Entanglement of three-qubit Greenberger-Horne-Zeilinger-symmetric states

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 of this result concerns mixtures of a pure entangled state (such as the Greenberger-Horne-Zeilinger [GHZ] state) and the completely unpolarized state. These mixed states serve as benchmark for the robustness of entanglement. They share the same symmetries as the GHZ state. We call such states GHZ-symmetric. Despite significant progress their multipartite entanglement properties have remained an open problem. 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 parameterization of the states and on the invariance of entanglement properties under general local operations. An immediate application of our results is the definition of a symmetrization witness for the entanglement class of arbitrary three-qubit states.Comment: 4 pages, 2 figure

Implementation of the Deutsch-Jozsa algorithm with Josephson charge qubits

We investigate the realization of a simple solid-state quantum computer by implementing the Deutsch-Jozsa algorithm in a system of Josephson charge qubits. Starting from a procedure to carry out the one-qubit Deutsch-Jozsa algorithm we show how the N-qubit version of the Bernstein-Vazirani algorithm can be realized. For the implementation of the three-qubit Deutsch-Jozsa algorithm we study in detail a setup which allows to produce entangled states.Comment: accepted for publication in Journal of Modern Optic

Advanced control with a Cooper-pair box: stimulated Raman adiabatic passage and Fock-state generation in a nanomechanical resonator

The rapid experimental progress in the field of superconducting nanocircuits gives rise to an increasing quest for advanced quantum-control techniques for these macroscopically coherent systems. Here we demonstrate theoretically that stimulated Raman adiabatic passage (STIRAP) should be possible with the quantronium setup of a Cooper-pair box. The scheme appears to be robust against decoherence and should be realizable even with the existing technology. As an application we present a method to generate single-phonon states of a nanomechnical resonator by vacuum-stimulated adiabatic passage with the superconducting nanocircuit coupled to the resonator

Monogamy equalities for qubit entanglement from Lorentz invariance

A striking result from nonrelativistic quantum mechanics is the monogamy of entanglement, which states that a particle can be maximally entangled only with one other party, not with several ones. While there is the exact quantitative relation for three qubits and also several inequalities describing monogamy properties it is not clear to what extent exact monogamy relations are a general feature of quantum mechanics. We prove that in all many-qubit systems there exist strict monogamy laws for quantum correlations. They come about through the curious relation between the nonrelativistic quantum mechanics of qubits and Minkowski space. We elucidate the origin of entanglement monogamy from this symmetry perspective and provide recipes to construct new families of such equalities.Comment: 4 pages, 3 figure

A method for defining down-wind evacuation areas for transportation accidents involving toxic propellant spills

Evacuation areas for accidental spills of toxic propellants along rail and highway shipping routes are defined to help local authorities reduce risks to people from excessive vapor concentrations. These criteria along with other emergency information are shown in propellant spill cards. The evacuation areas are based on current best estimates of propellant evaporation rates from various areas of spill puddles. These rates are used together with a continuous point-source, bi-normal model of plume dispersion. The rate at which the toxic plume disperses is based on a neutral atmospheric condition. This condition, which results in slow plume dispersion, represents the widest range of weather parameters which could occur during the day and nighttime periods. Evacuation areas are defined by the ground level boundaries of the plume within which the concentrations exceed the toxic Threshold Limit Value (TLV) or in some cases the Emergency Exposure Limit (EEL)