Hannover 2010 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 55: Poster II

Q 55.44: Poster

Thursday, March 11, 2010, 16:00–19:00, Lichthof

Quantum Decoherence of Two Qubits — •Julius Helm and Walter T. Strunz — Institut für Theoretische Physik, TU Dresden, 01062 Dresden

A widely accepted explanation of decoherence rests upon growing entanglement between the system and its environment. In practice, however, surprisingly often decoherence may equally well be described by random unitary dynamics without invoking a quantum environment at all. For a single qubit, for instance, pure decoherence (or phase damping) is always of random unitary type [1]. Here, we construct a simple example of true quantum decoherence of two qubits: we present a viable phase damping channel that cannot be understood in terms of random unitary dynamics [2]. We give a very intuitive geometrical measure for the positive distance of our channel to the convex set of random unitary channels, of which we find remarkable agreement with the norm distance based on the norm of complete boundedness [3].

[1] L. Landau and R.F. Streater, Lin. Alg. Appl. 193, 107 (1993).

[2] J. Helm and W.T. Strunz, Phys. Rev. A 80, 042108 (2009).

[3] V.I. Paulsen, Completely Bounded Maps and Operator Algebras (Cambridge University Press, Cambridge, U.K., 2002).