging field of quantum information science. The...
Generalized Ardehali-Bell inequalities for graph states (2008)
We derive Bell inequalities for graph states by generalizing the approach proposed by Ardehali [Phys. Rev. A 46, 5375 (1992)] for Greenberger-Horne-Zeilinger (GHZ) states. Using this method, we...
Experimental observation of an entire family of four-photon entangled states (2008)
Wieczorek, Witlef, Schmid, Christian, Kiesel, Nikolai, Pohlner, Reinhold, Gühne, Otfried, Weinfurter, Harald
A single linear optical set-up is used to observe an entire family of four-photon entangled states. This approach breaks with the inflexibility of present linear-optical set-ups usually designed for...
Spin squeezing and entanglement (2008)
Toth, Geza, Knapp, Christian, Gühne, Otfried, Briegel, Hans J.
What is the relation between spin squeezing and entanglement? To clarify this, we derive the full set of generalized spin squeezing inequalities for the detection of entanglement. These are...
Iterations of nonlinear entanglement witnesses (2008)
Moroder, Tobias, Gühne, Otfried, Lütkenhaus, Norbert
We describe a generic way to improve a given linear entanglement witness by a quadratic, nonlinear term. This method can be iterated, leading to a whole sequence of nonlinear witnesses, which become...
Unifying several separability conditions using the covariance matrix criterion (2008)
Gittsovich, Oleg, Gühne, Otfried, Hyllus, Philipp, Eisert, Jens
We present a framework for deciding whether a quantum state is separable or entangled using covariance matrices of locally measurable observables. This leads to the covariance matrix criterion as a...
Demonstrating anyonic fractional statistics with a six-qubit quantum simulator (2007)
Lu, Chao-Yang, Gao, Wei-Bo, Gühne, Otfried, Zhou, Xiao-Qi, Chen, Zeng-Bing, Pan, Jian-Wei
Anyons are exotic quasiparticles living in two dimensions that do not fit into the usual categories of fermions and bosons, but obey a new form of fractional statistics. Following a recent proposal...
Mermin inequalities for perfect correlations (2007)
Cabello, Adan, Gühne, Otfried, Rodriguez, David
Any n-qubit state with n independent perfect correlations is equivalent to a graph state. We present the optimal Bell inequalities for perfect correlations and maximal violation for all classes of...
Toolbox for entanglement detection and fidelity estimation (2007)
Gühne, Otfried, Lu, Chao-Yang, Gao, Wei-Bo, Pan, Jian-Wei
The determination of the state fidelity and the detection of entanglement are fundamental problems in quantum information experiments. We investigate how these goals can be achieved with a minimal...
Optimal spin squeezing inequalities detect bound entanglement in spin models (2007)
Toth, Geza, Knapp, Christian, Gühne, Otfried, Briegel, Hans J.
We determine the complete set of generalized spin squeezing inequalities. These are entanglement criteria that can be used for the experimental detection of entanglement in a system of spin-1/2...
Parameter estimation for mixed states from a single copy (2007)
Konrad, Thomas, Gühne, Otfried, Audretsch, Jürgen, Briegel, Hans J.
Given a single copy of a mixed state of the form \rho=\lambda\rho_1+(1-\lambda)\rho_2, what is the optimal measurement to estimate the parameter \lambda, if \rho_1 and \rho_2 are known? We present a...
Nonlinear entanglement witnesses, covariance matrices and the geometry of separable states (2006)
Gühne, Otfried, Lütkenhaus, Norbert
Entanglement witnesses provide a standard tool for the analysis of entanglement in experiments. We investigate possible nonlinear entanglement witnesses from several perspectives. First, we...
Experimental entanglement of six photons in graph states (2006)
Lu, Chao-Yang, Zhou, Xiao-Qi, Gühne, Otfried, Gao, Wei-Bo, Zhang, Jin, Yuan, Zhen-Sheng, ...
Graph states are special kinds of multipartite entangled states that correspond to mathematical graphs where the vertices take the role of quantum spin systems and the edges represent interactions....
Gühne, Otfried, Mechler, Matyas, Toth, Geza, Adam, Peter
We show that any state which violates the computable cross norm (or realignment) criterion for separability also violates the separability criterion of the local uncertainty relations. The converse...
Detection of multipartite entanglement with two-body correlations (2006)
We show how to detect entanglement with criteria built from simple two-body correlation terms. Since many natural Hamiltonians are sums of such correlation terms, our ideas can be used to detect...
Nonlinear entanglement witnesses (2005)
Gühne, Otfried, Lütkenhaus, Norbert
Entanglement detection typically relies on linear inequalities for mean values of certain observables (entanglement witnesses), where violation indicates entanglement. We provide a general method to...
Experimental Analysis of a Four-Qubit Photon Cluster State (2005)
Kiesel,Nikolai, Schmid,Christian, Weber,Ulrich, Tóth,Géza, Gühne,Otfried, Ursin,Rupert, ...
Energy and multipartite entanglement in multidimensional and frustrated spin models (2005)
We investigate the relation between the entanglement properties of a quantum state and its energy for macroscopic spin models. To this aim, we develop a general method to compute energy bounds for...
Rigas, Johannes, Gühne, Otfried, Lütkenhaus, Norbert
We consider entanglement detection for quantum key distribution systems that use two signal states and continuous variable measurements. This problem can be formulated as a separability problem in a...
Bell Inequalities for Graph States (2005)
Gühne, Otfried, Tóth, Géza, Hyllus, Philipp, Briegel, Hans J.
Experimental Analysis of a Four-Qubit Photon Cluster State (2005)
Kiesel, Nikolai, Schmid, Christian, Weber, Ulrich, Tóth, Géza, Gühne, Otfried, Ursin, Rupert, ...
Detecting two-party quantum correlations in quantum key distribution protocols (2004)
Curty, Marcos, Gühne, Otfried, Lewenstein, Maciej, Lütkenhaus, Norbert
A necessary precondition for secure quantum key distribution (QKD) is that sender and receiver can prove the presence of entanglement in a quantum state that is effectively distributed between them....