# Hannover 2003 – wissenschaftliches Programm

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# Q: Quantenoptik

## Q 37: Quanteninformation 4

### Q 37.6: Vortrag

### Donnerstag, 27. März 2003, 15:15–15:30, F102

**Entanglement and Decoherence of a Schrödinger cat state** — •Andrea Nemes Salgueiro and Juan Ignacio Cirac — Max-Planck-Institut für Quantenoptik, 85748 Garching

Multi-particle entangled states realized in many recent
experiments can be described to a good approximation by
|ψ⟩=1/√*K*(|φ_{1}⟩^{⊗
N}+|φ_{N}⟩^{⊗ N}), where |ψ⟩ is a state
of *N* two-level systems (qubits) and *K* is the normalization. We
investigate decoherence and quantify the entanglement of these
states when they are coupled collectively or independently with
the environment. In particular, we are interested in
characterizing the time scale for decoherence and for the decay of
entanglement. As a measure of entanglement we choose the
negativity which is defined as the sum of the absolute value of
the eigenstates of the partial transpose.