Measurement of qubits

James, Daniel F. V., Kwiat, Paul G., Munro, William J. and White, Andrew G. (2005). Measurement of qubits. In Masahito Hayashi (Ed.), Asymptotic theory of quantum statistical inference: Selected papers (pp. 509-523) Singapore: World Scientific.

Author James, Daniel F. V.
Kwiat, Paul G.
Munro, William J.
White, Andrew G.
Title of chapter Measurement of qubits
Title of book Asymptotic theory of quantum statistical inference: Selected papers
Place of Publication Singapore
Publisher World Scientific
Publication Year 2005
Sub-type Other
ISBN 9812560157
Editor Masahito Hayashi
Chapter number 34
Start page 509
End page 523
Total pages 15
Total chapters 34
Language eng
Subjects 0206 Quantum Physics
Abstract/Summary We describe in detail the theory underpinning the measurement of density matrices of a pair of quantum two-level systems ~‘‘qubits’’!. Our particular emphasis is on qubits realized by the two polarization degrees of freedom of a pair of entangled photons generated in a down-conversion experiment; however, the discussion applies in general, regardless of the actual physical realization. Two techniques are discussed, namely, a tomographic reconstruction ~in which the density matrix is linearly related to a set of measured quantities! and a maximum likelihood technique which requires numerical optimization ~but has the advantage of producing density matrices that are always non-negative definite!. In addition, a detailed error analysis is presented, allowing errors in quantities derived from the density matrix, such as the entropy or entanglement of formation, to be estimated. Examples based on down-conversion experiments are used to illustrate our results.
Keyword Qubits
Density matrices
Q-Index Code BX

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Created: Thu, 07 Jan 2010, 09:11:19 EST by Michael Affleck on behalf of Faculty of Science