# Dresden 2011 – wissenschaftliches Programm

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# Q: Fachverband Quantenoptik und Photonik

## Q 20: Quantum Information: Concepts and Methods 3

### Q 20.8: Vortrag

### Dienstag, 15. März 2011, 12:15–12:30, SCH A118

**Permutationally Invariant Quantum Tomography** — •Géza Tóth^{1,2,3}, Witlef Wieczorek^{4,5}, David Gross^{6}, Roland Krischek^{4,5}, Christian Schwemmer^{4,5}, and Harald Weinfurter^{4,5} — ^{1}Theoretical Physics, The University of the Basque Country, E-48080 Bilbao, Spain — ^{2}IKERBASQUE, Basque Foundation for Science, E-48011 Bilbao, Spain — ^{3}Research Institute for Solid State Physics and Optics, H-1525 Budapest, Hungary — ^{4}Max-Planck-Institut für Quantenoptik, D-85748 Garching, Germany — ^{5}Fakultät für Physik, Ludwig-Maximilians-Universität, D-80799 Garching, Germany — ^{6}Institute for Theoretical Physics, Leibniz University Hannover, D-30167 Hannover, Germany

We present a scalable method for the tomography of large multi-qubit quantum registers. It acquires information about the permutationally invariant part of the density operator, which is a good approximation to the true state in many, relevant cases. Our method gives the best measurement strategy to minimize the experimental effort as well as to minimize the uncertainties of the reconstructed density matrix. We calculate the measurements needed for up to 14 qubits, and also compute the required total count, i.e., how many times the experiments have to be repeated for obtaining sufficiently low uncertainties. We note that the method has been implemented for the experimental tomography of a four-qubit symmetric Dicke state [1].

[1] See the talk by C. Schwemmer et al.