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The Strathprints institutional repository is a digital archive of University of Strathclyde's Open Access research outputs. Strathprints provides access to thousands of Open Access research papers by University of Strathclyde researchers, including by researchers from the Department of Computer & Information Sciences involved in mathematically structured programming, similarity and metric search, computer security, software systems, combinatronics and digital health.

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Direct estimations of linear and nonlinear functionals of a quantum state

Ekert, A K and Alves, C M and Oi, D K L and Horodecki, M and Horodecki, P and Kwek, L C (2002) Direct estimations of linear and nonlinear functionals of a quantum state. Physical Review Letters, 88 (21). -. ISSN 0031-9007

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Abstract

We present a simple quantum network, based on the controlled-SWAP gate, that can extract certain properties of quantum states without recourse to quantum tomography. It can be used as a basic building block for direct quantum estimations of both linear and nonlinear functionals of any density operator. The network has many potential applications ranging from purity tests and eigenvalue estimations to direct characterization of some properties of quantum channels. Experimental realizations of the proposed network are within the reach of quantum technology that is currently being developed.