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Exploring Hilbert Space : accurate characterisation of quantum information
White, A.G.; James, D.F.V.; Munro, W.J.; Kwiat, P.G.
Keyword(s): controllable state production; tomographic reconstruction; experimental determination of entanglement
Abstract: We report the creation of a wide range of quantum states with controllable degrees of entanglement and entropy using an optical two-qubit source based on spontaneous parametric down conversion. The states are characterised using measures of entanglement and entropy determined from tomographically determined density matrices. The Tangle-Entropy plane is introduced as a graphical representation of these states, and the theoretic upper bound for the maximum amount of entanglement possible for a given entropy is presented. Such a combination of general quantum state creation and accurate characterisation is an essential prerequisite for quantum device development. Notes: A. G. White, Department of Physics, University of Queensland, Brisbane, Queensland 4072 Australia. D.F.V. James, Theory Division, T-4; Physics Division, P-23; Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA. P.G. Kwiat, Department of Physics, University of Illinois, Urbana-Champaign, Illinois 61801, USA
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