450 research outputs found

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

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

    On multipartite invariant states II. Orthogonal symmetry

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    We construct a new class of multipartite states possessing orthogonal symmetry. This new class defines a convex hull of multipartite states which are invariant under the action of local unitary operations introduced in our previous paper "On multipartite invariant states I. Unitary symmetry". We study basic properties of multipartite symmetric states: separability criteria and multi-PPT conditions.Comment: 6 pages; slight corrections + new reference

    Properties of Entanglement Monotones for Three-Qubit Pure States

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    Various parameterizations for the orbits under local unitary transformations of three-qubit pure states are analyzed. The interconvertibility, symmetry properties, parameter ranges, calculability and behavior under measurement are looked at. It is shown that the entanglement monotones of any multipartite pure state uniquely determine the orbit of that state under local unitary transformations. It follows that there must be an entanglement monotone for three-qubit pure states which depends on the Kempe invariant defined in [Phys. Rev. A 60, 910 (1999)]. A form for such an entanglement monotone is proposed. A theorem is proved that significantly reduces the number of entanglement monotones that must be looked at to find the maximal probability of transforming one multipartite state to another.Comment: 14 pages, REVTe

    Hubungan Antara Produsen Dan Konsumen: Sebuah Tinjauan Etis

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    The purpose of this article is to provide an ethical foundation for relationshipmarketing using a virtue ethics approach. A phrase: “The customer is a king” means thecustomer is essential to the welfare of the business. On one hand, buyer and seller have ashared interest in “doing the deal”. They want to do business with each other, and bothbenefit from the transaction. On the other hand, every rupiah a buyer saves is a rupiah lostfrom the seller\u27s point of view. Every buyer wants a low price and every seller wants a highprice. So, if fairness is good, then we should promote fairness in commercial transactions, justas we do in other areas of life. And that requires that buyer and seller at least see each otheras equals

    A paradox in bosonic energy computations via semidefinite programming relaxations

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    We show that the recent hierarchy of semidefinite programming relaxations based on non-commutative polynomial optimization and reduced density matrix variational methods exhibits an interesting paradox when applied to the bosonic case: even though it can be rigorously proven that the hierarchy collapses after the first step, numerical implementations of higher order steps generate a sequence of improving lower bounds that converges to the optimal solution. We analyze this effect and compare it with similar behavior observed in implementations of semidefinite programming relaxations for commutative polynomial minimization. We conclude that the method converges due to the rounding errors occurring during the execution of the numerical program, and show that convergence is lost as soon as computer precision is incremented. We support this conclusion by proving that for any element p of a Weyl algebra which is non-negative in the Schrodinger representation there exists another element p' arbitrarily close to p that admits a sum of squares decomposition.Comment: 22 pages, 4 figure

    Noisy metrology beyond the standard quantum limit

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    Parameter estimation is of fundamental importance in areas from atomic spectroscopy and atomic clocks to gravitational wave detection. Entangled probes provide a significant precision gain over classical strategies in the absence of noise. However, recent results seem to indicate that any small amount of realistic noise restricts the advantage of quantum strategies to an improvement by at most a multiplicative constant. Here, we identify a relevant scenario in which one can overcome this restriction and attain superclassical precision scaling even in the presence of uncorrelated noise. We show that precision can be significantly enhanced when the noise is concentrated along some spatial direction, while the Hamiltonian governing the evolution which depends on the parameter to be estimated can be engineered to point along a different direction. In the case of perpendicular orientation, we find superclassical scaling and identify a state which achieves the optimum.Comment: Erroneous expressions with inconsistent units have been corrected. 5 pages, 3 figures + Appendi